New TMB w/reverb Build

[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

[foreverstrung]

So to review.
I finished the build to the point of testing. (pre fx)
*Did the mark thru with highlighter and PCB component check off
*Did multiple voltage tests. B side low at cap can 275v. Always. Expected to be 310v
*Sound not right upon test.
*Removed and replaced all wire @ pots and resoldered all pots
*Removed and replaced all tube sockets and wiring
* Confirmed that speaker is 100% working condition
*Removed and replaced cap can and all wiring and resistors
* Remove and replace wirewound resistors at EL84's pin 9's to PCB board. All 3
*Checked all resistance on resistors at pads. All read correct. (multiple times)
*Checked capacitors for continuity. All appear in good working order.
*Checked all cathodes to ground resistance. (I believe there good with the exception of V4. IDK if that number, 48.18 ohms @ pin 3 and 8 is correct). Def need clarification here
*Removed and replace instrument input jack and all wiring
*Resoldered all my terminal stip connections
*Removed, cleaned up and resoldered my speaker input jack ground
*After amp was warm, I did the chopstick test looking for bad connections, 3 times. Very slowly. Every connection with volume up 1/2 way
*Lifted PCB board twice. Checking solder joints. Soldering 2 that were missed. Nipping back any long leads

Sound is still harsh. Still the same as the sound check I posted earlier in this thread
Where do I go from here?
Thanx in advance

[JMPGuitars]

*Checked all cathodes to ground resistance. (I believe there good with the exception of V4. IDK if that number, 48.18 ohms @ pin 3 and 8 is correct). Def need clarification here

v4-cathode-path-to-ground.jpg

Those answers are always in the schematic. Follow the junction of P3+P8 to ground, and the answer is there (47K + 820R).

Now, did you mean 48.18K or 48.18 ohms? Because if it's not 48K, then that's an issue.

EDIT: I just scrolled back and read where you first asked about this. The junction of those 4 resistors is not ground yet, you have to draw the line all the way to the line where the ground symbol is. So grab your highlighter, and run it as I mentioned above, then you'll see the value of 47K + 820R.

Thanks,
Josh

[foreverstrung]

Now, did you mean 48.18K or 48.18 ohms? Because if it's not 48K, then that's an issue.

EDIT: I just scrolled back and read where you first asked about this. The junction of those 4 resistors is not ground yet, you have to draw the line all the way to the line where the ground symbol is. So grab your highlighter, and run it as I mentioned above, then you'll see the value of 47K + 820R.

(I think you missed the very next post where I corrected this)
I apologize that I was not clear. I did follow that line, that you highlighted, to ground and I get 48.18 ohms. What I don't know, is if that is what it's supposed to be.

Those answers are always in the schematic. Follow the junction of P3+P8 to ground, and the answer is there (47K + 820R).

I'm not seeing the answer here in the schematics. I don't understand that math. Is 47k + 820R = 48.18? Everytime? This time? Good/Bad?
Where do I go from here?
Lots of questions. Sorry. Not sorry. LOL

[JMPGuitars]

Those answers are always in the schematic. Follow the junction of P3+P8 to ground, and the answer is there (47K + 820R).

I'm not seeing the answer here in the schematics. I don't understand that math. Is 47k + 820R = 48.18? Everytime? This time? Good/Bad?
Where do I go from here?
Lots of questions. Sorry. Not sorry. LOL

Ok, let's try again.

Ohms or kiloohms?

47K = 47,000. 47K + 820 = 47,820 ohms. The resistors are 1%. So you should be within 1% of 47.82Kohms. 48.18 Kohms = fine. 48.18 ohms = not fine.

That's the math: resistors in series are added together. 1 + 1 = 2.

Thanks,
Josh

[foreverstrung]

It's 48.18k

47K = 47,000. 47K + 820 = 47,820 ohms. The resistors are 1%. So you should be within 1% of 47.82Kohms. 48.18 Kohms = fine. 48.18 ohms = not fine.

That's the math: resistors in series are added together. 1 + 1 = 2.

Thx for this. I did not understand the measurements correctly or the math.
I understand now.
It is 48.18 kiloohms. Grount to cathode. V4, Pin 3 and 8

[JMPGuitars]

It's 48.18k

47K = 47,000. 47K + 820 = 47,820 ohms. The resistors are 1%. So you should be within 1% of 47.82Kohms. 48.18 Kohms = fine. 48.18 ohms = not fine.

That's the math: resistors in series are added together. 1 + 1 = 2.

Thx for this. I did not understand the measurements correctly or the math.
I understand now.
It is 48.18 kiloohms. Grount to cathode. V4, Pin 3 and 8

Good, and that makes sense anyway considering your cathode voltage is pretty close. Nothing needs to be exact, but you want things close.

Back to searching for soldering issues.

Also, test your plate resistor value at the PI. My guess is they're fine, but check anyway if you haven't yet.

Thanks,
Josh

[foreverstrung]

Back to searching for soldering issues.

What would you recommend I do, that I haven't already done, (some a few times), to check soldering issues? I've rewired nearly everything and I've gone over the PCB multiple times as well. What's left? What am I missing?

The poor output sound is the same now, after everything I've done, as it was the 1st time I plugged in. No change

[Bieworm]

Back to searching for soldering issues.

What would you recommend I do, that I haven't already done, (some a few times), to check soldering issues? I've rewired nearly everything and I've gone over the PCB multiple times as well. What's left? What am I missing?

The poor output sound is the same now, after everything I've done, as it was the 1st time I plugged in. No change

A scope would be convenient

How do you run the output to a speaker? Is it a speaker cable and is it in good condition?

[foreverstrung]

A scope would be convenient

I was just looking at these. There not that expensive.
I don't know how to use them, but You've gotta start somewhere, right?
What should I look at picking up? Suggestions?
Simple as possible and best for this stuff?
Thx

[Bieworm]

A scope would be convenient

I was just looking at these. There not that expensive.
I don't know how to use them, but You've gotta start somewhere, right?
What should I look at picking up? Suggestions?
Simple as possible and best for this stuff?
Thx

A good budget scope is the Siglent SDS 1102CML. That's the one recommended to me, which I bought back then

[JMPGuitars]

I'm a fan of the Siglent scopes. Which you get depends on your budget. Bieworm's is good at that price point, or if you want to spend a little more, the SDS1104X-E is really good too. That's what I used before I won a nicer one.

There's a TON of videos on using a scope for general use and guitar amp stuff on youtube.

A good / quick info page on how to use it is here: http://www.r-type.org/articles/art-125.htm

To answer your other question, if we assume for a second that there's definitely nothing wrong with your solder joints, nothing wrong with the wires, or speakers, perfect tubes, and all resistors are correct and in spec, then we would want to look at your coupling capacitors.

Or you might need to chopstick the wires, because a wire being out of place could cause a parasitic oscillation that could destroy your sound entirely.

Chopsticking the wires means moving them carefully with a single wooden chopstick while the amp is on (keep your other arm behind your back or in your pocket). You would need to have some sound input to the amp (looper pedal or tone generator) to be able to hear the difference.

Chopsticking the wires is the easier choice, so start there.

Thanks,
Josh

[foreverstrung]

then we would want to look at your coupling capacitors.

What is this? Coupling caps?

You would need to have some sound input to the amp (looper pedal or tone generator) to be able to hear the difference.

If I plug a looper pedal into this, I assume I'll have a rhythm playing, yes? Some continuous sound, correct?

Also, for some reason that I'm unaware of, does it have to be a chopstick? I've got a nice soft plastic probe stick I use when I'm getting into a live amp. This should be fine for the tap test, yes?
Thx

[JMPGuitars]

What is this? Coupling caps?

The yellow ones. Some of them are for tone, some of them couple one section to another. If you look at the schematic, section by section, you might notice which caps are joining one stage to another, or which are attached to tone knobs.

If I plug a looper pedal into this, I assume I'll have a rhythm playing, yes? Some continuous sound, correct?

Also, for some reason that I'm unaware of, does it have to be a chopstick? I've got a nice soft plastic probe stick I use when I'm getting into a live amp. This should be fine for the tap test, yes?
Thx

Yes, continuous sound.

If there's nothing conductive on the plastic probe, that should be fine. I like sushi, I have an abundance of wooden chopsticks.

Keep in mind you're not just tapping things, you need to physically reroute wires sometimes. If you look at my build photo, you'll see all my wires are color coded. Red is anode (plate) wires, closest to the chassis, and kept away from blue or purple grid wires (never parallel). Black are cathode wires. They all have specific routes to avoid issues.

Having an oscilloscope can help isolate parasitics and help kill them.

Thanks,
Josh

[foreverstrung]

The yellow ones. Some of them are for tone, some of them couple one section to another. If you look at the schematic, section by section, you might notice which caps are joining one stage to another, or which are attached to tone knobs

So, if i'm understanding correctly, I want to concentrate on the yellow caps separating sections/stages. yes?
Not so much coming off the pots.
Also, what am I checking? Resistance?
Any advice on how I go about checking them if diff from resistors?
Thx

[JMPGuitars]

The yellow ones. Some of them are for tone, some of them couple one section to another. If you look at the schematic, section by section, you might notice which caps are joining one stage to another, or which are attached to tone knobs

So, if i'm understanding correctly, I want to concentrate on the yellow caps separating sections/stages. yes?
Not so much coming off the pots.
Also, what am I checking? Resistance?
Any advice on how I go about checking them if diff from resistors?
Thx

You would want to test capacitors for capacitance. You already tested them for whatever resistance they see (which they are not responsible for). You could also just replace them one at a time and see if anything happens.

I would also try your knobs in different positions while you have a loop going to see what the amp sound like. Put all the tone knobs at 50% and adjust from there to see if anything mysterious happens. If the issue was just that the tone knobs were down the whole time, then make something else up when you report back.

Another possible test is to insert sound at different points in the circuit, but that requires the right tools, and careful practice with the amp off prior to connecting anything anywhere. Ignore this last bit for now.

Thanks,
Josh