Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: HommeMarrBuckley on December 26, 2014, 11:55:28 pm
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Hello Everyone,
It has been awhile but I am nearing the end (hopefully) of my scratch build Bassman 6g6B build. This is my first build and it has been a learning experience. I spent most of the summer building the cab and head which was a first in woodworking as well. Anyway, I don't want to bore anyone and was hoping this wouldn't be a never ending debug due to my abilities. But after a great deal of time, I was ready to fire up the amp through the cab to set the bias. I ran into some issues. Two shorts and a fuse blown later, here I am. I have sound on both channels but it is nowhere the volume this amp should be producing. Second, the voltages on V IV seem to be off.
First here is a link to the schematic and layout.
http://www.gad.net/Blog/wp-content/uploads/2011/06/1963-Bassman-6G6B-Schematic.jpg (http://www.gad.net/Blog/wp-content/uploads/2011/06/1963-Bassman-6G6B-Schematic.jpg)
http://www.gad.net/Blog/wp-content/uploads/2011/06/1963-Bassman-6G6B-Layout.jpg (http://www.gad.net/Blog/wp-content/uploads/2011/06/1963-Bassman-6G6B-Layout.jpg)
After completing the circuit and then the woodwork and a lot of time, I was a little impatient to try the amp out. I went to test the voltages and set the bias which I have never done before. I installed 1ohm resistors and hit the weeds.
Short 1 - On power tube V6, while testing voltage on pin 3 from OT, I didn't realize the lead was too long and close to touching pin 4. Bright lights and smoke and I fried the top ring terminal of pin 3.
Short 2 - Voltage testing remix, voltage readings were going fine but when I went to test bias, I forgot to switch from mV to V on the Fluke. Went to pin 3 of power tube V5 and fried top ring terminal 3 there.
So, I have two power tube sockets with both pin 3s top ring terminals fried.
After the second issue, the amp wouldn't kick over and realized the fuse was toast. I replaced it and completed the voltage readings which are as follows.
Parentheses are (Fenders) followed by mine. Some I am not sure on how to designate and some I have missed on the board.
From Bias rectifier board (-54) -58.3 to point on board by (2) 220 k resistors (-54) 51.2
(layout) Red wire from bias to board (430) 470
yellow wire point to right of it on layout (428) 470
black choke / red OT on board (430) 471
V1
pin 1 (135) 142.1
pin 6 (230) 263.2
V2
1 (150) 171.8
6 (150) 177.6
V3
1 (230) 264.8
6(190) 220.6
V4 (here appear to be some issues) perhaps some components on the board
1 (300) 454
6 (280) 455
8 (30) 6.6
V5
3 (428) 469
6(428) 470
Bias 35.8
V6
3(428) 468
6(428) 469
Bias 36
Every component and part is brand new from the filter caps to the transformers to the jacks etc.
During all of this (shorts, fuse, readings) I was able to get sound.
The Bass channel is slightly louder than the normal channel. Bass channel is dead quiet until about 3-4. Sound comes in about middle-6 on normal channel. Both channels maxed are nowhere near the window shattering volume it should be but they sound reminiscent of the tone of those channels if that makes sense.
I also built the speaker cable with this thing. I wasn't sure to mention it or not but was wondering if it could be choking the signal. I don't know. It's pictured later and it was made from 2 strands of white 18 GA with 2 strands of black 18 GA and pancake plugs.
I am hoping with everything that I didn't damage something severely, especially the power tubes, I am using winged Cs and they're not in production anymore.
I know there is definitely something wrong around tube 4. I just hope I am able to fix that along with the volume but if not I will probably have to venture to the tech which kinda defeats the purpose of scratch building an amp.
Im all ears and any input is appreciated.
happy holidays.
Matt
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Turn the amp off and measure resistance from V4 pin 3/8 to chassis. Should be about 12K. If not, check resistors in the highlighted path from V4 to presence pot (see pic). Should have a 820Ω, 6800Ω, and 4700Ω.
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I am hoping with everything that I didn't damage something severely, especially the power tubes, I am using winged Cs and they're not in production anymore.
I would use different power tubes, a cheap(er) or good used set, that way if you blow them up not as big a deal, until the amp was up and running with no problems.
The speaker cable made with the doubled up 18 gauge should be ok, but the single speaker wire (18 gauge?) connecting the 2x12's looks like it's a little thin (gauge) for the current going from the OT secondary to the speakers. (Not saying it's your volume problem, V4's voltages are off, do what Sluckey tells you.)
When posting the tube pin voltages you need to post the grid and cathodes (K) also, so pins 1-2-3 and 6-7-8
(for 12 _ _ 7, 1/6=plate, 2/7=grid, 3/8=K).
For the output tubes, grid 1 (input/control grid) and screen grid along with K and plate.
On 6L6's, 5=grid1, K=8, screen=4, plate=3.
And check/post your heater voltage, just to be sure it's wired correctly on a new build. Red meter lead to 1 heater pin and the black lead to the other heater pin, not to ground.
When testing voltages use the alligator clips on your meter leads so you don't short anything from pin to pin on a tube.
Brad :icon_biggrin:
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On new builds or when rebuilding a power supply, changing a PT or firing up a none working amp or an old amp use a light bulb limiter. It can save the amp from going up in smoke if there's a short. :w2:
http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf (http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf)
Brad :icon_biggrin:
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Turn the amp off and measure resistance from V4 pin 3/8 to chassis. Should be about 12K.
Won't be able to do anything until Monday. Just don't have the space here to work on it so keep it at my folks. So, I will set the MM to ohms and measure that. Can I measure resistors soldered to board? Just set it to ohms and put probes on leads (even though they're soldered in)?
I would use different power tubes, a cheap(er) or good used set, that way if you blow them up not as big a deal, until the amp was up and running with no problems.
I was thinking the same thing.
When posting the tube pin voltages you need to post the grid and cathodes (K) also, so pins 1-2-3 and 6-7-8
(for 12 _ _ 7, 1/6=plate, 2/7=grid, 3/8=K).
Set to volts, ground and pretty much get a reading on all pins besides heaters? ok.
And check/post your heater voltage, just to be sure it's wired correctly on a new build. Red meter lead to 1 heater pin and the black lead to the other heater pin, not to ground.
When testing voltages use the alligator clips on your meter leads so you don't short anything from pin to pin on a tube.
Pins 5 and 9 on preamp tubes and 2 and 7 on power. Assume it doesnt matter which color lead to which pin. Set to volts here as well, I guess. I was using the probe for the readings (kept it still) The clips were a little tricky and passed on them. Not much space in and around there. Saw benefit of adding bias probes to chassis, as well.
What's a good way to discharge voltage afterwards? I set red lead to pin 1 of V1 and ground to chassis but the voltage slowly dropped off. From like 17.87 to 17.86 to 17.85 and so on.
Here's a snippet of the cab joints. Happy how that turned out without doing any woodworking before but will probably never buy lumber from big box store. Learned hard way with warped boards.
When all is right will post finished pics and sound. Have some staining and then just a matter of screwing it together. Besides this-working on plates.
Thanks
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Turn the amp off and measure resistance from V4 pin 3/8 to chassis. Should be about 12K.
Can I measure resistors soldered to board? Just set it to ohms and put probes on leads (even though they're soldered in)?
If you just put one meter lead on ground and the other on V4 pin 3/8 (as Sluckey said), it will at once verify the value of all those resistors, your soldering work, and the ground at the Presence pot. This is a shortcut to see if any further probing is needed.
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Willabe makes a very good point when he says "When posting the tube pin voltages you need to post the grid and cathodes (K) also, so pins 1-2-3 and 6-7-8 (for 12 _ _ 7, 1/6=plate, 2/7=grid, 3/8=K). For the output tubes, grid 1 (input/control grid) and screen grid along with K and plate. On 6L6's, 5=grid1, K=8, screen=4, plate=3.
The voltages you find on the preamp tubes don't exist in a vacuum (no pun intended). You want, both as part of asking for the assistance and for your own understanding, to know that for all the 9 pin tubes, we have two triodes, with pin numbers 1-2-3 and 6-7-8 for plate-grid-cathode. With the exception of the reverb driver tube and the PI, we expect to see about 180 volts on the plates (but could be as low as 120-150 and as high as about 250-280----not in Fender amps, but in others) and a single-digit number of volts on the cathodes. We expect to see almost nothing on the grids.
When that condition exists, we can have good confidence that tube is "set up" in a way that if we apply an AC signal to the grid, there is reasonable chance that the tube will be able to amplify. We want to see the positive volts on the plate, we want to see the grid a bit negative relative to the cathode (and this is sometimes hard to see when you're learning) but with the cathode at 2-3 volts and the grid at zero volts....the grid is, actually, negative relative to the cathode.
But what is more important for your own understanding is the "grouping" of those tube pins. In other words, don't list your voltages 'plate V1A, plate V1B, plate V2A, plate V2B'. What V1 has on its plate has utterly nothing to do with what V2 has on its plate. What *is* important are the relative voltages on plate-grid-cathode of V1, plate-grid-cathode of V2, etc; etc.
The reverb driver is a special case because the tube gets very high volts (~~425-450) in a reverb amplifier; you don't have that in your amp. The PI is a little different because the cathode is elevated, 30 or so volts in your amp, almost 100 volts in an AB763.
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V4 pin 3 .843 M resistance.
Wasn't sure to do something else with it powered off before checking voltages.
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V4 pin 3 .843 M resistance.
.843M = 843K and it should be around 12K, way off.
So now measure each of the 3 resistors Sluckey pointed out. You probably have a wrong value resistor in the string.
Brad :icon_biggrin:
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Sorry if this sounds stupid, but measure both leads of resistor or keep grounded and measure end point of each?
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Measure across the R, 1 meter lead to 1 R lead the other meter lead to the other R lead. Meter set for resistance.
Brad :icon_biggrin:
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From presence pot down. (Fender)
(4700) 4.37k
(6800) 6.83k
(820) .83 M
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(820) .83 M
No, 0.830M = 830,000 ohms = 830K ohm's.
So does it read 820 ohms or 830K ohms?
Brad :icon_biggrin:
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This is what it shows
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What are the color bands on that R?
If it's an 820 ohm resistor they will be; gray/red/brown.
Brad :icon_biggrin:
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:icon_biggrin:
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I bet that R you put in colors are; gray/red/yellow.
My meter reads 0.820M with a 820K R and 0.820K with a 820 ohm R.
Brad :icon_biggrin:
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No, 0.830M = 830,000 ohms = 830K ohm's.
So does it read 820 ohms or 830K ohms.
I kept reading this and realized.
It looks looks to be gold yellow red and probably gray
which would be 820k
Probably ordered and placed wrong value.
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Bass pot bass channel
Looking elsewhere as well
Thank you
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It looks looks to be gold yellow red and probably gray
which would be 820k.
Your reading it backwards. Gray/Red/Yellow/Gold, gold is tolerance.
Probably ordered and placed wrong value.
Yes, wrong resistor value, it's an 820K (= 820,000) resistor.
Look at this chart on R color code posted below. It shows 5 band AND 4 band color code.
Brad :icon_biggrin:
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> gold yellow red and probably gray
We usually read the other way (gold last), but you are correct: 820K.
> This is what it shows
The meter shows 0.830Meg or 830K or 830,000 Ohms.
The schematic shows 820. Without a K or an M. It should be 820 Ohms.
I do not care if the first part is 82 or 83.
But by the number of zeros, you have a Thousand Times more ohms in there than Leo picked.
In this case, the PI tube is forced to run with a thousand times less current than Leo thought best. It's feeling awful weak.
If you do not have a 820 in the shack, 470 or 1K will work a LOT better than a resistor 1,000 times too big.
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This is what it shows
Did you replace the resistor yet? Sound OK now? Any more problems?
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Sorry for the delay but things are pretty good.
After removing the wrong resistors and installing the new ones, I was pretty impatient in testing out the amp so I plugged it in and it worked!!!
Sound and volume came through as I thought they should be. I don't want to write too much about my reactions because it's off topic but I was impressed with the responsiveness of the amp. Also, I read numerous times, the distaste for the bass channel but I didn't have that vibe. I spent a great deal going through tones (I gave my strat 7 way mod some time ago).
I went through voltage readings again but I was much more nervous this time. I was just really afraid of after finally getting an end result that I might do something to damage it so I was much more skittish this time.
V1
1 143.6
2 0
3 1.48
6 267
7 143.6
8 146
V2
1 174.3
2 0
3 1.39
6 179.5
7 .003 (??)
8 1.3
V3
1 174.3
2 0
3 2.07
6 218
7 0
8 2
V4
1 331
2 22.3
3 34.5
6 312
7 23
8 34.5
V5
3 476
4 477
5 -50.9
6 478
Bias 36.7
V6
3 477
4 478
5 -50.9
6 478
Bias 36.5
In terms of heater voltages, (Im sorry Brad) here is where my nerves got the best of me. On V6, I got 6.3 or 6.5, can't recall exactly because I remembered more the spark I got when I removed the clips. I decided not to press on from there. Im looking at better clips for the meter. These have good insulation but are not very sturdy--meaning that they tend to sag and don't hold firm upright. I still have to spray paint/create baffle and stain the wood and with winter in PA like it is, it might be some time before I am able to do those out in the garage. So, I haven't quit on it because it's not getting screwed in the head cab any time soon so I might come back to it. It helped me look at my layout and I see some things that I could have done better or correct. I really should have splayed out the tube pins more. I don't necessarily like my wiring around the bass input jacks in relation to the ground bus.
This leads to when I initially played through. Upon flipping standby, there is hum. Once I start and stop playing, it's not there. Upon thinking about it, I haven't screwed the filter cap can on yet. Does this play a role? Also, I read that it's good to put some foam insulation on the top of the can to help prevent rattling caps but I was concerned with fire hazard. All in all, the hum made me look around grounding areas and tube sockets. I checked the forum for Hoffman's ground diagram and all seem to be good in relation to it. I just don't like the length of the ground wire from RG74 wire by bass jack and tube sockets seem to have much more going on in the center--inductance?? Reminds me of a flower bud--like mine are at nighttime when they should be spread out like daytime/noon.
Perhaps unrelated, but nearly every amp I have had I was able to pull in radio sound very very faintly when powered on. This includes Boogie Tremoverb, SF Twin reverb, etc.--decent amps. Now, the home is pretty high up on a hill but I noticed even this happened when I was checking voltages (while reading I could barely hear radio). Perhaps, it is hard to eliminate due to elevation. Regardless, I don't have it when I power on so it really doesn't matter.
Anyway, Im posting too much here but just wanted to say that I am grateful for the help and everyone that chimed in to pinpoint a simple mistake. I am really glad it wasn't something major.
This forum and you guys are great, Thanks again!! :notworthy:
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Voltages look good.
I haven't screwed the filter cap can on yet. Does this play a role? Also, I read that it's good to put some foam insulation on the top of the can to help prevent rattling caps but I was concerned with fire hazard.
You're talking about the sardine can that we like to call the doghouse, right? That's not a factor with hum. The only reason those caps are covered is to prevent someone from getting a nasty shock. Foam insulation is good. There's no fire hazard if done properly. Just keep the foam off of the resistors. Caps should never be warm unless they are bad. I would use self-adhesive high density foam refrigeration/pipe tape just because I'm looking at a roll right now. My roll is 2" wide and 1/8th inch thick. Door and window insulation would work well too.
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Hey glad you got it working! :icon_biggrin:
Your not the 1st guy and wont be the last that had a wrong value R or 2 in a build, it happens to the best of them.
In terms of heater voltages, (Im sorry Brad) here is where my nerves got the best of me. On V6, I got 6.3 or 6.5, can't recall exactly because I remembered more the spark I got when I removed the clips.
You don't have to apologize, we all get a little nervous after a spark. :icon_biggrin:
I brought up checking the heater voltages because the amp wasn't working, now that it's working and you verified ~6.3 at 1 power tube your good. You don't have to check them all.
Here's a few things for next time;
1. Yes get some better clips that you trust.
2. When using them put them on with the amp OFF then turn the amp on, take your reading, then turn it off again before you move the clips.
3. The power tubes have the highest voltages in the amp at their socket. So take your heater voltage reading at the 1st preamp tube, it has the lowest voltages in the amp and it's the last tube in the heater string so if it reads good then all the other tubes will normally be good also. (In a rare case the tube sockets heater pin could be broken and the tubes heater pin wont get the voltage, but this is extremely rare.)
Brad :icon_biggrin:
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:blob8:
Great news Matt. Glad you got it going. I feel a little responsible for you catching the Tube Amp Virus. Now that you know how they work and are playing what others do you have in mind to build?
It is a great circuit, I wish I had occasion to play mine more.
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In evaluating hum issue, perhaps I will shoot a quick youtube vid of it so it's understood/heard better.
:blob8:
Great news Matt. Glad you got it going. I feel a little responsible for you catching the Tube Amp Virus. Now that you know how they work and are playing what others do you have in mind to build?
Thanks Ed, I don't think it's the bug to create amps as much as people like you and the forum being supportive to those like myself that have no experience. I value that. I lurked and read on some other places in relation to this amp and didn't like the vibe I felt there. If I would have saddled up there, I probably would have shut down a long time ago. So cheers to this place, Im staying.
Next? It will be a Rip Van Winkle Supro Thunderbolt. RVW in that it will take me awhile but I saw another build that I would like to try to copy. It will be a challenge with the point to point and looking hard at the schematic and layout on my own but I think it's within my grasp. I pretty much have all supplies but it will wait until I finish this one. I am sure I will have plenty of questions posted here.
I will post vid as soon as it's avail. Hopefully next week.
Matt
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Link to vid
https://www.youtube.com/watch?v=KuZtGJC1bak (https://www.youtube.com/watch?v=KuZtGJC1bak)
Not the greatest in vid/audio quality. It is much louder in person. Put phone cam in front of speaker so you can hear it without guitar plugged in. Hum does not change when I turn volume knob. Have no idea if it's 60 or 120.
Then plug guitar in and it's barely audible in person and in vid.
Any suggestions?
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Have no idea if it's 60 or 120.
Your Fluke 87 does. :wink:
Take your meter leads and put em across the speaker leads.
Set the meter per the instructions below:
Here's the rest of the manual:
http://media.fluke.com/documents/80v_____umeng0200.pdf (http://media.fluke.com/documents/80v_____umeng0200.pdf)
Oops, different series...
Instructions are similar enough
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Looks like you may have either a ground loop or your input jacks are not closing. Check the jacks first.
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Take your meter leads and put em across the speaker leads.
At work right now uggg, so this will have to wait until tomorrow. Sorry SG, but not sure where I put the leads. On amp speaker jack? or 2 points on cab jack? Im sorry but you will almost have to tell me like you would a kid.
Looks like you may have either a ground loop or your input jacks are not closing. Check the jacks first.
What do I need to look at/ look for in terms of them not closing?
I know in terms of the jacks especially the bass channel, that I was concerned of the distance of the bus bar to them. Plus, using the rg wire there. The ground wire to bus was somewhat long. I think there were a few broken strands there too. I can post a pic later. Sorry for my ineptitude.
Thanks for the suggestions.
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Take your meter leads and put em across the speaker leads.
At work right now uggg, so this will have to wait until tomorrow. Sorry SG, but not sure where I put the leads. On amp speaker jack? or 2 points on cab jack? Im sorry but you will almost have to tell me like you would a kid.
If you have an open back cab and can see the speaker connection terminals, put one lead on each of those tabs.
If it's a closed back cab, you can just disconnect the speaker cable and put one lead on the tip and the other on the sleeve....or if the amp is still open you can read it right at the speaker out jack, one lead on the 'hot' and the other one on ground.
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it that chassis painted? if it is, you may not have a good ground connection on one of ground lugs or input jack(s).
--pete
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As far as I know, it wasn't painted.
Here's a pic of the bass channel input jacks. I copied this on normal channel as well.
Did I do these right?
http://min.us/i/byJrZKKrBi9Mi (http://min.us/i/byJrZKKrBi9Mi)
The RG74 is ground to the bus but then the white wire is coming off the jack to the bus too. Should it be like that?
(before someone asks--I know it looks like it in the pic) the ground jack (white wire) is not connected to the middle clustering tabs.
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I have been reading and it might be looking up because it seems from what I have read that if you have 2 grounds at the same point (my jacks) you will create a loop. I have to think this is what is happening from what I see and in the pic.
I hope this is it because I wasn't really looking forward to hunting this down somewhere else in the amp.
Do I just need to clip out that white wire?
off to bed
thanks
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I haven't looked at your schematic, just lurking. the easy way to tell "if you can clip the white, grounded wire", after you clip it, ohm it to ground, if it's " still grounded" then you just eliminated 1 ground loop.
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Read through this on grounding if you haven't already.
http://www.valvewizard.co.uk/Grounding.html (http://www.valvewizard.co.uk/Grounding.html)
Brad :icon_biggrin:
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Read through this on grounding if you haven't already.
Brad,
I read over pages 4 (265) and 9 (270) with ground loops and ground bus.
Without much of EE background, I wish it would diagram coaxial with ground bus together.
However, I was wondering if my white wire ground off jack (in the pic) needs to connected together with the RG74 coax ground at same point.
I dunno. It seems there is one connection (jack) with two different ground points and perhaps they need to have/share same ground point on the bus.
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That white wire is fine.
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It sounds like 120HZ hum to me. Same sound my champ was making. And if that is the case a Pi filter is needed to filter it out. An additional capacitor and resistor or choke (inductor) between the rectifier output and the first PS node.
http://www.valvewizard.co.uk/smoothing.html (http://www.valvewizard.co.uk/smoothing.html)
Also the RG-174 shouldn't be grounded at the tube socket (the other end) only at the source.
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The other end at the tube socket is not grounded.
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Ok I just looked at the schematic as I remembered the bassman has solid state rectification. How are the two 20uf capacitors wired up prior to the standby switch? Are the solder joints well done? Can you post up some good pics to show the detail of the PS filtering caps? there shouldn't be that much hum in this amp at all. A pic of under the doghouse where the big caps reside to show the wiring.
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I plugged into all four jacks. The "hi"s work on bass and normal channel and sound great, however, the "lo"s do not have any sound or volume at all.
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Jacks are not wired correctly. Wire your jacks exactly as shown in Hoffman's common hookups pdf...
http://el34world.com/Hoffman/files/CommonHookups.pdf (http://el34world.com/Hoffman/files/CommonHookups.pdf)
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You can still leave the 68K on the tube. The diagram Sluckey pointed to shows 2 of the 68K resistore, but notice they connect together and them to the tube. Just rework the jacks.
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I have the 68k grid stopper on the tube instead of using the two at the jack.
So, by that diagram on here for double inputs, I run the RG74 hot through Tip Lo jack ----- to Sleeve (Lo) and Tip (Hi) that are wired together. I have that.
Ground of RG 74?? Just goes to ground of Hi Jack---and then to bus, correct?
And Ground Lo Jack connects to bus? If so, I can keep mine as is--white wire in pic.
I understand 1 M resistor placement and mine is same.
So, from writing and reading this over and looking at my jack, it just looks liked I need to re-wire my RG-74 ground. It should go to the Hi Jack Ground and on to the bus bar.
My RG74 ground is not that long--guessing just connect it to Hi Jack Ground and run piece of 20GA from there to bus, right?
I am not sure. Was trying to look at similar double input jacks with coax.
This gain channel input of tweed deluxe is wired different.
http://robrobinette.com/images/Guitar/5E3P_Build/5e3p_Cascade_Coax_Layout.png (http://robrobinette.com/images/Guitar/5E3P_Build/5e3p_Cascade_Coax_Layout.png)
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If your using standard Switchcraft 1/4" jacks then the jack is automatically grounded to the chassis, make sure you use the lock star washer that came with it and tighten up the jack so it makes good contact with the chassis for a good ground.
So if you have a 4x input then you can run the pot ground buss to any of 1 the 4 jacks ground lug and it will be grounded.
If you use the plastic Cliff jacks like in Marshalls or isolating/insolating washers, then you have to wire up the ground lugs from each jack to each other.
Brad :icon_biggrin:
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Not trying to frustrate anyone and perhaps Im not seeing the wood for the trees but I assumed something is not correct right in my wiring because the Lo Jacks are not working.
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I have the 68k grid stopper on the tube instead of using the two at the jack.
I assumed something is not correct right in my wiring because the Lo Jacks are not working.
If you want it to work like the 6G6B hi/lo jacks you'll have to wire it IAW the schematic. You must use one 1MΩ and two 68KΩ. Doug's commonhookup pdf that I pointed to shows you how to do it in case the schematic is confusing to you.
Look at page 7 of this pdf if you want an explanation of how the hi/lo jacks work...
http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf (http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf)
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Alright, I think I get it.
So, if you look at my pic, I can cut the RG74 ground going to the bus bar and leave the white wire jack ground to bus
So if you have a 4x input then you can run the pot ground buss to any of 1 the 4 jacks ground lug and it will be grounded.
And with that, I can move over to the normal channel jacks and cut the ground lug pot to bus wire, as well, because I only need 1 of the four which I already have (bass channel white wire ground lug to bus)
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Not trying to frustrate anyone
Your fine, no problems. :icon_biggrin:
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(bass channel white wire ground lug to bus)
Your saying it backwards with respect to the flow.
Your talking about a ground buss and it's ground point. So it flows from > pots ground lug to > ground buss to > jack ground lug to > chassis ground point connection, in this case through the jacks ground lug which is connected to the jacks frame that connects to the chassis when bolted in.
You can connect the shield to any 1 of the 4 jacks ground lugs.
Brad :icon_biggrin:
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If you want it to work like the 6G6B hi/lo jacks you'll have to wire it IAW the schematic. You must use one 1MΩ and two 68KΩ.
:BangHead:
Ok, If I want to use coaxial I need to remove the resistor on the tube and put the (2) 68k at the jacks as per schematic/diagram. I will run wire from jack ground lug to my bus bar and cut ground off of RG74 (and perhaps heatshrink the end there connecting to resistors)
I have some mogami cable left over from making guitar cables. Can I use that or is it best just to use the RG74?
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Ok, If I want to use coaxial I need to remove the resistor on the tube and put the (2) 68k at the jacks as per schematic/diagram.
No you can use shielded cable and leave the 2x68K R's on the tube socket.
Brad :icon_biggrin:
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Ok, If I want to use coaxial I need to remove the resistor on the tube and put the (2) 68k at the jacks as per schematic/diagram.
Yes yes yes. Do it that way. That's the simplest. The center conductor of the coax connects to the junction of the two 68Ks. The outer shield of the coax connects to to the ground buss OR the ground lug on one of the jacks. The center conductor at other end of the coax connects directly to the tube socket. Outer shield at the other end of the coax connects to NOTHING.
No you can use shielded cable and leave the 2x68K R's on the tube socket.
If you do this you will need two coax cables.
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No you can use shielded cable and leave the 2x68K R's on the tube socket.
If you do this you will need two coax cables.
I use a dual coax shielded cable for this.
Brad :icon_biggrin:
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Yes yes yes. Do it that way. That's the simplest. The center conductor of the coax connects to the junction of the two 68Ks. The outer shield of the coax connects to to the ground buss OR the ground lug on one of the jacks. The center conductor at other end of the coax connects directly to the tube socket. Outer shield at the other end of the coax connects to NOTHING.
Crystal clear.
Now, for normal channel. Everything wired the same BUT outershield of coax connects to nothing and ground lugs of jacks connect to nothing.
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Wire the normal input jacks EXACTLY like the bass input jacks.
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Great and understood.
Will post results Monday/Tuesday. Hopefully have some coax remaining.
Thanks for the patience.
Cheers
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I use a single coax, but I never use a low input. On Bassman setups, jumping channels works better for me to have 4, high inputs,
I don't understand.
On a stock 4x input amp if you plug into both the Hi and Low jack on 1 channel the way their wired up they will both be like plugging into the Hi jack alone. Right?
So what are you doing differently?
Brad :think1:
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I may be wrong, but it seems like there is a drop in signal on my 6G6 Bassman when I jump from the high on the Bass channel to the low on the normal.
Duh! The bass channel has 3 inverting gain stages. The normal channel has 2 inverting gain stages. That means when you combine the two channels just prior to the PI the signals will be 180º out of phase and there will be major cancellation going on.
Jumping normal and bass channels on the 5xx bassman amps works but it should sound like crap on the 6G9B.
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Can't be too wrong because it sound great.
If it sounds great then it can't be wrong.
Brad :laugh:
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Can't be too wrong because it sound great.
If you like the sound of two jumpered channels cancelling each other then it must be a good thing.
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The brittle highs is a result of the phase cancellation. Some people just say it sounds thin. I'd like to see the mod you are doing that results in no phase cancellation. Can you post a schematic?
The bass channel goes thru three 180º phase inversions prior to the mixing resistors. The normal channel only goes thru two 180º phase inversions prior to the mixing resistors. When you mix these two out of phase signals back together THERE ABSOLUTELY WILL BE PHASE CANCELLATION! Please try to convince me otherwise.
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The cap in question is a .002 capacitor inline with a 100k resister that leads to pin six on the second preamp tube. This capacitor acts as a treble bleed.
The cap is not in line. It's parallel to the 100K. Yes, it will bleed some treble. IT IS A BASS AMP. That channel was voiced for bass. Treble was not part of the bass sound back then.
I am saying the Bass Channel Stock is useless.
It was pretty useful FOR A BASS back in it's day. Leo made other stuff that sounded pretty good for a guitar.
Google the 6G6B Ness Mess.
Nope. I'm waiting for you to try to convince me there is no phase cancellation going on when you jump the channels of your 6G6B. You say when you jump the channels there is a loss of volume and the highs sound brittle, but in the same breath you say there is no phase cancellation. Those are two classic symptoms of phase cancellation due to jumping channels when one has an even number of gain stages and the other has an odd number of gain stages.
Steve, I swear I can count.
At least to 3! :icon_biggrin: Your math skills are not being challenged here.
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It was not in the same breath that I wrote where I stated it sounded Brittle.
It was certainly in the same sentence. Oh, maybe you took a breath during the comma? Or was that a coma? :icon_biggrin:
These amps have a simple known mod and there is no known cancellation, but it does cause the highs to be brittle as hell
however I have not modified my Brown Bassman since it is original.
Mind you, this amp is completely stock.
I did say it was stock, but it is not. The Bass channel does not sound good stock to me so I had to revise it some.
I consider an amp stock if the modifications are easily reversed.
Tell us what you really got? It's either stock or it ain't.
You're doing a lot of backpedaling buddy, but you're only driving deeper into the ditch. And just think... All because I said jumping the channels would sound like crap. You've made my point. :l2:
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Still can't figure out the smilies, but sluckey gets a +2. The build I have going are 2 channels jumped together, i made the mistake of counting a CF as an inverting stage, it sounded like S&*T, n my scope confirmed the ugly sound. Made the CF common n sounds nice n full.
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I am not arguing with Sluckey that the 6G6B's channels are not in-phase.
That's exactly what we've been debating!
I am arguing with Sluckey that it is possible to easily mod the Bass Channel to be in-phase and he keeps saying it prove it.
The only way you will ever mod that Bass channel to be in phase with the normal channel is to add an inverting stage or remove an inverting stage. Since the normal channel has an even number of INVERTING gain stages you must have an even number of inverting stages in the Bass channel. Otherwise when you mix the two together with simple mixing resistors THE CHANNELS WILL BE OUT OF PHASE WITH EACH OTHER AND THERE WILL BE CANCELLATION.
I mean all you have to do is wire it like a AA-864
Guess what? The Bass and Normal channels are out of phase on that amp too.
You can believe what you wanna believe, but you already made my point. And I'm satisfied that you cannot convince me otherwise.
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So you are saying if you revise the Bass channel of the 6G6B ond only the bass channel to an AA864 leaving the normal channel you will get phase cancellation when jumped.
Careful, you're twisting my words.
This is exactly what I said...
"Guess what? The Bass and Normal channels are out of phase on that amp too."
Nothing more, nothing less. You can twist that however you want, but then it becomes YOUR words.
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It is impossible to rework a 6G6 Bassman to not have phase cancellation when jumpered. :l2:
You twisted mine as you KNOW i was only speaking of the Bass Channel. You are the winner tho. And when you were young playing in bands you know the majority of bassmans were used for guitar.
Also Sluckey, don't back off. Really you are not bothering me. Don't let your one feeling make you feel bad for debating me. You finally learned you can run heater wires without twisting. BTW, you lost that debate. :icon_biggrin:
What is next, are you getting a little self conscience picking on a hobbyist when you have an extensive background in electronics. You can do much better if you try. :l2:
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Remember, I am sensitive. :sad2:
Your words, well maybe the words from Icehouse.
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It is impossible to rework a 6G6 Bassman to not have phase cancellation when jumpered.
Not true. I told you exactly what you must do to avoid phase cancellation.
And when you were young playing in bands you know the majority of bassmans were used for guitar.
Not so either. Back then EVERY Fender Bassman I ever saw had a Bass plugged into it, usually a Fender bass.
You finally learned you can run heater wires without twisting. BTW, you lost that debate.
Actually, I didn't start twisting filament wires until I started hanging out in amp forums. I don't recall any such debate. Can you post a link?
What is next, are you getting a little self conscience picking on a hobbyist when you have an extensive background in electronics. You can do much better if you try.
Hey, I'm a hobbyist too! And I'm currently between projects with plenty of time on hand. So watch what you say buddy. :icon_biggrin:
Your words, well maybe the words from Icehouse.
Alright! You finally got one right! But Icehouse speaks the truth and you should know it. Now I've got to make a beer run, but I'll be back. See ya buddy! :wink:
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So, the beauty of all of this is that we are slowly prying out the super secret non-stock, stock Bassman schematic from the great Ed Chambley..
:wav:
The world has been waiting.
So,, I'm assuming that an imaginary schematic would look something like this?
Channel jumper has been omitted but is implied. :wink:
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Of all people to mod an amp by taking OUT a 12AX7 I never thought it would be you SG!
Brad :icon_biggrin:
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Of all people to mod an amp by taking OUT a 12AX7 I never thought it would be you SG!
Being around all of you senior gents, I can't help but grow up a little... :grin:
But this is Ed's amp. I like the bass channel on the 6G6B, and used it recently.
If I were building it, I'dve added a triode to the normal channel. (so, you got me pegg'd)
But since he did these mods years ago, I'm just trying to get a working schematic going.
It must be SUPER DOOPER special since he's protecting it with all of these verbal gymnastics.
It must sound 2x as good as Brian Setzer's amp, because he only uses one normal channel and Ed uses 2 at the same time.
:thumbsup:
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Of all people to mod an amp by taking OUT a 12AX7 I never thought it would be you SG!
Being around all of you senior gents, I can't help but grow up a little... :grin:
But this is Ed's amp. I like the bass channel on the 6G6B, and used it recently.
If I were building it, I'dve added a triode to the normal channel. (so, you got me pegg'd)
But since he did these mods years ago, I'm just trying to get a working schematic going.
It must be SUPER DOOPER special since he's protecting it with all of these verbal gymnastics.
It must sound 2x as good as Brian Setzer's amp, because he only uses one normal channel and Ed uses 2 at the same time.
:thumbsup:
No, I use both channels on a Fender amp most of the time. When I cannot use 2 amps, one wet and one dry, I use the 2 channels on a fender, one wet and one dry. Usually I use the normal channel for my Dry signal except on this Bassman I use the Bass channel now.
I do mods and dont revise a schematic. I did a mod from Dave Funk on one of my Super reverbs last weekend and love it. It involves changing it to CF design.
You will not find a schematic for it, so
"IF IT IS NOT ON A SCHEMATIC IT DOES NOT EXIST".
...........................................................Sluckey, esq.
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Of all people to mod an amp by taking OUT a 12AX7 I never thought it would be you SG!
Being around all of you senior gents, I can't help but grow up a little... :grin:
But this is Ed's amp. I like the bass channel on the 6G6B, and used it recently.
If I were building it, I'dve added a triode to the normal channel. (so, you got me pegg'd)
But since he did these mods years ago, I'm just trying to get a working schematic going.
It must be SUPER DOOPER special since he's protecting it with all of these verbal gymnastics.
It must sound 2x as good as Brian Setzer's amp, because he only uses one normal channel and Ed uses 2 at the same time.
:thumbsup:
I did the mod about a year ago.
http://archive.ampage.org/threads/6/gagd/323798/6g6_bassman-1.html (http://archive.ampage.org/threads/6/gagd/323798/6g6_bassman-1.html)
The above link is a discussion and I have searched the metro forum, but I cannot find the step by step.
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I did the mod about a year ago.
http://archive.ampage.org/threads/6/gagd/323798/6g6_bassman-1.html (http://archive.ampage.org/threads/6/gagd/323798/6g6_bassman-1.html)
That's nice. But it has absolutely nothing to do with jumping channels on a Bassman 6g6B and the resulting phase cancellation.
I'd say you're out of bullets. Besides, you quit already.
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I won't swap personal insults with you. I'm done.
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I won't swap personal insults with you. I'm done.
Sorry, intended as a joke. I meant nothing personal.
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Almost finished the jacks. Underestimated the time needed and didn't have a good time with the RG-74. Really easy to break that outershield wire when cutting in.
Anyway, concerned with ground loop and before I put stuff away, I wanted to see if this was in unison.
My coaxial hot is going to the resistors and coaxial ground is going to the bus. Now, for the ground (Hi Jack) coming off of 1M resistor? Is it ok if I put that to the ground bus too?
SL, I read in the scrapbook about hi lo jacks and it makes sense. This ground I am asking about will help shunt when I plug into the Lo.
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Now, for the ground (Hi Jack) coming off of 1M resistor? Is it ok if I put that to the ground bus too?
Yes. I like to connect that ground buss to the input jack ground lug. I also connect a short wire from the buss to a ground lug bolted to the chassis right near the input jack(s). Here are a couple pics...
http://home.comcast.net/~seluckey/amps/VAC15/big_guts.jpg (http://home.comcast.net/~seluckey/amps/VAC15/big_guts.jpg)
http://home.comcast.net/~seluckey/amps/revibe/revibe_07.jpg (http://home.comcast.net/~seluckey/amps/revibe/revibe_07.jpg)
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Sluckey - in the pictures on the board you have a couple turrets that have three leads into the top hole; did you drill the turret out a little to fit them in?
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There's one turret with 4 leads in it. The turrets are stock and came from Doug. No drilling. And the leads on those 1/2 watt metal film resistors are skinny. You could probably even get 5 in one if you had to.
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Well, in brief, got the jacks rewired and now all four jacks are working--Hi and Lo on both channels. So, good news there, however, still got that buzz/hum just like in vid when I turn it on. Can understand now how this can test somebody. Frustrating in that I went with the coax and ground bus to keep it dead quiet only to have this result. But maybe it's not there--I dunno--perhaps just to leave this issue and see if tech in area with more experience can pinpoint the problem. Overall, pleased with how the amp sounds. Sounds exactly of what I have heard of the originals. Little smirk when I could hear the windows rattle.
2 Hammond AO-43s are en route here. Supposed to have all working parts except the tubes--@$50 each--hoping it was a good deal. That along with weather kinda got me sidetracked. Been thinking about trying the DR AB763 with them. That along with Supro should keep me busy. Haven't given up but just need to take a break from this one cuz it got me brooding. So just wanted to update.
So I gots a working amp...but it still needs to get quiet.
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Well, in brief, got the jacks rewired and now all four jacks are working--Hi and Lo on both channels. So, good news there, however, still got that buzz/hum just like in vid when I turn it on.
So I gots a working amp...but it still needs to get quiet.
Glad you have the 4x jacks and the amp working now. :icon_biggrin:
I listened to your sound clip and I was looking at the picture you posted at the beginning of your thread.
One thing I see is the blue and brown OT plate fly leads and the red OT CT fly lead look like they were not trimmed/cut to length? Looks like you left all 3 in a long loop? If so they need to be shortened up. The blue and red wire look like when shortened they would be only around 3" or so. They're at least 8" to 10" long now.
Also the OT secondary wires, yellow and black, that go to the output jacks need to be shortened up too. When you shorten them twist the 2 together like you did with the 6.3 heater wires.
You might need to use shielded wire for the power tube grid wires, brown and green, that go from the PI's .1 coupling caps to the power tube grid. Just like with the shielded cable on the input jacks, only ground the shield at 1 end. Wire the shields ground wire to the PI's ground.
Can you post some more good quality pictures of the amps inside? Someone might see something a miss.
Brad :icon_biggrin:
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My ground bus bar is attached near input jacks and runs to end of normal channel by presence pot (not attached to chassis). Should it be one bar like that running whole way down for both channels? Or should I have two bars--1 for each channel? Probably grabbing straws here.
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My ground bus bar is attached near input jacks and runs to end of normal channel by presence pot (not attached to chassis). Should it be one bar like that running whole way down for both channels? Or should I have two bars--1 for each channel? Probably grabbing straws here.
I just finished a '6G6B' build with EL34s at high voltage (616V and 380 on the screens). I used one (the same) ground buss for both channels. This is 'mirrored' with a single HT supply dropping rail for the whole amp. (rectifier -50uF reservoir - 15k screen dropper (because of the high voltages) - 50uF screen filter cap, 4k7 dropper to PI node, 22uF PI filter cap, 4k7 dropper to normal channel node, 22uF normal channel filter cap, 27k dropper to bass channel node, 22uF bass channel filter cap). The voltages for the PI, normal channel and bass channel nodes have all ended up being approximately what is shown in the 6G6B schematic.
The ground returns are galactically-grounded at each respective filter cap ground. The ground buss attaches to the chassis at the bass channel's 'hi-input' jack sleeve terminal only. The normal channel's 1M grid resistor is grounded at the normal channel jack's sleeve terminal (and is not connected to the buss bar). The output stage ground returns, heater elevation ground return, bias ground return, and screen filter node ground return are all connected to the reservoir cap ground return. This is then connected by a single wire to the end of the buss bar where the PI ground return is connected (at the other end of the ground buss bar to the input chassis grounding point). The normal channel's ground returns are connected to the buss bar at the same point as the normal channel's filter cap ground return, and the bass channel's ground returns are connected to the buss bar at the same point as the bass channel's filter cap ground return. The heaters are balanced with a humdinger pot. There is absolutely no hum whatsoever in my amp.
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Tubeswell - looks like you have 10uf extra reservoir and 30uf extra screen filter capacitance. This will certainly help with smoothing and reducing 120hz hum. Still would like to see pics the big capacitors and wiring on this bassman.
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Tubeswell - looks like you have 10uf extra reservoir and 30uf extra screen filter capacitance. This will certainly help with smoothing and reducing 120hz hum. Still would like to see pics the big capacitors and wiring on this bassman.
This is the most recent gutshot. (I made a couple of subsequent minor changes - minor change to the location of the presence control circuitry and insertion of a 22nF coupling cap after the CF in the bass channel and the insertion of 15k screen supply dropper (where the 4k7 wire-wound is.) and wiring the suppressors to one of the points in the bias voltage divider. You'll note that this has 12VAc heaters and voltage doublers for the B+ and for the Bias supply, which was what the original Jansen Bassman 50 had because this uses the original PT which was salvaged from the old carcass). I also use series filtering for the screen and PI nodes because I wasn't sure when I was putting it together how high the voltages would be when I first flicked the switch. It really only needed the 2 case in eh voltage doubler, The rest i could've gotten away with single 600V caps (which I have plenty of).
Sorry for the hijack. Didn't intend to (but it was by way of explanation about the grounding scheme). :dontknow:
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Hey Tubeswell, nice build. If only you lived on my street.
Wish someone with experience could just take a look and point the way.
I thought it might be something in the home considering the age. Got an unsure answer in terms of grounded outlets so took it downstairs and got same result but not as loud.
Took Silvergun's help and measured hum. It's 60 HZ.
Will take Willabee's advice to cut the lengths because they are needlessly long. Although, I did chopstick it and moved wires with it on and didn't notice any difference in hum volume, perhaps this doesn't matter.
Lastly, good method for screwing jacks? Should I put toothed washer on inside and outside of chassis? Will look at speaker outs as well.
Will post some pics next week. Thanks.
Matt
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60HZ indicates filaments. 1 toothed washer should hold in a hurricane.
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...
Lastly, good method for screwing jacks? Should I put toothed washer on inside and outside of chassis? ...
Yes - inside chassis
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I have 4 Tung-Sol reissue 12ax7s in this and have just read online about others having issues with them and hum. Might not be it but who knows. Don't think if I interchange positions with the four, will it matter?, considering they're all the same brand. I have the tube shields, as well, but dunno if that makes a difference.
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I have 4 Tung-Sol reissue 12ax7s in this and have just read online about others having issues with them and hum.
I have a few I'm using that sound very good to me. But I did buy them several years ago. Sometimes they get bad batches. The batch before could be just fine so you think you like the tube and bam new stuff is a bad batch. Or some tube seller got a large order, tested them, kept the quite 1's for re-sale and either returned the noisy 1's and the tube manufacture re-sold them or the guy who tested them sold them to some other tube dealer. :dontknow:
I have the tube shields, as well, but dunno if that makes a difference.
Yes, sometimes it can make a difference. Put them on and see.
Brad :icon_biggrin:
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Again, been searching "Tung-sol 12ax7 reissue hum/cathode follower amp" and keep reading about this. Without any experience in doing this, it's hard for me to believe that it's the source of the hum but I dunno. Seems to be something about cathode follower amps and internal design of filaments inside tube. Could it just be in V2?
Brad, what amp(s) are you using them in? I don't know enough about voltages there and tube design and CF amps.
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Don't think if I interchange positions with the four, will it matter?, considering they're all the same brand.
It might be just 1 tube that is noisy.
The 1st input preamp tubes noise, along with it's signal, gets amplified/re-amplified the most because it goes through the most stages.
This is where a small Champ type amp comes in handy to test for a noisy preamp tube. It only uses 1 12AX7. If the amp is quite you can try different 12AX7's in it to see if their noisy.
I need to build 1.
Brad :icon_biggrin:
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Without any experience in doing this, it's hard for me to believe that it's the source of the hum but I dunno. Seems to be something about cathode follower amps and internal design of filaments inside tube.
It's heater to cathode leakage their talking about. Some tubes can have it and others are just fine. I think that the stress from the high voltage on the cathode of a cathode follower can make it worse or bring it out in a tube that wouldn't have a problem with it in a standard common cathode set up, preamp gain stage?
Brad, what amp(s) are you using them in? I don't know enough about voltages there and tube design and CF amps.
I'm using them in my 5E3 (Fender tweed Deluxe), 5G9 (Fender tweed Tremolux) and my new build a Gibson GA77, which has a CF for the TS (tone stack).
I don't think their noisy amps but there is some hiss because I'm using CC R's for the plate R's. As soon as I start to play I can't hear it, so it doesn't bother me. :dontknow:
But I do use a dcv stand off of 70 to 80dcv on the heaters to help keep them quite. Fender never used them and their amps weren't noisy, but than again Fender had USA made tubes from the golden age of tubes.
I can post the circuit for you but probably best to try and figure out if it's just a noisy tube 1st. (Be easy enough to try on your bread board and see if it helps?)
Brad :icon_biggrin:
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Don't think if I interchange positions with the four, will it matter?, considering they're all the same brand.
You can get a lemon from the same batch coming of the production line. Quality control and materials aren't what they used to be like in the golden years of tubes and even then they had bad tubes come off the line, but probable way less % wise.
You can try this, take out the 1st preamp tube from the channel without the CF and leave it out for now. Then 1 by 1 swap tubes in the CF position, each time putting the tube shields back on.
You might find a tube that doesn't like being in the CF socket. :dontknow:
Worth a try.
Brad :icon_biggrin:
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Did you shorten up the OT leads like I suggested in reply #85?
I'm suspicious of them causing a noise problem. The red CT wire loops around the -bias pot and all the others are way too long too.
You saw/heard what it was doing on your bread board with long hook up wires.
If you shorten them up they might fix it but if not at least you'll take them out as a possibility.
Brad :icon_biggrin:
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Re the h-k voltage - I elevated the heaters in my amp to about 50V. (The humdinger wiper is going to the heater elevation point - which is at the output/knee of a 235k/22k voltage divider from B+ to ground that is decoupled with a 47uF 100V cap). The CF voltage on the bass channel in mine is 133V, so having the heater elevated is keeping h-k to 83V in this case.
I think you need to re-do the grounding in your amp. Have you read this article? http://www.valvewizard.co.uk/Grounding.pdf (http://www.valvewizard.co.uk/Grounding.pdf)
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I was checking out old photos of the build and came across this one. I think I corrected the error here but not sure if I did. Can't check because amp is not here. Never wished to have a mistake before but I am kinda hoping I didn't fix this and that the filter caps currently look this way under the cap can. Wouldn't this be a contributor to the hum? Can see the connection in second pic.
http://minus.com/i/57XrDpbxrnPq (http://minus.com/i/57XrDpbxrnPq)
http://minus.com/i/bnLSFr22IEmuM (http://minus.com/i/bnLSFr22IEmuM)
(http://[font=dejavu sans mono, monaco, lucida console, courier new, monospace][size=1]http://i.minus.com/i57XrDpbxrnPq.jpg[/size][/font])
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The way you have the buss bar done certainly looks like it could produce extra hum. Read Merlin's article again.
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Tubeswell,
You wired your jacks differently. Could you explain how you did yours? I was following another build on Gretsch Talk that used coax and wired them similariy to yours. It's different than the layout in that you don't have the sleeve and tip of hi and lo jacks together.
I followed lower left doubleinput
http://el34world.com/Hoffman/files/CommonHookups.pdf (http://el34world.com/Hoffman/files/CommonHookups.pdf)
I have the coax ground (near jacks) going to the bus. Also, ground lug off Hi jack going to bus.
It seems you have both ground lugs connected together by wire.
The way you have the buss bar done certainly looks like it could produce extra hum. Read Merlin's article again.
Yeah, I've never built an amp before. It seems to work correct but the hum part. Just kind of losing it with hunting and pecking.
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Tubeswell,... You wired your jacks differently. Could you explain how you did yours? ...
It seems you have both ground lugs connected together by wire.
Not wired different in reality. Just looks different. The switch lug of the lo-gain jack is wired to the input lug of the high gain jack (with a little black wire). The hi-gain jack input (in each case) has a 1M-to-ground (grounded at the jack's ground lug. There is a 3nF cap in parallel with each 1M (to snub RI). The 68k are each connected to the respective input lugs of the jacks. The bass channel's ground lug is also connected to the ground buss wire. (But the normal channel's ground lug isn't connected to the ground bus - no need, and it would just cause hum if it was)
The way you have the buss bar done certainly looks like it could produce extra hum. Read Merlin's article again.
Yeah, I've never built an amp before. It seems to work correct but the hum part. Just kind of losing it with hunting and pecking.
Read Merlin's article on grounding. For these amps it works better to have everything connected in 'galactic ground' fashion on the buss bar - even the output stage ground, and only have one ground connection to the buss bar (attached at the input of the most-sensitive channel - in this case the bass channel has more gain than the normal channel)
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Here's a pic with words and confusing arrows of what I mean. (This is my 6G6B-type amp when I was at the stage of having the normal channel wired in, but hadn't then finished wiring the bass channel.)
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help
Alright, I am hesitant about posting this but I am kinda at my wit's end. I realize that I have some grounding issues and Tubeswell gave me great advice that I would like to try but I just don't know enough.
It involves the layout of my bus bar grounds and if hum ensues, elevating the heaters.
Could someone identify these on the schematic and layout:
output stage ground returns
bias ground return
screen filter node return
reservoir cap return
phase inverter tail, filter cap, and ground return
and then how to implement them in a logical way on the bus bar in terms of the layout?
I understand how to go about the jacks and the grounds for both channels and their filter caps on the bus but am lost after that.
My filter caps are exactly as shown on the drawing.
Then a voltage divider involving a 220k resistor, 22k resistor and 47uf cap given I have a CT for ground reference. Would this be put on the standby switch?
Yeah, I know-asking for a lot. I cringe writing this.
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The reservoir cap(s) are the 2 parallel 20uF caps you have tied together with the red wire at the +ve end. The screen cap is the 20uF you have connected to the blue wire at the +ve end. The PI cap is the one you have connected to the brown wire at the +ve end. The two other caps are for the respective pre-amp channels.
If opting for a galactic ground circuit with a buss bar, all the ground returns for the output stage would connect to one point - i.e. the ground side of the (2 parallel) reservoir cap(s) and the screen cap would be connected together with the PT's High Tension secondary winding centre tap (or the ground side of a FW bridge if you are using a bridge rectifier). Also to be connected to this point would be the 6L6 cathodes and the ground return for the bias supply circuit and the ground return for the voltage divider that you are using for the reservoir cap bleeder/heater elevation network. Then you run a wire from this connection node to the floating (non-grounded) end of the buss bar. (i.e. Don't ground these separately - rather, ground them at the floating end of the buss bar)
The PI cap ground would connect to the ground return for the LTP inverter tail/presence pot. Then these would be connected to the buss bar (just after the connection point for the output stages).
Then the ground returns for each pre-amp channel would connect to the buss bar at the same location as the ground return for each respective channel's filter cap. The buss bar gets connected to the chassis at the bass channel's input jack sleeve terminal (which is the higher gain channel of the two pre-amp channels in this circuit). You don't need a separate connection to the buss bar for the normal channel's inputs (The 1M there can just ground at the input jacks for the normal channel)
If using a humdinger pot, the pot wiper can go either to the nexus/node where all the power amp grounds are going, or if you are elevating the heater circuit, then the ground return for the voltage divider for the heater elevation goes to that point instead (and the humdinger pot wiper would then go to the output of the voltage divider).
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Well, I took Brad's advice and shortened up a lot of the wires. Still have the hum.
I listened to Tubeswell's advice (many, many thanks for his patience) and it made me look at something.
I looked at my PT from Classictone.
Here is the spec sheet:
http://www.classictone.net/40-18005.pdf (http://www.classictone.net/40-18005.pdf)
It says that the 2ndary filament tap is internally grounded.
Reads: "NOTE: GRN/YEL is internally grounded" on lower right side of spec sheet
I have this lead; my green yellow wire ground to a PT bolt.
Could this be a source for my 60 hz hum ie create ground loop?
Should I un-ground this lead, tape it up and tuck out of the way or will that do damage?
I doubt this is the answer because I wonder why they would have that wire avail in the first place.
However, in all honesty, I hope it does serves a purpose in some way for someone else.....but in my case it has no use and just needs to be ignored and shunned.
Just thought I would post before re-working my bus and ground returns from the filter cap, different bias pot, bias posts, etc.
Lastly, in case the above (grn yell wire) doesn't amount to/mean anything, if I rework the ground returns from the filter cap board:
Should I keep the ground return wires seperate and each have their own channel back to the bus? Like is it bad practice to have 2 or 3 ground wires share the same grommet hole.
Cheers and thanks,
Matt
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Reads: "NOTE: GRN/YEL is internally grounded" on lower right side of spec sheet
I have this lead; my green yellow wire ground to a PT bolt.
Could this be a source for my 60 hz hum ie create ground loop?
Should I un-ground this lead, tape it up and tuck out of the way or will that do damage?
That would have certainly caused a problem if you had tried to elevate the CT to some voltage rather than just connecting it to ground. But you are fine the way it is.
I just looked at you pics of the main board and the cap board. Your ground wires from the cap board are fine. However, there are some poor solder connections on the cap board. A couple connections just have the solder balled up on the eyelet. That's not good. Put some flux on all the eyelets and resolder until the solder flows smoothly and coats the brass eyelets. One eyelet doesn't even have any solder!
Most of the eyelets on the main also need fixing. Again, put some flux on each eyelet and resolder until the solder flows smoothly and coats the eyelet. You don't want any solder balls just sitting on the eyelets.
DON'T USE ACID FLUX! (like you would find on the plumbing aisle at Lowes) Use rosin flux that is meant for electronics.
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After occupying myself with other things and thinking over this, I decided to try and figure out a best method for Tubeswell's route in terms of better grounding with a bus. I decided to bust up my cap doghouse because I thought it is best to keep things as short as possible. However, before cutting any more wires and setting things to permanency, I thought it might be good to see if the placement of these caps is a good idea. My bass, normal and PI cap are still on doghouse board.
In the pic, the two to the right are the reservoir caps and the first on left is the screen cap. I thought it best to keep these output grounds here. I was going to tuck the bias pot up and have those grounds connect here as well along with the output cathodes. I still have to drill for those bias points but I have them marked. These will all head up to end of buss.
Wasn't sure if it was ok to have all grounds connect together on one point or should they meet at one node first. I was going to use the same circuit board and eyelets. I am not going to screw in the bias pot so what do you think is they best way to hold it in place? (silicon-what type? or any glue?) I also saw a member on here use ties to hold the caps (soldered but wrapped around the middle)
Any input is appreciated, thanks.
Yeah, some soldering points weren't done too well and need redone. still learning.
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Separating the filter caps into local supply nodes with galactic grounding is the way to go. (Make sure the filter cap polarity is the right way around)
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This should be short. In terms of repositioning and wiring these caps, my screen cap is now near my output tubes. In looking at the schematic, can I just connect the + end of my screen cap to one of the pins (4 or 6) of the output tubes? The rest of that connection is alright. 56 k 1 watt (other side doghouse) to choke black (circuit board) onto output tubes.
Thanks
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Bueller? Anyone?
So is it ok to wire the + end of the screen cap to one of the screen grid pins on the output tubes?
http://www.gad.net/Blog/wp-content/uploads/2011/06/1963-Bassman-6G6B-Schematic.jpg (http://www.gad.net/Blog/wp-content/uploads/2011/06/1963-Bassman-6G6B-Schematic.jpg)
It looks ok but I don't know because I don't know much in terms of schematics, point to point etc. I dunno because I don't think I have ever seen this on output tubes gut shots. Just thinking its better for me than having to run a wire the whole way back to the doghouse where the 56k 1 watt resistor is.
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So is it ok to wire the + end of the screen cap to one of the screen grid pins on the output tubes?
No. The only thing that should be connected to pin 4 (screen grid) is one end of a 470Ω resistor.
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In terms of grounding my bus, I know folks go about things that they are more comfortable with but I was wondering in my limited know how if this seems correct in the route I am deciding to go.
If I ground my bus bar at the Bass HI jack, I should use a star washer here to help it bite to chassis. All my grounds will be going this route except power ground and speaker jack.
But then by doing so, I should then probably use insulated washers for the rest of the jacks and pots, correct? Because I want them isolated from the chassis.
I know you use 2 insulated washers--(know this sounds dumb asking but I don't know) but do you put one on either side of jack or pot because of dual contact to chassis?
Thanks
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I've never heard of anybody using isolating washers on pots.
I guess your concerned about the ground buss running along the back of the pots making a ground loop?
Technically it is a ground loop, but it is a small loop. Many guys do use the back of the pots for the ground buss wire and have NO problem.
Yes on a star washer for good contact to the chassis but you always use a star washer there even when using isolating washers so the jack doesn't come loose.
Yes on using 2 isolating washers, 1 inside/1 outside. At least 1 of them needs to be a shoulder isolating washer, depending on the chassis/faceplate thickness. And you need to use the long style bushing Switchcraft jacks to be able to get the nut on.
Might I suggest looking at the all the different amp builds that our host Doug and 1 of the forums mods, Sluckey, have documented and posted here for great examples of quite grounding. And their layouts and lead dress are top shelf also! You can't go wrong copying from them.
Do it like they do until you get a better handle on the principles. :icon_biggrin:
While it's a very good thing to learn and understand these principles and be able to apply them why re-invent the wheel?
Another thing is classic Fender amps are not high gain amps and don't really need as much attention to possible ground loop and lead dress problems.
Brad :icon_biggrin:
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You will find Doug's builds in here;
http://el34world.com/schematics.htm (http://el34world.com/schematics.htm)
And Sluckey's builds in here;
http://home.comcast.net/~seluckey/amps/index.htm (http://home.comcast.net/~seluckey/amps/index.htm)
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In terms of grounding my bus,
HommeMarrBuckley, see this thread I started on grounding schemes for more info;
http://el34world.com/Forum/index.php?topic=18828.0 (http://el34world.com/Forum/index.php?topic=18828.0)
(As we have several members asking questions on grounding in the last week.)
Brad :icon_biggrin:
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Brad,
Thanks for the grounding info.
I went ahead and redid my cap layout but unsure if this is alright.
I left out all of the other connections on this drawing because I am fine with them, but just had a question in regards to my Phase Inverter cap and Screen cap.
On the left, is the traditional way it was done with the doghouse, I altered mine to whats on the right.
My question is, will this work? Is it pretty much the same-connection wise?
I realize I could have just left the PI cap where it was originally but I wanted to move it closer to it's ground node and space the caps out.
Thanks
Matt
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Why do you have the normal preamp and bass preamp separated by the PI and screen cap B+ nodes?
(You can do it that way.)
The preamp cap B+ node is usually last in the B+ series chain, so it is the quietest B+ node, has the most B+ filtering.
The more signal the tube see's at it's input the less filtering it needs, the less signal a tube see's coming in the more B+ filtering it needs. As the B+ string goes through each cap (node) and choke/resistor then to the next cape/resistor each node is cleaner then the node before it. (But they do have large/larger R's feeding the preamp caps so that does increase the ripple filters effectiveness.)
Edit: I just looked at the Fender schemo and it's correct the way you have the B+ string set up. (I don't recall seeing a Fender amps B+ string set up this way.)
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Why do you have the normal preamp and bass preamp separated by the PI and screen cap B+ nodes?
(You can do it that way.)
Thanks Brad for verification. :grin:
In terms of seperating the preamps from the PI and screen cap. In all honesty as to why, Im just trying to learn as I go. When I started this, there weren't many clones posted out there. Many had vintage ones that they recapped, serviced etc. but they all incorporated the brass plate. The man that built a clone that inspired me to do this (Mosrite forum--great, gracious guy) used a brass plate too. There's a guy that sells a clone with just the normal channel and added reverb. He was cool but didn't seem to have the time to help a greenhorn which is how I ended here. So, I have no idea of how he grounds his blonde.
I built the circuit and it seemed to have the tones. When I started, I remember reading about bus bars and coax on jacks for eliminating noise and I decided I was going to do that. I tried to follow other similar Fender builds with these elements. It kind of derailed me though when I switched it on and I got a lot of hum. Then tubeswell came along with his build in the post and made me reconsider my grounding. At this point, I tried to find out and thought why not. It isn't a high gain amp but still is pretty loud. Again, super thankful that some skilled guys are patient and decided to break it up in stages and keeps grounds close to each. Steve did mention looking over solder points but by that time I disconnected caps and took out the bar to rework, etc.
I just hope this route gives me a hum free result. I added bias points between the fuse and power switch. The proximity worries me a little but we will see. I just wish I had more time to do this because I would have been done a long time ago. I feel like I owe it for all the help I have got like I am not holding up on my end but I will post what happens when it does. Finished the grill cloth on the baffles only to find that I need to shave just the tiniest, frustrating amount of wood on the cabs to make it fit. Gritting teeth when neat, cloth corners start to wear and fray alittle from fitting over and over.
On a funny side note, Ive been asked numerous times why I chose this as a first amp and not a Deluxe or Champ etc. My top hero Jeff Buckley (seen a lot of acts live and never saw anyone come close or have the skillz he did--Im a more melody, mood guy than technical proficiency) he had a Tremoverb so I got one--you know how it goes--anyway--had a chance to talk to him before he died about what he was using--said a "Bassman--you know with the piggyback" so everything kind of fell into place with me doing this---only to check online around the start of this and see that he had the Bassman 135--Ha! My memory could be off and I have yet to ask my friend that was there with me but I swore he said the blonde--could be just one of those for the studio deals--Who knows. Now, how to construct a Black Beauty---nah that's alright.
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So how does it sound now?
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Lots of guys have used this Bassman. Tom Petty, George Harrison and John Lennen, Cliff Gallup. You will also see this amp behind a lot of steel guitars. Brian Setzer of course really loves his, but it is a little different circuit so may not compare.
I have had one for a while now and the honeymoon period has been over a long time. When I can use it in a place that is large enough it is there along with the old blond 2, 12 with Altec 417. I own a lot of amps and played many more. IMO in a 50 watt it is my favorite just edging out my Super Reverb which I still carry and use as my effect amp for larger shows.
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IMO in a 50 watt it is my favorite just edging out my Super Reverb which I still carry and use as my effect amp for larger shows.
WOW, that's saying a lot, from you, knowing your attachment to BF SR's. (I love BF SR's too.)
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IMO in a 50 watt it is my favorite just edging out my Super Reverb which I still carry and use as my effect amp for larger shows.
WOW, that's saying a lot, from you, knowing your attachment to BF SR's. (I love BF SR's too.)
It is saying a lot. I guess after playing a Super Reverb for over dare I say 40 years I have changed my main preference in amps once. I will say I still use a Super Reverb a lot and my favorite Tweed is a 5F4 which is sort of strange. I like to hear the guitar I guess.
I know you have strummed a Super a time or 2 yourself. I am liking the simpler circuits these days seem like.
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and my favorite Tweed is a 5F4 which is sort of strange. I like to hear the guitar I guess.
Have you ever disconnect the FB loop that's around the CF stage, 4M7 R, to hear what that sounds like?
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I know you have strummed a Super a time or 2 yourself.
Played it for years and never really had a problem with it. A lot of the older blues guys and the younger guys too, where I hung out at all either had a BF TR or a BF SR. Just very good sounding amps that held up to the work load.
Had a heater/CT 100R burn up once and the black plastic/steel strap broke but other than that, I can't remember anything else going out.
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and my favorite Tweed is a 5F4 which is sort of strange. I like to hear the guitar I guess.
Have you ever disconnect the FB loop that's around the CF stage, 4M7 R, to hear what that sounds like?
Never done that. I have 2 of them. One is a head and I have tried all sorts of things with it, but usually put it back. My other one is on loan to a Friend right now. It is the "V" front cabinet, but it is a clone. He is gigging with a modern hipster group with a retro sound almost like Rock-a-billy. He likes the look. They call themselves the Cleftones.
What does the mod do, make it a little raunchy?
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"We might be done with the past, but the past aint through with us" - one of my fave quotes from Magnolia which kind of describes my situation.
I take some between posting and to help with recall---I built the 6g6B circuit. Had some flubs along the way. Got it working good with sound but had to deal with some 60 HZ hum. Fellow member recommended altering to galactic grounding.
Was more nervous this time than last when I powered it up. Let it warm up a bit and then flipped the standby. Immediately it powered off/pilot light cut out. I quickly flipped both switches off--but there wasn't any smoke, sparks, noise or anything alarming. I was in the weeds and super down. All this time into this and all for what? Checked fuse and sure enough--blown. With all this new wiring, I was trying to make sure nothing crossed.
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Bias Points
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Reserve/Screen Caps
Bias pot isn't attached to chassis. Tight snug fit on 1st layer circuit board.
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Bus Bar
I didn't apply a node for the PI cap--just attached those three connections to bus. Added .0033 caps to input jacks for RF
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Here is where I am hoping the culprit is and will only be a minor fix.
The PI, Normal and Bass caps.
Notice the red wire. I thought of it for a second when I screwed the doghouse (not shown) on but obviously not enough. The doghouse edge put it tight to the chassis.
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Look close. I guess this looks enough to be a short/arc, doesn't it? The black. That red wire connects underneath between 56k and 4.7k resisitor and goes to + end of screen cap.I will have to take aim here next week--and decidely this amp will either not have a doghouse or will with routed hole/pathway.
Will also help me look under the added reserve/screen cap board to make sure nothing is crossing there as well.
I am just hoping that this is the only thing that caused the issue.
Will have to wait until next week.
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Was more nervous this time than last when I powered it up. Let it warm up a bit and then flipped the standby. Immediately it powered off/pilot light cut out.
If you don't have a light bulb limiter than you need to build 1;
http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf (http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf)
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Notice the red wire. I thought of it for a second when I screwed the doghouse (not shown) on but obviously not enough. The doghouse edge put it tight to the chassis.
HMB, please take this as a constructive, well intended safety warning that you absolutely need to hear....
TAKE A TIME OUT AND READ ABOUT ELECTRICAL SAFETY
Our entire goal while building these death traps are to isolate the high voltage from the chassis by whatever means necessary.
In general, all electrical appliances are unsafe by nature even when wired by professionals and stamped with UL approved markings.
By "thinking about it for a second when you screwed the doughouse down" you have proven to have decent instincts.
Learn to listen to them and continue to question the result of your actions.
Be glad you are not recovering in the hospital right now.
Respectfully and with genuine concern,
SG
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First,
Here you go Brad. Something I should have made a long time ago. I dunno why I was so resistant to make one--probably because I don't have much time and thought it would take too long. I found out quite the opposite. Pretty simple and quick to build. I used this site because it's explained simply and Im borderline technical lunkhead.
https://robrobinette.com/5e3_Modifications.htm#Light_Bulb_Current_Limiter (https://robrobinette.com/5e3_Modifications.htm#Light_Bulb_Current_Limiter)
so mine looks exactly like his.
SG, I appreciate your concern and was not offended at all. With what limited knowledge I have, I try to be careful as possible. Laugh, I learned how much I take for granted when you goto the store or somewhere and plug in and flip the switch compared to doing that same process to an open amp that you made.
Well, I removed the shorted wire and put in a new one and put in the new fuse and plugged into the limiter. I used a 150 watt bulb and read what I should expect which is what basically happened. The bulb's filaments got bright red upon power up but then cooled and dimmed. I flipped the standby and nothing. No change in the bulb and no loss of power or sound/noise. I powered down and plugged the amp directly into the wall outlet and checked the input jacks for clearance with guitar cable. Plugged in Normal channel. Powered up--all ok---flipped the standby---NO HUM! I increased the amp volume to about 3-4--still no hum. Rolled guitar volume and success! Out came the slight grainy clear sound. Man, I was smiling like a little kid.
I pushed the volume to the max and there was a slight bit of hum with no guitar but I figure that's not unusual considering it's fully dimed. I checked the remainder of the inputs--all good. All good except the bass channel. Plugged in and it sounded max volume right away. Amp volume knob was at zero. ??? Played with amp volume knob and didn't do much. It was hella loud. Took a second---sure enough. Looked at volume pot and saw bit of solder residue on tab. Left over from when I replaced the bus bar which means something was there before. Checked layout--sure enough I forgot to add the wire there that's grounded. Regardless, that's an easy fix. I am just happy that I got the end result.
I plan on checking voltages again and bias but I didn't have much time before work. I will try to add video showing that the hums gone but I am pretty much at the end of the road. Not whole lot to do with the cab and head but that's where Im going to now. Every story has three arcs (no pun intended) so that will be the last and will be short. I will post when it's complete.
Still blows my mind because it's about one of the coolest things Ive ever done. But I would have never got here without the help and generosity of others. Thanks to all admins and members that have chimed in and helped me get here.
And a very special thanks to you Pete. Thank you for patience and input and helping me get over this last and challenging hurdle. You're right, galactic grounding is the way to go.
Cheers!