VOX AC15 Heritage... TB Channel bleeds into the EF86 channel.

[Leo_Gnardo]

I have a full set of Nichicon VX series and Mallory 150 caps for the amp. Should I just replace the caps?

That's called "shotgunning." We prefer to not do that around here.

Although... you may have seen the notorious YouseTube tech "guitologist" do it. He had an infamous case a couple months ago where he shotgunned a Mesa combo amp, and never did solve the problem. He ended up buying the amp, then dismantled it into components, just for spite. Then he cussed out commenters who called him a "parts changer." Which is exactly what he was doing. NOT the way to fix things... Let's us avoid doing like that.

You could use any of your filter caps for a test, I'd pick a 22 uF 450V. It's not necessary to match the value of the cap you're paralleling, just for a quick test. Please make sure you have the polarity right. Ask me how I know . . . yes I've wrecked a couple perfectly good caps. Oh well, live & learn. And better to learn from other people's misteaks, right?

[Cooper1962]

That's called "shotgunning." We prefer to not do that around here.

Although... you may have seen the notorious YouseTube tech "guitologist" do it. He had an infamous case a couple months ago where he shotgunned a Mesa combo amp, and never did solve the problem. He ended up buying the amp, then dismantled it into components, just for spite. Then he cussed out commenters who called him a "parts changer." Which is exactly what he was doing. NOT the way to fix things... Let's us avoid doing like that.

You could use any of your filter caps for a test, I'd pick a 22 uF 450V. It's not necessary to match the value of the cap you're paralleling, just for a quick test. Please make sure you have the polarity right. Ask me how I know . . . yes I've wrecked a couple perfectly good caps. Oh well, live & learn. And better to learn from other people's misteaks, right?

Thank you. I don't generally source YT for advice on repairs. I was speaking in general, since I already have the parts. Yes, I'd rather us track down the problem, and learn from the experience.

I just got through redressing the solder points on the tube sockets, and the TB channel volume pot. When I tested it, there was no bleed-over. Yay! I shut it down, then thought; Wait a minute, I better check it again... After turning it back on, it's back to doing the same thing! Why would it test fine at first, then go back to having the same issue?

I have some cables with alligator clips. Should I use these to position the caps in parallel?

[Leo_Gnardo]

I have some cables with alligator clips. Should I use these to position the caps in parallel?

Nice clip lead kit! Should work a treat.

Now I've had a peek at your close in photo of the circus board, interesting build they have, with turret posts for components, and those turret posts poking thru the board onto the solder land side. Imma thinkin' .... what if one of those turret posts broke free of its solder on the back of the board, you could have a perfectly good filter cap, but if its turret isn't firmly attached to the land side of the board, that is, has an intermittent connection there, that would give you the crosstalk symptom which cuts in & out. Yes a total PIA to have to access the back of the board, but that may be where your problem is.

[Cooper1962]

Nice clip lead kit! Should work a treat.

Now I've had a peek at your close in photo of the circus board, interesting build they have, with turret posts for components, and those turret posts poking thru the board onto the solder land side. Imma thinkin' .... what if one of those turret posts broke free of its solder on the back of the board, you could have a perfectly good filter cap, but if its turret isn't firmly attached to the land side of the board, that is, has an intermittent connection there, that would give you the crosstalk symptom which cuts in & out. Yes a total PIA to have to access the back of the board, but that may be where your problem is.

I'll try bypassing the caps.

[nosaj]

I'll try bypassing the caps.

Drain your FILTER CAPS!!!
So try this with power off, for C1 clip one lead to chassis ground, then the other lead to negative side of cap, then see if pressure or wiggling turret fluctuates the ohms seen.
For positive side clip one lead to positive side of C1 then the other lead to v7 pin3 and see if pressure on turret fluctuates reading

nosaj

[Cooper1962]

After checking several capacitors, I decided to just replace all the caps. I was planning on doing it anyway, so I figured I may as well just do it, then check for defects. I fired the amp up, and the issue remains. The bleed-over doesn't seem as bad as it was, but it's still there. So, I'm back to square-one. I'm out of Deoxit until Friday, so I can't clean the sockets until then. I'll retouch the rest of the pots tomorrow with 63/37 Kester solder.

Here's the amp, post capacitor replacement...

[nosaj]

After checking several capacitors, I decided to just replace all the caps. I was planning on doing it anyway, so I figured I may as well just do it, then check for defects. I fired the amp up, and the issue remains. The bleed-over doesn't seem as bad as it was, but it's still there. So, I'm back to square-one. I'm out of Deoxit until Friday, so I can't clean the sockets until then. I'll retouch the rest of the pots tomorrow, with some 63/37 Kester solder. I'm beginning to think this issue may not a circuitry problem, but possibly one of inductance.

Here's the amp, post capacitor replacement...

Have you chop sticked the wires an board to see if it affects noise? Making all these changes without a good reason can introduce other issues. I would turn amp on do what ever you need to do to make the noise then move the grey wires. we are trying to see if Lead Dress has any effect on noise.
nosaj

[Cooper1962]

I fired it up to do just that, but there's popping through the speaker due too lightening.

[Cooper1962]

Have you chop sticked the wires an board to see if it affects noise? Making all these changes without a good reason can introduce other issues. I would turn amp on do what ever you need to do to make the noise then move the grey wires. we are trying to see if Lead Dress has any effect on noise.
nosaj

Okay, I just got through probing the circuit. All seems good, so I'm thinking there's something going on with the volume pot. Sure, it tests good via DMM, but there does seem to be a delay in the way the volume rolls-on. I'm beginning to think this issue may be related to signal induction? Should I commit to wiring the pots with an independent lead at each terminal, vs the 3 into 1 bundled wire? I suppose I will also need to get some shielded wire as well. Maybe use a shielded wire to the V2 (TB channel) grid?

I'm also thinking about nixing those PCB inputs in favor of CLIFF jacks with metal panel nuts. What do you think?

[nosaj]

Okay, I just got through probing the circuit. All seems good, so I'm thinking there's something going on with the volume pot. Sure, it tests good via DMM, but there does seem to be a delay in the way the volume rolls-on. I'm beginning to think this issue may be related to signal induction? Should I commit to wiring the pots with an independent lead at each terminal, vs the 3 into 1 bundled wire? I suppose I will also need to get some shielded wire as well. Maybe use a shielded wire to the V2 (TB channel) grid?

I'm just gonna go ahead an say it..

All this from plugging in a NOS rectifier tube? If it was truly working before you put the EZ81 in , I fail to see how changing the volume wires will help this.
In this case I think a scope is warranted.

nosaj

[olddawg]

I see the ORIGINAL problem as possibly being caused by 2 things.. microponic tubes physically coupling or the power supply being modulated. It may be normal. If you are having a volume control issue now.. check for DC on the pot and suspect a coupling cap. It seems like you are throwing parts at a problem.. not analyzing it first.

[SoulFetish]

okay, does the volume on the EF86 channel have any effect on the signal that's bleeding through?

Try grounding the grid to V3B. Does the signal/noise bleeding go away?

[Cooper1962]

I see the ORIGINAL problem as possibly being caused by 2 things.. microponic tubes physically coupling or the power supply being modulated. It may be normal. If you are having a volume control issue now.. check for DC on the pot and suspect a coupling cap. It seems like you are throwing parts at a problem.. not analyzing it first.

Thank you, I will do as you recommend. How do I check for DC on the pot?

I was planning recapping it anyway, so nothing has been wasted. It actually enjoy doing it. I love the look of blue Nichicon + Mallory 150 mustard caps!

I forgot to mention... I had also replaced the OEM EF86 with a =C= EF86 when I installed the RCA EZ81. Sounds fabulous! The OEM EF86 tube comes heavily shielded in shrink wrap. It has been said this was done to lessen vibration, though I don't believe this is entirely accurate. The VOX AC15 (AC30) Heritage combo version chassis' come equipped with a "floating" EF86 socket. The head version chassis' do not. The cushioned EF86 socket minimizes vibration, and wrapping EF86 helps minimize microphonic effects.

Could an unshielded EF86 valve pick up signal from the TB channel V2? They sit less than 3" apart, so...

[Cooper1962]

okay, does the volume on the EF86 channel have any effect on the signal that's bleeding through?

Try grounding the grid to V3B. Does the signal/noise bleeding go away?

This was something that I checked on day 1 or day 2... I'm going to say, no. It's difficult to tell, really, as there is limited equalization on that channel. 1 x 3 way voicing select + 1 x bass shift switch.

I'm a bit nervous about grounding things, as I've never done this before. As long as a terminal or lead references to ground, is it okay to bypass these points directly to the chassis?

[nosaj]

Thank you, I will do as you recommend. How do I check for DC on the pot?

I was planning recapping it anyway, so nothing has been wasted. It actually enjoy doing it. I love the look of blue Nichicon + Mallory 150 mustard caps!

I forgot to mention... I had also replaced the OEM EF86 with a =C= EF86 when I installed the RCA EZ81. Sounds fabulous! The OEM EF86 tube comes heavily shielded in shrink wrap. It has been said this was done to lessen vibration, though I don't believe this is entirely accurate. The VOX AC15 (AC30) Heritage combo version chassis' come equipped with a "floating" EF86 socket. The head version chassis' do not. The cushioned EF86 socket minimizes vibration, and wrapping EF86 helps minimize microphonic effects.

Could an unshielded EF86 valve pick up signal from the TB channel V2? They sit less than 3" apart, so...

Do you have a pic of the oem tube shielded in shrink wrap?

nosaj