1970s Ampeg V4 Low Distorted Output

[ca7922303]

Good output and all controls operational when running external amp out to input of another amp. Magnavox era V4 w/6550s.

[Jon Snell]

The Ampeg V4 has 7027A output valves in it!

Someone being playing in it?

[ca7922303]

The Ampeg V4 has 7027A output valves in it!

Someone being playing in it?

I haven't come across one in probably 10 years that didn't have 6L6s or 6550s in it but I understand now 7027s are much more available than they were for awhile .

[g1]

The later ones had 6550 option listed right on the schematic (see note 6 of attachment). Lots of earlier ones have been changed to 6550 as well. Good quality 6L6 work fine in any Ampeg calling for 7027, and modern 7027 are just 6L6 with extra pins that Ampeg's don't need anyway (at extra cost).
Does this one have a 'distortion' control?

[ca7922303]

The later ones had 6550 option listed right on the schematic (see note 6 of attachment). Lots of earlier ones have been changed to 6550 as well. Good quality 6L6 work fine in any Ampeg calling for 7027, and modern 7027 are just 6L6 with extra pins that Ampeg's don't need anyway (at extra cost).
Does this one have a 'distortion' control?

No distortion on this one. I recognize this one because I had one in 1976. It's a Magnavox before they changed to plastic control knobs. It cost $350.00 new in '76 and the whole 2-4x12 stack cost $850.00. You got time to mess with this one while I'm waiting on parts?

[g1]

You said you get good signal to another amp from ext.amp jack. So preamp and probably power supply should be good. Check DC voltages on power tubes.

[ca7922303]

You said you get good signal to another amp from ext.amp jack. So preamp and probably power supply should be good. Check DC voltages on power tubes.

All four(4) power tubes pin 3(575vdc).

[Enzo]

COme one, power tubes need plate voltages - pin 3, But they also need screen voltages - pin 4 and VERY importantly they need bias voltage on the grids - pin 5.

[ca7922303]

COme one, power tubes need plate voltages - pin 3, But they also need screen voltages - pin 4 and VERY importantly they need bias voltage on the grids - pin 5.

Power tubes pin 4(-0.7vdc)
. pin 5(-54vdc)

[Helmholtz]

No screen voltage (pin 4) = no power tube gain.
Check screen supply (point E).

[ca7922303]

No screen voltage (pin 4) = no power tube gain.
Check screen supply (point E).

Can I bother you to point me to screen supply point E?;Thanks

[g1]

Sorry, that schematic I posted above (post # 4) is the wrong one. That's for the later models with 'distortion' curcuit.
Schematic attached below should be correct.
Screens are fed from point 'B' which comes through R55.

[ca7922303]

Sorry, that schematic I posted above (post # 4) is the wrong one. That's for the later models with 'distortion' curcuit.
Schematic attached below should be correct.
Screens are fed from point 'B' which comes through R55.

R55(570/-0.7vdc)

[ca7922303]

R55(570/-0.7vdc)

[Helmholtz]

R55(570/-0.7vdc)

R55 is open - replace it.
But you might have power tube with a shorting screen which caused R55 to blow.