loading 4x6v6

[FUCHSAUDIO]

Think of 6V6's as "half a 6L6". Half the plate load, heater current and plate current. You can use Bassman iron (stay under 450 V) 4 x 6V6 can be treated the same way 2 X 6L6 can, same load on PT and OT. Have fun...

[Andy Le Blanc]

I'm coming to the same conclusions. Its fun fun fun. I am having a debate
with my self around the power side. I want to drop the plate volts and push
current as much as possible, and use cathode bias. The math works in that
direction as far as max plate dissipation goes. ie: 50ma @ 450v = 22.5w
But a hundred volts less it takes 65ma. for the same dissipation.
That's 130% of expectations for say, 50w iron. Where's the line?

[FUCHSAUDIO]

Experimentation will lead to the best solution. We're doing almost 475 on 4 x 6V6 330 ohm Cathode resistor 33 volts = 100 ma 25 ma per tube, deduct the 33 from the 475 and you are running in the low 400's, which is safe, and the 25 M is no issue for old 6V6's or new JJ's. Just a tad over "normal" which is 20 or 22 ma per tube. You can do fixed bias too 400 volts is fair, higher if you're daring. They sound great, but cathode bias has "it"...lol. There is a certain grind in 6V6's that is quite nice.

OK, cool part: Run 2 6L6's in the same circuit if you like !

[Andy Le Blanc]

6V6 with cathode bias really are very nice. I'm tending to go the other way.
With a lower plate voltage, closer to the push-pull Class A figure.
I do know that the outcome will not meet the "definition" of "class A", but close.
An intentional load mismatch, upwards, so the tube still will see an appropriate load,
also drops the Xr (I think I remember) with the OPT loading.
Another approach. My worry is more for the longevity of the OPT, it must handle the current.
An over rated PT should run nicely cool.

[FUCHSAUDIO]

Outputs fail basically for four reasons: From manufacturing issues, from being run with a badly shorted tube (and over sized fuse) causing an arc that burns something, ultrasonic oscillations, or mismatches or use with a crappy attenuator. If you go with a quality piece, I doubt high currents will bother it.

[Andy Le Blanc]

I haven't had one go personally (yet). Seen some cheesy one's that were
BBQ, and have done work on some beat to piss fenders, operated beyond
tube death.
The matching I implement is not extreme, but it is a guitar amp, the inclination
is to make it strong enough , then double it.

Hi freq. oscillation is a different story, does opt loading effect that?
Beside putting a cap between the PI plate's for the insurance, or stoppers
on the power tube circuit, RFC on the plate leads etc...
Is there a good way to measure for it with minimal bench resources?
Hz, KHz, MHz?