Biasing question

[chocopower]

Hi!

I´m trying to bias my Guyatone GA-1050 (Fender Proreverb clon). It is a 2 6L6 amp, whit diode rectifier...
recently, i installed the 1ohm resistors in Pin 8.

Please, cheak this readings..

Plate voltage:
523 volt - without power valves installed.
495 volt - with power valves installed

Readings across the 1 ohm resistors:
40.1
46.2

I´m trying a 22 or 23 watts maximun static disipation.....

Is this ok?

[MWJB]

You are risking premature wear/failure. I'd back off the current to 30-35ma. Most 6L6 Fender style amps sound pretty good at those kind of currents.

[chocopower]

Yes, i know it.
But i supose those amps should have a lower plate voltage.

If MAX STATIC DISSIPATION WATTAGE for 6L6 is 23 watts...

523 x 46= 24
523 x 40= 20.9

495 x 46= 22.7
495 x 40= 19.8

Is this ok?

[MWJB]

Max idle plate dissipation, in most cases is NOT 23W for a 6L6 in FIXED bias. You don't say what brand of 6L6s you are using, many current production 6L6GCs are not true 30W tubes. For a safe margin assume 25W for a current 6L6/5881 and bias to 70% of that = 17.5W...and then have a listen.

Even so, I still would not recommend 46mA for any brand of 6L6 at 495v. You might get away with it with the JJ or a US made NOS 7581A, but I would still recommend 30-35mA for 6L6s in a Fender, whether that Fender is running 400v or 525v (the upper limit that I have seen) at the plate, if you want a typical Fendery tone (I wouldn't necessarily panic if you have 27-28mA).

It is not usually necessary to hit bang on 17.5W, anywhere from 12W to 17.5W will usually be fine...as long as you like the tone (the real deciding factor, as long as you are not exceeding 70% dissipation).

Many Fenders run the same voltages that your amp runs, it is not unusual in that respect.

[Jerry]

Here's some good info on biasing amps. I'd probably want to run the tubes a little cooler.

http://www.aikenamps.com/Biasing.html

[chocopower]

They are TAD valves!!


I´ll chek a colder ajustment this weekend!!


Thanks!!!