OD pedal?

[sruffinc]

Josh,

I rewired my amp and it seems much better. Voltage chart attached.

TMB_Voltage_Test_Chart - 6.1.20.pdf

Sounds good, less noise, but seems to have more bass than before. I used a 1000uf cathode bias cap with a 150ohm cathode resistor on the power tubes. I'm going to try a 2200uf and 180ohm combination to see how that does. Any thoughts on my voltages. See anything that looks off?

[sruffinc]

Might be hearing the fizzy distortion I've read about.

[JMPGuitars]

Might be hearing the fizzy distortion I've read about.

You've got a few things going on there. But first...

Your voltages, including your B+ are too low. Pin 3 of the rectifier is your B+. Do you have a different rectifier you can test? It doesn't make sense for you to be only getting 334VDC at pin 3 with pins 1 and 7 VAC so high.

Also fill the bottom box on the sheet. Those numbers are important too. A and B are the two halves of the first filter can, A being the higher voltage where the standby switch connects to the cap. C is the point on the board that feeds the PI plate resistors. You can just measure that at the point where the PI plate resistors usually share a turret.

B+ ideally should be 345VDC +/- 5V. Under 340VDC usually sounds muddier, with lower headroom.

Oh yeah, definitely go up to 180R and 2200uF on the cathode. You're currently biased too hot.

Thanks,
Josh

[Bieworm]

Try a SS rectifier?

[sruffinc]

TMB_Voltage_Test_Chart - 6.1.20.pdf

Added the ABC readings to the chart.

No I don't have another rectifier tube. What I'm using is an old stock German made ez-81. Perhaps I need to get a new one. I need to replace the JJ EL-84s anyway.

Just noticed it does sound a little dull. That nice crispy top end that it had previously is not there.

[Bieworm]

TMB_Voltage_Test_Chart - 6.1.20.pdf

Added the ABC readings to the chart.

No I don't have another rectifier tube. What I'm using is an old stock German made ez-81. Perhaps I need to get a new one. I need to replace the JJ EL-84s anyway.

Just noticed it does sound a little dull. That nice crispy top end that it had previously is not there.

There is something wrong on your chart .. A is right after the rectifier and B is after the filter cap. I think you swapped your values...
Trying a solid state rectifier is easy. Just a couple of 1N4007 diodes and perhaps a 100R resistor ... at least then you're sure your voltages are more in the right ballpark

[sruffinc]

I'll try that.

[JMPGuitars]

TMB_Voltage_Test_Chart - 6.1.20.pdf

Added the ABC readings to the chart.

No I don't have another rectifier tube. What I'm using is an old stock German made ez-81. Perhaps I need to get a new one. I need to replace the JJ EL-84s anyway.

Just noticed it does sound a little dull. That nice crispy top end that it had previously is not there.

JJ EZ81 tubes have been fine, and not expensive. Get a couple. I think your old stock is too old.

Bieworm is correct, your voltages don't make sense. If you don't have a dropping resistor or zener diode between Pin 3 of the rectifier, and "A" (the first filter cap), then the voltage should be exactly the same. There's a resistor between A and B, so B should be lower than A.

In addition to getting new tubes, I would also highlighter verify your build.

Trying a solid state rectifier is easy. Just a couple of 1N4007 diodes and perhaps a 100R resistor ...

Solid state rectifiers are cool, but UF4007 is superior to 1N4007. They're better/faster diodes with less noise. The SS rectifier should have 4 of the diodes either way.

[sruffinc]

I'll try all of that. If I can't get it on this try I may have to admit defeat and turn it over to a pro. I'm getting tired of spinning my wheels. I do appreciate all of the help.

[Bieworm]

I'll try all of that. If I can't get it on this try I may have to admit defeat and turn it over to a pro. I'm getting tired of spinning my wheels. I do appreciate all of the help.

Patience, soldier!!! Don't give up on it yet...
We'll get this fixed, don't sweat

[Bieworm]

TMB_Voltage_Test_Chart - 6.1.20.pdf

Added the ABC readings to the chart.

No I don't have another rectifier tube. What I'm using is an old stock German made ez-81. Perhaps I need to get a new one. I need to replace the JJ EL-84s anyway.

Just noticed it does sound a little dull. That nice crispy top end that it had previously is not there.

JJ EZ81 tubes have been fine, and not expensive. Get a couple. I think your old stock is too old.

Bieworm is correct, your voltages don't make sense. If you don't have a dropping resistor or zener diode between Pin 3 of the rectifier, and "A" (the first filter cap), then the voltage should be exactly the same. There's a resistor between A and B, so B should be lower than A.

In addition to getting new tubes, I would also highlighter verify your build.

Trying a solid state rectifier is easy. Just a couple of 1N4007 diodes and perhaps a 100R resistor ...

Solid state rectifiers are cool, but UF4007 is superior to 1N4007. They're better/faster diodes with less noise. The SS rectifier should have 4 of the diodes either way.

What do you mean by less noise? What kind of noise?

[JMPGuitars]

What do you mean by less noise? What kind of noise?

Diodes can be noisy (usually buzz when it happens), 1N4007 is noisier than UF4007. I don't think it matters enough to swap out old ones for another (assuming no problems), but when building anything new, I'd go with the UF4007.

[crgfrench]

Any reason to avoid 1N5408s? Cost about the same and heftier...

15914081033897597165729372720553.jpg

[sruffinc]

Ok, rewired the amp and put in a new JJ EZ-81 and new Tung-Sol EL-84s. Preamp tubes are the same JJs. Voltage chart attached.

Voltage 6.7.20.pdf

Numbers look better. B+ is up to 340. V4 and V5 bias looks good at 12. Some of the voltages on V1 and V2 look a little off. Cause for concern?

Attaching sound file also.

New Recording(2).mp3

No hum, so all grounds seem good. Some hiss, but not enough to bother me. I started with no signal then went through normal channel lo and hi, then tmb channel, lo and hi. It seems I have a bad MV pot. I had trouble with it going in, so I think that is why it is cutting out as I rotate it around the dial. I'll replace that as soon as I can get a new one ordered.

Sounds decent. Have 50uf caps in the inputs, so maybe too much bass. Treble/highs sound kinda thin, but I'm only running volume at 2. Maybe this is just EL84s?

If I keep MV low and crank volume up to 6-8 it gets some distortion, but not a lot. I would need to run some pedals to get a sound I like at this volume. Not sure if this is normal? I don't know what to expect I guess. I've listened to some youtube videos of similar builds/amps and I don't know if mine sounds the same or not. Variances in volume and recording techniques have some factor. I'm not sure I like the amp as much as my tweed princeton for cleans. With a tube screamer I like it better for Marshall rock tones.

Thoughts, suggestions?

[Bieworm]

The plate voltages on your PI are too low. You should get them to spec. That would make a huge difference.
I think the resistor between B and C (rated 8.2K normally) is off. Maybe wrong resistor? Did you put something else there? If not, I would try lowering it to 4.7k and measure the voltages again

[JMPGuitars]

I would try lowering it to 4.7k and measure the voltages again

That doesn't make sense. That 8.2K resistor feeds the plates for all the preamp tubes, and V3 plates are slightly high.

I would start by swapping V2 and V3 and see what the voltages look like.

[JMPGuitars]

Any reason to avoid 1N5408s? Cost about the same and heftier...

IIRC those are basically the same as 1N4007 but 3A instead of 1A. I think it's probably overkill either way, but personally still prefer the UF series.

[JMPGuitars]

Ok, rewired the amp and put in a new JJ EZ-81 and new Tung-Sol EL-84s. Preamp tubes are the same JJs. Voltage chart attached.

Which schematic/layout did you use to build? Did you make any changes, or stick to the docs?

Numbers look better. B+ is up to 340. V4 and V5 bias looks good at 12. Some of the voltages on V1 and V2 look a little off. Cause for concern?

Only your PI is that far off. I would swap V2 and V3 and retest the voltages. If they're still that low, maybe check the soldering around the PI plate resistors, and make sure they're the correct value.

Sounds decent. Have 50uf caps in the inputs, so maybe too much bass. Treble/highs sound kinda thin, but I'm only running volume at 2. Maybe this is just EL84s?

These amps are usually considered bright, so if you think the top end is weak, then you probably need to do some tweaking.

If I keep MV low and crank volume up to 6-8 it gets some distortion, but not a lot. I would need to run some pedals to get a sound I like at this volume. Not sure if this is normal? I don't know what to expect I guess. I've listened to some youtube videos of similar builds/amps and I don't know if mine sounds the same or not. Variances in volume and recording techniques have some factor. I'm not sure I like the amp as much as my tweed princeton for cleans. With a tube screamer I like it better for Marshall rock tones.

Thoughts, suggestions?

It sounds like you have an issue with your master volume, and maybe the wiring. Typically these amps get to full volume around 3ish, and then you're mostly increasing overdrive/distortion.

Make sure your guitar volume knob isn't turned down.

Thanks,
Josh

[sruffinc]

I used the stock Richie's TMB. After replacing the Master Volume pot, which I think I had damaged by tightening it too hard, its sounding really good now. I haven't checked the voltages on the PI because it was sounding so good I had to button it up and play for a while. Maybe I switched the preamp tubes when I put it back together, but it seems to sound right now. I'll get back in and check the PI voltages again soon.

Just to be sure, which are the PI plate resistors?

One interesting I noticed is I put the Master Volume control on the back of chassis and used a shielded cable, with the shield connected to the wire running to ground. Then noticed I was getting RF. Unsoldered the ground on the cable and the RF went away. Guess it was acting as an antenna.

[JMPGuitars]

Just to be sure, which are the PI plate resistors?

One interesting I noticed is I put the Master Volume control on the back of chassis and used a shielded cable, with the shield connected to the wire running to ground. Then noticed I was getting RF. Unsoldered the ground on the cable and the RF went away. Guess it was acting as an antenna.

The plates (anodes) of a 12AX7 are pins 1 and 6. If you follow the wires from pins 1 and 6 from the PI, you should see a pair of resistors connected together on the opposite end of the wires.


Any time you use shielded wire, make sure you're only connecting one end of the shielding. Shielded wire is usually used for long runs on the pots to tube(s), input jack(s) to the tube(s), and sometimes the plates on the tremolo tube. It is not generally used for ground wires.

Thanks,
Josh