bias 66 Super Reverb w/JJ 6L6's

[mkaye]

i got a pair of JJ 6L6's for my super, but i don't have enough range in the bias control
i can only get 26ma @430V (~11W)
i would like them closer to 40ma (17W)
should i just alter the circuit to allow less bias voltage or i am missing something?

mark

ps - all the caps have been changed

[phsyconoodler]

Yes,just change the bias range resistor to get it in the correct range for the tubes.
At 430v it sounds like you may be using a 5U4 rectifier tube.If so,try a 5AR4 first.That circuit should be up around 455v or so.

[mkaye]

i was wondering if the voltage was a little low
i use the standard 5AR4 already, but have ordered a replacement
i won't play with it until i can replace the rectifier & see if the voltage comes up

mark

[Rosewood]

Does this amp have the old filter caps? If so I would do a cap job along with trying another 5AR4.

[SatelliteAmps]

Bumping up the overall voltage won't bump up your range enough. The issue with biasing is the actual power tube draw, rather than the B+ supply. When you draw more current, your B+ will respond slightly and rise. When the bias is low (as is yours) the B+ will be a bit low. Which could explain the slightly low B+ (which I assume is actually being checked on the power tube, not the rectifier. You should also check it there.)

If the B+ is low at the rectifier, then the rectifier might not be working correctly. If the B+ is fine at the rectifier, then a new rectifier tube won't do anything at all about the bias supply.

Change the resistor to put the bias supply into the correct range for those tubes. This is very common, and very easy.

If you don't have the skills to do the work, or to understand the safety issues that arise from working on amps, then please take it to tech to have them do the work for you.

[SatelliteAmps]

Does this amp have the old filter caps? If so I would do a cap job along with trying another 5AR4.

It is probably a good idea to replace the caps if they are original. But that probably won't help the biasing issue at hand.

[s2amps]

When you draw more current, your B+ will respond slightly and rise.

Methinks you meant to say when you draw more current, your B+ will fall.

[SatelliteAmps]

I did mean that. Thanks for the correction.

[mkaye]

I replaced the rectifier & now i have 461V instead of 430V
i can get 35ma thru the 6L6's without modifying the voltage divider, so i'll leave it as it is

mark

[afenderman67]

how did you like the jj's?, these are my favorite power tubes for my super and my bassman!

as in new tubes!