65amps Ventura cathode bias ?

[jamme61]

I just got the amp this week, put about an hour of playing, with no problems. Today I checked the tubes with a bias rite and measured 50 ma at 322 plate volts. Isn't this way to hot? Thanks

[roberto]

322V and 0.05A are 16.1W that exceeds 12W plate dissipation of 6V6.
Did you measured only one tube or both together?

[rhinson]

for cathode biased amps you subtract the cathode voltage from the plate voltage to get the actual voltage the plate "sees"-----so you can always run them a little hotter than you think with cathode bias. i'm guessing you have around 20v on the cathodes here, give or take. rh

[roberto]

I think between 18 and 20V too, but it still remains 15W with 50mA.
It's a bit hot, but is not unusual to run small pentodes higher than suggested.

[jamme61]

I measured both tubes using a weber bias rite (with voltage option) one tube is running at 50 ma and the other at 48 ma. The voltage is the plate voltage but, again it is with the weber bias tool. I have the chasiss out and it has a 220 ohm cathode bias resistor(with cap 63 volts 150uf) I could raise that value to bias them colder but, maybe the amp is supposed to run this hot? dosen't make sense to me to run 6v6's that hot (but I know very little about this stuff) I have e-mailed 65amps to see but would like to play the amp (I just got it) but I don't want to blow it up. Thanks for all your time on this.

[roberto]

Just call them!

65amps
11439 Vanowen Street
North Hollywood, CA 91605

Information and Customer Service
818-760-5089

[jamme61]

I would but, with the holiday over here, they're closed. I'm sure they'll get back asap.

[jamme61]

figured I post my findings for future ventura owners. 65amps Mike Franceschini, told me to treat the jj 6v6's like a 6l6, when it comes to biasing. Myles e-mailed, that I'm good with the hot bias unless I see red plating. Mike Franceschini said, go play the amp, have fun, if it blows its covered under warraty.

[neon333]

Interesting comment from DB about how they run the 6v6's in the venture at 1:05:25.

http://youtu.be/mYVyKEEIF3M?t=1h5m25s

[jamme61]

yea I saw that. I have to say the 65 amp guys have been very nice answering all my questions. seem like great guys.

[barfoden]

I guess 65 amps found out that higher plate voltage, larger value
cathode resistor is not a great idea if you like to dime the amp..

A Fender 5e3 tweed deluxe with a 360V plate/320V screen has a 250 ohm bias resistor. It ran its vintage 6v6gt tubes really hot.

The ventura around 322V plate (302V true plate voltage if the cathode voltage is 20V) at 0.048mA is not that bad at 14.5W to 15W total dissipation for the strong jj6v6 tube. Deduct around 1W for screen current and you get an idle plate dissipation around 14W which is the datasheet value for the jj6v6.
Again 20V/220 ohm should be = 91mA which is around 45.5mA total draw pr tube.