Need advice on Biasing my amp .

[sidehatch]

I have a Carr slant 6 that has 4 6v6's. 2 have an adjustable bias and 2 are cathode bias.

The manual and amp itself says adjust the pot to it says 66ma using the built in terminals( Everyone I tell that to says thats way too high for 6v6s but thats what Carr says)

Carr told me years ago when I got it that I can run a duet of 6l6's in the fixed bias pair and the amp will take it(He also asked me not to spread it around -I guess incase people blow them up).

Anyway, I decided to try a set of winged C 6l6's in there a few minutes ago just for the heck of it.

I Installed them and played for about 5 mins as is. I think it sounds great-especially on all 4 tubes.

My question is about biasing the 6l6's. I checked it and its at 176ma!. the range is somewhere from 58 to 180ma. I put it to 66ma like with the 6v6's.

Is there any way of knowing the range that is safe without knowing the amp? I could ask Carr but I think they are PO'd at me for doing the redplate mods and posting the better clips and letting everyone know. I asked a question a while back and they seemed aggravated.

It doesnt have to be perfectly biased but I'd like to know a range of safe if there is such a thing without knowng plate voltage etc.

Sorry for the long winded question.

Thanks

[Structo]

It depends what your plate voltage is.
On a cathode biased amp you can bias them at 100% because they are self limiting but the fixed bias shouldn't be more than 70% of their rated dissipation.
According to one chart, 42ma is 70% at a plate voltage of 200v.

Not familiar with that amp so I can't really make a judgement.

I would however keep an eye on the tubes and see if any are redplating with such a high bias current.

[MBD115]

I too know nothing so don't listen to me.... ok

My 6L6 amp I have tried several different bias points and when doing the math on my plate voltage I find I can run 19 watts and the tubes seems to be pretty happy. I've tried higher and lower points and have settled on this after much tinkering. The tone seems to be pretty good and the tube life also seems to be ok for my $$. I just divide that 19 watts into my plate voltage then set the bias to that amount. In my case the plate voltage is 450 volts and the bias setting comes out to about 42mV.

But I guess I must say that in my case 50mV did sound awful good and punchy and very toneful, but I would guess (speculation only) tube life would be shortened running them at those settings, lol. I don't know.

Hope this helps some.
MD

Like I said... I don't know anything, so don't listen to me.

[sidehatch]

I'll email henry. Maybe he remembers the plate voltage from when he worked on it.

Thanks guys!

[Alex R]

Do you know what those terminals are actually connected to? Do you have to connect an ammeter to them, or a voltmeter? I'm wondering if they're the usual thing, a one-ohm resistor on the cathode and read off the voltage drop across it (because mV = mA x 1). Those resistors can drift in value and give odd readings, specially if the tubes have overheated.