Question on how ohm's selection of OT affects current draw on output tubes

[ron vogel]

I have a selectable 4/8/16 OT....an amp with too much voltage on the output tubes...and a bias vary trem that wants a cold bias (sending my voltage too high).

Will using the 4 ohm taps on the OT with an 8 ohm speaker work the tubes harder? I have been meaning to try this...I'm thinking I may be able to get the trem working better (deeper) in this circuit if I can get the output tubes to pull down the b+.

This is a 6G2 based amp.

[g1]

A load impedance lower than the tap will work the tubes harder, so 8 ohm speaker on 16ohm tap.

[Enzo]

If I read right, I think he is hoping the impedance "mismatch" will drag the B+ down. That being the purpose of "working the tubes harder."

I think he will be disappointed in that regard.

[g1]

Yes, I don't it will make any difference at idle (even into a short), but perhaps under power there may be some benefit.

[Chuck H]

Self bias the tubes? If a fixed bias is desired maybe strap a zener across a cathode resistor. The voltage across the cathode circuit effectively subtracts from the plate.

On the macro view there is a problem that needs to be corrected at a fundamental level. Creative ways to solve problems that shouldn't have happened is our specialty

[J M Fahey]

Mismatching the output load "just to bring +B down" won't work.

First deal wit way too much +B and then properly match load for good sound and long tube life.

[ron vogel]

Well, I should point out...it's not a major problem. It's just something I want to play with. Amp sounds better biased a little hotter...but then the trem gets weak. I did play with the trem circuit. It's better, but not there enough. I'd be happy with 15 to 20 volts. Maybe I should go ahead and put another tube in the design somehow...lol

[Audiotexan]

Amp sounds better biased a little hotter...but then the trem gets weak.

Might be a silly question on my part... but why would the trem be affected by biasing the output tubes??

I'd be thinking that:

I did play with the trem circuit.

would be more of a cause.

Or did I miss the thread this "sprang off" of?
Not trying to be a smartass, just geniunely lost.

[ron vogel]

It's a bias wiggle trem...

[Dave H]

Might be a silly question on my part... but why would the trem be affected by biasing the output tubes??

It's a bias vary trem. I'd guess (I don't have an amp with this circuit) biasing the amp hotter would mean that the trem circuit needs to provide more voltage to turn the tubes off.

[Dave H]

Ron beat me to it.

[jazbo8]

If there isn't enough range on the tremolo, try bringing down the screen voltage, that will allow you to use a lower bias voltage.

[J M Fahey]

Might be a silly question on my part... but why would the trem be affected by biasing the output tubes??

Agree and add: varying bias trem plays with the transconductance variation tubes (in this case pentodes) present with varying current.

That effect is much more pronounced near cutoff and much weaker with higher idle currents; weakest in a truly class A biased amp.