Volume issue wit TD Deluxe

[Oddvar R]

Ok, thanks for clearing that up. I have now also changed the OT, a Weber "022855 bassman one. No change,

[pompeiisneaks]

Okay so I still don't recall you posting results of testing a signal into the amp and tracing with a DMM on ac volts to see if you can find 'where' it seems to be losing it. (the post you did, didn't seem to make any sense, so I'm trying to understand what it meant)

If you suddenly see a huge drop somewhere, that is the stage where you're losing signal and you can narrow it down to that region.

Please use a common terminology for measurements like:

V1a/b grid: 25mVAC
V1a/b anode post coupling cap: 3VAC
(v1a or v1b should be roughly the same, both use the differing input jacks so you just repor ton whichever jack you've inserted into)

V2A grid: 2.6VAC
V2A post coupling cap 20VAC
V2B anode post coupling cap 50VAC
V2B grid post coupling cap 51VAC


I invented those voltages. They aren't real, just an example of soemthing that would look 'right' to me. I'd expect the first gain stage to increase voltages a lot. then I'd expect the job post PI is unity gain roughly to recover from the losses of the volume/tone stack. Then the next stage is the PI and it does a decent amplification again, before the power tubes.

You could also measure the VAC at the anodes of the power tubes, if you want to see what signal is coming out of them as well.

Basically I still haven't seen any clear indication of 'where' you're losing signal.

~Phil

[Oddvar R]

V1a/b grid: 9mVAC
V1a/b anode post coupling cap: 30mV/18mV

V2A grid: 1.6VAC
V2A post coupling cap 74mVAC

My meter doesn't decide what to measure her, it alternates very quickly
between 100/4.6/1.4/0.51 VAC:
V2B anode post coupling cap/V2B grid post coupling cap 51VAC.

I might not understand exactly where to measure according to your suggestions, but...

[erwin_ve]

V1a/b grid: 9mVAC
V1a/b anode post coupling cap: 30mV/18mV

V2A grid: 1.6VAC
V2A post coupling cap 74mVAC

V1b after coupling cap to v2a grid doesnt look right!

[pompeiisneaks]

Yes that's definitely not good, nor are most of the other readings.

The 9mV AC input is a bit smallish (would be better around 50mV instead of 9), but should still be about 1-5 VAC after the coupling caps. Your blue circles are the perfect spot to measure.

This means something either in the tube is not allowing it to conduct well, or there's a problem somewhere leaking signal to ground where it shouldn't.

Also post phase inverter, your second blue circles by the larger coupling caps should be 20-40VAC I'd expect.

One thing to note, though, is that you mentioned the voltages jumping all over.

What frequency are you inputting into the amp? What multimeter are you using? Some DMM's have a pretty specific frequency range where they can measure well. You'd need to be sure you're in that range.

You said you're inputting a signal, but how? where? You might want to

A. get the exact frequency measured or at least known, and make sure it's in a range your DMM can measure
B. get the measurement of the output at the device itself, before plugging it into the amp. This can ensure you know if it's dropping on plugging in.

I.e. maybe you have 50mV coming out of it until you plug it in, then you get 9mV at the grid, then you've got a problem at the input jacks.

If it's 9mV out of the device, try raising the output level to 50mV and retry.

Basically it sounds like your first gain stage isn't amplifying, but it could be measurement error.
most, but not all, multimeters can measure mVAC accurately up to maybe 1k Hz, but if you're inputting 10kHz or the device is less fancy and only supports common power line frequencies like 50/60 or 100/120 (rectified) Hz range, then you'll be getting really bad readings.

~Phil

[Oddvar R]

Tested again with 2000 hz and the V1a/b had no change, but he V2A had 1.8VAC, V2A post Coupling had 66vac and the anode/grid post C's show a variable voltage (ac) up till 32 and 40v. (Measured at full volume.)

[pompeiisneaks]

Well 1.8vac seems maybe a bit low, but going from 66VAC to 32 to 40, so you lost signal somehow between the PI input and it's output.
Normally you should see gain between input and output of the PI or only very minor loss depending. that's nearly half. I'd check the components around the output side of the PI for path to ground that's 'lower' than you'd expect. Maybe one or both of the 220k to ground were accidentally 2.2k or 220ohm or somehting weird like that?

Either that or try swapping the PI tube, maybe it's not conducting well?

~Phil

[Oddvar R]

So, finally solved, thanks to you guys. Since I have changed everything on the board, even the board itself, i figured it had to be something I hadn't changed, so the grounding issues mentioned by you became the issue. I have three speaker outputs, and the grounding of the third jack was connected to the switch, the jacks themselves are different, so I didn't reflect on that. Changed it to ground, and suddenly the amp was very loud.

I can't say enough the great help I get on this site. Thank you very much.

[Oddvar R]

So now I have made 4 Dumble amps, 1 Trainwreck Express, great sounding amps they are.

[pompeiisneaks]

Glad you got it sorted!

~Phil

[ChopSauce]

Very happy for you.

On a side note: that black face defintely suits the trainwreck, according to my taste...

I'll keep the idea...