Rocket Bias

[sliberty]

According to my Compu-Bias, my newly completed Rocket has 275V on the plates, draws about 39mA, and is dissapating around 10 watts per tube. I am using the Russian 6P14P (6N14N) tubes. Maybe they can handle it, maybe not.

Should I look at changing the cathode resistor a bit? The amp sounds great by the way

[jaysg]

It's less than 12W. I think you're good. That's basically what's happening with a lot of these cathode biased amps -- they're running close to or above 100% of the dissipation rating. They eat tubes and could use a built-in fan.

[RJ Guitars]

Sounds like a good report... I'm hoping that "Eating Tubes" still means some sort of useful lifetime to them though.

I have noticed that in all the Rockets I've built using EL84's and KT66's that you can push the bias up really hot and the tubes don't red plate. Maybe all of you already knew that and understand it, but it seems that on a couple occasions when I thought they were biased way to hot, nothing bad happened. I'm starting to get some serious hours on these builds now and all is well... Makes me wonder about some other physics happening in cathode biasing. Has anybody got the technical explanation for that?

rj

[Blind Lemon]

I am running all the Saratov's I put in the Rockets right at 12w and they sound great. Terry(aka Sgt Overdrive) says they are tuff as nails, they don't appear to be even breaking a sweat and I've been watching them pretty close.

BL

[sst4270]

Steve,

The 6P14P's have an anode dissipation rating of 14W.

I used the 6P14P-EV's in mine. They are the russian equivalent to a JAN type tube. They were designed to handle higher G-forces and they prone to less microphonics.

Your current bias setup should be fine.

Regards,

Steve

[Structo]

It's my understanding that you can bias a cathode bias amp to 100% with no ill effects.

[sliberty]

Steve,
Thanks for the tip on the Russina tubes. I got them for exactly that reason - they were supposed to be very sturdy. So I'll stop worrying. Besides - they are really cheap, so even if they die in a year, I can live with that.
Steve

[dartanion]

I'd be a bit more concerned about eating GZ34s with that first filter node of 80uF. With that said, I have used up to 100uF without any issues using NOS GZ34s.