JCM800 build bias

[fossilshark]

Howdy. it's been about a year since I've been on this forum, and I figure this would be the place for this question. My bandmate "commissioned" me a JCM800 head and it's coming along great (cramming it into a slightly smaller than usual kit chassis that clearly isn't a JCM800) and I just need to know if the negative bias supply on the original 2204 schematic (coming off the plate voltage tap) is you know, more stable than the 1970s standards it was designed by. That being said I dont have a 50v tap on the power transformer for bias so it would be nice.

Also the schematic I'm using I downloaded as a PDF (preamp and power seperate) and seems to be different than the newer looking 2204 lead series schematic that's a single image on el34, what should I use?

Trying to do things as safe as possible since blowing a pair of tubes would set the band budget back $40 and we still need a PA.   

[sluckey]

The 2204 bias circuit shown below is widely used. It is dead simple and very reliable.

Trying to do things as safe as possible since blowing a pair of tubes would set the band budget back $40 and we still need a PA.

Well then, ***DON'T PLUG THE POWER TUBES IN*** until you are certain you have about -40v to -50v on pin 5 of both power tube sockets. Set the bias pot for max negative on pin 5. Now it's safe to plug the output tubes in.

[pdf64]

Consider fitting 1 ohm resistors between the power tube cathodes and 0V; then it's easy and safe(ish) to check their current draw., and so ascertain whether the bias setting is suitable.

[fossilshark]

Awesome, that's the circuit I've been building off. I'll use that thanks