Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: uki on November 01, 2015, 11:33:23 am
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Hey guys
I got into the next step on this amp, the amp worked well in the 1st power up (I had someone skilled helping me with it). I've managed to build almost everything right except for some not recommended grounding(I should had read some more about it), there is hum and it is very present, the normal channel works well but in the vibrato channel there is some whistle or high pitch frequency noise. When volume is turned down to zero there is still a little guitar signal going out the speaker(probably due to bad grounding also there is some messy wiring). Oh and when the standby is turned off, there is a loud pop. How to proced now to trace down the sources of the problems?
Related links to this amp:
http://el34world.com/Forum/index.php?topic=18650.msg190792#msg190792 (http://el34world.com/Forum/index.php?topic=18650.msg190792#msg190792)
http://el34world.com/Forum/index.php?topic=18968.msg194798#msg194798 (http://el34world.com/Forum/index.php?topic=18968.msg194798#msg194798)
http://el34world.com/Forum/index.php?topic=19225.msg198141#msg198141 (http://el34world.com/Forum/index.php?topic=19225.msg198141#msg198141)
Here some pics:
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Good eye!
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It's a Beast! What you got, 4 6L6's in there? 100W output? Extremely loud I bet. :l2:
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In the third photo it looks like the ground connected to the transformer bolt is not tightened down. Can you check that?
Yes, that was loose while doing the sodering, aluminum chassis is too cold and acts as heat sink while sodering the ground wires making it dificult, once sodering was done it was bolted down to the chassis. I know there is some bad grounding there that will be changed, didn't had time yet to modify that.
Good eye!
Indeed !
It's a Beast! What you got, 4 6L6's in there? 100W output? Extremely loud I bet. :l2:
Yeah 4 6L6GC 100W !! It is LOUD !!
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The brown twin is loud, but normally they have a early breakup so it makes them easier on the ears to get a good tone at a lower volume. I remember getting backstage during Ted Nugents heyday and he was playing a stack of them.
This is a nice looking build.
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The brown twin is loud, but normally they have a early breakup so it makes them easier on the ears to get a good tone at a lower volume. I remember getting backstage during Ted Nugents heyday and he was playing a stack of them.
You mean those? https://courses.physics.illinois.edu/phys406/Amps/Amp_Pix/5G8_Twin_Amp/5G8_Twin_Amp_Stack4.JPG
Would the Brown be model 5G8 ?
This is a nice looking build.
Thanks ! This is the "Blonde Twin" 6G8.
This is my 1st built, I did learn a lot in the process, there is lots more to learn I know and things to get right in this amp, it is working surprisingly well without major problems for a 1st, still there is the hum to fix and the whistle in the second channel, didn't get the chance/time yet to work on it. The chassis still out of the cabinet, only going in when the amp is 100% ready.
Here some more pics:
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The brown twin is loud, but normally they have a early breakup so it makes them easier on the ears to get a good tone at a lower volume. I remember getting backstage during Ted Nugents heyday and he was playing a stack of them.
You mean those? https://courses.physics.illinois.edu/phys406/Amps/Amp_Pix/5G8_Twin_Amp/5G8_Twin_Amp_Stack4.JPG (https://courses.physics.illinois.edu/phys406/Amps/Amp_Pix/5G8_Twin_Amp/5G8_Twin_Amp_Stack4.JPG)
Would the Brown be model 5G8 ?
This is a nice looking build.
Thanks ! This is the "Blonde Twin" 6G8.
This is my 1st built, I did learn a lot in the process, there is lots more to learn I know and things to get right in this amp, it is working surprisingly well without major problems for a 1st, still there is the hum to fix and the whistle in the second channel, didn't get the chance/time yet to work on it. The chassis still out of the cabinet, only going in when the amp is 100% ready.
Here some more pics:
No, when I say Brown, I mean Brownface and not the Tolex Color. His was the Blond Rough Tolex, the same thing I use on most of my cabinets. I really like the Blond/Oxblood look.
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No, when I say Brown, I mean Brownface and not the Tolex Color. His was the Blond Rough Tolex, the same thing I use on most of my cabinets. I really like the Blond/Oxblood look.
I didn't know that, those details are a way to identify the amps ? And would the 1st half of 60's the golden age of Fender amps? Those Twins are just awesome !
Got some more pics:
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:anyone: :bump1: :help:
Can the hum be fixed, or did I messed up too much with the layout? I did read somewhere to not mess with the layout.
What about the whistle or hight pitch frequency when volume is turned up in the second channel, what can that be ?
I would like to hear sincere views from the gurus about the layout and everything else, what did I do that I shouldn't and what can be done to get this to work right if that is the case.
Thank you so much for your time and patience, I really appreciate that !
Here pics with full view of the amp:
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I'm not a guru or anything, but I did notice one thing I suspect could be a problem. You have 3 signal wires going above what I believe is your just rectified unfiltered source HV, and then under the yellow and green twisted wires that may also have some AC hum on them. I would try replacing those with shielded wires, I would suggest using shielded wires wherever your signal leaves the board, and not running them between or close to other unfiltered HV or AC heater wires. :dontknow: Those three wires might also explain the pop you get when going to standby. You cut the HV and there is a big change in the magnetic field around your HV source wire that those signal wires pick up and amplify before the rest of the DC drains from the system. :dontknow:
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Perhaps at least rewire the PT HV CT to just go to the first filter cap, and then back to a star 0V. Similarly, take B+ from the first filter cap, not the diodes. Look up the excellent schematics showing 0V grounding around first filter layout from the likes of RG Keen and Merlin.
After that, it probably gets harder to diagnose for anyone without time up their sleeve - perhaps then look up ways to diagnose where hum is coming from - eg. get an AC meter on the output and check levels with pot settings, and with various stages with AC shorted signal inputs.
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I'm curious as to your grounding scheme, Is everything running back to the same star point at the PT lug?
On my builds I had bad hum if I didn't separate the preamp and the power amp grounds
preamp grounded at the input jack
power amp grounded at the PT lug
This made a huge difference in hum
Also I'm curious as to the picture 'ground 3' It looks like there is a brown cap with one lead just touching the back of the pot Is that right?
Are your preamp tubes new? a bad tube could cause a whistling
I think having the power supply near the inputs is pretty unconventional, that's an area which is VERY sensitive to noise, could you move that board to an external doghouse ala the blackface later amps?
THat's all I can think of with my limited knowledge
And this is a nice looking build
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I'm curious as to your grounding scheme, Is everything running back to the same star point at the PT lug?
Almost everything is going to the PT lug, there are grounding at the back of the pots(more about this ahead).
preamp grounded at the input jack
power amp grounded at the PT lug
This made a huge difference in hum
So saparete the ground by section of the amp?
Also I'm curious as to the picture 'ground 3' It looks like there is a brown cap with one lead just touching the back of the pot Is that right?
It is soldered there, I used the back of the pots to ground those capacitors, because the pots' back are all grounded, there is more like this in all pots. This is bad right :w2: ?
Are your preamp tubes new? a bad tube could cause a whistling
All tubes are new, I thought about that too, I'm going to switch tubes to see what happen.
I think having the power supply near the inputs is pretty unconventional, that's an area which is VERY sensitive to noise, could you move that board to an external doghouse ala the blackface later amps?
Yeah bad layout, Inexperience paid its price here, too much inthusiasm and not enough knowledge. :BangHead:
There is no way around moving the filter caps to the botton of the chassis in this case ?
THat's all I can think of with my limited knowledge
And this is a nice looking build
Tell me if any more info would help,
Thanks a lot Toxophilite
@Paul1453 Thanks for the tips!
@trobbins I'm no so sure about what you are saying, but I'll keep that in mind(my electronic knowledge is limited), Many Thanks for the reply !!
I still would like very much to hear from those that have large experience with amps their sincere thoughs about this layout and everything else, I want to get this working properly, for me this is a dream comming through, Fender amps like this, down here in South America cost over 10 grands and this kind of price is for a 50watts or less, I couldn't afford to pay so much for it, so building was the only way to have a decent Fender amp and it did cost much much less, than the prices you are about to see in the following links.
Here is the reality:
http://www.playtech.com.br/combo-guitarra-fender-68-custom-twin-reverb-32125.aspx/p?gclid=CLaDtrvBg8kCFQYJkQodSGIP2w (http://www.playtech.com.br/combo-guitarra-fender-68-custom-twin-reverb-32125.aspx/p?gclid=CLaDtrvBg8kCFQYJkQodSGIP2w)
https://www.madeinbrazil.com.br/combo-fender-59-bassman-ltd-para-guitarra,product,11714,515.aspx (https://www.madeinbrazil.com.br/combo-fender-59-bassman-ltd-para-guitarra,product,11714,515.aspx)
Here is a small 40w amp:
https://www.madeinbrazil.com.br/combo-pguitarra-hot-rod-iii-deluxe-se-2340200900,product,38248,515.aspx (https://www.madeinbrazil.com.br/combo-pguitarra-hot-rod-iii-deluxe-se-2340200900,product,38248,515.aspx)
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@Paul1453 Thanks for the tips!
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Just checking to verify you see the 3 green wires going to your pots I'm talking about? I definitely think those unshielded signal wires running so close to other power wires is at least part of the hum problem you are experiencing. A simple troubleshooting test. Strum a chord, switch to standby. After the POP, is the hum gone as the chord fades away? If not, you still have your unshielded signal wires, or something else, picking up hum from your AC heater circuit. :think1: Best regards.
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Just checking to verify you see the 3 green wires going to your pots I'm talking about? I definitely think those unshielded signal wires running so close to other power wires is at least part of the hum problem you are experiencing. A simple troubleshooting test. Strum a chord, switch to standby. After the POP, is the hum gone as the chord fades away? If not, you still have your unshielded signal wires, or something else, picking up hum from your AC heater circuit. :think1: Best regards.
Thanks Paul ! I will check that too, making a todo list. Did you see the prices down here ??! OUCH !!
I still would like very much to hear from those that have large experience with amps their sincere thoughs about this layout and everything else, I want to get this working properly, for me this is a dream comming through, Fender amps like this, down here in South America cost over 10 grands and this kind of price is for a 50watts or less, I couldn't afford to pay so much for it, so building was the only way to have a decent Fender amp and it did cost much much less, than the prices you are about to see in the following links.
Here is the reality:
http://www.playtech.com.br/combo-guitarra-fender-68-custom-twin-reverb-32125.aspx/p?gclid=CLaDtrvBg8kCFQYJkQodSGIP2w (http://www.playtech.com.br/combo-guitarra-fender-68-custom-twin-reverb-32125.aspx/p?gclid=CLaDtrvBg8kCFQYJkQodSGIP2w)
https://www.madeinbrazil.com.br/combo-fender-59-bassman-ltd-para-guitarra,product,11714,515.aspx (https://www.madeinbrazil.com.br/combo-fender-59-bassman-ltd-para-guitarra,product,11714,515.aspx)
Here is a small 40w amp:
https://www.madeinbrazil.com.br/combo-pguitarra-hot-rod-iii-deluxe-se-2340200900,product,38248,515.aspx (https://www.madeinbrazil.com.br/combo-pguitarra-hot-rod-iii-deluxe-se-2340200900,product,38248,515.aspx)
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I can't afford the prices here in the US, and don't really want to see how much more they rape you for down there. But I'll take a look. That is why I try to salvage/scavenge most of my parts. :l2:
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I'm one of the less experienced on this forum, though I have built a few amps, with help from the folks here.
I too build my own amps because I an't afford to buy them
regarding your power supply(filter cap board)(and I could be wrong about this some chime in if I am)
Is there no room on the outside of the chassis to mount the board, run the wires through a few grommeted holes and then have a small metal box covering them?
Could you put a busbar(long thick copper wire) behind the pots and solder all the grounds to it and have it ground at the input jack?
I asked about the cap because that sort of attachment(end of wire to flat surface) doesn't look too strong
I'm really hoping someone lot more experienced than me will jump in but I'm betting a lot of your hum could be grounding
All the best!
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I'm one of the less experienced on this forum, though I have built a few amps, with help from the folks here.
Still you are probably much more than I am !! :laugh:
regarding your power supply(filter cap board)(and I could be wrong about this some chime in if I am)
Is there no room on the outside of the chassis to mount the board, run the wires through a few grommeted holes and then have a small metal box covering them?
Maybe that could be possible the space is very tight, I got a picture of that side of the chassis with a piece of paper simulating the power supply.
Maybe could spin the choke to fit the power supply, or is that a bad idea ? Tell me what do you think.
Could you put a busbar(long thick copper wire) behind the pots and solder all the grounds to it and have it ground at the input jack?
You are probably talking about what is shown in this link: http://el34world.com/charts/grounds.htm (http://el34world.com/charts/grounds.htm)
And yes I will do that.
My thoughts was if the back pots are touching the chassis then I could use them as ground points, is that bad ?
I asked about the cap because that sort of attachment(end of wire to flat surface) doesn't look too strong
All solders on pots are well done. But, is that a good or bad practice to do the groundings there ?
I'm really hoping someone lot more experienced than me will jump in but I'm betting a lot of your hum could be grounding
All the best!
You are a great help Toxophilite THANKS, and I'm taking notes about all your guidance, from the others too.
Been learning tons from you guys!
I just want to hear the thoughts of those that are very experienced with amps, If it is really possible to fix all that AC close to the signal wires, only now on this thread I've grasp what is going on with the amp(bad layout). Also I been thinking if it is not fixable, I got the idea to remove the vibrato(don't really need or want it) and maybe the second channel too making a much smaller circuit board putting it alway from all the AC, that would also give me 3-4 spare tubes and components, yet before taking that extreme decision and change, the comments of those that have large experience would be very much helpfull. The amp works for the most part, one important thing I forgot to mention it worked with a 250mA fuse all the time in the 3-4 powers it had so far without getting blowed. Is that a good thing ?
:anyone:
Thank you in advance !
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Slow down and think about it some more and wait for any more input before you start tearing things out. :icon_biggrin:
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+1 on that
I was just making suggestions from my limited experience but ideally you should wait for more experienced people to chime in
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Recommended learning curve:
R.G.Keen's article on grounding. http://www.geofex.com/Article_Folders/star%20grounding%20amps.pdf (http://www.geofex.com/Article_Folders/star%20grounding%20amps.pdf)
Merlin Blencowe’s article on grounding. http://www.valvewizard.co.uk/Grounding.pdf (http://www.valvewizard.co.uk/Grounding.pdf)
RG's schematic has a few inconsistencies, but is 99% a good target.
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I'm waiting, not doing anything without knowing exactly what to do. Thanks for the advice guys.
Recommended learning curve:
R.G.Keen's article on grounding. http://www.geofex.com/Article_Folders/star%20grounding%20amps.pdf (http://www.geofex.com/Article_Folders/star%20grounding%20amps.pdf)
Merlin Blencowe’s article on grounding. http://www.valvewizard.co.uk/Grounding.pdf (http://www.valvewizard.co.uk/Grounding.pdf)
RG's schematic has a few inconsistencies, but is 99% a good target.
Thanks for the links ! 1st paper is contradictory thou where it says to not solder a bus in the back of the pots, but that looks like depend on the amp in question.
I've download the 2nd paper already but they are slitghly different, same paper different versions, there are some differences between the 2.
Some of you might be interested.
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1st paper is contradictory thou where it says to not solder a bus in the back of the pots,
Technically it is a ground loop soldering to the back of the pots. But, it is a small loop with not as much current as the output tubes and their filter caps flowing through it.
Look in Doug's library of tube amp information (link found at the very bottom of any page in the forum) and study his grounding scheme. It works, proven here many times by many guy's on many builds.
Doug separates the high current B+ grounds, ie, power tubes/filter caps from the low current B+ preamp tubes/filter caps.
If it was my amp the 1st thing I'd try is like Doug shows in his library. Then go from there. It might be all you need.
but that looks like depend on the amp in question.
No, I don't think that's why.
I've download the 2nd paper already but they are slitghly different, same paper different versions, there are some differences between the 2.
With the free on line info at Merlin's web site there's sections missing from his books. And with the web site he can change/update the info as he want's/needs to for what ever the reasons.
I'd probably go with the latest info from him and not the earlier writings.
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There does seem to be many different possible grounding schemes that work
Separating the power amp from the preamp like Doug does does seem to help a lot and is relatively easy/non-destructive to implement
Apologies I should looked closer at the exterior of your chassis before suggesting mounting a cap doghouse on it
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Your High Volt PT winding has three leads. On Fender they are Red-Red-Red-Yellow; yours seems to be plain Yellow.
Where does that (Red)Yellow wire go?
It MUST go direct to the first filter cap "-" leg.
It seems to snake off in the other direction and get lost?
That wire has BIG current spikes. If it goes anyplace except the first filter cap, it will inject buzz everywhere.
Grey cases. Hoffman returns the yellow, the first-cap, and all other grounds to one transformer bolt. This works because the resistance of the bolt is very-very small, the BIG current spikes induce very-very small buzz, he does not have a problem. There are other variations which "do work". However since you have buzz, I would trace that wire and wonder what trouble it may be injecting along the way.
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Your High Volt PT winding has three leads. On Fender they are Red-Red-Red-Yellow; yours seems to be plain Yellow.
Where does that (Red)Yellow wire go?
It MUST go direct to the first filter cap "-" leg.
I got 3 wires going to the diodes red red and yellow, green green going to pilot lamp and then heaters, black and blue going to ground transformer bolt, I've followed what is in the schematic, the colors are not exact as they should be, seen like they are:
Red-Blue = Yellow
Red-Yellow = Blue
Green-Yellow = Black
Confusing I know , the makers have flipped the colors.
It seems to snake off in the other direction and get lost?
That wire has BIG current spikes. If it goes anyplace except the first filter cap, it will inject buzz everywhere.
Grey cases. Hoffman returns the yellow, the first-cap, and all other grounds to one transformer bolt. This works because the resistance of the bolt is very-very small, the BIG current spikes induce very-very small buzz, he does not have a problem. There are other variations which "do work". However since you have buzz, I would trace that wire and wonder what trouble it may be injecting along the way.
Yea things looks a bit confusing there, I will arrange that better it isn't totally done yet, some wires from PT still too long(this maybe one source of the buzz?), also I'll probably flip the rectifier board 90° so the red 330v wires get alway a lil more from the pots.
So one of those wires or black or blue should then go to the 1st filter cap "-" leg , is that cap the one also receiving the stanby switch and one leg of the choke ? Ok what is the trick with that? How does it work , what changes instead of sending that wire directly to the transformer bolt? Aren't the "-" legs of the filter caps going to that bolt too ? :w2:
The presence pot wire going from the pot to the circuit board is going around the PT and in the other side the wire going to the speaker jack, it is just beside the PT primary, that is a big problem yes? So shield those two wires ?
Another thing I been told about is: the wires to ground from the circuit board they are in a bus and then going to the transformer bolt, I know already that they have to be separated but where to send them? To the back of the pots bus?
Here a picture of those wires and PT schematic.
Thanks tons PRR for the insights !!
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> red 330v wires get alway a lil more from the pots.
I missed that, but it is a very likely part of the problem.
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those red wires also go under the board close to signal wires. go over it and keep them short. if you want to have them longer (for future re-use or whatever) have all the excess wire at the transformer itself, away from boards and signal paths.
use shielded wire for your inputs, they are crossing the psu caps board. (shield grounded on 1 side!)
i would also try to make the black/white mains wires follow the chassis as tight as possible. i'd probably tape it in the folded edge of the chassis with aluminum tape.
your layout would make much more sense if the pots were on the side of the tubes.
i tend to keep high voltage and AC wiring as far as possible from signal wire, especially preamp wiring. like crossing them at minimal points instead of running them parallel. thinking in 3 dimensions and keeping them bottom or top in the chassis... and good grounding. i've used star grounding, a ground buss for each section combined in a star and variations on that. i don't trust the backside of pots for a good ground and i'm very paranoid about grounding but many commercial amplifiers have proved in the past that you might be able to get away with pretty shitty grounding schemes.
this is a good read as well: http://www.valvewizard.co.uk/Grounding.pdf (http://www.valvewizard.co.uk/Grounding.pdf)
but if my own 'layout rules' are not possible i've resorted to "excessive" shielding. like metal plates bolted or riveted to the chassis separating sections of the circuit. shielding multiple wires together using braided wire 'socks' taped to the chassis with aluminum tape. i've done this with mains wiring instead of shielding all the wires around it. drilling holes in the chassis to have certain wires run over the outside avoiding parts of the circuit... i guess this is not good design practice but some situations make you get creative. it might work for you too.
this is the messiest one i guess. all connections are on the same front panel and the PT is in the back, so you in the left and right of the chassis you can see the mains and standby wiring going through these "socks". there is a metal plate around the power and standby rotary switch. part of the tone stack is on the outside of the chassis because the controls are there. there is shielded wire used on the input as well.
(http://imagizer.imageshack.us/v2/150x100q90/43/dsc06128t.jpg) (http://imageshack.com/f/17dsc06128tj)
(http://imagizer.imageshack.us/v2/150x100q90/62/dsc06131le.jpg) (http://imageshack.com/f/1qdsc06131lej)
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those red wires also go under the board close to signal wires. go over it and keep them short. if you want to have them longer (for future re-use or whatever) have all the excess wire at the transformer itself, away from boards and signal paths.
use shielded wire for your inputs, they are crossing the psu caps board. (shield grounded on 1 side!)
i would also try to make the black/white mains wires follow the chassis as tight as possible. i'd probably tape it in the folded edge of the chassis with aluminum tape.
your layout would make much more sense if the pots were on the side of the tubes.
i tend to keep high voltage and AC wiring as far as possible from signal wire, especially preamp wiring. like crossing them at minimal points instead of running them parallel. thinking in 3 dimensions and keeping them bottom or top in the chassis... and good grounding. i've used star grounding, a ground buss for each section combined in a star and variations on that. i don't trust the backside of pots for a good ground and i'm very paranoid about grounding but many commercial amplifiers have proved in the past that you might be able to get away with pretty shitty grounding schemes.
this is a good read as well: http://www.valvewizard.co.uk/Grounding.pdf (http://www.valvewizard.co.uk/Grounding.pdf)
but if my own 'layout rules' are not possible i've resorted to "excessive" shielding. like metal plates bolted or riveted to the chassis separating sections of the circuit. shielding multiple wires together using braided wire 'socks' taped to the chassis with aluminum tape. i've done this with mains wiring instead of shielding all the wires around it. drilling holes in the chassis to have certain wires run over the outside avoiding parts of the circuit... i guess this is not good design practice but some situations make you get creative. it might work for you too.
this is the messiest one i guess. all connections are on the same front panel and the PT is in the back, so you in the left and right of the chassis you can see the mains and standby wiring going through these "socks". there is a metal plate around the power and standby rotary switch. part of the tone stack is on the outside of the chassis because the controls are there. there is shielded wire used on the input as well.
(http://imagizer.imageshack.us/v2/150x100q90/43/dsc06128t.jpg) (http://imageshack.com/f/17dsc06128tj)
(http://imagizer.imageshack.us/v2/150x100q90/62/dsc06131le.jpg) (http://imageshack.com/f/1qdsc06131lej)
Hey thank you very much for the reply ! Those seen to be great Tricks, so you put a plate close to the PT ? Is that thick shielded wire the main AC input ? I see the idea and looks good anything that help get rid of the hum helps !!
Your High Volt PT winding has three leads. On Fender they are Red-Red-Red-Yellow; yours seems to be plain Yellow.
Where does that (Red)Yellow wire go?
It MUST go direct to the first filter cap "-" leg.
Please explain what is the trick with that connection, as far as I understand the filter cap "-" leg is going to the same transformer bolt as this wire is already, what changes ? Does it get grounded differently ? Thanks in advance!
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Your High Volt PT winding has three leads. On Fender they are Red-Red-Red-Yellow; yours seems to be plain Yellow.
Where does that (Red)Yellow wire go?
It MUST go direct to the first filter cap "-" leg.
Please explain what is the trick with that connection, as far as I understand the filter cap "-" leg is going to the same transformer bolt as this wire is already, what changes ? Does it get grounded differently ? Thanks in advance!
Uki, it's explained in Merlins grounding info and he has drawings of it.
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Those seen to be great Tricks, so you put a plate close to the PT ? Is that thick shielded wire the main AC input ? I see the idea and looks good anything that help get rid of the hum helps !!
Adding a metal shield and/or things like shielding to the AC power wires are not the 1st things to go to in trying to eliminate hum in and amp. They are mostly used as a last resort when other attempts have failed.
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It's important that the filter caps for the power amp be connected directly to the HT center tap lead. This is usually done at a PT bolt. It's also important that the filter caps for the preamp to NOT be connected to the power amp ground, especially in the case you have where a single ground wire connects ALL of your filter caps to the PT bolt. The power amp caps put big dirty stuff on that single ground wire and it will show up in the preamp because the caps for the preamp share that same ground wire. The answer is to separate the power amp ground and the preamp ground.
Fender did this on the original 6G8. It's hard to see on the layout, but if you look closely you'll see two grounds coming from the cap board. I've circled them in red on the attached pic.
So, separate your grounds. Cut the ground buss at the "X" on the pic. Leave your gray ground wire (this is now part of your power amp ground) connected to the PT bolt. Insure that the PT center tap is connected to this same bolt. Now drill a small hole and install a screw/nut near your input jacks and connect the right end of the cap board ground buss to that screw. This becomes part of the preamp ground.
Hopefully this will help with the hum issues. I see several other issues also but they will not be so easy to correct. Make this simple ground change first to see if it helps. Then I'll discuss the other issues I see.
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@Willabe thanks for the hints, I'll do 1st things 1st and progress on the fixing as sugested, I'm still reading the grounding doc.
Actually I've been reading lots of things about tube amps.. :laugh:
It's important that the filter caps for the power amp be connected directly to the HT center tap lead. This is usually done at a PT bolt. It's also important that the filter caps for the preamp to NOT be connected to the power amp ground, especially in the case you have where a single ground wire connects ALL of your filter caps to the PT bolt. The power amp caps put big dirty stuff on that single ground wire and it will show up in the preamp because the caps for the preamp share that same ground wire. The answer is to separate the power amp ground and the preamp ground.
I did seen some on that but I didn't understand before why, now I know that it is important to saparete those caps grounds.
Fender did this on the original 6G8. It's hard to see on the layout, but if you look closely you'll see two grounds coming from the cap board. I've circled them in red on the attached pic.
I had no clue :dontknow: about that! Thanks for clarifying this.
So, separate your grounds. Cut the ground buss at the "X" on the pic. Leave your gray ground wire (this is now part of your power amp ground) connected to the PT bolt. Insure that the PT center tap is connected to this same bolt. Now drill a small hole and install a screw/nut near your input jacks and connect the right end of the cap board ground buss to that screw. This becomes part of the preamp ground.
Hmmm I think that will be a bit more than that, I did switch the order of the caps to have the resistors legs all sodered to the next one(got pictures and schematics), and not having one floating around, I think I'll have to do 2 or 3 cuts and link the power cap ground in the middle to the ones in the edge, check out the pics, and also by looking at it I found something that maybe a mistake, the choke is connected directly to the stanby switch and the OT center wire also is connected there, could it be the source of the pop noise when turning the stanby switch off?
Hopefully this will help with the hum issues. I see several other issues also but they will not be so easy to correct. Make this simple ground change first to see if it helps. Then I'll discuss the other issues I see.
Thanks tons sluckey, I'll do 1st things 1st and then procede from there.
Ok here is the pics, A is what it should be, probably. B is how I did it. (the PS board schematic was done by Pete or DummyLoad (thanks)).
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I would personally rewire the cap board as per drawing A. However, here's a simple mod to drawing B that will separate the grounds with minimum rewiring. Should be fairly easy. Give this a try. If the hum improves, consider rewiring the board as per drawing A.
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I would personally rewire the cap board as per drawing A.
Thanks Sluckey, I did A to get things right.
I got questions:
-> About the ground wires comming from the main board, there are 5 of them, I did at 1st a buss and send all of them to the transformer bold(removed it already), I know it was a bad choice because the guy that helped me with the 1st power up told me to change that, so I'm doing it but I don't know what is the best way, are there preamp and power sections of those wires, can the sections be put in separated busses or in busses at all, or they must go to ground with separated wires? I did look at the grounds doc but I'm still in doubt about how to do it http://el34world.com/charts/grounds.htm (http://el34world.com/charts/grounds.htm)
-> The pots, do they must have a buss soldered in the back or just touching the chassis works ? (as is now the back of the pots are closing circuit with the chassis)
Got pics.
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You have ground loops set up with the way you daisy chained the grounds on the cap board AND daisy chained the grounds on the turret/eyelet board AND then ran a wire from each filter cap ground end to each ground star connection on the turret/eyelet board.
Look at Sluckey's drawing and look at my drawing below. Ground loops are red arrows. To many/multiple paths for the ground to flow through.
You should remove the daisy chain on the turret/eyelet board, purple in my drawing. This will break the loops and the circuit grounds will now have only 1 path to ground.
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Or, like this;
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You should remove the daisy chain on the turret/eyelet board, purple in my drawing. This will break the loops and the circuit grounds will now have only 1 path to ground.
Thanks Willabe,
When you say turret/eyelet board you mean the main circuit board yes?
Are you referring to the black wire in the picture, same as purple in your draw ?
If that is what your are talking about, it was already removed(it was just sitting there when I took the pic),
I see your are pulling wires from those points, to the minus legs of the filter caps, but there are 5 of them,
do they all go to the minus legs of the pre-amp section of the filter caps ? :w2:
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When you say turret/eyelet board you mean the main circuit board yes?
Yes.
Are you referring to the black wire in the picture, same as purple in your draw ?
Yes.
I see your are pulling wires from those points, to the minus legs of the filter caps, but there are 5 of them,
do they all go to the minus legs of the pre-amp section of the filter caps ? :w2:
There's 2 basic ways you can run these grounds, 1. like Merlin in the ground loop 2 drawing, 2. Like Doug in the ground loop 3 drawing.
Look at them again.
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I see your are pulling wires from those points, to the minus legs of the filter caps, but there are 5 of them,
do they all go to the minus legs of the pre-amp section of the filter caps ? :w2:
I only drew out 3 gain stages with 3 B+ filter caps as an example.
In 1 of your pictures you 5 ground(?) wires numbered. Each of those ground wires are going from the main circuit board to the B+ filter cap board, each ground wire going to a single filter cap's ground end? Like in the groung loop 3 drawing?
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Merlin points out in his grounding info about the circuit grounds from the gain stage(s) goes back/is grounded to the B+ filter cap's ground end of the filter cap that supplies the B+ for that gain stage. This forms a ground star. Then he runs a wire from that ground star to the next ground star. Look at Merlins drawings.
This daisy chain string of ground stars gets grounded to the chassis with a single wire from the ground star string to the chassis.
Sluckey showed you how to separate the power tubes chassis ground connection from the preamp chassis ground connection so the heavy/noisy power tube ground current doesn't get picked up by the preamp tubes grounds.
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... Like Doug in the ground loop 3 drawing.
Look at them again.
I did look at them again and the answer looks to be yes.
In 1 of your pictures you 5 ground(?) wires numbered. Each of those ground wires are going from the main circuit board to the B+ filter cap board, each ground wire going to a single filter cap's ground end? Like in the groung loop 3 drawing?
I had those 5 wires soldered to that black buss wire before, but going to the transformer bolt, would that cause the hum?
I've been told to separate those five wires, like in your ground loop 2 drawing, would that be a better choice ? Or is the ground loop 3 drawing type better ?
Merlin points out in his grounding info about the circuit grounds from the gain stage(s) goes back/is grounded to the B+ filter cap's ground end of the filter cap that supplies the B+ for that gain stage. This forms a ground star. Then he runs a wire from that ground star to the next ground star.
This daisy chain string of ground stars gets grounded to the chassis with a single wire from the ground star string to the chassis.
Oh I think I got this, sounds like a stair of grounding scheme, like going down step by step in a stair.
Sluckey showed you how to separate the power tubes chassis ground connection from the preamp chassis ground connection.
Yes I did that in the filter caps board.
Ok I think I got the groundings of this part at least, I'm also remaking the diode board to it have a little more distance from the pots, also going to rewire the pots in that area taking the wires away from the diodes board. Once that is done then turn up the amp and see what happens to the hum.
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Sluckey showed you how to separate the power tubes chassis ground connection from the preamp chassis ground connection.
Yes I did that in the filter caps board.
What happened? Did it make a difference in hum?
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Sluckey showed you how to separate the power tubes chassis ground connection from the preamp chassis ground connection.
Yes I did that in the filter caps board.
What happened? Did it make a difference in hum?
I'm still working on the amp, can't turn it on yet, the diode board is out, I'm remaking it. I'll post news as soon as it is done.
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When your trying to track down a source of hum you want to try 1 thing at a time. That way you'll know what caused the hum.
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Don't for get this;
Your High Volt PT winding has three leads. On Fender they are Red-Red-Red-Yellow; yours seems to be plain Yellow.
Where does that (Red)Yellow wire go?
It MUST go direct to the first filter cap "-" leg.
It seems to snake off in the other direction and get lost?
That wire has BIG current spikes. If it goes anyplace except the first filter cap, it will inject buzz everywhere.
Grey cases. Hoffman returns the yellow, the first-cap, and all other grounds to one transformer bolt. This works because the resistance of the bolt is very-very small, the BIG current spikes induce very-very small buzz, he does not have a problem. There are other variations which "do work". However since you have buzz, I would trace that wire and wonder what trouble it may be injecting along the way.
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When your trying to track down a source of hum you want to try 1 thing at a time. That way you'll know what caused the hum.
OH!! That is totaly true, ok I wont change anything else yet but those grounds.
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The changes on the grounding are done as suggested by Willabe. But the hum persist at the same amount.
Ok what next ?
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Which changes?
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I think that most of your hum issues are caused by poor layout based on your choice of chassis. The 6G8 chassis dimensions are 26.1875" x 1.586" x 8.25", think long and narrow. But you chose to build a short and wide chassis (why???), so now you have to squeeze the tube lineup and front panel controls lineup to fit your chassis. But you are still using a board designed to fit the long and narrow chassis. This causes some very long wires to go from the board to the sockets and control panel. Plenty of opportunity to pick up extra hum.
The cap board needs to be moved away from the sensitive preamp section and input jacks. The first three filter caps are used in the power amp and have lot's of BIG 120Hz AC ripple (hum) on them. This hum is easily picked up by the very sensitive input section. The wiring from all 4 of your input jacks pass right by all this noise and hum. So, move the cap board.
Moving the cap board reveals another big layout problem... OT placement. All 4 of your very sensitive input wires are passing right by the OT wires. The OT wires are carrying the biggest signals in the amp. This is a huge design flaw. Also, your speaker jacks are mounted near the first preamp tube and your OT secondary wires (high current carriers) are routed very close to the preamp tube. So, move the OT and the speaker jacks and keep all OT wires away from sensitive preamp circuits.
Using properly shielded wire for your 4 input wires will help with the present cap board and OT placement issues, but I'm afraid it's like putting a band aid on a broken leg. I know that moving that board and OT will be more difficult to do than to say. And you won't know if things will improve until you move them. I'm really skeptical about the success of this project in the confines of the chassis you have chosen.
I know you have a lot of time and money invested in this amp. And I love the sound of the harmonic vibrator circuit. So, what to do? I'd cut my loses on the time and put all those components in a proper chassis. There are 6G8 chassis for sale on eBay right now. Then study the original Fender layout. Collect as many pics of 6G8s as you can. Then wire the amp as close as you can to Fender's proven layout. And ask questions about anything you are not sure of, especially concerning grounding.
This is the first time I've ever recommended changing the chassis, but I really think it will take less time than trying band aids on your present chassis. An I'm confident you will have better results in a proper chassis.
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@Sluckey thanks for your honest !
But you chose to build a short and wide chassis (why???), so now you have to squeeze the tube lineup and front panel controls lineup to fit your chassis. But you are still using a board designed to fit the long and narrow chassis. This causes some very long wires to go from the board to the sockets and control panel.
I've found that out when I was already soldering those wires :sad2: leaving the feeling that would cause problems.
I didn't want to have one of those long bulk head cabinets, had some of those before, transport is difficult and they take space.
Poor chassis layout, my idea was to compact it in a smaller case, but that seen to be a mistake, the lack of experience and knowledge paid the price.
My toughts are to remake the main circuit board removing the tremolo and maybe even the second channel making a much smaller board to be able to move it alway from all that AC, but probably that isn't a good idea either, more planning 1st than action have to be done.
I'm open to other suggestions.
Thanks.
@Willabe , I did change the filter caps and main board grounds.
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I did turn it up yesterday late in the night after done with the grounding changes, I didn't had much chance to really hear it, but now it is on again and seen like the hum not as much as before but still there. Maybe there is still a change to get rid of it ? Also when i plug or unplug the guitar cable there is a sound of it been amplified, a bad tube maybe?
Oh and by the way IT SOUNDS AMAZING , MARVELOUS!!!
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Shield the 4 wires that run from the input jacks to the board. Run these shielded wires over the top of the cap board. This will get them away from the OT.
What size is your chassis? I want to play around with layout to see if I can come up with anything useful.
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Could you move the choke right beside the PT , move the OT as close to the choke (but on the tube socket edge of the amp) as possible and then put a cap doghouse on the outside of the chassis and move the cap board to it?
I think there would be room especially if the cap doghouse is run front to back with the preamp filter caps near the inputs.
Move the speaker jack(s) accordingly.
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It looks like you have the OT secondary speaker wires running across the back, then up the side by the preamp end of eyelet board, then running past the preamp tube sockets over to the speaker jacks. That's a long run of OT secondary wires that have the most signal current going past very low signal level components.
Can you run those OT secondary wires more direct, away from the preamp circuity and in between the PI and 1st power tube that's closest to the PI tube?
Or maybe up in the air above the eyelet board?
And what is the gray wire that's running/laying parallel with the OT secondary wires? That could be a problem too?
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Shield the 4 wires that run from the input jacks to the board. Run these shielded wires over the top of the cap board. This will get them away from the OT.
What size is your chassis? I want to play around with layout to see if I can come up with anything useful.
Man I was playing on it for about 25 mins or more THAT IS A SWEET SOUND AMP !!
I got a chassis blueprint I did before making it, the amp parts were all planned before the start of building, I'm no engineer thou :laugh:.
The chassis layout pic is attached.
Could you move the choke right beside the PT , move the OT as close to the choke (but on the tube socket edge of the amp) as possible and then put a cap doghouse on the outside of the chassis and move the cap board to it?
I think there would be room especially if the cap doghouse is run front to back with the preamp filter caps near the inputs.
Move the speaker jack(s) accordingly.
Thanks for the input Toxophilite, I'll keep those suggestion in the list, and use it as last resort, gonna try 1st the less intrusive suggestions.
It looks like you have the OT secondary speaker wires running across the back, then up the side by the preamp end of eyelet board, then running past the preamp tube sockets over to the speaker jacks. That's a long run of OT secondary wires that have the most signal current going past very low signal level components.
Can you run those OT secondary wires more direct, away from the preamp circuity and in between the PI and 1st power tube that's closest to the PI tube?
Yes it could be possible to change that ,what about shielding those wires ? My 1st though when reading your suggestion was to move the sockets but there is not much where to go !!! So what about shielding those 2 wires, I actually though about shielding the jacks as well with a small shielded box, which end of the shielded wire should be grounded, how about that ?
Here is the chassis layout:
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And what is the gray wire that's running/laying parallel with the OT secondary wires? That could be a problem too?
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Can you post a picture of the top side of the chassis so we can see how/where you placed the PT/OT and choke?
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And what is the gray wire that's running/laying parallel with the OT secondary wires? That could be a problem too?
That gray wire is comming from one of the preamp tubes, pin 5 to the 1st filter cap in the preamp side of the cap board. Take it away from the OT 2nds ?
What about shielding those OT 2nds and the jacks ? Sounds good ?
Can you post a picture of the top side of the chassis so we can see how/where you placed the PT/OT and choke?
There is one few posts above! But ill post again.
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And what is the gray wire that's running/laying parallel with the OT secondary wires? That could be a problem too?
That gray wire is comming from one of the preamp tubes, pin 5 to the 1st filter cap in the preamp side of the cap board. Take it away from the OT 2nds?
Pin 5? On a 12A_ _ 7 that's 1 of the 3 heater pins.
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There is one few posts above! But ill post again.
Thanks, I missed where it was.
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What about shielding those OT 2nds and the jacks ? Sounds good ?
:dontknow: I'd try moving them 1st. Just moving them might be enough?
But like Sluckey said, the speaker jacks are right next to a preamp tube.
I think you could move those 2 speaker jacks towards the power tube end of the chassis. Would be better then it is now.
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And what is the gray wire that's running/laying parallel with the OT secondary wires? That could be a problem too?
Pin 5? On a 12A_ _ 7 that's 1 of the 3 heater pins.
Ooops my mistake I've counted 4 and 5 as it was one, the pin where the gray wire is at, is the pin 6. Tube type is ECC83 S .
:dontknow: I'd try moving them 1st. Just moving them might be enough?
But like Sluckey said, the speaker jacks are right next to a preamp tube.
I think you could move those 2 speaker jacks towards the power tube end of the chassis. Would be better then it is now.
Not much where to go with the jacks, what if there is a small shielded box covering the jacks and the wires from the OT ? There is just enough room for it, would that work?
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ECC83 = 12AX7. Pin 6 = plate. Still a long way around to go from the filter cap to the tubes plate.
You could move to jack in between the switch and the 2nd jack. Then move the OT secondary wires up and over the eyelet board up in the air. That's what I would try 1st. :dontknow:
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ECC83 = 12AX7. Pin 6 = plate. Still a long way around to go from the filter cap to the tubes plate.
You could move to jack in between the switch and the 2nd jack. Then move the OT secondary wires up and over the eyelet board up in the air. That's what I would try 1st. :dontknow:
You mean those 2 wires and jacks are better alway from V1 and V2 ?
PRR mentioned to solder that blue or black wire from the PT to the "-" leg of the power section of the filter caps, but I don't know which one of those 2 wires is the one he mentioned, colors aren't correct.
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You mean those 2 wires and jacks are better alway from V1 and V2 ?
YES. :icon_biggrin:
Most guitar amps are laid out keeping the ACV, power cord/PT primary wires/AC power switch/fuse AND all the hi DCV/hi DC current wires and components as far away as possible from the low voltage/low current/low signal components, the input jacks/preamp circuits/preamp tubes.
Both Sluckey and PRR have said things about this to you in this thread already. So have I.
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Your High Volt PT winding has three leads. On Fender they are Red-Red-Red-Yellow; yours seems to be plain Yellow.
Where does that (Red)Yellow wire go?
It MUST go direct to the first filter cap "-" leg.
It seems to snake off in the other direction and get lost?
That wire has BIG current spikes. If it goes anyplace except the first filter cap, it will inject buzz everywhere.
Grey cases. Hoffman returns the yellow, the first-cap, and all other grounds to one transformer bolt. This works because the resistance of the bolt is very-very small, the BIG current spikes induce very-very small buzz, he does not have a problem. There are other variations which "do work". However since you have buzz, I would trace that wire and wonder what trouble it may be injecting along the way.
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I think that most of your hum issues are caused by poor layout based on your choice of chassis. The 6G8 chassis dimensions are 26.1875" x 1.586" x 8.25", think long and narrow. But you chose to build a short and wide chassis (why???), so now you have to squeeze the tube lineup and front panel controls lineup to fit your chassis. But you are still using a board designed to fit the long and narrow chassis. This causes some very long wires to go from the board to the sockets and control panel. Plenty of opportunity to pick up extra hum.
The cap board needs to be moved away from the sensitive preamp section and input jacks. The first three filter caps are used in the power amp and have lot's of BIG 120Hz AC ripple (hum) on them. This hum is easily picked up by the very sensitive input section. The wiring from all 4 of your input jacks pass right by all this noise and hum. So, move the cap board.
Moving the cap board reveals another big layout problem... OT placement. All 4 of your very sensitive input wires are passing right by the OT wires. The OT wires are carrying the biggest signals in the amp. This is a huge design flaw. Also, your speaker jacks are mounted near the first preamp tube and your OT secondary wires (high current carriers) are routed very close to the preamp tube. So, move the OT and the speaker jacks and keep all OT wires away from sensitive preamp circuits.
Using properly shielded wire for your 4 input wires will help with the present cap board and OT placement issues, but I'm afraid it's like putting a band aid on a broken leg. I know that moving that board and OT will be more difficult to do than to say. And you won't know if things will improve until you move them. I'm really skeptical about the success of this project in the confines of the chassis you have chosen......................
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I'm going to do the other suggested measures, starting with shielding the sensitive wires mentioned above.
I got a small recording sample of the amp. I'll let you guys know as soon as the changes are done.
The quality is not as it should be due to size limit it is a 60ish seconds audio sample.
Rename the file extention to .mp3 can't upload in .mp3 format.
From 6G8-sample.jpg to 6G8-sample.mp3 , I think that will work.
Thanks a lot for all the help, you guys rock !!
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I didn't hear any hum???
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I can't get it open. :dontknow: :BangHead:
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Don't try to open it from the net. Save it to the desktop. Then change the file extension from .jpg to .mp3. Now open it.
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I didn't hear any hum???
I did reduce the quality of the audio to fit the size, there is hum thou in the normal quality audio, can't upload thou too big.
The quality of this audio is actually really bad. The original is much better.
I got one file with just the hum.
I can't get it open. :dontknow: :BangHead:
Rename the file from 6G8-sample.jpg to 6G8-sample.mp3
Maybe you have the extentions hidden, if you are using Windows, in the explorer under the menu tools > folder options(or something like that)> then the 1st tab there is a list of many things, search for something like show/hide known file extentions. Mark or Unmark , then you can see the extentions. Or if you use "" quotes while naming the file it will work as well, but extentions will remain hidden.
Same as before rename the file from 6G8-hum.jpg to 6G8-hum.mp3.
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What were the conditions for that hum recording? Volume set to zero? Volume set to max? Does the volume control even affect the hum? Hum on both channels? Only one channel? If so, which channel?
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I can't figure it out. That's all right.
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I was reading what PRR said about the PT B+ CT.
You have 3 very long untrimmed wires coming out of the PT. 2 go to the PT ground lug bolt. I think 1 is the B+ CT and the other is the heater CT, or is an internal shield? Anyway 1 of those is your PT B+ CT.
All 3 of those wires that you have looped around need to be trimmed way down in length.
What PT are do you have in there? Does it have a heater CT? Or did you use 2 resistors for a faux heater CT?
If not there's a source of hum.
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What were the conditions for that hum recording? Volume set to zero? Volume set to max? Does the volume control even affect the hum? Hum on both channels? Only one channel? If so, which channel?
The hum happen in both channels at zero or any volume, in the second channel there is a whistle like sound as the volume is turned up and it changes as the volume goes up. Could play with that just spinning the volume control would sound like a feedback modulation !! :laugh:
In the channel 1 the there is a leak of sound with volume at zero, not sure if this happen in the second channel as well, didn't check.
I can't figure it out. That's all right.
Save the file in the computer where suites you best, put quotes around the name while remaning it like this: "file_name.mp3"
that will fix the extention and you'll be able to listen/open the audio file.
I was reading what PRR said about the PT B+ CT.
You have 3 very long untrimmed wires coming out of the PT. 2 go to the PT ground lug bolt. I think 1 is the B+ CT and the other is the heater CT, or is an internal shield? Anyway 1 of those is your PT B+ CT.
All 3 of those wires that you have looped around need to be trimmed way down in length.
What PT are do you have in there?
There is a schematic above, but I'll post again.
Yes I know those wires need to be trimmed, I just need to find out 1st which one goes to the minus legs of the filter caps, does it go to the power portion of the filter caps ?
The PT was made by a company down here it is a copy of the fender PT 67233 or 125P7D or 022814 , I took the schematic to them and they made it for me. Here their website: http://www.wmtransformadores.com.br/ (http://www.wmtransformadores.com.br/)
The colors maybe different for the CTs, that is why the doubt. A guy helped me with it, but I didn't have notes about that. :BangHead: I should have.
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Ok, you have a yellow wire going to the bias/B+ rectifier board. If you have -bias dcv at the tubes then that yellow wire should be the bias tap.
And you have a blue and a black wire going to the PT ground lug. They have to be the B+ CT and the heater CT.
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Sluckey could he have the B+ CT and the bias tap switched?
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Ok, you have a yellow wire going to the bias/B+ rectifier board. If you have -bias dcv at the tubes then that yellow wire should be the bias tap.
And you have a blue and a black wire going to the PT ground lug. They have to be the B+ CT and the heater CT.
Could this, if inverted, cause hum ? How to identify the wires with multmeter ?
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Could this, if inverted, cause hum ?
Yes I think so.
How to identify the wires with multmeter ?
Yes.
The PT B+ CT should read, resistance, about 1/2 way in between the 2 B+ red wire leads.
The bias tap should have a little more resistance from 1 B+ red wire then from the other B+ wire. Not as centered resistance wise as the B+ CT.
The heater CT should read in resistance about 1/2 way in between the 2 green heater wires. I think you need to take all the tubes out to measure them or you'll be measuring the tube filaments too and that will through off the reading.
If it were me I would fix/trim those 3 PT wires 1st, then listen for hum. The longer they are the more noise they can push/transmit into the air that can/will get picked up by other circuitry in the amp. That's why you shorten them.
If there's still hum then I would use shielded wire on the input jacks.
Sometimes there's 3 or 4 things causing an amp to hum, as you track them down 1 at a time each fix will get rid of some hum, the next fix will get rid of some more hum.
You have that very long B+ CT wire looping around AND the very long OT secondary speaker wires running around the end of the preamp end of the circuit board and preamp tubes.
These both could be major hum sources.
You could run the OT secondary wires outside the chassis over to the speaker jacks then drill a hole there, use a rubber grommet in the chassis, then feed those 2 wires into the hole. I'd use some type of cloth insulator tubing or shrink wrap around them, on the outside of the chassis, to give them extra protection.
This will keep them away from the circuit board and preamp tubes and the chassis will act as shielding.
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Sluckey could he have the B+ CT and the bias tap switched?
Maybe. Easy to check. I'm betting the blue wire is the bias tap and the yellow wire is the center tap, which means they are reversed.
Could this, if inverted, cause hum ? How to identify the wires with multmeter ?
Connect one meter lead to chassis. Measure the AC voltage on pins 4 and 6 of the rectifier socket. ***CORRECTION*** Measure the AC voltage on the red wires that connect to the rectifier diodes on the small board. If they are the same (or close), then it's wired correctly. If they are not the same then you have the CT and bias tap reversed.
Whichever wire you determine is really the center tap needs to be trimmed and CONNECTED TO THE PT BOLT. Then you run a separate 18AWG stranded wire from the cap board power amp ground to the same PT bolt that the center tap wire is connected to.
EDIT... see correction in red above. Sorry 'bout that.
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Could this, if inverted, cause hum ? How to identify the wires with multmeter ?
Connect one meter lead to chassis. Measure the AC voltage on pins 4 and 6 of the rectifier socket. If they are the same (or close), then it's wired correctly. If they are not the same then you have the CT and bias tap reversed.
Ah, much easier way.
The bias tap is not centered on the B+ leads so that will throw off the B+ leads ACV's from one another/won't be the same, at the rectifier tube socket.
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The bias tap is not centered on the B+ leads so that will throw off the B+ leads ACV's from one another/won't be the same, at the rectifier tube socket.
Yes. And that will produce a huge 60Hz ripple that may be difficult or even impossible to remove with the filter caps.
So, uki. Have you sorted out the PT wiring yet? And?...
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The bias tap is not centered on the B+ leads so that will throw off the B+ leads ACV's from one another/won't be the same, at the rectifier tube socket.
Yes. And that will produce a huge 60Hz ripple that may be difficult or even impossible to remove with the filter caps.
Ahhh, I wasn't sure if that would cause a noise problem. I did think that the AC sine wave from the PT B+ would be an odd/ugly shape. And I thought the PT wouldn't like being wired/used like that.
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The bias tap is not centered on the B+ leads so that will throw off the B+ leads ACV's from one another/won't be the same, at the rectifier tube socket.
Yes. And that will produce a huge 60Hz ripple that may be difficult or even impossible to remove with the filter caps.
So, uki. Have you sorted out the PT wiring yet? And?...
I did read the wires both red are at 320-321vac
The yellow going to the diode is at 48vac
Working on it, also I got some shielded wire to replace the ones comming from the input jacks, You said to go with those wires over the filter caps ? The OT is right bellow the cap board, that is the reason why ? Replace all pots wires as well yes, for shielded ones?
Tell me if those wires are good enough, in the pic, the yellow wire is the type that is in the amp:
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That shielded cable looks fine. Hold off on using it for now. Take care of the PT wiring first.
Do one thing at a time.
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That shielded cable looks fine. Hold off on using it for now. Take care of the PT wiring first.
Do one thing at a time.
The wires are trimmed and soldered, no audible difference on hum thou, what next ?
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Shield the four input wires and get them away from the OT wires. Look at the 6G8-A layout. It has the 68K resistors mounted directly on the NOR channel input jacks and a single wire that runs from the jacks to V1 pin 2. Same deal for the VIB channel inputs and V2. I would do it like that.
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Shield the four input wires and get them away from the OT wires. Look at the 6G8-A layout. It has the 68K resistors mounted directly on the NOR channel input jacks and a single wire that runs from the jacks to V1 pin 2. Same deal for the VIB channel inputs and V2. I would do it like that.
Already did the 1st input!
What about the pots? Doing at the moment the volume and tones of 1st channel. And moving the wires from bellow the cap board to above.
The treble pot is inverted treble goes down as it is turned up, I did exactly as in the layout, was this done this way originally? How do I come about to reverse the action? I've never seen a 4 pin pot before this ones, do those have 2 wipers, or what?
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I would connect a shielded wire DIRECTLY between the wiper of each volume pot and pin 7 of V1 and V2.
Your treble pot is probably wired incorrectly. That pot is a standard pot with only one wiper... BUT... It has a fixed tap at 70KΩ resistance as measured between the tap and the bottom lug as shown on the schematic. You'll have to use your ohm meter to determine which lugs are which unless you have a data sheet for the pot.
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I would connect a shielded wire DIRECTLY between the wiper of each volume pot and pin 7 of V1 and V2.
Will do !
Your treble pot is probably wired incorrectly. That pot is a standard pot with only one wiper... BUT... It has a fixed tap at 70KΩ resistance as measured between the tap and the bottom lug as shown on the schematic. You'll have to use your ohm meter to determine which lugs are which unless you have a data sheet for the pot.
Do you mean wiper? "between the wiper and the bottom lug".
Hmmm I've been looking at this for the last hour or so and my conclusion is: that pot is really inverted in the layout, maybe because of that tap, at zero position it is trebler because of the 0.00025 cap, and in the other side it is bassy because of the 0.005 cap with one leg to ground. I've followed it exactly as is in the layout. Reverting the outer pins of the pot wont give the same result because of the position of the tap pin. Can't swap tap and wiper, if my logic is correct. Is the layout incorrect ? :dontknow: I think the layout is incorrect.
I got a pic(fixed):
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Layout is fine. You just wired the pot wrong. Wire it like this...
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Oh I see ! The pins in the pot are not in the same order as in the layout. Thanks for clarify that !!
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It has a fixed tap at 70KΩ resistance as measured between the tap and the bottom lug as shown on the schematic.
Do you mean wiper? "between the wiper and the bottom lug".
No. I meant exactly what I said.
Look at the schematic in the pic I posted...
1 = top
2 = wiper
3 = bottom
4 = 70K tap
Using your ohm meter, you should have fixed 350K between 1 and 3. You should have fixed 70K between 3 and 4. You should have a variable resistance between 2 and any other lug.
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That tapped Alpha pot you have looks quite different from the tapped pots that were available when Fender built that amp. Still functions the same though.
This is what that tapped pot would have looked like back in 1960. This is what the original Fender layout is based on. Make more sense now?
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That tapped Alpha pot you have looks quite different from the tapped pots that were available when Fender built that amp. Still functions the same though.
This is what that tapped pot would have looked like back in 1960. This is what the original Fender layout is based on. Make more sense now?
Oh yeah makes lot of sense now !! Man you really know amp stuff !!! Thanks for teaching me this and all else, I really appreaciate it !! :happy1:
I'm replacing the wires, as soon as it is done I'll post. Got some work to finish 1st thou.
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I have replaced the wires of the input jacks and pots for the shielded ones, the hum still there
but I've noticed a slightly improvement in the NOR channel. The VIB channel is noisier,
here is the good news, when turning up the volume the whistle/squeal is now gone!!!
I havent replaced the Presence pot wire, due to its position, I'm not sure what route to take, it is right beside de PT,
now the new cable, should it go around the PT as is now as far as possible ? I take short route above the PT is a nono ?
I know the OT secondary wires need some work too. Willabe suggested to go under the chassis :sad2: that is gonna be awful,
can it be shielded or pass inside an aluminum or copper pipe ? Would it insulate those wires ? :think1: Would that work?
Besides replacing those wires what else can be done to eliminate the hum, I've the feeling about those wires from the vibrato pre-amp tubes all packed right beside the heater wires should be shielded as well ?
What next ?
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:think1:
Hey guys I've found some great deal of information it looks like, something nobody has mention in this thread yet, the coupling capacitors have a outer foil side leg. The cap should be installed with this side of the leg to the lowest impedance side of the circuit.
Now how much hum it would do if lets say half of more the caps are backwards, or at least the most sensitive ones in the input part of the circuit?
I got some videos with good info on this one:
This one is long but the 1st 5-7minutes will do.
https://www.youtube.com/watch?v=BnR_DLd1PDI (https://www.youtube.com/watch?v=BnR_DLd1PDI)
This ones are short:
https://www.youtube.com/watch?v=1f-LdpJiAk4 (https://www.youtube.com/watch?v=1f-LdpJiAk4)
https://www.youtube.com/watch?v=0BD5pxxwxe0 (https://www.youtube.com/watch?v=0BD5pxxwxe0)
I got this images with the outer foil side of the caps marked with an F, which ones are reversed, which way those caps should have the outer foil leg soldered? :w2:
Thanks in advance!
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Does your treble pot work correctly now?
I don't think flipping coupling caps around is going to fix your hum issues. Assuming there are no more wiring errors or incorrect component values, it's time to tackle the layout issues. I'm out of ideas so I'm gonna repeat what I think is the real issue. Read this again...
I think that most of your hum issues are caused by poor layout based on your choice of chassis. The 6G8 chassis dimensions are 26.1875" x 1.586" x 8.25", think long and narrow. But you chose to build a short and wide chassis (why???), so now you have to squeeze the tube lineup and front panel controls lineup to fit your chassis. But you are still using a board designed to fit the long and narrow chassis. This causes some very long wires to go from the board to the sockets and control panel. Plenty of opportunity to pick up extra hum.
The cap board needs to be moved away from the sensitive preamp section and input jacks. The first three filter caps are used in the power amp and have lot's of BIG 120Hz AC ripple (hum) on them. This hum is easily picked up by the very sensitive input section. The wiring from all 4 of your input jacks pass right by all this noise and hum. So, move the cap board.
Moving the cap board reveals another big layout problem... OT placement. All 4 of your very sensitive input wires are passing right by the OT wires. The OT wires are carrying the biggest signals in the amp. This is a huge design flaw. Also, your speaker jacks are mounted near the first preamp tube and your OT secondary wires (high current carriers) are routed very close to the preamp tube. So, move the OT and the speaker jacks and keep all OT wires away from sensitive preamp circuits.
Using properly shielded wire for your 4 input wires will help with the present cap board and OT placement issues, but I'm afraid it's like putting a band aid on a broken leg. I know that moving that board and OT will be more difficult to do than to say. And you won't know if things will improve until you move them. I'm really skeptical about the success of this project in the confines of the chassis you have chosen.
I know you have a lot of time and money invested in this amp. And I love the sound of the harmonic vibrator circuit. So, what to do? I'd cut my loses on the time and put all those components in a proper chassis. There are 6G8 chassis for sale on eBay right now. Then study the original Fender layout. Collect as many pics of 6G8s as you can. Then wire the amp as close as you can to Fender's proven layout. And ask questions about anything you are not sure of, especially concerning grounding.
This is the first time I've ever recommended changing the chassis, but I really think it will take less time than trying band aids on your present chassis. An I'm confident you will have better results in a proper chassis.
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For *future* builds here's a link, for the present, check-do what Sluckey is suggesting.
http://el34world.com/Forum/index.php?topic=11427.0
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For *future* builds here's a link, for the present, check-do what Sluckey is suggesting.
http://el34world.com/Forum/index.php?topic=11427.0
Man this is great thread thanks for this link !!
Does your treble pot work correctly now?
Yes it does thank you !
I don't think flipping coupling caps around is going to fix your hum issues. Assuming there are no more wiring errors or incorrect component values, it's time to tackle the layout issues. I'm out of ideas so I'm gonna repeat what I think is the real issue. Read this again...
I'm going to do that anyway, better lil improvement than no improvement at all.
I did read that several times, and probably more, I'm in a mission Sluckey , the hum must be gone. Gonna grab some mesh to insulate the AC wires, as suggested above.
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> something nobody has mention in this thread
Because it hardly matters.
Yes, you can get hum on an UN-loaded cap when you touch it. Sometimes a very dramatic difference one way or the other.
In circuit the difference is far-far less.
Also you can't touch the caps when both your hands are on the guitar.
If you must explore this: *very carefully* touch caps with the amplifier on (and dangerous). That will hum much more than normal (no finger) operation. Any cap which seems exceptionally hummy, see if its orientation matches the direction suggested in that guru video.
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Coupling caps with the outer foil orientation installed backwards will not cause the hum you are getting. I promise :icon_biggrin:
Now if you had a small amount of floor noise and had use all MF resistors and wanted to get dead quiet maybe then it would be something to try. The problem is stuffing 10 pounds of manure into a 5 pound bag. Something is bound to stink.
I have built a 4 power tube amp in a chassis the size you are using, but I also shielded the power section from the preamp. All 4 power tubes were between the transformers. Choke was inside and 2 cap cans, one for the power side and the other for the preamp. Also, inside the chassis I installed a plate separating the rear of the chassis from the preamp with a hold drilled and a rubber grommet for the signal wires to pass through.
When I installed the chassis cover it essentially isolated all the PA eddy currents from the preamp. I wish I had a photo, but the amp is long gone, but I did have to design my own board for the preamp and the bias board was affixed to the side of the chassis.
I made the same mistake on my second scratch build by wanting to stuff a high gain 2 El34 amp into a 10 x 6 x 2.5 chassis and put all the tubes in a row.
Now when someone ask me about a chassis I will say layout one to fit and then get a one larger. :icon_biggrin:
The main problem is if you do get it quiet a simple tube change in the future could bring it back. Yes, shielded will and can help, but you have already spent most of the money on your parts. You can use the chassis you have for a smaller amp that I am sure you will want.
I have used a 19 x 8 x 2 to build a Marshall Super Lead and put it in a head box 22 wide, but I still put the power tubes towards the back of the chassis and preamp tubes to the front.
Search for a Soldano SLO 100 watter. He uses some nice ideas to layout a shorter chassis, but they are wider.
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Uki, where did you buy the nice blue epoxy ceramic disk caps?
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Now if you had a small amount of floor noise and had use all MF resistors and wanted to get dead quiet maybe then it would be something to try.
I read somewhere , carbon composition resistors do good at high voltages, but where the voltage isn't that high, they are noisy and don't do much in tone terms at those spots, so something else could be used, like the MF as you mentioned in those noise sections of the circuit, how do I find where to use the MF in the circuit?
I have built a 4 power tube amp in a chassis the size you are using, but I also shielded the power section from the preamp. All 4 power tubes were between the transformers. Choke was inside and 2 cap cans, one for the power side and the other for the preamp. Also, inside the chassis I installed a plate separating the rear of the chassis from the preamp with a hold drilled and a rubber grommet for the signal wires to pass through.
There was hum? How much of it worked?
Search for a Soldano SLO 100 watter. He uses some nice ideas to layout a shorter chassis, but they are wider.
Will do.
I got a pic and video of an 6G8 with some MF resistors, are those at key spots?
https://www.youtube.com/watch?v=7dChBeEYIkM (https://www.youtube.com/watch?v=7dChBeEYIkM)
Uki, where did you buy the nice blue epoxy ceramic disk caps?
Here :icon_biggrin: shipping was pricy thou, no cheaper options.
http://www.tedweber.com/amps/capacitors?limit=all (http://www.tedweber.com/amps/capacitors?limit=all)
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I would suggest you use all flameproof metal film resistors everywhere.
Safer, quieter, less prone to drift and failure
I don't see the advantage of carbon comp resistors myself.
I try to never use them unless I need one while I'm building and it happens to be all I have or it's all I can get in a particular value.
In my opinion, that's on par with orientating capacitors
I think addressing layout would be a more efficient way of tackling hum, provided you've sorted out your grounds etc
As many people have suggested.(ALL of them WAY more experienced than me)
-Your output transformer placement. It should be as far from your inputs as possible
Right on top of the inputs is usually the worst position possible (sorry)
-And your power supply, which also should be far from your preamp section (keeps the high B+ away from your sensitive inputs and preamp)
Your inputs and preamps are the most sensitive portion of your amp regarding picking up noise.
I've never found it too hard to move transformers and or chokes if they are sitting on top of the chassis(not half inside) It's merely a matter of a couple holes and a little rerouting of a few wires.
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Thanks Uki. :icon_biggrin:
The places to maybe use CC R's is where there's a high DCV, plate R's, CF R's. Grid return/grid leak R's and K R's don't have high DCV on them so no advantage to using CC's in those places.
You'll have to try them for yourself to see if you think they make a difference in the tone/sound. :icon_biggrin:
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Uki
That's just my opinion on Carbon comp resistors, as Willabe suggested do some testing and decide for yourself
It really is a debatable point and like many things there's a lot of opinions on all sides of the argument, like capacitors, tubes, wire, speaker magnets, etc etc etc.
I tend to fall into the , 'if it can't really be proven one way or the other then it might not be a factor', camp
I think the layout stuff is really important though
Willabe - My local electronics store sells those very capacitors, I bought a couple today for a Baxandall preamp I build into the Akai/Roberts preamps I convert
I'm betting digikey and similar companies have them as well.
They certainly do the job and are relatively inexpensive.
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Thanks Toxo. :icon_biggrin:
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Now if you had a small amount of floor noise and had use all MF resistors and wanted to get dead quiet maybe then it would be something to try.
I read somewhere , carbon composition resistors do good at high voltages, but where the voltage isn't that high, they are noisy and don't do much in tone terms at those spots, so something else could be used, like the MF as you mentioned in those noise sections of the circuit, how do I find where to use the MF in the circuit?
I have built a 4 power tube amp in a chassis the size you are using, but I also shielded the power section from the preamp. All 4 power tubes were between the transformers. Choke was inside and 2 cap cans, one for the power side and the other for the preamp. Also, inside the chassis I installed a plate separating the rear of the chassis from the preamp with a hold drilled and a rubber grommet for the signal wires to pass through.
There was hum? How much of it worked?
Search for a Soldano SLO 100 watter. He uses some nice ideas to layout a shorter chassis, but they are wider.
Will do.
I got a pic and video of an 6G8 with some MF resistors, are those at key spots?
http://www.youtube.com/watch?v=7dChBeEYIkM (http://www.youtube.com/watch?v=7dChBeEYIkM)
Uki, where did you buy the nice blue epoxy ceramic disk caps?
Here :icon_biggrin: shipping was pricy thou, no cheaper options.
http://www.tedweber.com/amps/capacitors?limit=all (http://www.tedweber.com/amps/capacitors?limit=all)
A Picture is worth 1,000 words.
Here is a Hiwatt. Look at the layout. It would be possible to reduce the chassis size more, but with your build you have a Tremolo to consider. If you eliminate the tremolo you lose everything special about a Blond Twin. Might as well build a Showman. While there is nothing wrong with a Showman as Dick Dale seemed to get by with one, the Twin is very special IMO.
This is what I was talking about. If you want a amp that is not as wide, you have to put your tubes in separate rows.
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Thanks Uki. :icon_biggrin:
The places to maybe use CC R's is where there's a high DCV, plate R's, CF R's. Grid return/grid leak R's and K R's don't have high DCV on them so no advantage to using CC's in those places.
You'll have to try them for yourself to see if you think they make a difference in the tone/sound. :icon_biggrin:
- What is CF ?
- K is kathode yes?
Thanks Willabe
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... I think addressing layout would be a more efficient way of tackling hum, provided you've sorted out your grounds etc
...
-Your output transformer placement. It should be as far from your inputs as possible
Right on top of the inputs is usually the worst position possible (sorry)
-And your power supply, which also should be far from your preamp section (keeps the high B+ away from your sensitive inputs and preamp)
Don't be sorry, you are right, I did put all of it together without some very important key information about how to do the layout, I appreciate your honest and that is a BIG help to get it working the way it should, I been thinking about it since you 1st mentioned to move things around, I've been gathering all this information and still processing it. The amp does work for the most part, have a marvelous sound, its a big sound amp, just that darn hum ..... :laugh:
Your inputs and preamps are the most sensitive portion of your amp regarding picking up noise.
I've never found it too hard to move transformers and or chokes if they are sitting on top of the chassis(not half inside) It's merely a matter of a couple holes and a little rerouting of a few wires.
That isn't something to easy to accomplish in my case things are really tight there! I did this image edition to see what it would looks like moving things around. Tough thou and this is just an image edition. I have no idea where to put the choke.
__________________________________________________________________________
A Picture is worth 1,000 words.
It does !!!
Here is a Hiwatt. Look at the layout. It would be possible to reduce the chassis size more, but with your build you have a Tremolo to consider. If you eliminate the tremolo you lose everything special about a Blond Twin. Might as well build a Showman. While there is nothing wrong with a Showman as Dick Dale seemed to get by with one, the Twin is very special IMO.
This is what I was talking about. If you want a amp that is not as wide, you have to put your tubes in separate rows.
This is good point. Although I'll barely be using the tremolo/vibrato, when I saw the schematics/layouts online all what I was concerned about was an amp with 100watts, I did search a lot on about Fender amps, this is the one I found that did match, latter I found some other twin with 100w but no tremolo/vibrato the 5F8-a (that is what I should have build), but I was already building the 6G8. I see now that I did reduce the chassis way too much, but man it looks so cool. :icon_biggrin:
You see I'm green about all this electronic stuff, I didn't know any of it when I started, details... details...
Now about the tremolo/vibrato, it isn't working , do I need a foot switch ?
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K = cathode, CF = cathode follower.
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Now about the tremolo/vibrato, it isn't working , do I need a foot switch ?
The 6G8 vibrato will work just fine without a footswitch.
You keep finding more stuff that isn't working. It may still be possible that a wiring error is contributing to your hum. I know your layout is not good and is likely the real reason for the hum, but disregarding the layout for a moment, I just don't have any confidence that the amp is wired correctly.
I'd like to revisit something for a moment. Would you recheck the AC voltage on the red wires coming from the power transformer? One probe connected to chassis, the other probe on a red wire where it connects to a diode on the small board. Do this for each red wire. What do you get?
Now, with your meter still set to measure AC volts, move the probe to the junction of two diodes and the red wire that goes to the first filter cap on the cap board. I know there's big DC volts at that point but I'm not interested in that. I want to know how much AC voltage (ripple) is at that point. What's the number?
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Now about the tremolo/vibrato, it isn't working , do I need a foot switch ?
The 6G8 vibrato will work just fine without a footswitch.
You keep finding more stuff that isn't working. It may still be possible that a wiring error is contributing to your hum. I know your layout is not good and is likely the real reason for the hum, but disregarding the layout for a moment, I just don't have any confidence that the amp is wired correctly.
I'd like to revisit something for a moment. Would you recheck the AC voltage on the red wires coming from the power transformer? One probe connected to chassis, the other probe on a red wire where it connects to a diode on the small board. Do this for each red wire. What do you get?
Now, with your meter still set to measure AC volts, move the probe to the junction of two diodes and the red wire that goes to the first filter cap on the cap board. I know there's big DC volts at that point but I'm not interested in that. I want to know how much AC voltage (ripple) is at that point. What's the number?
I did read the red wires and the reading on each wire is 320vac both do jump back and forth between 319-320.
The junction of the diodes, with the meter in AC it does 992 ,, what?? :dontknow: , with the meter in DC it does 450vdc.
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I did read the red wires and the reading on each wire is 320vac
Did you measure that 320VAC since you read my last post?
Your meter may not be able to read AC ripple. What name brand and model is your meter? How much did it cost?
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I did read the red wires and the reading on each wire is 320vac
Did you measure that 320VAC since you read my last post?
Your meter may not be able to read AC ripple. What name brand and model is your meter? How much did it cost?
Yes , I just read it just few minutes ago, the amp is on right now.
Here is the meters I got, cheap stuff 50 bucks both:
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I had to clip a .001/630v film cap in my red meter lead to get it to read ripple voltage on the B+.
1 end of cap in red gator clip the other end as prob to B+, meter set for ACV.
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I had to clip a .001/630v film cap in my red meter lead to get it to read ripple voltage on the B+.
1 end of cap in red gator clip the other end as prob to B+, meter set for ACV.
I only have .0033/630v at the moment would that do ? What kind of reading it will be? And will the cap charge up ?
Thanks for the hint !!
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Yes, I think that value should be fine. You set your meter for ACV.
I'm not sure about it charging up, be careful and check it with your meter for dcv after you use it.
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I did the readings and I got the following
With the digital meter at 200vac i got readings at 0.03 , 0.04 , 0.05 and some peaks at 01.2
Also I've measured with the analog meter at 10vac, so it does about +- 1 , see pics.
I this good or bad, what does it mean?
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Found a possible bad cap :cry: at the rectifier board. When detached from the circuit the hum didn't get worse, stayed the same, so gonna replace that cap, probably both 8µ-150v and see if hum goes away. If not then back to the tests.
Got some pics of the shielding done as suggest in previous posts. Thanks for the tips !!
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I am concerned about your layout with filter caps being where they are causing your hum?
with respect, Tubenit
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I am concerned about your layout with filter caps being where they are causing your hum?
with respect, Tubenit
Hey Tubenit !
I've been looking at every possibility, if gets to the point where that board need to be moved from there, it will move.
For now looking after what is easier to deal with, that bad cap isn't doing what it should be doing. No effect in smoothing the signal.
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The 8 x 150uf cap is part of your -dc bias supply it's not a filter cap for the B+ power supply.
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I've been looking at every possibility, if gets to the point where that board need to be moved from there, it will move.
For now looking after what is easier to deal with, that bad cap isn't doing what it should be doing. No effect in smoothing the signal.
It's been at that point from the beginning. Just waiting for you to actually move it. Same goes for the OT.
I don't think a new bias cap will do any better than the one that's in there now. There is such a light load on the bias supply that a single cap is often used by Fender in some of it's most popular amps.
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Uki, have you got the vibrato to work yet?
I agree with Sluckey, that if the vibrato is miswired that could be a source for your hum.
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Uki, have you got the vibrato to work yet?
I agree with Sluckey, that if the vibrato is miswired that could be a source for your hum.
I haven't got the vibrato working yet, gonna check that part of the circuit all over.
Any hints ?
Thanks
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Uki, have you got the vibrato to work yet?
I agree with Sluckey, that if the vibrato is miswired that could be a source for your hum.
I haven't got the vibrato working yet, gonna check that part of the circuit all over.
Any hints ?
Thanks
I got a hint for you. Order a doghouse cover and move your filter caps to the outside of the chassis. I did not notice your cap board was right at your input jack(s)
You can try another experiment if you need more convincing. Un-bolt your input jacks and swing them over to the back of the amp and ground them to the chassis and see if your hum drops. Think of it as if you were installing your input jacks on the back of the amp.
I am not sure if the tremolo is causing hum or not, but you can bypass the tremolo for the moment.
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I got a hint for you. Order a doghouse cover and move your filter caps to the outside of the chassis. I did not notice your cap board was right at your input jack(s)
You can try another experiment if you need more convincing. Un-bolt your input jacks and swing them over to the back of the amp and ground them to the chassis and see if your hum drops. Think of it as if you were installing your input jacks on the back of the amp.
I am not sure if the tremolo is causing hum or not, but you can bypass the tremolo for the moment.
Hey this sounds great !! Also bypassing the tremolo is a good hint !
Thanks !!
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Hey guys
I did some tests, and by removing every preamp tube one at a time, like: remove V1, listen, put back; then remove V2 listen, put back, then V3 and so on; I have found something very interesting !!
Without V5 the amp is quiet no hum. :icon_biggrin: :happy1:
The tubes are good I did swap them to make sure they are good.
Right now I'm checking if components are connected correctly. But I'm no technician, all I can do is to look for wrong connections, I have no clue how to find a bad component if that is the case.
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Without V5 the amp is quiet no hum.
That kills only the vibrato channel. Does the normal channel sound good with no hum?
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Without V5 the amp is quiet no hum.
That kills only the vibrato channel. Does the normal channel sound good with no hum?
I was playing and it does sound so awesome !!!
Yes the NOR channel does sound really clean quiet and no hum, the VIB channel have a very small volume, but also no hum. What is the source of the problem?
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Sounds like the problem lies in the vibrato channel.
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Sounds like the problem lies in the vibrato channel.
What part V4 and V5 have in this amp, do they only act with the vibrato circuit or does it have any other effect in the sound signal ?
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Sounds like the problem lies in the vibrato channel.
What part V4 and V5 have in this amp, do they only act with the vibrato circuit or does it have any other effect in the sound signal ?
I would like to understand what is the role of those two tubes.
The 5E3, 5E5 and other Fender tweed amps have interactive volume controls. When you plug into 1 channel the volume control on the other channel will also effect the amps sound and tone. Comes in very handy.
Turn the volume control on the channel your plugged into to 12:00 and the volume control on the channel your not plugged into full up and it scoops the mids and you get a nice clean tone. Keep the controls the same but plug into the other channel and you get full drive/distortion with the most amount of mids the amp can give.
Use an A/B box to act as a channel switcher. :icon_biggrin:
Does the Twin Amp 6G8 also have some of this tricks?
I did play with the amp today for about 2 hours with the NOR channel, I though it as already good with hum, but now without hum it does sound SO AWESOME !!! I was concerned about having to move stuff around the chassis but it turned out not to be the problem, It is dead quiet and crystal clean sound , the shielding did help big time with the squeal in the VIB channel that was a great hint. Now the bug is about to be found, but again I'm no technician and I do not know what to do, I'll replace the wirings from V5 to the main board, for shielded ones, that is the only thing I can think about, what can be done besides that ?
Again I want to thank everyone that steped by and put 2 or more cents in this thread, that is very much appreciated.
Thank you !!
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Does the Twin Amp 6G8 also have some of this tricks?
No.
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I would like to understand what is the role of those two tubes.
They are this part of the circuit and are for the vibrato.
(Sorry about the poor quality.)
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What part V4 and V5 have in this amp, do they only act with the vibrato circuit or does it have any other effect in the sound signal ?
I would like to understand what is the role of those two tubes.
Those tubes affect only the vibrato channel. Read this pdf...
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Those tubes affect only the vibrato channel. Read this pdf...
Thanks Sluckey !!
I'm still working to fix the problem with the vibrato circuit. Rechecked everything, all looks to be at the right places. Gonna recheck again to make sure.
I've shielded the wires for V5 and it did reduced the hum a bit.
I think the position of the diode board is interacting with the vibrato wires from the pots. Gonna redesign it and flip it back like in the original layout, to fit better with my layout, moving those AC wires alway as possible from pots and main board, then see what happen.
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Sounds like you are zeroing in on the source of the hum. Beginning to look like it's the V5 circuit. I've seen that circuit cause hum in another guy's amp. The tube itself was humming. So, try several different tubes in the V5 socket to see it that helps.
I've got a good way to totally bypass the V5 tube. Look at the attached pic and move the cap as indicated. You'll probably have to solder some pigtails onto the leads of that cap. Don't worry too much about how this looks, just don't let the cap leads touch anything they should not touch. The vibrato effect will not work but the vib preamp should sound just like the normal preamp and hum should be gone.
If the hum is indeed gone, then the V5 circuit is the culprit and we can concentrate on fixing that. So, put the .05 cap back where it's supposed to be.
Once the hum is fixed we can move on to make the vibrato effect work. (NOTE... The hum and the broken vibrato effect may be related).
Do this simple test and report back.
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I did the test rerouting that cap/circuit with and without V5, with V5 same hum,
without V5 dead quiet and the VIB channel works like the NOR channel no hum at all. :smiley:
I had another though on the problem and might be related to the hum, remember the other thread about “missing link” http://el34world.com/Forum/index.php?topic=19225.msg198141#msg198141 (http://el34world.com/Forum/index.php?topic=19225.msg198141#msg198141) there is a wire rerouted that goes to filter cap it is now passing by the V5 part of the circuit and it carries 350v, that could be part of the problem as well yes ?
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there is a wire rerouted that goes to filter cap it is now passing by the V5 part of the circuit and it carries 350v, that could be part of the problem as well yes ?
I doubt that wire is a problem. The B+ on that wire is very well filtered and would be no more noisy than a ground wire.
You have just proved that the hum is associated with V5. Put the .05 back in its original position and plug V5 back in. Now remove V3 and V4 and put aside until the V5 hum is fixed. Now start subbing some other 12AX7s for V5. (You can use the V3 and V4 that you just put aside). Do you find one tube that kills the hum? If not, measure the DC voltages on V5 pins 1, 2, 3 and 6, 7, 8. Measure the AC filament voltage between pin 9 and pin 4/5, not from each pin to ground (Should be about 6.3VAC). What are the measured numbers?
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The .05 is back in its place.
Tried 4 different tubes at V5 , without V3 and V4, the hum still there. I've used good tubes from other amp.
No room to put the meter probe right in some of the tube pins, so I read at the other end of the wires, does it effect the reading?
Reading from V5 pins are:
P1 - 315vdc
P2 - 0-1vdc
P3 P8 - 5vdc
P6 - 330vdc
P7 - 0vdc
P4,5+9 - 15vac
I do have the feeling that something is wrong, don't know what it is.
Note: while touching P1 and P6 with the probe it does a loud noise.
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P4,5+9 - 15vac
Check this again. It should be about 6.3VAC. Put one probe on pin 9. Put the other probe on pin 4. Pins 4 and 5 should be connected together. Put the standby switch in the STANDBY position so there wont be any B+ on the socket while measuring the filament voltage.
While you're set up to measure filament voltage, do so for V3 and V4 also. And make sure pins 4 and 5 are connected together on these tubes as well.
What are the new filament readings?
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Ok I did read it again, this time with standby off, the reading was 5.8vac.
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OK. Next, turn power off and measure resistance from V5 pins 2, 7, 3, 8 to chassis. Pins 2 and 7 should each read 1 megohm to chassis. Pins 3 and 8 (tied together) should each read 4700 ohms to chassis. What are your actual measurements?
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Ok the readings are:
P2 1.105M ohms
P7 1.077M ohms
P3/8 4.76K ohms
The readings are about what you said above.
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Those resistance readings are all good. Now I have two things for you to do...
1. Look at the attached pic. I've circled two .05 caps. I also circled the turret at the top of the board where a lead of each cap connects. Unsolder the cap lead at the turret that is circled in red. Do this for both caps. Just stand the cap up a bit so those loose leads will not touch anything. We're gonna leave the caps like this until the V5 hum issue is fixed. This disconnects the vibrato oscillator (V3/V4) from the modulator (V5). We don't need that in the way while we troubleshoot the V5 hum issue.
2. Look at the last pic you posted. There is a black 5 conductor cable connected between the board and V5 socket. Remove that cable and replace it with five individual wires between the board and V5 socket. And don't bundle the 5 wires together. Leave them long enough to keep them separated from each other.
When you have done both of these things test for hum and report back.
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I forgot to mention, 2 things, 1- the electrolytic cap in the V5 part of the circuit, I couldn't find the 4µF-25v the one there now is 4.7µF-25v ; 2 - The pot for Speed isn't the 4m as it says in the schematic, but 3m the only one I could find, would that interfere with the vibrato?
Remove that cable and replace it with five individual wires between the board and V5 socket. And don't bundle the 5 wires together. Leave them long enough to keep them separated from each other.
Aw man that was some work to put it there(it is bolted to ground), but let me guess it doesn't help anything with the hum, is that correct? Bundling them can also cause problems? :dontknow:
What about just remove the outer cover of that cable, it will leave just the 5 wires, that will do yes?
Thanks a lot for all the help !! Already got the caps disconnected.
What next ?
I did recheck all components and connections in that area, they are in a correct position, so it looks like to be a bad component.
With those two caps disconnected there is even more hum, so I take the problem really lies in the V5 part of the circuit.
Wires replaced.
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Waiting for instructions ! :bump1:
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I think you have narrowed the hum issue down to the V5 circuit. Use the attached pic to check every component in that circuit. Be sure the values are correct and the solder connections are good and in the right place. Check the ground connection. Check the B+ connection and be sure it connects to the right place on the cap board. Use a chopstick or other insulated utensil to move wires around and tap on components. Any effect on the hum?
I want to see some hi-rez pics of the V5 circuit, V5 socket, and interconnecting wires. I'm talking about the resolution like on your 'missing link' photo, but I want to see it all in one pic if possible. And take several pics from different angles.
I don't understand why the hum increased when you lifted the two caps from the trem oscillator. That may be a clue.
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I think you have narrowed the hum issue down to the V5 circuit.
Well not without lots of very skilled helpers !! :laugh:
After replacing the wires, the hum is the same, louder as before with the caps disconnected, there is also a whistle like sound when turning on/off the standby switch, and then if turning off right the after, the power switch does the same whistle.
... check every component in that circuit. Be sure the values are correct
I was reading resistors yesterday on that section, all looks fine but the two 470k (yellow-violet-yellow-silver) , they are reading 288k each, problem there or this happen because they are connected to other components?
I Don't have how to measure caps, no cap meter.
Use a chopstick or other insulated utensil to move wires around and tap on components. Any effect on the hum?
One wire coming from V5 from P7 does increase hum when touched. Besides that, while chopping B+ turret that is connect to filter cap does amplify a bit the tap.
Check the B+ connection and be sure it connects to the right place on the cap board.
It does go to the right point in the cap board, between those two 27k/1w resistors. It does read about 389-390dcv.... its off right? Or is it because of those detached caps ?
I did read again V5 pins:
P1 331dcv
P2 342dcv
P7 0dcv
P8 5dcv
P2 0-1dcv
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What a brave build by uki for his experience level. You guys are all saints and should get a 12-pack each at least... (I just breezed over this about 15 mins ago & am surprised it took so long to recognize the filter cap string right at the input jacks - you guys are slippin' :laugh:) With so many lo & hi Z and B+ wires all over the place next to each other it's amazing it's quiet at all? Well done just to get to this point everyone. This is like one big class project?
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What a brave build by uki for his experience level. You guys are all saints and should get a 12-pack each at least... (I just breezed over this about 15 mins ago & am surprised it took so long to recognize the filter cap string right at the input jacks - you guys are slippin' :laugh:) With so many lo & hi Z and B+ wires all over the place next to each other it's amazing it's quiet at all? Well done just to get to this point everyone.
Crazy stuff isn't it ?! :laugh: Yup I did got lots of help, hints and tricks from the good folks around here. I'm too surprised with the result, for a first build and my lack of knowledge about tube amps and electronics. :icon_biggrin:
Some shielded wires here and there, some rerouting of those Z(whatever it is) and B+ did the quiet state come about, it is indeed quiet, really quiet(without V5 tube)!! Just the V5 circuit hum to fix and then looks like it is good to gig !!!
This is like one big class project?
Just something I've always dreamed about, but those amps down here where I live are way too expensive, when I've found the schematics online I saw the way to make it happen !! It is been a big learning curve and I'm enjoying it a lot!! Thanks for step by !!
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I want you to reconnect the two yellow caps that have one lead dangling back to the turrets they were originally on. Continue to have V3 and V4 unplugged.
Next I want you to ground V5 pin 2 and pin 7 to chassis ground. Look at the attached pic to see how to do this. You will see three turrets circled in red. Solder two short pieces of wire to connect all three of those turrets together. Does the hum go away?
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Yes the hum is gone with this connection, standby switch does some pop when turning off, very low volume at VIB channel, I think that is the expected behavior since V3-4 are out.
We are getting very close I take !!! :icon_biggrin:
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What a brave build by uki for his experience level. You guys are all saints and should get a 12-pack each at least... (I just breezed over this about 15 mins ago & am surprised it took so long to recognize the filter cap string right at the input jacks - you guys are slippin' :laugh: ) With so many lo & hi Z and B+ wires all over the place next to each other it's amazing it's quiet at all? Well done just to get to this point everyone. This is like one big class project?
I did not notice either because I did not consider someone putting one there. It is quite a project at any skill level.
I cant believe the normal channel is quiet, but if it works it must be ok. I am surprised, but it looks like he may just get this thing quiet.
UKI, keep on going man.
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Ok, remove those two short jumper wires. Now look at the attached pic and remove the two 1M resistors that are circled in red. How's the hum?
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What a brave build by uki for his experience level. You guys are all saints and should get a 12-pack each at least... (I just breezed over this about 15 mins ago & am surprised it took so long to recognize the filter cap string right at the input jacks - you guys are slippin' :laugh: ) With so many lo & hi Z and B+ wires all over the place next to each other it's amazing it's quiet at all? Well done just to get to this point everyone. This is like one big class project?
I did not notice either because I did not consider someone putting one there. It is quite a project at any skill level.
I cant believe the normal channel is quiet, but if it works it must be ok. I am surprised, but it looks like he may just get this thing quiet.
UKI, keep on going man.
This is the same issue that caused hum in Mike's Tweed build recently in that the B+ was right next to his input grid resistors and wiring. However I think uki changed his to using shielded cable on his inputs right?
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This is the same issue that caused hum in Mike's Tweed build recently in that the B+ was right next to his input grid resistors and wiring.
We thought that about a hundred posts ago, but it's not the case in uki's amp.
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Without that two resistors there is a little hum like if a guitar was plugged, not the big bad hum like before, a louder pop noise now when turning off standby switch.
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How does the guitar sound through the vibrato channel?
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I had one of the wires to V5 a bit loose its soldered properly now. There is some hum not as much as with the components, the VIB channel works, the guitar sound is coming through now, not as before in really low volume.
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Trying to get some kind of benchmark here. Would you say the level of hum is acceptable? Would you say the guitar sounds good through the vibrato channel? Would you say the only issue with the vibrato channel is the fact that the vibrato effect does not work?
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The hum is loud enough, not as bad as with the components attached, but not acceptable, sounds bad, the guitar sounds good in the VIB channel like it should be, besides the hum.
I did remove V5 again to compare, very quiet that way, very good.
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OK. Leave those two resistors out for now. Pulling those resistors should have had the same result as disconnecting those two caps. I'm running out of ideas. I suspect a grounding problem in the V5 circuit. Or maybe a poor solder joint. Also, there are jumpers under the board in this circuit. Do you know they are securely in place? Describe how you did the under-board jumpers. Connect a gator jumper lead to the turret that serves as a ground point for V5 and connect the other end to chassis. Any better?
I'd heat up every turret in the V5 circuit and reflow some fresh solder. Make sure the solder connections at the socket are secure also. Make sure the B+ connection to the filter cap board is good. And make sure the negative side of that filter cap is securely connected to chassis.
Tell me what you find.
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Also, there are jumpers under the board in this circuit. Do you know they are securely in place? Describe how you did the under-board jumpers.
There are 3 jumpers in that section.
I did check those jumpers several times and just now as I read your last post, did the checking with meter for continuity, they are secure, unless this isn't a good way to check. I did plugged the tip of the wire in the bottom end of the turrets and soldered them, I've used the same type of solid wires as all else.
Connect a gator jumper lead to the turret that serves as a ground point for V5 and connect the other end to chassis. Any better?
I tried that and no difference.
I'd heat up every turret in the V5 circuit and reflow some fresh solder. Make sure the solder connections at the socket are secure also.
Did that as recommended but no change.
Make sure the B+ connection to the filter cap board is good. And make sure the negative side of that filter cap is securely connected to chassis.
Checked the connections for those points as well they read good with the meter.
With the digital meter at 200 the connection from the board to ground read 1.2 ohms, that is the lowest my meter can go.
When reading B+ point in the board to ground in ohms, it does close circuit and then start dropping slowly like the a cap been discharged.
Tell me what you find.
Did the chopping again, and there are 3 noise points that does get amplified, all else doesn't do it.
The noise points are the 2 ceramic caps(blue ones) when tapped at the top, the noise does get amplified, and the P1 connection to the 470k and 100k turret.
I did read the electrolitic cap there under ohms, it does give some reading at the max of the meter, did it with the analog one.
Mentioning again that cap is a bit out of specification, schematic says 4µF/25v the installed one is 4,7µF-25v, also the 470k resistors are reading 288k.
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Mentioning again that cap is a bit out of specification, schematic says 4µF/25v the installed one is 4,7µF-25v, also the 470k resistors are reading 288k.
The cap is fine. The resistance reading is fine too. When you put your probes across one of those 470Ks if you look you will see that the probes are also across a 100K + another 100K + the other 470K. That adds up to 670K. The 670K is parallel to the 470K so the total resistance calculates to be 276K.
The problem has to be right there around the V5 circuit. I don't think I can do anymore without actually having the amp in my hands. I seem to remember that at one time you were using double sided carpet tape as an insulator under the board? (Or was that not you?) That has been fixed, right? And there is no carpet tape residue on the bottom side of the board?
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I don't think I can do anymore without actually having the amp in my hands.
Man you did a lot and I'm forever thankful for all your help !! :happy2:
I seem to remember that at one time you were using double sided carpet tape as an insulator under the board? (Or was that not you?) That has been fixed, right? And there is no carpet tape residue on the bottom side of the board?
Nop, nothing like that in the amp, nothing bellow the board but some wires and the chassis.
The problem has to be right there around the V5 circuit.
It is probably right in front of us but we can't see it, someone with fresh eyes and mind would help.
A bad component maybe? Maybe the other guys come up with some ideas! :anyone:
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I would be inclined to replace all the V5 vibrato components ...... OR change vibrato to reverb (dwell & reverb pot).
Sluckey's the best there is in trouble shooting help on this forum. If you haven't goten it fixed with his help, I'd look at plan B.
With respect, Tubenit
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I would be inclined to replace all the V5 vibrato components ...... OR change vibrato to reverb (dwell & reverb pot).
Sluckey's the best there is in trouble shooting help on this forum. If you haven't goten it fixed with his help, I'd look at plan B.
With respect, Tubenit
My plan B is to completely remove the vibrato. I'll look for replacing components for now. Which ones in V5 you think are the more critical to problems ?
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I don't really suspect a failed component, but you never know for sure. There are only 14 resistor/capacitors in the V5 circuit. I would replace all of them. And there's always a chance that the problem will inadvertently be fixed during the process of replacing them.
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What is the chance of the wires from OT primary(they are going right bellow that area) and that red wire B+ from the diode board and/or even the diode board position be the cause of hum? All that is very close to V5 circuit.
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Sure it could be something like that. It all goes back to the layout issues that have been discussed. I don't know how to fix that. Well, I do, but I know you don't want to do that.
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A - What would you do? What do you have in mind?
B - Lets say plan B, I've modified the schematic/layout without vibrato would that work? (Did it as some study few days ago)
(Images fixed)
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B - Lets say plan B, I've modified the schematic/layout without vibrato would that work? (Did it as some study few days ago)
That's not quite what we did. That will leave your vib channel much much weaker than the nor channel. This is what you need to do for plan B...
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Cool thanks !!
So I did somewhat good redraw, I wouldn't know about that little detail.
It is good to have a plan B, but I'm not at plan B yet, nono, I'll try harder, gonna get some spare components and replace them, one at a time to find out where the problem lies, gonna take a few days until I have those components thou, some break will also be a good thing.
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I did tried plan B, but it didn't was what I was thinking, so I went back to plan A and thanks to plan B I found a missing link, from a resistor to ground, that didn't make the vibrato to work but it did reduced the hum about 40%, but I'm not fiddling with it for now, gonna just play and enjoy w/o V5 which makes all the hum disappear.
Here a sample of the amp sound !! (https://youtu.be/re_MZq_dmyo)
! No longer available (http://www.youtube.com/watch?v=re_MZq_dmyo#)
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... it does seem to be finicky about what tube is used in the vibrato circuit. I made a list of 7 brands and only two were usable the other 4 had a loud hum increasing and decreasing with the vibrato. With the right tube it doesn't do it at all....
http://el34world.com/Forum/index.php?topic=20798.msg222410#msg222410 (http://el34world.com/Forum/index.php?topic=20798.msg222410#msg222410)
The JAN, and Sovtek were both quiet. I have the Jan in now. The JJ's were the absolute worst they made it into a hum vibrato. China made were next to the worst...
So vibratos are picky about tubes...
After reading this I got a new perspective about the problem in the 6G8 amp, since my amp had the same problem, a bad hum in the second channel "related to the vibrato"... well it was the JJ tubes.... I have replaced all of them(JJs) for old tubes and the hum is completely gone!!
:happy1:
Well but the vibrato still not working, the only thing I get is some noise when turning the intensity pot between 9 and 10.
What can I do about it ?!
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It was working but with the hum reduced in post 179, and you haven't changed anything since it was working except for swapping tubes?
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It was working but with the hum reduced in post 179, and you haven't changed anything since it was working except for swapping tubes?
Vibrato never worked. :sad:
Haven't changed anything besides the addition of the wire that connect the board to the jack for the foot switch which were missing.
I have swapped all the preamp tubes, they were all JJ(cheap stuff man) now I got only old tubes into it, the tone is way better now, the tube in V5 have less gain than all others, it has no print, it is maybe a 12at7 or 12au7 or something like that for sure not a 12ax7.
The only thing remaining to complete the amp is the vibrato effect !!
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:bump1:
Hey guys I have managed to get the amp working nicely, no more hum or anything weird going on, like when I've started. :laugh:
Now the last thing to get working is the vibrato, :dontknow: :help: :anyone:
The only thing happening is a small noise when turning the intensity pot to max or zero, nothing on speed pot, what to do ? :w2:
Thanks in advance ! :icon_biggrin:
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Hey guys I have managed to get the amp working nicely, no more hum or anything weird going on, like when I've started.
That's great, what did you do to fix it?
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Check the voltages on V3, oscillator tube. If pin 1 is not jumping all over the place the oscillator is not working. Check voltages on V4 also.
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Hi Willabe ! Here how !! :icon_biggrin:
That's great, what did you do to fix it?
I have swapped all the preamp tubes, they were all JJ(cheap stuff man) now I got only old tubes into it, the tone is way better now, the tube in V5 have less gain than all others, it has no print, it is maybe a 12at7 or 12au7 or something like that for sure not a 12ax7.
See: I got my cabinet in today. It turned out great. This is a very good tube effects project. it does seem to be finicky about what tube is used in the vibrato circuit. I made a list of 7 brands and only two were usable the other 4 had a loud hum increasing and decreasing with the vibrato. With the right tube it doesn't do it at all. I would recommend it because you can use it with any amp. The cost was pretty low to build because of the small trannies and one output tube. Thankfully Sluckey didn't give up on me getting it fixed and helped throughout the project. Thanks to Sluckey and everyone else that helped out!
The JAN, and Sovtek were both quiet. I have the Jan in now. The JJ's were the absolute worst they made it into a hum vibrato. China made were next to the worst...
@Sluckey here are the readings.
The voltages on V3 and V4:
V3
P1: 111-160vdc (jumping)
P2: 0
P3: 0
P6: 280vdc
P7: 112-160vdc
P8: 61vdc
V4
P6: 248vdc
P7: 0
P8: 61vdc
Ok what next ?
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V3 pin 8 should be more than pin 7. Probably about 165V. Why is it so low?
V4 pin 7 should be some relatively big positive voltage, but less than pin 8. Why is it zero?
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> V3 pin 8 should be more than pin 7. Probably about 165V. Why is it so low?
> V4 pin 7 should be some relatively big positive voltage, but less than pin 8. Why is it zero?
Meter loading in high-resistance grid circuits?
May not be a classic 11Meg VTVM meter.
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V3 pin 8 should be more than pin 7. Probably about 165V. Why is it so low?
V4 pin 7 should be some relatively big positive voltage, but less than pin 8. Why is it zero?
I have no idea :dontknow:
> V3 pin 8 should be more than pin 7. Probably about 165V. Why is it so low?
> V4 pin 7 should be some relatively big positive voltage, but less than pin 8. Why is it zero?
Meter loading in high-resistance grid circuits?
May not be a classic 11Meg VTVM meter.
What is that :w2:
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Oh man i got it wrong ... :BangHead:
V3 P8 have indeed more voltage than P7
I did the readings again:
V3
P1: 105-158 vdc (jumping)
P2: 0
P3: 1.1-1.4 vdc
P6: 277 vdc
P7: 105-158 vdc
P8: 122-193 vdc
V4
P6: 239 vdc
P7: 3.46 vdc
P8: 53 vdc
While reading pins 6 there is a loud noise.
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Go back to reply #159. Did you put those two 1M resistors back?
Read forward from reply #159 to present. Several things were tried to bypass the vibrato circuit. Has all that stuff been returned to original?
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Yes all that stuff is been put back as original at that time, the circuit is as in the schematic/layout. The small alterations for testing were undone short after the tests. Does the voltages read good ? What should I look after next ?
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Those voltages indicate that the oscillator (V3 and V4) are working. That just leaves V5. And we have been all over V5 chasing the hum issue. I'm out of gas and I'm not gonna go back over that old stuff again. I can't fix it without being able to put my hands on the amp.
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All good Sluckey !!
Thank you so much for the help !!
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Uki, you have come a long way from when you 1st got here. :icon_biggrin:
I think you can fix it now. The oscillator/LFO is working and Sluckey said "That just leaves V5."
So focus on V5.
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Uki, you have come a long way from when you 1st got here. :icon_biggrin:
I think you can fix it now. The oscillator/LFO is working and Sluckey said "That just leaves V5."
So focus on V5.
Thanks Willabe !! I will keep looking, it is probably something trick and almost invisible that I'm missing...
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Hey guys !
You know I wont give up on this, I have been playing with the amp, and now that the second channel works, after fiddling with the controls I notice a 2 things:
1- When volume is at zero on both channels there is a low guitar sound coming through the speakers.
2- The second channel when treble is at max and volume at about 8-9 the amp squeals, and the noise change as the pot goes up until 10.
Could this info help solve the problem ?