OD pedal?

[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

[sruffinc]

So R18 and R19? The 100k resistors?

[JMPGuitars]

So R18 and R19? The 100k resistors?

Yup. Though that numbering is based on the classic schematic, and not all schematics follow it.

[sruffinc]

All resistors seem to be in spec. I had a lot of carbon comp, but replaced all but those 100k PI plate resistors with carbon film. B+ came up to 350. PI plates at 200 and grids still a little low at 34.

One thing to note - I have trouble getting a reading on the V5 plate attached to the OT. Very noisy and hard to get a reading. I re-soldered the wire, but no change. Does that mean anything?

Voltages -

Voltage 6.14.2020.pdf

Amp sounds very good, but I want it to hold up. Anything else I should check?

[JMPGuitars]

All resistors seem to be in spec. I had a lot of carbon comp, but replaced all but those 100k PI plate resistors with carbon film. B+ came up to 350. PI plates at 200 and grids still a little low at 34.

One thing to note - I have trouble getting a reading on the V5 plate attached to the OT. Very noisy and hard to get a reading. I re-soldered the wire, but no change. Does that mean anything?

That's funny, the PI plates are the only place carbon comp are actually a good thing.

It sounds to me like you have an oscillation affecting your OT. Check the wires in the vicinity of the power tubes and OT wires. Make sure there's no parallel ground or anything like that (the OT black wire is negative, not ground - don't worry about that one). Chopstick them a bit and see if you can get a reading.

[zaphod_phil]

The PI anode ("plate") resistors are the two 100k resistors on pins 1 and 6 of the last 12AX7 (V2) before the two EL84s, labelled R18 and R19 on the standard Marshall 18W schematic. Carbon composition resistors are ideal used there, for maximum tone benefit and minimum hiss.

[sruffinc]

Seems like I solved the problem with oscillation on the V5 plate. Tightened up some things and discovered a dangling ground wire near the TMB input. The PI plates still register at around 200 and the grids at 34. Guess I can try some other tubes? Amp sounds nice. If those values are too low what would the result on the sound be?

Thanks,

[JMPGuitars]

Seems like I solved the problem with oscillation on the V5 plate. Tightened up some things and discovered a dangling ground wire near the TMB input. The PI plates still register at around 200 and the grids at 34. Guess I can try some other tubes? Amp sounds nice. If those values are too low what would the result on the sound be?

Thanks,

If you think the amp sounds nice, and the oscillation is gone, enjoy it. And post a demo.

Thanks,
Josh

[sruffinc]

Will do. Thanks for all the help!