6V6 Screen Voltage in 5E1 Champ

[WesFanMan]

I'm new to amp design and understand the basics but I'm stumped by something. I've got a Fender Champ 5E1 that I'm working on and looking at the schematic the Screen Voltage shows to be 305v. When I look at the data sheets for the GE 6V6 which is in the amp the max Vscreen they recommend is 250v. When I put a meter on it its close to 320v (I get why on that). Is 305v-320v operation OK for the tube?

Thanks.

[Chuck H]

It's fine. Champs have been running that way for many decades. Many early SF era Champs have considerably higher plate and screen voltages than the max data spec.

One thing you should change about the screen circuit is to add an independent screen grid resistor. The 5e1 doesn't include one. These amps weren't designed for overdrive but that's how most players use them. The lack of a screen grid resistor allows too low an impedance through the screen circuit compared to the plate circuit and this will cause over dissipation of the screen when the amp is clipping. Adding a screen grid resistor will only drop a few volts, but it will actually improve the overdrive tone and help protect the screen from excessive current. 1k is usually suggested but you can go to something like 2.2k for extra margin and I would suggest that. Use a 3W metal oxide or wire wound resistor.

[Old Tele man]

That data sheet 250V screen voltage was a "typical" industry-standardized (for the times) "test" voltage...it was NOT the tubes maximum permitted/recommended screen voltage.

[mort]

I recently built an amp with about 500v to the plates and slightly less to the screens of 6v6's. It was a straight copy of a well respected amp. Seems that it's liable to be rough on tubes but it works, so far hasn't failed and sounds incredible.