Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: daveyajd on January 26, 2015, 12:49:09 am
-
Hello all,
It has been a couple of years and many miles of life since I have been here. But damn it's good to be back! My original project and all of the info I was gathering at that time can be found here.
http://el34world.com/Forum/index.php?topic=13510.msg126422#msg126422 (http://el34world.com/Forum/index.php?topic=13510.msg126422#msg126422)
I am back on the TOS build and hoping to establish some communication with those of you who have the answers. Just placed an order with Doug and the service is still OUTSTANDING! Thank you. Here are some pics.
(http://i422.photobucket.com/albums/pp301/drivenbyastronauts/TOS%20Build/IMG_3270_zpsum1q3zus.jpg) (http://s422.photobucket.com/user/drivenbyastronauts/media/TOS%20Build/IMG_3270_zpsum1q3zus.jpg.html)
(http://i422.photobucket.com/albums/pp301/drivenbyastronauts/TOS%20Build/IMG_3272_zpsydhs83ll.jpg) (http://s422.photobucket.com/user/drivenbyastronauts/media/TOS%20Build/IMG_3272_zpsydhs83ll.jpg.html)
(http://i422.photobucket.com/albums/pp301/drivenbyastronauts/TOS%20Build/IMG_3275_zpsp7uabzrj.jpg) (http://s422.photobucket.com/user/drivenbyastronauts/media/TOS%20Build/IMG_3275_zpsp7uabzrj.jpg.html)
-
NICE :thumbsup:
-
Impressive beginning! Take it slowly and do great work particularly on the soldering. We'll help you when and if that is needed.
I think you are going to end up with a great sounding amp!
with respect, Tubenit
-
Thank you for the kind words. I am pretty meticulous (see: Anal) :) so I plan on being very clean with all my wiring. I am wondering about one thing though. When I am connecting my pots to my 9 pin sockets should I use shielded cable across the chassis? And if yes do I just ground that shield at the nearest ground? Thanks.
Aaron
-
When I am connecting my pots to my 9 pin sockets should I use shielded cable across the chassis? And if yes do I just ground that shield at the nearest ground?
I do. I ground the shield at the source of the signal only. That is the pot in most cases.
-
So no shield connection at the tube then? Great I will just ground it on my Buss bar. Thanks
Aaron
-
Ok, so I have a couple more questions. I am putting my parts list together for pots but I'm not sure what all of them are. I have moved things around on the faceplate a little and renamed them but heres what I have.
CLEAN: Gain(Vol) 1M audio, Tone 1M audio, Level 1M audio, Fatness(moved to the front) 250k audio
OVERDRIVE: Lean(Trim pot) 50k linear, Gain(drive) 250k linear, Tone 1M audio, Level 1M audio
Then of course the PPIMV Dual gang 250k audio.
Does this all seem right?
How does the Trim pot affect the OD channel?
Do you guys prefer CTS or Alpha? Can I mix and match?
Thanks,
Aaron
-
Only thing I'd probably change is the OD gain/drive 250kl to 250ka. I think you'll find 250ka to be more useful.
The rest seems fine.
Not sure what your trim pot question is? The trim impacts how much clean signal is fed into the overdrive.
I don't have any preference at all. I usually use Alpha and they've worked fine for me. I also mix and match which has been fine too.
with respect, Tubenit
-
One other thing I'd change on the TOS is to add an "enhance" cap to the entrance plate resistor of the LTPI.
I find this smooths the high frequencies and actually has helped the "blooming" effect on my amps where the note opens up and blossoms more. I am thinking that somehow this may be eliminating some really high frequency oscillations which helps the tone?
I'd probably try a 220p but anything between 120p to 250p would work fine.
With respect, Tubenit
-
That sounds good thanks for the help. I will try that cap.
So I am getting my wiring straight for the PT using these diagrams. Couple of questions on connections.
I understand the yellow 5v to the rectifier pins 2 and 8, greens and green/white to heaters and center tap(ground) respectively.
Now I believe that the reds are high voltage and would go to rectifier pins 4 and 6. Which is my ground with those, the red/green 50v or the red/yellow 0v? What do I do with the other one?
I also believe that one black would go to my power outlet and one would go to a switch/standby lug. Is that correct? And then the orange (shield) is my ground?
Thanks,
Aaron
-
Look at the Fender Super Reverb layout for some help:
http://el34world.com/charts/Schematics/files/fender/Fender_Super-Reverb-AA763-layout.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_Super-Reverb-AA763-layout.pdf)
http://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf (http://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf)
Red/green 50v is for bias. Red/yellow CT means center tap.
If you dig around on the internet and look at different schematics/layouts, you usually can find an example that helps answer the question.
With respect, Tubenit
-
Ok thanks. So I am correct in all of my thinking. The red/yellow 0v will go to ground but I'm still confused where the 50v bias will tie in. The Super Reverb I understand but that has a bias pot. This TOS will be cathode biased so where will it connect. Sorry if my ignorance is showing. :dontknow:
Aaron
-
but I'm still confused where the 50v bias will tie in. The Super Reverb I understand but that has a bias pot.
The red/green is a tap off the high voltage (B+) PT secondary wind and provides the acv that is sent to the -bias circuit where it is rectified through a reversed biased diode from +acv to -dcv and the -bias dcv is filtered with a revesed filter cap, + cap lead to ground. This is the raw -bias dcv.
Then the filtered raw bias goes to a voltage divider, 2xR's, 1. -bias set R (or pot) and 2. -bias range R. Some have a 2nd filter cap, some have an adjustable bias pot some don't. The bias pot just replaces an R in the -bias circuit to make it adjustable.
Here's link to Doug's tube library of information on how -bias circuits work;
http://el34world.com/charts/Biascircuits.htm (http://el34world.com/charts/Biascircuits.htm)
Brad :icon_biggrin:
-
If the amp is cathode biased, meaning the cathodes are not tied directly to ground, but rather through a resistor. This resistor allows voltage to rise on cathode, which means the grid is below cathode voltage, or negative in relation to the cathode. This accomplishes biasing the grid without a negative supply voltage, so your 50v bias winding is unused on a cathode biased amp. It is possible to prepare the bias supply and install a switch that allows switching between cathode biasing OR fixed bias via a negative voltage to the grids, but that would be a considerable modification to the amp as designed.
-
This TOS will be cathode biased so where will it connect.
Doh! Missed this.
It doesn't, you just shrink wrap it off and stow.
Brad :icon_biggrin:
-
I'm confused by something else I am seeing on the layout and schematic. Why does the relay for the channel switching seem to connect to the effects loop? Shouldn't it just be wired up to the foot switch jack?
Thanks,
Aaron
-
The relay is connected to both channels and it's output then goes to the effects loop jack, which is bypassed when no jack is in, and then to phase inverter input. The coil of the relay would be connected to the footswitch jack. That part of the switch or relay, shows signal routing in the relay or switch.
-
AZJimC gave a great explanation for you.
Put very simply ..................
Footswitch operates (switches) the relay sending either the clean or overdrive signal to the phase invertor.
One part of the relay connects to the footswitch. Another part of the relay connects to the phase invertor.
There is a ton of info in ARCHIVES on relays which would be useful to you to read when you get around to wiring up the relays: http://el34world.com/Forum/index.php?topic=14348.0 (http://el34world.com/Forum/index.php?topic=14348.0)
with respect, Tubenit
-
Ahhhh, that makes perfect sense. Thank you both.
Aaron
-
So I am fitting all my heater wires and I have a question on the 5879 tube. It only has one heater connection on pins 4 and 5. Do I just connect that from my PI 4 and 5 pin connection and leave my pin 9 connection untouched until the next 12a_7? Hope the wording of that makes sense.
Thanks,
Aaron
-
The 9 pin sockets are wired with 6.3vac heater power. The 12a*7 tubes are 12.6vac heaters. They are internally wired with a center tap on the heater, that connects to pin 9. This allows one leg of the 6.3vac to be on the ends of the 12.6v heater at pins 4-5, while the other leg is on pin 9, so 6.3v will heat a 12.6v tube.
The 5879 is a 6.3v tube, so it's heater connections are on pin 4 & 5, and the pin 9 center tap is not required. the short answer then is one wire from pin 4-5 of a 12a*7 socket goes to pin 4, and the wire from pin 9 of a 12a*7 would go to pin 5. This completes the circuit for that tube type.
-
Very good explanation. Thank you. Now, I know how the power light is connected using 6.3v heater wires but how will I power the LED that lights when I am on my OD channel? I have some very good info that tubenit sent me previously that explains how the wiring between the relay and manual switch/foot switch works but I don't see any connection to an LED or anything in what I have.
Thanks,
Aaron
-
Here's the link for relay switching from Doug's tube amp library of information;
http://el34world.com/projects/relay_switch.htm (http://el34world.com/projects/relay_switch.htm)
Brad :icon_biggrin:
-
Thanks for the reply Willabe. It is pretty confusing to decipher that page.
I am using this prebuilt low power relay board from Weber if that changes anything.
https://taweber.powweb.com/store/chansword.htm
I understand the connections to and from this board that allow me to switch channels. But the LED is still unclear.
Thanks,
Aaron
-
I am using this prebuilt low power relay board from Weber if that changes anything.
I have two Weber relay boards in a drawer that I removed from the amps I had them in because of the amount of noise they produced. One of the boards had a tolerable amount of noise. The other one was simply unusable for my standards because of excessive noise.
I did not have the same noise using Doug's boards. Just an FYI.
I am not sure how to hook up LED lights on the foot switch using the Weber relay boards?
With respect, Tubenit
-
Do you need to operate a LED mounted on the amp chassis or in a footswitch?
-
The LED is mounted on the chassis not on a footswitch. I'm bummed to hear that these have been found to be noisy. Wish I would have known that years ago when they were recommended to me. I definetly would have gone with Doug's option.
Aaron
-
There is a diode mounted near the relay. It is connected across the coil of the relay. Solder a wire to each lead of that diode. These two wires should be long enough to reach your LED. Connect the wire from the cathode of the relay board diode to the ANODE of the LED. Now solder a 470Ω resistor to the CATHODE of the LED. Finally, solder the other wire to the other end of the 470Ω resistor. The LED will now light up whenever the relay is energized.
Basically you have just put a LED and series current limiting resistor in parallel to the relay coil.
-
That is awesome! Thank you so much for that!
Aaron
-
To be fair to the Weber relay, the one that was unusable for me was the 4 relay one. The single relay noise was tolerable in my amp. I used one relay (Weber) in an amp I built for my son and it seemed to work out OK in his amp. I don't remember his amp switching being noisy. And, I've learned a lot about relays since I first used one.
Having said that, I've used Doug's relays in 3 amps now and his relay system is very quiet & I'm very happy with it.
With respect, Tubenit
-
Wish I would have known that years ago when they were recommended to me. I definetly would have gone with Doug's option.
Doug's relay boards have only been around for a year or so?
Brad :icon_biggrin:
-
So a couple quick questions on my power supply wiring. Is it beneficial for me to twist my primary and secondary CT's together when I ground them? Not sure if that may cause weird issues.
Next, can I ground everything (CT's, PT ground, Mains) all to the main ground on the PT bolt? Or should I ground my main AC seperatly?
I know to run a buss bar along my pots to ground them but does that need to ground to that main PT bolt ground also?
Thanks,
Aaron
-
Here are a few new pics. Heater wiring is run, jumper wires on the 5879 and PI.
Aaron
-
Looking good! :icon_biggrin:
So a couple quick questions on my power supply wiring. Is it beneficial for me to twist my primary and secondary CT's together when I ground them? Not sure if that may cause weird issues.
Some use twisted pairs when ever they can others don't. Sluckey just post a great build and he did not use twisted pairs on everything and the amp is very quite.
Next, can I ground everything (CT's, PT ground, Mains) all to the main ground on the PT bolt? Or should I ground my main AC separately?I know to run a buss bar along my pots to ground them but does that need to ground to that main PT bolt ground also?
Read this on grounding, if you haven't yet, it will help you.
http://www.valvewizard.co.uk/Grounding.html (http://www.valvewizard.co.uk/Grounding.html)
Here's a pic of my GA77 build and I twisted pairs where ever I could. It's very quite but it takes more time, not saying it's any more quite that Sluckey's. I look at it like preventive medicine, just in case.
Merlin likes to run the heater wires on 12 _ _ 7 type tubes over the middle of the tube socket and not loop them around the socket. You can see how I did this in 1 of the pics.
Brad :icon_biggrin:
-
Wow! Great link. Lots of good info in there. And I even understand some of it. :icon_biggrin: So I think I will plan on going back to my original plan of having a bus bar off of the pots. But the article mentions not connecting that third lug to the back of the pot, should I just connect it to that bus bar and not solder the back then? I guess I will ground my IEC, and CT's at one point, then just connect my filter capacitors ground to the bus bar. I am still a little ways from that point so I will continue my research.
Aaron
-
Alright. I just got my pots in. All except for the PPIMV dual gang. I will have to order that from AES I think. So I am going to start wiring the pots up a bit and I'm wondering a couple things. When looking at the layouts are they drawn from the viewpoint of lugs on top? In other words if I'm standing in front of the amp looking down the ground lug is on the right? What about the shorting jack for the input?
Also, after reading the link posted above it mentioned not grounding that lug to the back of the pot. I normally don't bend that to the back but I have always connected that to the lug with a jumper wire and then to ground. Is that correct?
One more thing, I found a dual gang pot at a military/government surplus store that measured about 180k on each pot. Will this be close enough to 250k to use?
Thanks,
Aaron
-
Take at look at Willabe's POTS (picture above)and this is how you will see them drawn on most layout plans (viewed from the back and ground lug on the left).
Willabe has opted to string all his ground lugs (preamp) together (green wire) some guys use a heavy gauge wire and make a BUSS and feed this through the loop in the lug. This works great till you have to replace a pot, so I snip a section out of the lug enough to slip the wire onto the lug.
You can ground your input jack to your pots and most ground this string at the input jack.
You can try use the 180k pot but you will have to change the parallel resistor to equal the grid leak resistor that the pot replaces.
-
Alright thank you. So I picked that dual gang up and I'm putting a meter on it. It measures about 185 or so and both pots are pretty close to each other which is good. Which resistor would I be replacing? Is it the 10K on the tube or the 2.2M on the pot going to ground?
Aaron
-
Where the dual pot is at the moment there would be two 220k resistors connected to ground, the dual pot replaces these resistors and therefore the pots needs to measure approx. 220k.
Your 180k is a bit shy of the 220k resistors and I'm not sure if you can use the pot without the parallel resistor, so hopefully one of the smarter guys will confirm. Doing great :icon_biggrin:
-
You could consider doing this. However, you wouldn't be able to turn the PPIMV volume to zero. But when would you do that anyway?
With respect, Tubenit
-
One more thing, I found a dual gang pot at a military/government surplus store that measured about 180k on each pot. Will this be close enough to 250k to use?
I'd use it.
-
-In regards to the info that Sluckey gave me above about putting an LED and limiting resistor parallel with the relay coil for my OD indicator.-
I have twisted the two wires that will come from the diode. Can I run these close to my heater wires that are running to the relay board or will this maybe cause some noise and hum problems?
Aaron
-
I have twisted the two wires that will come from the diode. Can I run these close to my heater wires that are running to the relay board or will this maybe cause some noise and hum problems?
Not a problem.
-
I am ordering a few more parts soon and hopefully part of that order will be the electrolytics. The BOM calls for 150uf/50v. Seems to be pretty hard to find so the substitution is a 100uf/100v and a 47uf/100v in parallel. I have the 100uf/100v and the only 47uf/100v I find is an Illinois. Since the specs call for 150/50v I should be able to use a Sprague 50uf/50v right?
Also having a hard time finding the 10 watt resistor in 430R value. The closest I find is a 400R or 500R. Will either of these work. Or can I run the 400R and a 30R in parallel?
Thanks,
Aaron
-
The 10w resistor can be 400R. Honestly, you probably could use anything between 270R to 430R. If you are ordering them, maybe get 270R, 330R, 360R, 400R. Start with the higher value and work down listening to the tone.
Regarding the power tube cathode filter caps. Anything 50v-100v should be fine. Why don't you try the 100uf/100v you have and see how you like that. You can later parallel a 47uf to 50uf in the 50v-100v range if you want to.
With respect, Tubenit
-
That's great! Thank you. So the filtering will be fine with just 100uf? Interesting. What kind of changes to the tone are typical as I go down in resistor value?
Aaron
-
What kind of changes to the tone are typical as I go down in resistor value?
Smaller resistor will increase the gain & sometimes warmth. Larger increases headroom and sometimes clarity.
I have said it before ........... the Tweed Overdrive Special is a tweaker's build. Build it reasonably close to original and then adjust to personal taste in tone. You can try different size filter caps for the cathode biasing. Larger sized caps get it closer to sounding like
fixed biased tone, IMO. Lower value caps can give a remarkable smooth tone but you do lose some bass tone as a result.
The area I would leave alone or tweak the least is the OD section.
With respect, Tubenit
-
Here is one of my questions of the night. Looking at pin 7 of V1. Do I need to run 2 wires from the it? One wire to the outer lug of FAT pot, the other to the middle lug of the volume pot? Or can I run 1 wire from the pin to the FAT pot and the on to the Volume pot? Thanks for all the help.
Aaron
-
Hi daveyajd
I'm in Australia not USA but I think it is standard electrical practice to have a separate chassis ground bolt near you IEC mains socket and to run the IEC ground wire lug to that bolt.
The idea being that for electrical safety reasons the metal chassis has an easily inspectable / verifiable and very robust connection to earth.
Run all other grounds to a star point bolted securely to the metal chassis.
In my opinion, the heavier duty your ground wires and busses the better. I use 50 amp (copper) cable for ground wires and busses.
I may be in error on this.
-
Thank you Glennjeff. Yes, I did choose to ground my IEC at its own bolt. I just thought it would be the easiest and best way to go.
Aaron
-
Hey all,
Got a new dose of parts in so I'm working on my filter cap layout. Will you all look at these pics if you get a chance to make sure it looks ok? Initially I was going to put them all on their own PS board and run wires but I like the way they fit on the main board. Plus this keeps the run to each stage as short as possible so I think I will add turrets where I need them and do it like this. Thanks for all your help.
Aaron
http://i422.photobucket.com/albums/pp301/drivenbyastronauts/Amp%20Pictures/CAPS%202_zpsgmexqr7d.jpeg (http://i422.photobucket.com/albums/pp301/drivenbyastronauts/Amp%20Pictures/CAPS%202_zpsgmexqr7d.jpeg)
http://i422.photobucket.com/albums/pp301/drivenbyastronauts/Amp%20Pictures/CAPS%201_zpsw8eycbxk.jpeg (http://i422.photobucket.com/albums/pp301/drivenbyastronauts/Amp%20Pictures/CAPS%201_zpsw8eycbxk.jpeg)
-
That looks fine to me to have the filter caps on the main turret board. I think you are going to have a very nice sounding build.
with respect, Tubenit
-
Thank you. I am so excited to finally finish this amp! Another question on running heater wires. I'm planning on running my PT heaters to a terminal strip and from there it will "branch out" and run to my lamp assembly, my relay and my tubes. I just want to make sure this is correct and that I don't have to connect everything one to the other to the other and so on. Here is a photo to show you what I mean.
Thanks,
Aaron
-
I'm planning on running my PT heaters to a terminal strip and from there it will "branch out" and run to my lamp assembly, my relay and my tubes.
I like that plan.
-
Then that is what I will do. I'm sorry if these questions seem simple. I've been pretty sure about my layouts and wiring throughout this build and I've usually been on the right track. Largely thanks to all the great info and people on this board. Sometimes I just need to hear a confirmation.
That being said one more question tonight. The black wires from the PT are not polarized right? Either wire can go to the neutral from the wall or the switch, right?
Aaron
-
That's correct.
-
In my last parts order I got some Mogami shielded cable. This stuff seems weird. The core wire is mixed with a fiber of some sort. Mogami says it adds tensile strength. Maybe so but I find it almost impossible to work with. I can't twist it like normal stranded and it won't seem to tin at all. Anybody have any experience with this stuff?
So I am re-evaluating my shielded runs and I'm wondering how effective it is to twist two wires together, just like heaters, and use one as the signal and the other grounded at one end for the shield. Does that work? The wire I'm using would be 20ga solid.
Aaron
-
So I am re-evaluating my shielded runs and I'm wondering how effective it is to twist two wires together, just like heaters, and use one as the signal and the other grounded at one end for the shield. Does that work? The wire I'm using would be 20ga solid.
I would not do that. I'd use shielded cable.
With respect, Tubenit
-
Can you pull the fiber strands to side of the of wire strands and cut them?
Brad :icon_biggrin:
-
Yeah Brad I can separate them but I still don't like the way they work out. I may fool with them a bit more but I may just move on with something else.
Another question on how to connect the trim pot. I moved it to the front so will I just run my cables like I show in the pics? The trim pot doesn't appear to have a lug that's grounded so can I still use shielded cable and ground the shield to my bus? Is shielded needed in this run?
Aaron
-
Deleted
-
Good idea.
Brad :icon_biggrin:
-
Great news. I will try that.
Aaron
-
Another question on running heater wires. I'm planning on running my PT heaters to a terminal strip and from there it will "branch out" and run to my lamp assembly, my relay and my tubes
That is what I do on my builds.
Another question on how to connect the trim pot. I moved it to the front so will I just run my cables like I show in the pics? The trim pot doesn't appear to have a lug that's grounded so can I still use shielded cable and ground the shield to my bus? Is shielded needed in this run?
I just use shielded wire for long runs & wiring runs that are close to something that I think might induce noise. And yes you can ground the shield of shielded wiring on the buss wire. I do that all the time with no issues & have quiet amps.
IF I am looking at your photo correctly, you have a short run from the relay to the trim pot. I would not use shielded wiring for that. You have a long run from the trim pot wiper to V2-7, and I would use shielded wiring for that.
with respect, Tubenit
-
Thank you for the reply Tubenit. I apologize for the confusion in my pics. I will use a shielded cable from the wiper to the tube, but the other runs that you thought went to the relay actually go back across to the turrets where the trim pot is drawn on the scheme. (I think) Picture 2 tries to show that. I'm thinking I won't use shielded since it just connects to the board.
Thanks,
Aaron
-
Most of the time it's the longer grid wires that need to be shielded.
Especially the low signal grid wires, ie, from the input jacks and from a reverb tanks output/return to the grid of the reverb recovery tube, which has less of a signal than from a guitars PUP's.
Some guys like to put the 1st input tube directly under/next to the input jacks and just run the 68K input tube grid stopper from the hot of the jack to the input tubes grid. So no need for shielded cable. But if you have a pre punched chassis you have to work with that.
I've built a few scratch amps that I sent the signal from the 1st preamp tubes plate to the 2nd stage but I had the coupling caps hanging off the volume pots with very little lead wire on the pot side and did the same with a PI but in a twisted pair, since the 2 are out of phase with each other, to the power tube coupling caps but I put those caps very close, right to the power tube grid stoppers. Worked fine.
Brad :icon_biggrin:
-
Like this;
Purple/black in 1st pic, preamp plate to coupling caps.
Purple/yellow in 2nd pic, PI to power tube grid stops.
-
Just want to make sure I have wired this up right. 5v from the PT to rect tube pins 2 and 8. From pin 8 to the top of the Off-Stby-On switch. The bottom of that switch side will go to my reservoir filter cap. The other side of the switch has the AC on top and the PT primary on the bottom.
Aaron
-
Just want to make sure I have wired this up right.
That's correct.
-
Thank you. Got a little more done today. Here are some new pics. Feedback about possible issues you see is always welcome.
Thanks,
Aaron
-
I think you are doing a great job and that it will be a very fine sounding amp!
With respect, Tubenit
-
Is it better to have the 470R resistors as close as possible to the power tube pin? I've considered mounting them on the terminal strip I have pictured above and running wires to and from. Wondering if this is poor form?
Aaron
-
It's not critical where you put them. Some people put them on the board. I like to put them directly on the socket between pins 4 and 6. I mount them standing about half inch above the socket pins. Like this...
http://home.comcast.net/~seluckey/amps/6v6plexi/P-6V6_05_big.jpg (http://home.comcast.net/~seluckey/amps/6v6plexi/P-6V6_05_big.jpg)
-
Thank you you for that. How are you able to use pin 6? My layout shows a 110k between pins 5 and 6. The PPIMV connects to pin 6. And it looks like pin 4 connects to the filter stage through the 470.
-
Different power tubes have different pin outs. 6L6's and 6V6's allowed Fender to do this;
http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-layout.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-layout.pdf)
Brad :icon_biggrin:
-
This layout is drawn for 5881, 6L6, 6V6. So I'm not sure that I could wire it between those pins. If it's not a big deal I will probably just wire them on the terminal strip.
Aaron
-
Look at my pic again. You'll see two resistors on each socket. The little one is the control grid stopper. It's mounted between pins 1 and 5. The big resistor is the 470Ω screen resistor. It's mounted between pins 4 and 6.
Pin 1 and pin 6 are not used in the 5881, 6L6, 6V6 tubes. You can use them as you wish. I copied my layout with those two resistors from Fender. Anyhow, I was just showing you how I mount that 470Ω resistor for your consideration.
Which layout are you using that has a 110K resistor mounted between pins 4 and 5?
-
Ahh. Now I'm seeing it. The layout I'm using shows a 10k resistor from pin 5 to 6. Then my shielded cable goes from PPIMV to pin 6 so that pin is simply a landing spot for one leg of that resistor and my PPIMV. In other words I can use 1 or 6 as landing pins for filter caps or PPIMV as long as the cap wire goes through the 470 to pin 4 and the grid stopper (10k) is between pin 5 and the master volume. Thank you all so much.
Aaron
-
Alright, so my LED for the OD is a blue light using 5 volts at 30mA which should be a limiting resistor of about 48R. I am fine using something like an 82 1/4 watt, right. Is the brightness affected at all with different values.
Also, I'm sure I've seen it posted somewhere before but can someone direct me to an explaination of how this type of cliff type jack is wired up as the footswitch jack.
Thanks,
Aaron
-
Alright, so my LED for the OD is a blue light using 5 volts at 30mA which should be a limiting resistor of about 48R. I am fine using something like an 82 1/4 watt, right. Is the brightness affected at all with different values.
I've never heard of a 5 volt LED before. That sounds like a REVERSE VOLTAGE rating. We need to know the FORWARD VOLTAGE rating. The forward voltage would be something like 1.7v, or 2.1v, or even 3.5v for a super bright blue LED such as RadioShack sells.
Once you know the forward voltage rating and the forward current rating it's easy to calculate the value for the current limiting resistor (CLR). But you still need one more piece of info... What is the supply voltage?
Here's an example of how to calculate the value of the resistor for a 3.5v @ 30mA LED when the supply voltage is a 9v battery. The LED will be max bright when 30mA flows thru it. This 30mA must also flow thru the CLR. Since the LED will have 3.5v across it, the CLR must drop 9v-3.5v = 5.5v. And since there will be 30mA flowing thru the CLR, the resistance will be the voltage across the resistor divided by the current thru the resistor which is 5.5v/.03mA = 183.3Ω. So, the CLR should be 183.3Ω with this LED used on a 9v supply voltage to allow full/safe brightness. In reality you don't need maximum brightness (max forward current). Even half the current will usually give plenty of brightness, so just increase the value of the CLR to reduce the brightness, but never go lower than the calculated 183.3Ω or you will exceed the rating of this LED. In this example, I'd probably just use a 470Ω CLR.
So now, what wattage should the CLR be? That's also easy to calculate. The power dissipated by the CLR will equal to the square of the voltage across it divided by the value of the resistor. For the 183.3Ω CLR that would be 5.5v x 5.5v / 183.3Ω = 0.165W. Double that power for a safety margin so use a .33W resistor. Just get the next large wattage which is half watt. Applying the same math to the 470Ω CLR will show that a quarter watt would be sufficient.
In summary, RCLR = (Vsupply - VLED)/ILED. Oh, and it's important to remember that the LED forward voltage will remain constant (within reason!). It does not depend on the current flowing thru the LED.
-
Also, I'm sure I've seen it posted somewhere before but can someone direct me to an explaination of how this type of cliff type jack is wired up as the footswitch jack.
The cliff jack in the pic is a two circuit (stereo) jack. It is capable of being used with a double footswitch to control two circuits.
We need to see the schematic you are working from to tell you specifically how to wire it. We also need to see the footswitch or a schematic of the footswitch.
See pic for terminal identification...
-
Thanks Sluckey. I attached a couple of pics of the LED package. It is from Radio Shack and the forward voltage rating is 5v. I have done the calculations that you were talking about and that's how I got to a resistor of about 48. (43.33 actually)
My assumption in that calc was the supply voltage. I was using 6.3v in my equation because that's my heater voltage. This LED is connected to the diode on the relay as learned from your post above. Would that still be the 6.3v? As for the wattage of the resistor. If I follow your calculations (using the numbers I have been using) the wattage is so small it seems that a 1/8 watt would be fine.
6.3-5 =1.3
1.3 x 1.3 =1.69
1.69/48 =.035
.035x2 =.07
Of course if my supply voltage is something else than this all falls apart.
As for the cliff jack. Here is the diagram that I got from Tubenit so long ago. How would a cliff jack fit in with the wiring it shows? I don't know for sure what foot switch I will use. I may build my own or I may use the single button style that Doug sells. I think the original BOM called for this type of jack so it was isolated from ground but I'm not sure.
Thanks,
Aaron
-
You will not use 6.3 as your supply voltage. Leave the LED disconnected until you get the relay board working. Then, with the relay energized, measure the dc voltage across that diode on the relay board. That is the voltage you will use for the supply voltage to the LED. Recalculate based on that number, then connect the LED.
-
Well, shite. Ok, I will wait until the end to dial that in. Thank you for that.
I am still trying to figure out the wiring for channel switching. Can't seem to quite wrap my head around it.
I found another diagram showing a cliff jack so maybe you can help me get it. I am going to open Inkscape and sketch it out a bit.
-
You only have one relay, right?
Will you also have a front panel switch to control the relay?
-
Yes, one relay. A manual switch on the front. (SPDT right?) and the stereo cliff jack on the back. This is what I came up with.
Aaron
-
That will work but it is a little more complicated. It relies on two sets of contacts to work. I would suggest a simpler drawing using only one set of contacts. Less moving stuff to fail.
Your drawing is "A". My suggestion is "B". Use the one you like better.
EDIT.... And you only need a SPST switch on the panel and in the footswitch.
-
Ok. Yours does seem more straight forward. And I do not have to ground that sleeve on the switched side,right? And these should not need to be shielded at all as it is only switching the relay, right?
Aaron
-
Don't ground anything in those pics. Shielded cable is not necessary.
-
I didn't mean "ground" as in to the bus or chassis. I just meant connecting it to the common on the relay.
Aaron
-
Alright, I asked this question earlier in this thread and didn't really get an answer to it. I just want to make sure I wire up the Fatness pot correctly. I'm wondering if I run two wires from V1 pin 7, one to the wiper on the Gain (vol) and the other to lug 1 on the fatness. Or run one wire from V1 pin 7 to lug 1 on the fat pot and then connect that lug to the wiper on the Gain(vol) pot. I attached a picture highlighting the areas.
Aaron
-
Depends on where the fat pot is physically located. Isn't it on the front panel? If so, I'd do it like this...
Connect a wire between the vol pot wiper and the hot side of the fat pot. Now connect one shielded cable between the wiper of the vol pot and V1-7. Connect another shielded cable between the wiper of the fat pot and V2-2. Ground both shields at the pots (or pot buss) only.
-
So I think I may have gotten the wrong jacks for my input and effects send. These look like TRS jacks instead of the 12A jacks they should be. Will these still work for either my input of effects sends. I am about to order a few more parts so I can include the right jacks if I need to.
Thanks,
Aaron
-
So I think I may have gotten the wrong jacks for my input and effects send.
You need the switch function on the 12A.
-
Ok. Thanks. I will add those to my upcoming order from Doug.
Is this how I will wire up my impedance selector switch?
Thanks,
Aaron
-
That's basically correct. I'd move the NFB wire from the switch wiper to the 16Ω (or 8, or 4) lug so the NFB will remain the same regardless of which impedance selection you make.
-
So how does that work? Wouldn't you only get signal on the NFB when that impedance is selected?
Aaron
-
No, because the output signal is present at/on all 3 OT secondary taps all the time.
Brad :icon_biggrin:
-
Ok. Ii get it. Also, think I made a mistake on my selector switch picture above. I drew my arrows as if the red wire from the OT went to the selector switch. After looking at Hammonds wiring diagrams I see that the primary side red, blue, brown go to filter cap A, and my output tubes respectively and the secondary taps all go to the selector , the ground to the output jack. Then a wire to connect the selector switch to the tip of the jack.
Do I just ground the output jack at my main ground with my PT and heaters?
Aaron
-
Do I just ground the output jack at my main ground with my PT and heaters?
If your using a Switchcraft jack then it is already grounded to the chassis through it's metal frame. If your using a plastic body Cliff type jack (Marshall jack) then you have to run a dedicated ground wire to some ground point.
With amps that have -FB loops, like yours, they often ground the OT at the phase inverter (PI) filter cap star ground point, because the -FB loop is fed to the PI, so the PI is part of the power amp output loop.
Here's a link to grounding schemes that might help you;
http://www.valvewizard.co.uk/Grounding.html (http://www.valvewizard.co.uk/Grounding.html)
Brad :icon_biggrin:
-
Thanks for all the help everybody. I have gotten a fair bit done so here are some update pics. I will be placing an order with Doug in the next day or so then I will be on the homestretch. If you notice any possible issues, please let me know.
Aaron
-
Here are a couple more.
Aaron
-
Alright my final parts order is shipping to me as I type this. A couple questions about my tubes. I have some JJ 6L6s around here so that is what I will start with for power tubes, though I will probably try to acquire a set of 5881s down the road. I also have some JJ 12ax7s and an ecc81 PI tube I will use. The only tube I don't have is the 5879. I know tube depot has them and AES has them ( theirs state "short cut off" what does this mean?) Any other recommendations for where to source these? Also, I will start with the solid state rectifier and then try a gz34, 5y3, etc with different tube types. What have you guys found to be the best pre, PI, PT, rect combination?
I also came across a thread on here where Geezer mentions adding another 10uf or 25uf cap in parallel across V2-A cathode. I happen to have a 5uf 25v and a 25uf 50v lying around. Are those sufficient voltage ratings? It seems like they are considering voltage from there should be about 2 volts I just want to be sure.
One last question for the day. I have a .0047 and .0022 on my order to make the .0068 cap on the plate of V2 b. I need to run those in series to get the proper value, right? How have you all accomplished this? Put another turret on the board?
Thanks,
Aaron
-
I have maybe 10 different 5879 tubes all bought off ebay. I have not found a brand to be better than others.
Yes, the cathode caps you suggested are fine with the voltages you mentioned.
Parallel the caps to make the .0068. However, I would build it first with .0047 & try it. Then parallel safely the .002 with insulated alligator clipped wires and see what you like best.
With respect, Tubenit
-
So I have been searching for some step by step for powering this up when the time comes and I came upon this thread
http://el34world.com/Forum/index.php?topic=2376.0 (http://el34world.com/Forum/index.php?topic=2376.0)
where sluckey lays out a his procedure very well. Trouble is, I have not powered anything up so far. According to this list I will be jumping in after PHASE 3 I think. My PT is completely wired up. Primary, rect tube, heaters, grounds, etc. My OT is also wired to the tubes and all impedance taps are wired and soldered. I have not connected any of the filter caps yet. but I do have wires running from my tubes to my pots.
I do have a lightbulb limiter ready so I can put a fuse and lamp in and fire it up right? Then I can check voltages at the tube sockets with no tubes in at which point I will power down and move on to phase 4 and down the list. Can I also check my DC voltage across my relay diode at this point to determine my CLR for the OD LED? :laugh: (damn, that's a lot of abbreviations!) Am I also able to check my switching for the relay coil?
Any other thoughts to add?
Thanks,
Aaron
-
Very nice looking build working here. Lots of goodies in this design.
Consider making a Decade Box with Caps and Resistors. It will make tweaking this baby much more pleasant.
-
Do all your relay checks and calculate your CLR for the LED at the same time you check your filament operation. Phase two. Your PT and mains wiring should have been already verified at this point. Don't use the lamp limiter while testing the relay. Voltages may be too low for proper relay and LED operation.
Be sure to put the amp back on the lamp limiter when you move forward for initial B+ testing.
-
Ok. Since I did not get a test on the PT right away I will be jumping into the testing process a little further down the list. I will plug it in with my limiter and look, listen and smell. Then I will have to measure my heater filaments at the tubes and my text tube pins 4 and 6, 2 and 8 at the same time. With the limiter on how close to spec should my HV and heaters be?
Then I will power it back on with no limiter to check for my CLR value. I am very excited to see this thing come to life and confident in my attention to detail thus far but I am still nervous.
Aaron
-
Don't measure any voltages while plugged into the lamp limiter. They will be low.
-
Ok so I will use the limiter to protect my first power up to check the PT primary. Then I will power it up without and measure everything.
Aaron
-
Very nice looking build working here. Lots of goodies in this design.
Consider making a Decade Box with Caps and Resistors. It will make tweaking this baby much more pleasant.
The only bad thing about making your first decade box. Is then you end up like me with about 6 for every spot in the amp. (LOL) its an addiction I tell ya.
Bill
:help:
-
Alright! Powered up with no pop, fizzle, or smoke. :worthy1: When I measure the voltages at the recto socket should I measure across pins or from pin to chassis ground? Heater voltage was right on 6.3. I measured the voltage from the diode at 4.68v. Can I even use the 5v LED mentioned above?
Aaron
-
Can I even use the 5v LED mentioned above?
I would think so, but put a 220Ω or 470Ω resistor in series with it just to be safe. I still don't trust that Radio Shack label for that LED. If it doesn't work then you can get a bagful of LEDs from eBay for about a dollar.
-
I went ahead and put a resistor in there to try it out. It worked fine. I didn't put anything as big as 220 or 470 though so maybe I'll up it a little before I solder it in. All my switching worked perfectly. I only had to move my red wire from the top switch lug to the bottom so it switched correctly. What about measuring the recto? Measure between pins 4 and 6 or from each to ground? I didn't measure that cause I wasn't sure. What about pins 2 and 8?
Aaron
-
I went ahead and put a resistor in there to try it out. It worked fine. I didn't put anything as big as 220 or 470 though
Good. What value resistor? Now that you have a CLR installed, measure the voltage directly across the LED leads. What do you get?
Measure between pins 4 and 6 or from each to ground?
Do both. The AC voltage from each pin to ground will be half as much as the voltage between pins 4 and 6.
What about pins 2 and 8?
Measure that also. Should be 5VAC across the pins. Later on when you plug the recto tube in you will measure DC B+ voltage from pin 8 to ground.
-
The resistor on the LED measured about 110. The voltage across the LED now measures 3v.
Rectifier tube voltages:
-across pins 2 and 8 = 4.8 VAC
-from each pin to ground I don't get any reading
-across pins 4 and 6 = 118 VAC
-from each pin to ground =357 VAC
What's going on with my last set of voltage readings?
Aaron
-
The voltage across the LED now measures 3v
Kinda what I thought would happen! RadioShack just labeled the voltage wrong on the package. Not the first time.
What's going on with my last set of voltage readings?
I don't know yet, but don't do anything else until you find out what's going on. There should be over 700VAC between pins 4 and 6. Some cheap meters cannot measure that high. Look at the specs for your meter. Which meter do you have?
-
I am using a Centech meter from Harbor Freight. Cheap I know, but it says it should measure up to 750 VAC.
Aaron
-
Ok. I think I see what may be happening. And it is because of the cheap meter. Voltage reads something like 117 but when I tap the display all of a sudden the top LED crystal in the display appears making it actually 717. But then the voltage starts climbing up in the 800 and beyond. I will have to round up a better meter and try again tonight.
Thanks,
Aaron
-
What is the best way to ground the input and effect sends jacks? They are all switch craft type and someone mentioned earlier that I don't need to run a ground wire from my speaker jack because it is already grounded at the chassis. Is it the same for these jacks or should I ground them at the bus bar?
Aaron
-
I have quiet amps at idle. I use Hoffman's grounding scheme and ground the input jack on to the buss wire.
Regarding the FX loop jacks. I ground them to each other and not to the buss wire. . IF it is an active FX loop & there is a potentiometer
on the back chassis where the jacks are, then I ground the potentiometer ground on to the FX loop jack's ground.
IF it is an active FX loop and there is an FX potentiometer on the front of the chassis such as an FX level pot, then I ground it on the buss wire.
With respect, Tubenit
-
Thank you. No pot for the FX so I will connect them and ground the input.
Rechecked my voltages and I was right. The meter display was failing. I got 724 VAC across the pins. Onto the next phase.
Aaron
-
I am so close! Here is something I just realized I might have done wrong. I arranged my pots a little different than they are on the layout so it's tough for me to easily draw a picture of what I did. Basically, I connected the grounds from lug to lug in the overdrive controls and then connected the last pot's lug to the bus. Same thing in the clean section and in that section I also connected the ground from the relay to a lug. I'm wondering if I have a problem because quite a few grounds go through the .0047 caps that ground the tone pots. That should affect them, right? Here is the layout and a picture to help visualize.
Aaron
-
IF I am understanding how you everything wired to ground, I think it should be just fine. Look at Hoffman's grounding scheme. It works.
It's what I use and my amps are quiet at idle.
http://el34world.com/charts/grounds.htm (http://el34world.com/charts/grounds.htm)
With respect, Tubenit
-
Ok. Thanks. I have been very good on my grounding. Everything has been done pretty much like Hoffman suggests. I guess my concern was that with each ground connected to the next pot and then ultimately running through that cap to the buss it is almost like I grounded every pot through a .0047 cap. Instead of just the tone pot. Clear as mud, huh? I may change it or I may not worry to much. I just have to finish populating the main board and then check and recheck the scheme and layout and I will be giving it a test run.
Aaron
-
it is almost like I grounded every pot through a .0047 cap
IF I am understanding what you have done, ............ you simply have grounded a .0047 cap to a buss wire which is ground?
I don't understand the "through the cap" comment?
With respect, Tubenit
-
I look at it like this:
Lug 3 on the tone pot connects to the ground with a .0047 cap. (Not a wire)
Lug 3 on any other pot connects directly with a wire.
So it seems like what I have done is the equivalent of using a .0047 cap on every pot (because they all use that cap to get to the buss) instead of just a wire on as it would show in the schem. Not to worried about it but it was something I wondered about.
Aaron
-
So it seems like what I have done is the equivalent of using a .0047 cap on every pot (because they all use that cap to get to the buss) instead of just a wire on as it would show in the schem. Not to worried about it but it was something I wondered about.
If they all must get to ground thru that cap then it ain't gonna work. Just run a wire from each pot lug that should be grounded DIRECTLY to the buss. Otherwise, why even use a buss? Don't daisy chain your ground wires.
-
OK, I finally understood what you are saying. You threw me off saying you followed Hoffman's grounding scheme. (which you haven't actually followed)
Follow Sluckey's excellent advice.
With respect, Tubenit
-
Just tracing my schematic against my build and I noticed these two resistors from the power tubes to the cathode cap and resistor. Have these really gotten overlooked on the layout? Seems they would have been caught by someone and corrected. They were on the BOM so I have them, just not sure how/if I need to install these.
Aaron
-
Those two 1 Ohm resistors are so you can measure the bias of each individual output valve, IIRC they are a new addition to the circuit diagram and may have been overlooked on the layout. (Tubenit emphasises that one should use the circuit diagram and not the layout as the accurate reference.)
They are traditionally soldered directly onto the cathode pin (pin 8) of the tube socket, soldered together at the opposite ends and then wired to the cathode bias resistor/cap junction.
The circuit will work fine without them but you will only be able to measure the average bias of the tube pair, which is fine if you buy matched tubes.
I'm getting anxious with anticipation for switch on, plug in and strum :icon_biggrin:
-
I'm getting anxious with anticipation for switch on, plug in and strum :icon_biggrin:
Man, me too! :blob10:
Thanks for the info. I will just go ahead without those for right now. I also noticed that the layout I used (flipped version) also used a 150k plate resistor for the 5879. The scheme called for a 56k so I switched that over. How would a 150k affect that tube. More gain?
Should be completing it very soon.
Aaron
-
Higher plate resistance = more gain, less headroom before hard clipping I believe :dontknow:
My 5879 has 82k plate R.
Tweak to taste in the future.
-
I also noticed that the layout I used (flipped version) also used a 150k plate resistor for the 5879.
I am not seeing that? I looked at 3 layouts for the TOS in the SCH library. All of them including the flipped layout show 56K for the plate resistor for the 5879?
http://el34world.com/Forum/index.php?topic=9636.0 (http://el34world.com/Forum/index.php?topic=9636.0)
With respect, Tubenit
-
This is the version I have always had. Granted this is probably the original download from a couple years ago.
Aaron
-
SUCCESS!!! :wav:
Well, mostly. I did have a nasty squeal on first attempt, switched the OT leads and solved that. I do have a few things to look into so I'll list them here and see what you guys think.
My OD and Clean channels are reversed. When the switch is down(clean) I actually get the OD signal and when the switch is up the LED lights up and I get the cleans. What is the simplest move to make to turn these around?
My PPIMV works very well but from about the 2 o'clock position to just before all the way up it has a weird and vey present noise. Below that the amp is very quiet. All the way up and there is still just a little something there.
Lastly are my voltages. I have posted my readings and they are all pretty close. Take a look at my PI numbers though. Not sure why those seem so off.
The only component differences I have from the schematic are my cathode cap and resistor values. (100uf and 360R) and the cap connected to V2 pin 6 is .0047 instead of the .0068.
Thanks for all your help. I will be getting some recordings as soon as I can.
Aaron
-
What is the simplest move to make to turn these around?
Rotate the switch 180º.
-
V4-6 LTPI plate is just 60V?? In contrast V4-1 is 211v?
I would expect close to 200v plus or minus on V4-6. Maybe that is part of the problem with the PPIMV?
I currently would not be concerned about the .0047 instead of the .0068. And the power tubes 360R and 100uf is fine also for now. You can tweak those later.
With respect, Tubenit
-
Rotate the switch 180º.
Ha! yes that would make the switch positioning correct but then the LED would light in the down/clean position.
I am going to investigate this PI voltage thing.
Aaron
-
Ha! yes that would make the switch positioning correct but then the LED would light in the down/clean position.
Picky, picky! Are you saying you want the LED to light up when in overdrive mode? If so, you'll need to reverse the NO (normally open) and NC (normally closed) contact connections on your relay board.
-
WOW! Un-f'ing believable! Just spent the last hour+ lost in playing this thing.
I popped a different ECC81 in the PI. Seems to have evened things out. Voltages are around 177v on 1 and 6 now. I will post a new voltage table in a bit. As well as a completed chassis pic.
So to switch the NO and NC would I do something like this?
Aaron
-
Alright I'm going to say it again. This amp is a lot of fun to play! Right now I am playing it just as the open chassis playing through a cab with 2 vintage Jensen 12" and this thing is very quiet. And flexible.
This was my first build ever so I am going to consider this a huge success. I genuinely want to thank everyone who visits this forum and took the time to answer any of my questions and help to keep me on the right track. Now that it's done let the tweaking begin.
A few notes on fixes I had to do after power up:
- Had to swap the OT leads
- A new PI to trouble shoot odd voltages. ( I posted a table with my current readings)
- Flip the wires coming back to the board from the trim pot. (Knob on 10 was full OD)
- Still need to figure out how to get the LED light working as it should.
That's it.
One more anomaly I had was a weird squawk/squeal when OD was engaged and I turned the PPIMV past the 3 o'clock position. Not sure about that. It happened but I can't really reproduce it.
My 4 year old was hanging around and she said "Your amp is beautiful daddy but that sound is not nice." :laugh:
Here are a few pictures of the final chassis build and I will have some sound files up soon.
Aaron
-
Hi daveyajd,
Great eh! :thumbsup:
Some of those squeals and noisies when the PPMIV is turned up high may indicate an instability.
Make note of them and any other strange behaviours, they cam usually be addressed fairly easily.
Sound clips of any strange noises would also be helpful.
Some sound clips of the amps tone would be great too.
All the best.
Glenn
-
So to switch the NO and NC would I do something like this?
Yes. Since you have a double pole relay swap NO and NC for both poles.
-
Congratulations on a successful amp build! It was a complex amp and it looks like you did a great job with it. I would love to hear soundclips.
Glad you got the LTPI plate voltages corrected. That may have resolved the PPIMV issue since you said you have not been able to reproduce it?
With respect, Tubenit
-
So I'm not sure what happened but my amp has fallen apart sonically. Everything was working great and I was playing it everyday and loving the sound. But of course I could not leave well enough alone and had to mess with it just to see. :BangHead: So I decided to adjust the power tube cathode cap and resistor. I was putting a 47uf cap parallel to the 100uf and increasing the resistor from 360 to 428 by putting a 68ohm in series with it. When I fired it back up there was hum and hiss on the OD channel especially when the PPIMV was anywhere but all the way up and the Lean was all the way down. Clean channel seemed to still be fine. Also the relay switching now seems to make an audible pop that it never made before.
So I changed the cathode back to its original values and still have this ungodly squeal and squawk in pretty much the whole range of PPIMV.
Here is a sound clip recorded with my phone. The background noises are my daughter playing around but you will hear a hiss (now on the clean channel) and then a switch to OD and the crazy noise.
https://soundcloud.com/daveyajd/weird-sounds
-
When you increased the cathode resistance, you probably put more voltage on the plates. I am wondering if you damaged a power tube?
Do you have another set of tubes to try?
Also keep in mind, sometimes we bump or move something other then what we are working on ......................... & when that happens, we think the problem is related to the area we are modifying and it may be related to something else. Go back and measure voltages on your tubes. Does everything look OK to you?
With resepect, Tubenit
-
I was afraid I might have damaged the tubes. Like the amateur I am I accidentally did my desoldering of the old components with the tubes still in. Dumb ass! I do not have another set of matched tubes to try out but I have a couple of randoms I could try. The voltages are all still measuring the same. I am bumming right now until I get this figured out.
Aaron
-
Do you have a pair of 6V6's that you can try? Or some 6L6's that are close to matched? If so, maybe use those if the plate voltages are not too high?
With respect, Tubenit
-
Hi daveyajd.
Can't seem to get to your sound clip, sound cloud says it's "not there" or "private".
Desoldering with valves in is not likely to have been a problem, it is often standard factory procedure to solder up sockets with valves in place so the socket pins seat correctly. Nor is the small increase in cathode resistor likely to have been a real budgie killer. If you put the second capacitor in with wrong polarity it could have been a problem.
Just for giggles, TEMPORARILY put a 630 volt coupling capacitor between pins 3 of the output tubes. (Pin 3 of one output tube to pin 3 of the other output tube), Any value from 0.001uF to 0.01 should do for the sake of diagnosis.) Does this cause any change ?
The obvious question is "Why did you feel the need to alter cathode bias component values ?".
You must have had a reason.
All the best
Glenn.
-
I have another pair of 6L6 that I tried. They are not matched but there was no improvement when I installed those. I can't imagine that I bumped another component. The resistor still measures about 360 and the cap seemed to still be good though I switched that out just to check. I guess I'll have to start a process of checking but I'm not sure where to start.
Hey Glenn, I will try that cap test. How TEMPORARILY?
The answer to your question is simple. I was tweaking for amp feel. The scheme called for 430R and 147uf and I was just trying to see how the amp feel would change if I brought the cathode section up to the schematic specs. I changed the private setting on the clip so you should be able to listen now.
-
Tried pins 3 jumper cap. Did not affect anything.
Aaron
-
Temporarily, like put it on test it for 10 seconds, then take it off.
Got that sound clip, that is an oscillation / motorboating problem for sure. Could be a dozen reasons for it so........
Try these as TEMPORARY diagnostic mods (change, test, unchange). Do them one at a time.
Be especially carefull that you turn off, remove from wall socket and allow time for capacitors to discharge between each step. ( Safety First Always, no running red lights in a panic to get to work on time )
Mod 1 ) Remove the 4.7 k Ohm NFB resistor from the output transformer secondary tap. The amp may be much louder and more distorted so plan the test accordingly by lowering all volumes.
Mod 2 ) Put an alligator clip test lead to the FX return loop plug tip connection and ground the other end. The amp should make no sound of any kind (except maybe an almost inaudible little bit of hum)
( Or to achieve the same effect, remove the lead of 0.022 coupling capacitor to V4 pin 2.
Not on the tube side but on the side of the FX return send, and ground that cap lead. )
Mod 3) Do both 1 & 2 at the same time.
What happened.
-
Ok, I tried those diagnostics and here is what I found. The first thing I said was "What 4.7k resistor?" I looked at my schematic and my build and discovered that I had never put that in. I had a wire going from the OT secondary to the NFB.
So I put that resistor in and it helped control the noise but it was still very present.
I then grounded the FX RETURN tip and there was in fact, no sound from the amp.
My voltages are all pretty much the same although the PI voltages are at about 191v up from 176v. The other thing I noticed was that the buzz was greatly reduced when I put my probe on V4 pin 7.
Aaron
-
I was a little ambiguous. I wanted you to lift the 4.7 k resistor so there was no connection between output transformer and NFB.
The changes in voltage on PI are suspicious. Have you tried changing that valve ?
Check that all components in ORANGE are secure, well soldered and don't have any stray bits of wire or solder connecting them. You may have fried the 47 ohm to ground in the PI having the output transformer connected directly to it. (GREEN)
Try the RED and BLUE mod and tell us what that results in, should be nice clean sound.
(See attached diagram, ignore the red box near output tubes cathode resistors)
Another good trick is to take a dry piece of wood or non conductive plastic, like a chop-stick or drum stick, and lightly tap around the circuit with the amp going, being very careful not to let cats or children jump into the amp. You can often find faulty connections or components that way. ALSO move any wires around with the drumstick and see if that changes the weird noise.
-
I was a little ambiguous. I wanted you to lift the 4.7 k resistor so there was no connection between output transformer and NFB.
The changes in voltage on PI are suspicious. Have you tried changing that valve ?
Another good trick is to take a dry piece of wood or non conductive plastic, like a chop-stick or drum stick, and lightly tap around the circuit with the amp going, being very careful not to let cats or children jump into the amp. You can often find faulty connections or components that way. ALSO move any wires around with the drumstick and see if that changes the weird noise.
Yes I also tried lifting the NFB completely. Still a very bad sound. I did try another PI tube. The sound was unchanged but I did not take measurements on it.
I also tried pushing things around with a stick. When I push down on my ground bus right around the FAT pot the buzz goes away (almost) but I still get the nasty motorboat/squeal.
I will check and try the changes highlighted in your diagram tonight and see what I can figure out. I may also remove that 47 ohm resistor and take a measurement on it. Thanks for your help. I will report back.
Aaron
-
Re check and post all voltages if possible, especially around the PI. That should not have changed.
Sometimes components can measure OK but be faulty in some way, although it is rare in resistors.
Try shorting out that resistor, 0.1uF cap of pin 7, other side to 47 Ohm, instead just ground other side (PURPLE).
Swap that 0.1uF cap if possible also.
The fact that touching pin 7 with probe reduced buzz, and that voltages have changed in the PI, suggests that region has problems.
-
So I started poking around my grounds and found that the ground from the relay was not cutting it. Resoldered it and a couple in that area and that made a big difference. It is actually playable again now. There still seems to be a bit more noise and a few weird oscillation type sounds as I fiddle with the knobs. I won't be able to give it full out test run until tomorrow and then I will take all the measurements and look closer at the PI section because I think there is still something going on there. Thanks for your help Glenn and I will keep you posted.
Aaron
-
Aaron,
Glenn has been giving you excellent advice in trouble shooting! Keep working with his suggestions if you're not satisfied the issue is resolved yet. Truly sorry to hear your fine amp has developed a glitch in the tone. You will get it fixed!
With respect, Tubenit
-
Alright, here's where I'm at.
Checked all components and solder joints in the circle and replaced the .1 cap. Voltages came down a bit to 180v and the hum reduction when I touch pin 7 is gone. I do have a few more things so I will address them one at a time.
There is a hiss when the PPMIV is rotated to a few spots. I attached a sound clip for a listen.
https://soundcloud.com/daveyajd/clean-channel-hiss (https://soundcloud.com/daveyajd/clean-channel-hiss)
The PPIMV is just backed off from full. (all the way up and there a hiss unless I have the clean channel level all the way up)
I play a little something, then I turn the PPIMV down until you can hear the hiss come on, then I put my meter probe on lug 1 and the hiss goes away but the guitar sound is unchanged.
I did not use shielded cable from here to the .047 caps. Would rewiring this help?
One other strange thing I noticed is that there is a lot more noise when I use a 4.7k resistor on the NFB versus just connecting it with a wire only.
Aaron
-
Try once again. disconnecting the feedback, note what happens, reconnect feedback 4.7k and place .001 - 0.01 across anodes of output tubes, note any changes. Sorry, but these diagnosis things can be a bit circular.
It is definitely WRONG (nonsensical) to have output transformer connected directly to NFB without a reduction resistor (4.7k)
It does sound like a NFB oscillation problem but I'm not there with a CRO so I can't do much more than make suggestions based upon unfounded assumptions. These amps are as quiet as the dead when working correctly. Sorry for the somewhat macabre reference but they are so quiet, I as a technician often panic when I first switch them on coz there is nothing.
The THING is, you just have to keep trying different solutions. It is a learning experience, and when you finally beat a tough one , you feel really good, "empowered" to use a modern terminology.
I happen to have a thousand yards of lightweight shielded cable, I use it for everything. My amps are noise free. Try shielding or twisting the cables that connect PI to PA. (I don't think it's that coz you get no changes poking lead dress with a chopstick)
Did you try shorting the 47 Ohm resistor to ground to see what effect it had.
Was this recording done with the suggested RED/BLUE MOD which bypasses all switching and connects clean preamp directly to PI.
What is the voltage on the PI cathodes (42 V whatever, what is it)
My strategy here is to try and isolate the faulty LOGICAL BLOCK (Preamp Clean, Preamp Dist, PI, PA, NFB). Unfortunately with Oscillation Instabilities they can be occurring in the Radio spectrum, way above audible frequencies, and, just like radio they go everywhere and are difficult to isolate without the correct test equipment.
I am willing to stick with it if you are Aaron, (Speaking of sticking, nice picking by the way)
Glenn.
-
Again, follow Glenn's advice! I think he is heading you the right direction. Stick with it, you will get this resolved.
With respect, Tubenit
-
I just had an idea.
With the amp wired as per diagram you should be able to plug your guitar directly into the effects return and get a "bedroom comfortable" sound. I just did it with my very similar amp and it is quite a nice clean sound. Like a 2 watt amp. What happens with your amp when you do this.
-
I just had an idea.
With the amp wired as per diagram you should be able to plug your guitar directly into the effects return and get a "bedroom comfortable" sound. I just did it with my very similar amp and it is quite a nice clean sound. Like a 2 watt amp. What happens with your amp when you do this.
Good idea, that can further define where the problem is.
As a side note, playing an acoustic guitar with a very slight delay thru the effects return can actually sound pretty good with an amp like this.
With respect, Tubenit
-
Again, follow Glenn's advice! I think he is heading you the right direction. Stick with it, you will get this resolved.With respect, Tubenit
Oh, I plan on sticking with this all the way. I'm hooked now! :icon_biggrin: And everyone here has been awesome throughout this adventure.
It seems like this is almost a different amp today. Very playable and no real oscillations. Changes her attitude on a dime. I guess I should give her a name! :l2:
So I disconnected and recounted the 4.7k NFB. Much less noise with the resistor in. (As it should be) So now that is good. I then put a .001 cap jumper the across the tube anodes. I didn't notice much of a difference but if there was any it seemed to be a bit noisier.
With the amp wired as per diagram you should be able to plug your guitar directly into the effects return and get a "bedroom comfortable" sound. I just did it with my very similar amp and it is quite a nice clean sound. Like a 2 watt amp. What happens with your amp when you do this.
I did plug in to the FX return and that is a very cool trick. The amp is sooooo quiet that way. That is the noise level I want to achieve through the main input.
The recordings last time were done with the switching relay connected not using the red/blue mod.
I attached a new voltage chart and a couple of recordings of the clean and OD. On the recordings you hear me talk, then play a bit, then I turn each knob up full then back down to half one at a time so you can hear the hiss added by each pot.
Since everything sounds much better I would love to know how to go about eliminating that hiss?
https://soundcloud.com/daveyajd/clean-channel
https://soundcloud.com/daveyajd/od-channel
-
OK, you have made progress.
The fact that there are no problems when you plug into the FX return suggests that the PA, PI and NFB systems are all OK.
The amp will not sound that quiet once the preamp is in and the guitar is plugged in and turned up.
What happened to the horrible wailing, moaning and farting sounds we were listening to a couple of days ago ?
I thought they maybe had the makings of the latest trend in modern music :icon_biggrin:
I hope they stay away forever personally, I'm a bit old fashioned.
Noise ( normal hum and hiss) assessments are only realistic if the PPIMV is set to full volume.
When the guitar is NOT plugged in there should be a noticeable hum and hiss on the CLEAN channel when all controls are set to full throttle. What do I mean by "noticeable" , much louder than a cats purr-r-r-r-r-r-r-r-r, but nowhere near as loud as a cat's meow.
(That is the only way I can express it in somewhat realistic everyday terms)
The CLEAN channel should be basically inaudible when all controls are set to 2 o'clock with the guitar not plugged in.
Just to clarify, where is the PPIMV set during these recordings. I would suggest turning all you knobs to about 2-3 o'clock with the guitar plugged in but turned down to like 1/8 volume (so that it doesn't howl and feedback) and then adjusting the PPIMV to make sure it is stable at all settings. Then turn all controls to full and adjust PPIMV making sure there are no signs of moaning / motor boating. Moaning and Hissing are very different things. Moaning can be very high pitched and sound like hiss but it is very different, it has a definite note ( fixed pitch or pitch bending up and down) buried in it.
There should be no hint of oscillation (moaning / wailing sounds), and no put put putter fart motor boating at any gain settings really, but at everything on spinal tapping 11 some amps may never be absolutely stable.
All the noise I am hearing on those recordings is coming from the clean channel, they are just made worse by the extra gain when overdrive is engaged. I am not sure if they are terribly abnormal although they do sound a bit too load to me. Depends once again on where the PPIMV is set.
Could the wailing / motor boating have been due to the lack of 4.7k NFB resistor and we got side-tracked / knocked of our rails inadvertently chasing ghosts. Possibly.
What type of resistors are you using around the first valve.
Now that was very long winded wasn't it. The actual sound of the amp is GREAT. What loudspeaker are you using.
If you could do those assessments and get back to us it would be helpful. We all love to hear others play on the amps they build so record some more with PPIMV at full tilt. If it's anything like my D'Mars you may need to put earplugs in and warn / bribe the neighbours.
PS: Ken Fischer of Trainwreck fame had his reasons I'm sure.
-
Overall, your amp sounds good to me & I like the tone of it. OD channel tone is very nice.
My opinion is the Dumblish type builds, the Tweed BluezMeister, the Tweed Overdrive Special and the D'Mars are not designed to have all the potentiometers dimed.
And some of the real Dumble and Dumble clone videos I've watched left me thinking that some of those amps have waaayyy more hiss then I'd be comfortable with personally.
I don't play my TBM or the D'Mars with the volume knob (clean channel) past 5. It's usually closer to 4. My D'Mars is the quietest amp at idle that I've ever owned. It is considerably quieter at idle then the original Princeton Reverb or the Carvin amp that I owned even with the D'Mars at a louder volume then the PR or Carvin.
The TBM and the D'Mars is quiet enough at idle (at the volumes I normally play at) that one might enter the room and not realize the amp is on. (on clean channel)
Having said that, I have no doubt that IF I cranked pots to 10 that I'd have unwanted noise/hiss.
I use a 12AY7 in V1 in both of my amps. And a 5751 in the OD channel. My current D'Mars has a 5879 in the OD also.
I use Vishay Dale RN65 resistors on the plates for the gain stages. I think those may add to helping eliminate noise/hiss. Note those on 2, 4, & 6 turret rows in picture.
I'd recommend using a 12AY7 (Doug carries EH 12AY7's that I like) or a 5751 in V1. You can also put a 220p cap from pin 6 to pin 8 on V1b to lower hiss.
With respect, Tubenit
-
I would also like you to note that I did the cap foil orientation on my turret board for the D'Mars. I am convinced that greatly helps reducing noise.
http://el34world.com/Forum/index.php?topic=11427.0 (http://el34world.com/Forum/index.php?topic=11427.0)
The "enhance cap" across the LTPI entrance plate resistor helps ALOT also in reducing unwanted noise in my experience.
I have plenty of sustain for my playing in my amps with just the clean channel using a 12AY7. I don't think one needs a 12AX7 in V1. If you don't want a 12AY7 then use a old stock or NOS 5751.
This sound clip is the D'Mars with just the clean channel only using a 12AY7. Notice that there is no noticeable hiss at all.
http://www.soundclick.com/player/single_player.cfm?songid=12595832&q=hi&newref=1 (http://www.soundclick.com/player/single_player.cfm?songid=12595832&q=hi&newref=1)
This sound clip is repetitively obnoxious but shows the sound differences & contrasts between clean and OD with the Tweed Overdrive Special I had. It starts with clean to slight overdrive to more overdrive. IIRC, this had either a 12AY7 or 5751 in V1 and then a 5751 in V2? The amp was not noisey at idle.
http://www.soundclick.com/player/single_player.cfm?songid=11332809&q=hi&newref=1 (http://www.soundclick.com/player/single_player.cfm?songid=11332809&q=hi&newref=1)
With respect, Tubenit
-
Yes the recordings were done with the PPIMV all the way up with the exception of the last bit on the OD channel recording where I turned it down to reduce hiss and check for any oscillations. The cab I'm running through is a two twelve with two vintage Jensen P12Q or P12N (can't recall which) installed.
My tube line up right now is RCA 7025s in both V1 and V2, JJ ECC81 in PI and JJ 6L6GC PTs.
Could the wailing / motor boating have been due to the lack of 4.7k NFB resistor and we got side-tracked / knocked of our rails inadvertently chasing ghosts. Possibly.
What type of resistors are you using around the first valve.
All of my resistors are metal film and did research and test all of my Mallory 150s for outer foil and orient them correctly. I also have the 220 enhance cap across the LTPI as per Tubenits suggestion. I may put one on V1b pins 6-8 .
It's interesting to me that I had finished my build and played with it for a week or so and it was dead quiet. I mean REALLY quiet on both clean and overdrive with the knobs dimed. And that was with the NFB connected without the resistor. All of this hiss really started after I tried to mess with the PT cathodes. I will try setting knobs as you suggest and get a recording of each channel like that.
I know that this can be quieter so I am working towards that. But it is playable again now and that is a great thing.
Aaron
-
It's interesting to me that I had finished my build and played with it for a week or so and it was dead quiet
Yeah, if you had it dead quiet ........ I would definitely invest the energy into getting it back to that. Just remember what you originally did was successful so you can recreate that.
with respect, Tubenit