What the ?????

[Valvehead]

Ive got an Orange Rocker 30 combo here. The bias is very hot , 62ma per tube. 2-EL34 model .

Looking at the board, ALL of the bias supply parts are missing ! See picture ...

But the amp has bias, testing with the shunt method.

How is this possible ? I checked the traces and nothing is going to the tubes that is supposed to . It looks like it came like this from the factory---again, look at the picture.

Any thoughts ??

[Enzo]

Are the power tubes cathode biased on this model?

Lots of companies use circuit boards for more than one model. Look in the Peavey Rage and see the empty spots where the reverb circuits would be when they use the board in a Blazer.

I suspect your5 board does not have the bias supply loaded onto the board because it is a feature for some other model, and your bias comes from a cathode resistor. MAybe?

[g1]

As Enzo suspected, they are indeed a cathode biased amp. They are marketed as "Class A", so I would expect them biased hot, in the ballpark of 25Watts per tube. At 62mA per tube, if your plate voltage is somewhere around 400V, you are in that 25W per tube area.

[Valvehead]

ahh-- good to know. I guess i assumed an EL34 would not be cathode biased. I will look at it when my bench clears. thanks guys. I still think its a little hot on the bias---the tube emblems are burning off.....but maybe they are just old . Thanks guys

[Mick Bailey]

This amp needs to run hot. I made the mistake of reducing the bias on the first one I saw, to give the tubes an easier life, but got crossover distortion way too easily with only a minor change. The cathode biasing is done with a pair of resistors (they're usually dissimilar values in parallel - 270R & 330R). My advice is to leave them alone - it's very easy to make this amp sound bad.

[Gtr_tech]

If you can run the amp in a dark room while looking at the output tubes and not see the plates develop orange spots on them after a half hour of playing it, I'd say its OK.