Volume issue wit TD Deluxe

[Charlie Wilson]

OK, one quick check you can do is touch the plates of all the tubes with your multimeter. Maybe start with the power tubes and work your way to the first preamp tube. It should be a pretty loud pop starting with the power tubes and then quieter as you work your way across the preamp tubes. It could give you some general idea of where the issue is. Ideally, like Phil describes, would be to inject a signal and trace through the circuit.
CW

[Oddvar R]

Seems you're missing one of the nodes, B+4, either that or the B+3 voltages seem a bit low, so that might be b+4 instead and one of the earlier ones is missing.

Note the schematic shows expected estimates of B+:

https://ampgarage.com/forum/download/fi ... &mode=view

but at any rate, that does seem to show a possibly significantly lower voltages on B+. That might make it quieter by a little. but I don't know by how much. it lists the output post rectifier should be almost 400VAC, then after that first dropper about your noted 360VDC so that's a 40V difference.

Another process you could try would be to inject a known signal into the input, and measure AC volts after each gain stage to see if somewhere it seems to go down/lose signal. In this amp, the first two triodes of V1 each handle a different input, so that will depend on which input you're using, but the outputs go to the volume/tone network before going to the first half of the recovery triode in V2. Then the other half of V2 is the PI. if you can find somewhere that the signal seems to suddenly drop out, that will help.

Usually I see mV of AC signal in the grid, and then a volt to maybe 5vAC after the first gain stage, etc, if you don't see that constantly increasing in every stage except the V2A where it's recovering from the tone/volume losses, then you have at least an area to research.

~Phil

Here is my measurements with 300hz audio in the right column and without in the left. Fairly loud, but would be different at different volumes

[pompeiisneaks]

That seems to make sense. All the voltages are lower than they should be due to the PT giving you lower B+ but the tubes are conducting more and doing more when signal is passing, therefore dropping the voltage down even more.

I think honestly to help find it, if you've got that signal going in, as i said, you should trace the AC voltage with the multimeter as mentioned to see where you are losing signal instead of gaining it.

at each stages coupling capacitor you should record the VAC (not DC!) and see how it's going up.

Example, I'd expect maybe 50-100mV of signal at the input grid of the first triode of whichever side you're plugged into. Then the second tube should show a few volts before it's grid, maybe 1-5VAC, (each amp is going to be a bit different)

Then after the Phase Inverter I often see like 20V or so going into the power tubes.

Those values vary drastically per amp setup, but the point is to see where it suddenly goes from 'good output here, to OMG it's back to mV here why?'

Also pictures that are clear and well lit will help figure out if we can see something obviously wrong.

~Phil

[Oddvar R]

I have measured the AC voltage on the CC's.

[pompeiisneaks]

Two things

1. the table doesn't help show 'where' in the amp that actually is? V1a/b, V2a/b?
2. if any of those are the input of v1a or v1b 22VAC is WAY too hot of a signal for the amp. Input ac signals for guitars usually run around that mentioned 40-100mV Milli Volts, not Volts. Therefore numbers seem really confusing in general.
3. I don't understand what 'input side' vs 'tube side' means? Do you mean to the left and right of the coupling cap? You really only need one measurement after a coupling cap to ensure the DC from the previous stage doesn't have any impact on the reading. Not mandatory though.

I'd expect these readings :

V1a/b (depending on which input you're using) grid: 55mVAC
V1a/b anode post coupling capacitor: 5VAC
V2a input 4VAC (maybe a little less in the tone stack losses)
V2a Anode/post coupling cap: 20VAC
V2b at either anode or cathode post coupling caps: 20VAC (this type of PI has no gain to it if I recall)

Those are again made up measurements that may never match a real amp, just showing the increasing voltages as it's going through the gain stages.

as a random guess if you're saying you have 66VAC prior to the PI before going to the power tubes and you have 29V after, then that is the stage losing your signal somehow. Something around that part of the circuit is losing signal to ground instead of passing it on, or the tube itself is having issues.

~Phil

[Oddvar R]

Hi and thanks for this. I will measure my way through what you describe. The measures I did above are the two sides of the five Coupling Caps-

[Oddvar R]

Hi again. I have now changed the PT on this, ClassicTone 40-18078, new board with all new parts and new potentiometers, Still there is a reasonably low volume. Sounds great, very over driven, but must be on full to be fairly usable.

I have encloses some pics, if anyone cared to have a look and see if there is some obvius mistakes.

I reminds me of my Soldano Slo 100w build, where the output was low, but one of the jumpers on the board was loose.

Is there a grounding that isn't marked on the layout or obscured maybe?

[pompeiisneaks]

I might be missing something, but I don't see any connections from the input jacks 'tip' connection to anything but the lead between the switch and it, via the 1M resistor. How is any signal getting in? The angle is a bit odd to know for sure, and I'm guessing that it's connected somewhere, but maybe the jacks are connected in a way that is sending signal to earth to easily there?

~Phil

[Oddvar R]

The two red wires comes from the jacks.

[pompeiisneaks]

Ok so I'm looking and was already backwards, but now I don't see a ground connection at all on the middle jack and can't see one on the left jack either, but maybe that's just going below it?

see my red circle in the picture attachment? I see nothing on this one, and I see the 1M resistor between the switch and ground on the other, but no wire from gnd (same as the red in pictures) on the left one that connects to ground there either?

or am I just missing it?

~Phil

[Oddvar R]

You are right, there is no grounding there, but there isn't any grounding on the layout here. I was thinking maybe the jack itself acted as one, connected to the chassis? But if I was to wire one, where should it go?

[pompeiisneaks]

You should ground it to a similar location as the preamp board. the chassis connections can sometimes not be the best, and I see isolation washers on at least one of them which means you're not getting it there. You could check with a resistance or continuity check from the ground lug to chassis I guess.

~Phil

[Oddvar R]

I tried to connect the ground, but there is no difference in volume.

[Oddvar R]

What i haven't changed is the way the pots are wired. Looking at the pics from Jelle in the "pics of Tweedle D thread", it seems a bit different than the layout? Seems to have omitted the 500p and sending tone lug 3 (left to right) on the tone and 1 and 2 from volume next to it to ground? Am I missing something?

[pompeiisneaks]

Jelle's follows the layout perfectly. He's not omitted the 500pF cap, see my screenshot comparing the two.


~Phil