70s Ampeg V4B Blows Fuses

[vintagekiki]

Appreciate the help, can you give me more details on how to proceed? Thanks.

To start

https://www.ampegv4.com/

https://www.ampegv4.com/schematics.php

https://www.ampegv4.com/images/schematics/V4.jpg

https://www.ampegv4.com/images/schematics/V4B.jpg

1)
http://guitar-gear.ru/forum/index.php?app=core&module=attach&section=attach&attach_i d=14475
The Electric Guitar Amplifier Handbook - Jack Darr

https://documents.pub/document/designing-v-t-amplifiers.html
Designing Vacuum Tube Amplifiers and Related Topics

[g1]

Measure AC volts (200VAC range) from one leg of C16 with other meter probe to ground. Then check other leg of C16.

[ca7922303]

Appreciate the help, can you give me more details on how to proceed? Thanks.

[g1]

Like the others said, you are missing the bias voltage. There should be AC voltage on both sides of C16, which sometimes explodes in these amplifiers.

[Helmholtz]

C23 reads -454mv on 2000mv scale.

If that's DCV, you have a bias supply problem. Acc .to schematic you should have -64VDC here. Low bias voltage causes excessive power tube currents.
Check all bias supply components.

[ca7922303]

C23 reads -454mv on 2000mv scale.

[vintagekiki]

-364mv on 2000mv range

Pin 5 is g1
You no negative bias voltage.

[Helmholtz]

Not much sense measuring grid voltage with a cheap DMM, as the reading will depend on meter resistance.
Bias should be measured at the negative terminal of C23 instead.

[ca7922303]

-364mv on 2000mv range

[vintagekiki]

All four(4) pin#5s read -364mv on 2000mv range.

What did you measure on pin5 ???
Pin 5 is g1

See post
https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/928158-70s-ampeg-v4b-blows-fuses?p=928217

[ca7922303]

All four(4) pin#3&4 read 480v on 500v range. All four(4) pin#5s read -364mv on 2000mv range.

[g1]

If those are the Russian style '5881/6L6' tubes, they will work fine here. Not sure what you mean about the pin 8's, but you should not have to worry about it. Any regular 6L6 variant will work ok with the amp wired up stock. Real NOS 5881 or the authentic re-issues will not be able to handle the high voltages.

It is powering up without the power tubes? Then something power tube related was probably causing the fuse to blow. Check for proper DC voltages at power tube sockets before you put them back in. Especially pin5, which needs to be somewhere in the --60VDC range.
Whatever you smelt around the 6K11 probably got burnt and will have to be dealt with as well.

[ca7922303]

Shows continuity*

[ca7922303]

Looks like all 4-pin#8s(according to the bottom of a 5881) so continuity to ground on power tube sockets. I guess 7027s or V4 schematic is different.

[ca7922303]

Amp has not blown 6 amp fuse for me. Guy I got it from claimed it was blowing fuses.