70s Ampeg V4B Blows Fuses

[ca7922303]

Pin#1 & 6 were 542v on V4 with V6/V8 tubes installed, now all four(4) pin# 1 & #6 are 246v?

[ca7922303]

Correction: R28 is 1.5k, R203 is 10k( should be 7.5k, but got

[ca7922303]

10k R203:temporary.

[ca7922303]

Also, R203 with four(4) power tubes installed measured(0.0mv/0.0mv).

[DrGonz78]

For some reason now all four power tubes pin #1(245v),pin#3(10.5v), pin#6(246v), pin#8(10.5v),

Which tube are you referencing in the above quote?

[Jazz P Bass]

245 POSTS!!!
What is with this guy???

[g1]

Some of the voltage measurements are just plain impossible. Either something is wrong with the meter or the measurement technique.

[g1]

R28 with V6/V8 installed(10.6v/0mv), R28 with V5/V7 installed(10 6v/0mv).For some reason now all four power tubes pin #1(245v),pin#3(10.5v), pin#6(246v), pin#8(10.5v),

Those are good numbers for V4, not sure what you mean about 'all four power tubes' because those readings can not apply to the power tubes.

[DrGonz78]

Pin#1 & 6 were 542v on V4 with V6/V8 tubes installed, now all four(4) pin# 1 & #6 are 246v?

It appears that those are measurements on v4

[DrGonz78]

So the question now is there a signal at ext jack? I think that answer is a yes. Now you need to trace the signal past v3. Look at c10. The signal rides on the DC voltage out of the plate of v3. The other side of c10 will have signal voltage as the DC voltage is filtered away by c10. Just focus on this next step or we will get lost again. Build a signal tracer if you don’t already have one. Something simple like this.

http://musicfromouterspace.com/analo...naltracer.html

look up videos about tracing audio signal tracing on YouTube

[ca7922303]

Which tube are you referencing in the above quote?

I was saying that finally I have all four power tube sockets with tubes working now and that V4 was reading with the 245v(1 & 6 pins) and 10.5v( 3 & 8 pins).

[DrGonz78]

I was saying that finally I have all four power tube sockets with tubes working now and that V4 was reading with the 245v(1 & 6 pins) and 10.5v( 3 & 8 pins).

So the amp is passing signal past v4 into the power tubes? You got output from the output tubes?

[ca7922303]

So the amp is passing signal past v4 into the power tubes? You got output from the output tubes?

Yes, I'm using four tubes, and i've got signal when plugged into external amp jack, but no preamp out. Thanks for your help.

[ca7922303]

So the question now is there a signal at ext jack? I think that answer is a yes. Now you need to trace the signal past v3. Look at c10. The signal rides on the DC voltage out of the plate of v3. The other side of c10 will have signal voltage as the DC voltage is filtered away by c10. Just focus on this next step or we will get lost again. Build a signal tracer if you don’t already have one. Something simple like this.

http://musicfromouterspace.com/analo...naltracer.html

look up videos about tracing audio signal tracing on YouTube

I can check C10 when I get off work this evening. Thanks. Appreciate your help.

[DrGonz78]

I can check C10 when I get off work this evening. Thanks. Appreciate your help.

As per your last post I was definitely confused by the symptoms of the amp. I thought we had signal from input up to V3. There were issues going on with the power tubes that threw me off. Anyhow disregard C10 and checking it as that is not needed now. Still my advice to build and use a signal tracer is very much needed. Got to trace this signal through the preamp circuit to find where it might be dropping out.