Voltages idle and under load

[surfsup]

VV, thanks for checking in! I am considering changing the cap at B5, feeding stages 1&2. But...I just make-shift decoupled stage 1 and stage 2 with another cap (10u) and a 2k2 resistor, essentially creating a B6 so all stages have their own discrete node. With v2 out i still get guitar at the speaker! This is very frustrating. The amp is smoother but double stops on some frets are still not sounding good and i fear it is due to this unknown signal leakage.

Going back to before, with the stage 2 disconnected i get no guitar out of the speaker so I'm wondering if my v1 socket is bad? I tried different tubes.

[VacuumVoodoo]

With v2 out i still get guitar at the speaker! This is very frustrating

Try this: disconnect all wires from V2 socket. Signal still leaking over? Ditch the board, rebuild in true PTP or using tag strips.

[surfsup]

VV, not what i wanted to hear, for sure! I have to believe its not the board. I built this from the same sheet of G10 as my last few amps...i'll try that though.

[Structo]

I don't think it is unusual for the signal to be leaking there.

It goes from the plates of V1 then through the 10K dropper in the supply then back up to next plate supply.

As far as the distortion on double stops, perhaps it is a type of blocking distortion.

I would look at the PI couplers to the power amp or the grid stoppers on the power tubes.

[VacuumVoodoo]

I don't think it is unusual for the signal to be leaking there.
It goes from the plates of V1 then through the 10K dropper in the supply then back up to next plate supply.

This would require C19, C20 both to fail, miss ground connection or be out the circuit in some way. These caps should be like a short circuit to ground for AC signals at guitar frequencies i.e. above 82Hz. 10k/15uF is low pass filter with cut off at 1Hz. Signal present at V1B anode sees plate resistor (100k) and C20 as low pass with 0.15Hz cut off.

[Structo]

You're right as usual Alex.

[katopan]

The volume of leakage you're talking about isn't just cross-talk too. There's something wrong. It's a matter of disconnecting stuff until you find something that still meters resistance when disconnected (alternate path - board or whatever). Surfsup - this must be testing your patience so bad, but persevere man.

[surfsup]

Well I was on vaca (much needed) for a week. Feeling more relaxed...

Not that I'm back and forgot all that I did (oops) I lifted the ground side of the C5 cap supplying B+5 for the input tube's first two stages. I put in a 47u 450v electro. No difference. There seems to be something with the second stage and/or tone stack. But again if I disconnect the tone stack after the TMB caps, I still have the issue.

I don't get it. I am going to work on it more this weekend but am taking tonight off to hang out and chill...maybe actually PLAY a guitar!? ya think?

[surfsup]

b/c I'm a glutton for punishment, I worked on this again tonight. I disconnected the CC from first stage and jumpered to the next tone stack. I don't have the problem (no guitar at speaker with V2 (stage3) removed). Per previous post, I lifted the B5 filter cap ground and put an electro in its place and this confirmed the B5 filter cap was good (unless bad luck is really screwing me and the new electro was bad too!).

So 99.5% the problem lies in between the gain pot and the plate load resistor of stage2 as I started to suspect. See pic below, red jumper wire. At this point, since the grounds for the first two stages all go to the filter cap, and from there to chassis ground, I have to suspect a bad socket? I would think if the chassis ground was bad, stage 1 would still have a prblem.

However, can a bad socket cause this? I am still failing to see how I would get signal at the speaker from some sort of problem with stage 2. Any and all comments appreciated.

[katopan]

Hopefully one step closer surfsup.

Next test - move your input resistor R2 to feed the 2nd stage grid (R5 & R6 junction disconnected from 2nd stage grid). Pull V2 and see if you still get signal through. That will narrow it down to the 2nd stage or the gain pot and divider resistors.

Someone might see something with a full gut shot if you want to post one. I didn't see one reading back over the thread but also can't remember if you did put one up already in another thread.

[surfsup]

I hope so. Thanks for sticking with me. Jumping amp input to stage 2 grid I get no guitar with V2 out! So that shoots my idea of stage2 being the problem. Now it is as if the problem only exists if both stages are used simultaneously.

Here are some pictures. V1 cathodes both go to the (-) of B5 filter cap. Same with the ground off gain pot and 470k/470k divider. The 470k divider was also moved to pin 7 and grounded at the socket on the tab. No difference. Apologies, but the soldering iron has warmed this one up quite a bit since originally built...

[surfsup]

Try this: disconnect all wires from V2 socket. Signal still leaking over? Ditch the board, rebuild in true PTP or using tag strips

I disconnected:
-plate lead at plate resistor
-grid lead at grid pin
-cathode lead at cathode resistor

Still get guitar at speaker!

I really don't want to tear this all out...ANY other ideas?

[katopan]

Keep disconnecting 'til you find it.

Any chance of a clear whole amp gut shot? Then we can trace through the whole preamp and PI wiring.

[surfsup]

It's midnight but original gutshots are here. Not much has changed aside from pulling out the led circuit, the voltage scaling circuit, and swapping leads or cap/resistor values. Grounds are all the same, turrets don't move, etc.

https://tubeamparchive.com/viewtopic.php?t=14565

[cobalt]

Just a little silly question. Are ALL pre amp and PI grounds going to the same grounding place/potential?
Maybe a little cathode drive goin' on?

weirddave