major DC coming through Marshall cathode follower? help

[jamme61]

my marshall 2204 (http://ceriatone.com/images/layoutPic/m ... iatone.jpg ) is measuring around 283 volts coming through the catode rollower into the cathode resitor on v2a to ground? If I take the V2 preamp tube out the 283 volts to ground goes away. I have checked and replaced all preamp tubes and blocking caps. Checking with my meter it's coming through V2 the CF. I can't figure this out if someone can help, please let me know. Thanks

[Cameron]

my marshall 2204 (http://ceriatone.com/images/layoutPic/m ... iatone.jpg ) is measuring around 283 volts coming through the catode rollower into the cathode resitor on v2a to ground? If I take the V2 preamp tube out the 283 volts to ground goes away. I have checked and replaced all preamp tubes and blocking caps. Checking with my meter it's coming through V2 the CF. I can't figure this out if someone can help, please let me know. Thanks

Check the ground of the 100k resistor off pin 8 next to the treble cap or try another tube.

[jamme61]

If V3 (phase inverter) is in with V! and V2 out there's no DC on the ground. If V1 or V2 are in there is dc on the ground. So V1 could be in and V2 and v3 could be out and I'd get DC on the ground by the input jack. Same with V2 by itself but V3 by itself no DC? I have changed all the 12ax7's and replaced all blocking caps still a problem. Help please if anyother ideas

[Reeltarded]

This is a brand new build?

[guitarmike2107]

Do you know what you are doing? you say you are measuring DC voltage at a ground point, if that is the case something is very wrong and you need to find out what before you start touching things all over the place. more than likely you do not have all the ground points connected.

if you are measuring voltage at the valve pins can you be more specific, i.e. voltage measured at the grid or the cathode or the anode/plate.

thanks

[jamme61]

This is a brand new build?

no this is a 1978 marshall jmp which has been running fine. The master pot got scatchy there was a lot of noise like when a preamp tube goes bad. So first I changed tubes and then the pot and then when that didn't work I figured I must have dc on the pot (leaky caps old amp right happens) thats when I measured the ground on the master pot for dc and found 283 volts? I tried to see which cap was leaking in circuit ( not gonna work that way) Started to clip caps out of the circuit and got a big mess. Lifted the circuit board and started to replace all the caps did that and still same problem.

with all tubes in
V1 pin 1 =312 volts
2 =312
3 =328
6 =324
7 =281
8 =316

V2 pin 1 = 323
2 =212
3 =311
6 =360
7 =324
8 =348

Preamp pot measures 312 volts
Master volume pot measures 312 volts
other pots in tone stack seem normal
let me know if I can measure something else to give you guys a better idea of whats wrong

[Blackburn]

You seem to have bitten off a lot more than you can chew. A simple master vol pot change and cap check and all this happens. I'm surprised the amp is still running at all!

You might need to post pics and maybe this will turn out to be a successful 24 pager with a properly working 2204 as the end result.

[Colossal]

my marshall 2204 is measuring around 283 volts coming through the catode rollower into the cathode resitor on v2a to ground?

Check the ground of the 100k resistor off pin 8 next to the treble cap or try another tube.

+1 to Cameron. Also, check the value of that CF resistor to ensure that it is still 100k. 283V is way more than double what a modern 12AX7 (or any 12AX7) should see on the cathode in operation. In clones, I elevate the heaters to 80VDC or so specifically because Marshall CFs run over 100V.

[jamme61]

you guys are right way over my head. It's going to the real tech. Thanks for the time on this.

[Reeltarded]

Need pics. I think the problem might be ..

Oh, hey.. the master is way over ----> and the DC is coming from that side of the CF.

Hmm my head.

[Firestorm]

with all tubes in
V1 pin 1 =312 volts
2 =312
3 =328
6 =324
7 =281
8 =316

V2 pin 1 = 323
2 =212
3 =311
6 =360
7 =324
8 =348

I don't think readings like that are even possible (unless you really "fixed" it). Gotta be pilot error...

[rock_mumbles]

AC mV ???

[alvarezh]

When you get readings of this sort, I would suspect a bad meter. Could be wrong though!

Cheers.

[jamme61]

I know none of this makes sense maybe it is a bad DVM I'll check that today. I'm giving it one more shot this morning and then on to a real tech. Sorry if I pissed anyone off with this stupid post.

[vibratoking]

You're just asking good questions and trying to learn. We like that. I seriously doubt that anyone is mad in any way. We only get mad when you ask and then tell us the answer is stupid.