What is typical max 6V6 plate V?

[tubeswell]

HI Daz

I've just been through this with my 2nd build (a push-pull tweed). MWJB and Bruce from Mission amps were (as usual) extremely helpful to go out of their way to reassure me that its okay to run the tubes at higher dissipation. I'm using the new sensor "Tung-Sol 6V6GT" re-issues, and have the amp set up with switchable fixed or cathode bias.

On fixed bias I get 368VDC on the Plates, 364VDC on the screens and have the tubes biased at 28mA (measured using the 1R cthode resistor method - so there's a little bit of screen current in the equation) giving 10.5W per tube

On cathode bias I have a 330R (measures at 327R with each 1R cathode resistor) and the plates are 355-356, screens are 357-358 and the cathode is 24V, giving 36mA per tube and 12W.

They do sound a lot better, and I'm not getting any red plates yet

[daz]

Using Weber's bias calculator :

http://www.webervst.com/tubes/calcbias.htm

and entering 6V6GTA and 404 volts into the top line of the calculator
produces 24.2ma of bias current which seems reasonable.

Oh, I just figured out that you must have entered 6v6s. You sure you
don't have 6V6GTs ?

Paul P

I got my data from the tables below, not the calculator. It says "EL84/6V6GT" and it says at 400v 21ma is 70% and "average" for that tube is 60% which is 18ma. However, i didn't know there is a difference between 6V6Gt and 6V6. I thought it was just some regional designation or such. Mine are JJ's and on the tube they say 6V6S, so i have no idea what that means. But looking at webers data i'm even more confused because in the tables it shows 21 ma at 400v for 6V6GT. yet if you use the calculator and choose 6V6 without the "GT", it also shows 21 at 400. And to add to the confusion there IS no GT in the calculator menu, only a "GTA". So i don't kno what to think.

[Diablo]

DAZ:
the JJ 6v6S tube can handle high plate voltage. A lot of folks are using them in Hot Rod Deluxes with 430 V on the plates. 70% idle current at this voltage is 22mA per tube.

[daz]

I thought i had read something like that about them. Guess i'll leave it there then. Thanks.

[MWJB]

Published plate dissipation for the JJ is 14W, though some suspect that they'll take more than that (15-16W?). However, at 424v they'll happily take the 22mA Diablo suggests, probably a little more? As you dial in a little more current the plate voltage will drop some, so you may beable to squeeze a few more mA, say 75% of 14W should be safe enough with these (10.5W).

However, listen to the amp with the tubes set at what you think is a safe limit, then a little hotter, then say at 75% and set at what you like the sound of best. If you don't hear a major advantage to running them hot, then don't bother. However I would suspect that at 17mA they're going to start getting overly crunchy?

Max plate voltage for NOS 6V6s is often considered to be 425vdc, however it's likely to be the screens that go first above this voltage.

All the above refers to fixed bias applications. Don't forget that cathode bias will allow the tubes to run up to 13W, IF desired, and that cathode voltage should be subtracted from plate & screen voltage to give corrected figures.

[Chuck_Farlee]

Just to add:

As an experiment, I biased a JJ 6V6S up to 19w dissipation in a Tweed Champ clone. I didn't see any red plating in the tube.

Try this at your own risk, though.

chuck

[MWJB]

The JJ and pretty well any brand of 6V6 should take that, in that scenario - they would have to cope with more than that in a stock SF champ.

Definitely not recommended for Push-Pull & definitely not for fixed bias, though.