New TMB w/reverb Build

[foreverstrung]

My money would be on a bad solder joint somewhere, or a questionable tube. You could try swapping out the preamp tubes and see if that changes anything.

I've swapped out all the pre amp tubes with no change and I've rewired all the heaters and pots. That does not leave many solder joints considering I went thru the PCB board checking pad connections....... I'll go thru the PCB board again. Slow and careful, but soldering the PCB board was extremely simple. I found it very easy to complete and I went thru and verified that everything was where it was supposed to be.
I'll go thru it all again. It would have to be something I've missed already 2-3 times, or something got fried or is defective.

[Bieworm]

Just fired up my new built Tremolo TMB. It works, voltages check out.. but no reverb. I will have to dig into that.. lol

I posted a quick video on instagram. @Bieworm

Edit: found the problem. I put the coupling cap from the recovery plate to node C of the B+ instead of on the plate. Lol!

[JMPGuitars]

I've swapped out all the pre amp tubes with no change and I've rewired all the heaters and pots. That does not leave many solder joints considering I went thru the PCB board checking pad connections....... I'll go thru the PCB board again. Slow and careful, but soldering the PCB board was extremely simple. I found it very easy to complete and I went thru and verified that everything was where it was supposed to be.
I'll go thru it all again. It would have to be something I've missed already 2-3 times, or something got fried or is defective.

Fried is possible, defective is less likely. I tested everything (for value specs) prior to sending it out.

With the amp powered off and unplugged, test your capacitors for continuity.

If possible, good photos of the bottom of the PCB might be helpful.

Thanks,
Josh

[foreverstrung]

If possible, good photos of the bottom of the PCB might be helpful.

I had to pull half the amp apart a few days ago to get to the underside of the PCB board. I really don't want to do it again. It's clean. I'm not a ace solder-er, but it's clean. If I thought for a min there'd be something there, I'd take it apart again. I took it apart then to check for anything suspicious. I wish now I had photographed it

Logically I was trying to follow the schematic and before pulling that cap can, I thought I'd try changing that 2.2k resistor from the lug after the zener diodes to B+ on the cap can to 1K. It brought my voltages up. B went from 275v to 311.9 v.....everything went up closer to what the sheet called for. However the sound is still tinny. Like a blown speaker. And I tried another speaker to be sure.

I do not know all the termanology yet, so please bare with me, but the 1k resistors from pin 9 on the el84's to the terminal strip and the 2,2k to the PCB board, I removed and replaced all 3. Slow and clean.

Right now, with the 1k @ the terminal strip to the B side of the cap can, all my voltages look good, but the amp still sounds like ****.
IDK where to go from here. I've rewired almost everything

[foreverstrung]

OK. I found one .01uF yellow cap. (I can locate it in the schematics and the layout, but I don't know the correct description to identify for you guys. At least I believe I can identify the location on the schematic.) .Cap between the el84's and the v4 preamp.
Anyways, 0ne side of this cap was not soldered. So I did. Obviously.
I REALLY believed this was going to be the problem I was looking for. So much so, That I put back the 2.2k 5w resistor @ the B side of the cap can.When I did, the voltage there dropped back down to 275 (after being at 311 with the 1k resistor 3w resistor I swapped out thinking to increase voltage to the B side of the can). This is how it's in the schematic and layout. With the 2.2k 5w......However, we have the same tinny sound. It's something else.

With the amp powered off and unplugged, test your capacitors for continuity

None of the yellow "foil" caps have continuity. The other caps do. Unless I'm not checking right. Please advise.


After you guys comments, if there nothing else, I will pull the PCB board back up again. I spent the better part of saturday doing this last time. Although I did rewire/solder all new sockets. This took up most of the time
I could, I guess, solder the pads on top. Just a thought. Wouldn't be real clean, but whatever it takes.

[JMPGuitars]

Which caps have continuity? Use a photo, and circle the ones that do.

The easiest way to take photos of the other side of the PCB is to disconnect the pots from the front panel carefully (hardware only, no need to desolder), and bend the whole thing up. Clear photos of this will help more eyes see if there's anything else not soldered correctly.

I'm hoping you're keeping a list of what I need to add to the manual, so add this to the list: "Take photos of the bottom of the PCB and review before mounting."

Thanks,
Josh

[Bieworm]

+1 on that! I learned that you can not make enough photos during the build. That's why I take a lot of photos after each soldering session.

20221130_084221.jpg

[Bieworm]

Just to rule something out ... unsolder the ground wire and the black wire from the OT at the speaker jack. Remove the solder and make those connections again. I recall having trouble with the sound once, which was solved right there. I apparently accidentally soldered the wire isolation into the lug, making a bad connection.
I also pull all wires slightly when soldering, just to make sure the mechanical connection is solid. I do that with components too.

[foreverstrung]

So I spent my time on the underside. I did find another missed solder joint, but it didn’t change the sound.
Going over this pic I see a 1.2k resistor that looks to be a weak solder joint, tho I tested from the top side pads, over 3 times and I’m getting a clear 1.2k reading every time. Interested in what think to do with this.
Also, my voltage on the B side of the cap can stays at 275v. As I said, when I replace the 2.2k with a 1k wirewound resistor, it increases voltage to 311v. Should I put the 1k back and bring the voltage to the B side up?
I’m interested in anything else you guys recommend to get this dialed in. It’s so close.
Lastly, you asked which caps I was not getting continuity. Every yellow cap. Every other cap I checked, I got continuity. Even the radial caps when I check in line at the B+ pad in front of them.




Sent from my iPhone

[lavrgs]

Amp building helped me learn the practical use of V=iR. In my case the voltage was low because not enough current could flow = bad solder joint. Checking voltages is a very good indicator of what is working and what isn't. I'll go back and look at your charts but I'm solidly in the new builder camp. Perhaps there is a schematic showing voltages at different points that could provide a go/no go path.
I'm monitoring this thread as I have this amp stalled on the bench...the weather is really starting to s*ck so it must be getting close to amp building season. Happy Hunting

[Bieworm]

To me the PCB soldering looks acceptabele. I would clip the piece of cathode wire sticking through ( V5+6 pin 3)
This reduces the error to solder joints on the other hardware parts ( pots, switches, tube sockets, terminals, cliff jacks,...) OR .. component failure.

I didn't get info from you wether you did the un- and resoldering at the output jack. Neither on the swapping of the can capacitor. I know that it's doubtful that that would be the problem.. the main symptom would have been excessive hum, but if the cap is leaking DC to ground there would also be a larger current consumption, resulting in a lower voltage. V=IR !
I think it's not normal that you have to use a 1K dropping resistor where on all other builds Josh and I use 2k2 in that position.
Just try the cap swap. If it's not the problem, you lose nothing. If it turns out to be the problem... look at all the excess trouble you went through. I suggested this days ago...

Did you chopstick all solder joints? While adding heat shrink on the tube sockets look good and secure things from arcing and accidental shorting while prodding, it now makes things harder to check. I never do the heat shrink there. I regretted covering solder joints too many times. Josh does that because he's very competent and pretty sure the joints are solid.

Do you have access to a scope? What can be heard, should also be seen on a wave form...

[JMPGuitars]

I regretted covering solder joints too many times. Josh does that because he's very competent and pretty sure the joints are solid.

Two things.

1. I know they're solid.

2. I have razor blade pen knives, and they easily remove the heat shrink if needed.

2a. While my joints are solid, it's not impossible to wire the wrong thing and need to redo it.

2b. I can still hit the base of the solder tab with a probe if I need to, though it's not so easy to see without zooming in:

socket.jpg

[foreverstrung]

I didn't get info from you wether you did the un- and resoldering at the output jack. Neither on the swapping of the can capacitor. I know that it's doubtful that that would be the problem.. the main symptom would have been excessive hum, but if the cap is leaking DC to ground there would also be a larger current consumption, resulting in a lower voltage. V=IR !
I think it's not normal that you have to use a 1K dropping resistor where on all other builds Josh and I use 2k2 in that position.
Just try the cap swap. If it's not the problem, you lose nothing. If it turns out to be the problem... look at all the excess trouble you went through. I suggested this days ago...

I did remove the ground wires from the speaker input. Cleaned up and re soldered it. No change and I did drop the 2.2k resistor to a 1k between A and B on the cap can and all my Voltage readings got better, but the sound did not improve. (Josh suggested a 1.5k, not 1k, if I was to change out the 2.2k)

I have not switched out the cap can. Perhaps I'll do it this wknd. I've got 2 extra on hand. I don't believe there's anything wrong with this one, but it's something else to consider.
Thx

[foreverstrung]

I replaced the cap can this afternoon. Many of the components around it too. Made sure I got solid solder connections. Then I went thru all the terminal strips and resoldered the connection to ensure they were solid.
Still the same sound. I even tried a 3rd speaker. To triple check. It's not the speaker. 100%
I've replaced all pre amp tubes. With other used pre amp tubes. No change
I'm believing strongly I've got a cold joint somewhere. My soldering is not bad, but the small stuff, or stuff that's real crowded, it's difficult for me to see. I've got a good lighted magnifying lense, but it's tricky, as I'm sure you guys are aware, to solder looking thru these.

Checking voltages is a very good indicator of what is working and what isn't. I'll go back and look at your charts but I'm solidly in the new builder camp. Perhaps there is a schematic showing voltages at different points that could provide a go/no go path.

I'm going to follow up this way, best I'm able, using the my schematic for this amp as it does have voltages marked.

[JMPGuitars]

Did you check on the PI plate resistors, and the wires and resistor nearby that I mentioned?

[foreverstrung]

Did you check on the PI plate resistors, and the wires and resistor nearby that I mentioned?

I did check the wires. Cleaned them up and resoldered. Nice and clean. I don't recall if I checked the resistors. I didn't checked the resistance. I did check that everything was where it was supposed to be and checked that it looked solid.
I'll go over all that tonight.

[foreverstrung]

OK. todays troubleshooting.
I rebuilt the entire instrument input jack. Because
I also rewired the 1st terminal strip on the right to match what the layout shows and what Josh's photos of this amp shows. This was pointed out to me as something I missed. To be helpful when grounding out the tremolo for sound check. I also think the footswitch jumps off this lug too. Assuming I ever get to the bottom of this.

Then I went through and checked the resistance to ground on all cathode pins using the schematic, they all are correct resistance, except maybe the PI, V4. Tho it's hard to read as it's diff than the others. If I'm reading the schematic correctly, it should be 820 ohms, but I'm getting 48.18 ohms at both the # 3 pin and the #8. I don't understand if this is correct or not.
And then were to go next.

[foreverstrung]

Upon further observation, I see the 47k resistor inline with the 820 ohm coming off V4. When I measure it across on the PCB board, I get 48.18 ohms. Just like at the pins.

So that means all the cathode to ground pins "resistance" is as it's laid out in the schematic. Tho IDK if 48.18 is what is supposed to be produced with the 47k and 820 in line. IDK this math.

Where should I go next? I do believe I've now checked and done everything suggested to me so far. Still the same sound. Volume low and light picking it's clear. Give it any volume and play hard and it breaks up and not in a good way.

[Bieworm]

Did you chopstick the solder joints already? I don't remember you doing this throughout the thread.. it vould be something as simple as a cold solder joint somewhere...

[foreverstrung]

Did you chopstick the solder joints already? I don't remember you doing this throughout the thread.. it vould be something as simple as a cold solder joint somewhere...

I did do this, but maybe not as thoroughly as I could have. I'll go back thru and at a slower more efficient pace.
Thx