Ampeg V4 power tubes

[Prairie Dawg]

I've got an Ampeg V4 head in the shop and I'm doing a little barter with the guy who owns it.

About all it really needs is a retube, as it has a badly mismatched quad of JJ 7027As. It runs them at a measured 525 volts at the plates, and it is one where pins 1 and 6 are unoccupied.

So here's what I think my choices are for a retube.

Go with a good set of 6L6GCs and be happy.
Go with a good set of 6L6GCs and use a zener diode to get the plate voltage down, say, 50 volts.
Go with another set of JJ or Sovtek 7027As
Go with 6550s or KT88s, knowing that the filament current load will increase by about 40 per cent
Convert it to use EL34s knowing that the filament current load will increase.

As for choice 1, I did this with an Ampeg B25, but being tube rectified I dropped in a 5U4GB to get the plate voltage down a bit.

What's your opinion, Mike?

Thanks all.

[Blue Strat]

Too bad 7581As are no longer easy to find. They're your best option.

If you're confident in the new 7027s go that route. If not, go the zener and 6L6GC route...or go NOS 6L6GCs without the zener.

There's no simple answer that you'll love.

[Prairie Dawg]

Originally Posted by Blue Strat

Too bad 7581As are no longer easy to find. They're your best option.

If you're confident in the new 7027s go that route. If not, go the zener and 6L6GC route...or go NOS 6L6GCs without the zener.

There's no simple answer that you'll love.

That's my inclination. to go with 6L6GCs and a zener. I've installed three quads of Ruby 6L6GCs in the past year in a trio of Mesa Boogie Mark IIs and they're surviving well, but when the plate voltage starts getting up there I get nervous. I just do not like plate voltages north of 500.

[Prairie Dawg]

As another point of information, the V4 power transformer does not have a center tapped secondary.

I recollect I did this mod on a Rose Morris Vox AC30 which used solid state rectification and I put the zener diode in series with the diode bridge ground.

Does my memory serve me correctly here?

[Blue Strat]

That should work. Effectively, you're moving the ground of the source negative which is what that would do. Test with no load first.