70s Ampeg V4B Blows Fuses

[ca7922303]

Under same conditions, measure DC volts at both sides of standby switch.

SW4(9v/9v).

[ca7922303]

Under same conditions, measure DC volts at both sides of standby switch.

What do you make of those measurements and the diodes? Thanks.

[g1]

Try it with one probe on each side of the diode, black probe to cathode end (silver band).

[ca7922303]

Try it with one probe on each side of the diode, black probe to cathode end (silver band).

D-1/D-2(-290v), D-3/D-4(-261v), D-5(-9.9v), D-6(-107v).

[g1]

It's just D5 I was wondering about, and I think that is normal but I'll double check mine tomorrow.
How many of the tube heaters are not lit up? They can be hard to see sometimes so checking in the dark can help, also feel them for any heat.

[ca7922303]

It's just D5 I was wondering about, and I think that is normal but I'll double check mine tomorrow.
How many of the tube heaters are not lit up? They can be hard to see sometimes so checking in the dark can help, also feel them for any heat.

Checked power tubes in dark, had one(1) power tube not lighting or warming up. Thanks for your help.

[Enzo]

I'm not going back through 171 posts, but any chance that dark tube has the center plastic post broken off the base?

[vintagekiki]

Thanks for your help.

Thank you for spin yourself.

[ca7922303]

I'm not going back through 171 posts, but any chance that dark tube has the center plastic post broken off the base?

Checked the bad tube socket with several different tubes, all had center plastic post intact.

[vintagekiki]

Do checked several different tubes lighting or dark (not lighting)?

[ca7922303]

Do checked several different tubes lighting or dark (not lighting)?

Only one(1) tube socket is not producing a lighted or warm tube. This socket has been tested with several known good tubes.

[vintagekiki]

Only one(1) tube socket is not producing a lighted or warm tube. This socket has been tested with several known good tubes.

On a tube socket that is not producing a lighted or warm tube, check between pin 2 and pin 7 that there is a voltage of 6.3 VAC.
On the same tube socket check if there is soot between pin 2 and pin 3.
If the tube socket damaged, burned replace with a new socket.

https://drtube.com/datasheets/7027a-rca1959.pdf

[g1]

After you get that socket working, try this test again to see if power amp & supply are still basically working: https://music-electronics-forum.com/...556#post929556

[ca7922303]

On a tube socket that is not producing a lighted or warm tube, check between pin 2 and pin 7 that there is a voltage of 6.3 VAC.
On the same tube socket check if there is soot between pin 2 and pin 3.
If the tube socket damaged, burned replace with a new socket.

https://drtube.com/datasheets/7027a-rca1959.pdf

All four(4) power tube sockets measure 6.3vdc between pin#2 & pin#7. Not sure what soot between pin#2 and pin#3 means? Can you clarify? Thanks.

[ca7922303]

After you get that socket working, try this test again to see if power amp & supply are still basically working: https://music-electronics-forum.com/...556#post929556

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.