70s Ampeg V4B Blows Fuses

[Enzo]

Not sure what soot between pin#2 and pin#3 means? Can you clarify?

You look at the socket, specifically pins 2 and 3, and see if you see any soot there. Soot, as in the stuff from a chimney, black residue. If there was any arcing between the two it usually leaves a sooty trail.

[vintagekiki]

Measuring vdc on all four(4) power tube sockets: #1(10.5mv), #2(28.5v), #3(586v), #4(596v), #5(-63v), #6(9mv), #7(104mv), #8(10mv on 1), 3 at -0 ¹⁾.

¹⁾ Explain what you measured this.
It is obvious that the power tubes are in an untested state (as-as)
At one power tube socket, make a test circuit (red color on schematic) to test and possibly matched power tubes.
During the test, from V4B remove all power tubes from his sockets, and insert into the test socket only one by one, which you test.
During the test all pots set to min (0)
This way you can test all the 6L6s you have, to get to the condition of what is for possible use.
During testing power tubes, speaker must be connected to the V4B.

[ca7922303]

¹⁾ Explain what you measured this.
It is obvious that the power tubes are in an untested state (as-as)
At one power tube socket, make a test circuit (red color on schematic) to test and possibly matched power tubes.
During the test, from V4B remove all power tubes from his sockets, and insert into the test socket only one by one, which you test.
During the test all pots set to min (0)
This way you can test all the 6L6s you have, to get to the condition of what is for possible use.
During testing power tubes, speaker must be connected to the V4B.

Pin 8(10mv on 1 of 4 tubes), the other three(3) are 0.00 mv on pin#8. This is socket only, no tube installed.

[vintagekiki]

Pin 8(10mv on 1 of 4 tubes), the other three(3) are 0.00 mv on pin#8. This is socket only, no tube installed.

Thank you.
Voltages without power tubes are OK.
Pin 8 (c) is the cathode of power tubes and it is at a chassis potential (0 mV).
Now on one socket make a test circuit, and boldly start to test power tubes, as described in post #182

[ca7922303]

You look at the socket, specifically pins 2 and 3, and see if you see any soot there. Soot, as in the stuff from a chimney, black residue. If there was any arcing between the two it usually leaves a sooty trail.

Not seeing any soot between 2 & 3 pins on V5,6,7, or V8 sockets.

[ca7922303]

¹⁾ Explain what you measured this.
It is obvious that the power tubes are in an untested state (as-as)
At one power tube socket, make a test circuit (red color on schematic) to test and possibly matched power tubes.
During the test, from V4B remove all power tubes from his sockets, and insert into the test socket only one by one, which you test.
During the test all pots set to min (0)
This way you can test all the 6L6s you have, to get to the condition of what is for possible use.
During testing power tubes, speaker must be connected to the V4B.

Can I make sure I understand the test. With stanby on, speaker connected, one tube at a time, install tube in V5 and get neasuremeasu off of test points 1, 2, 3, 4. Am I missing anything? Thanks.

[vintagekiki]

Can I make sure I understand the test. With stanby on, speaker connected, one tube at a time, install tube in V5 and get neasuremeasu off of test points 1, 2, 3, 4. Am I missing anything? Thanks.

Speaker connected.The tube you measure, you put in the test circuit V5. Wait a few minutes for the tube to warm up.
Standby on. On the DVM (range 200mVDC) you read how much voltage (so much current through the tubes because the sensor is R = 1 Ohm)
Standby off. Remove measured tube and on base tube glue the paper with the current you read.
Put in a new tube. And so in this way test all the 6L6 you have in stock.

[ca7922303]

Speaker connected.The tube you measure, you put in the test circuit V5. Wait a few minutes for the tube to warm up.
Standby on. On the DVM (range 200mVDC) you read how much voltage (so much current through the tubes because the sensor is R = 1 Ohm)
Standby off. Remove measured tube and on base tube glue the paper with the current you read.
Put in a new tube. And so in this way test all the 6L6 you have in stock.

I'm hesutant because i've heard never to turn on a 100 watt amp with less than two(2) properly placed tubes, but I'm willing to do this if I fully understand. Where do I get voltage reading at? I thought the red 1,2,3,4 on schematic you posted would be test points? Thanks for your help.

[Helmholtz]

The method described by VK is good and safe as long as the increased B+ doesn't exceed the voltage ratings of the filter caps.

[vintagekiki]

I'm hesutant because i've heard never to turn on a 100 watt amp¹⁾ with less than two(2) properly placed tubes, but I'm willing to do this if I fully understand. Where do I get voltage reading at? I thought the red 1,2,3,4 on schematic you posted would be test points? Thanks for your help.

Speaker connected.The tube you measure, you put in the test circuit V5. Wait a few minutes for the tube to warm up.
Standby on. On the DVM (range 200mVDC) you read how much voltage (so much current through the tubes because the sensor is R = 1 Ohm)
Standby off. Remove measured tube and on base tube glue the paper with the current you read.
Put in a new tube. And so in this way test all the 6L6 you have in stock.

Read #182

1)
You don't turn on amp. You test old power tubes, to choose two (2) that are correct.

[ca7922303]

Speaker connected.The tube you measure, you put in the test circuit V5. Wait a few minutes for the tube to warm up.
Standby on. On the DVM (range 200mVDC) you read how much voltage (so much current through the tubes because the sensor is R = 1 Ohm)
Standby off. Remove measured tube and on base tube glue the paper with the current you read.
Put in a new tube. And so in this way test all the 6L6 you have in stock.

Read #182

1)
You don't turn on amp. You test old power tubes, to choose two (2) that are correct.

How do I warm up tube before turning standby on, then you say you don't turn on amp? Not making any sense to me?

[vintagekiki]

Read as it is written.
Don't philosophize.

[ca7922303]

Also, fir this tube test, where do I put the black dmm prove and where do I put the red dmm probe? Thanks.

[ca7922303]

Also, took measurements previously on caps, diodes, and resistors. Capacitor test, diode test, and resistance. Any of these look off?

[vintagekiki]

Also, fir this tube test, where do I put the black dmm prove and where do I put the red dmm probe? Thanks.

black dmm probe to chassis
red dmm probe to pin 8 (c) cathode V5.

If something is not clear look at the schematic
https://music-electronics-forum.com/filedata/fetch?id=930419&d=1619849061

[ca7922303]

Measurements on caps and resistors vdc @ 60v on variac previously. Anything look wrong with these neadmeasurem?