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I just traded the crappy Marshall 4210 I had posted about a while back for a Silverface Pro Reverb. The sticker on the inside says it's the AA165 circuit, but I thought this was a blackface circuit. I know that's it's at least early 70's by a sticker showing it was serviced in 72. But it doesn't have the silver trim around the grill cloth, so I didn't think it could be one of the real early silverfaces. But that said, the stamp on the chassis dates it to 1968. I'm confused.....
Also, this is the first of these I've had opened up, and I was measuring voltages and noticed that the screen is basically at the same voltage as the plate (even a touch above on occasion). Should I step up the 470 ohm resistors to get a little voltage drop? I have a set of RCA blackplates to go in it, and even though they can supposedly take the abuse, I'd like to make sure that it's safe to run that way. Usually on every amp I work on the screen voltage is a bit below the plate voltage, and I thought this was necessary. Insight?
Also, anyone familiar with this circuit could fill me in on typical issues to be addressed would be great...Thanks....
Also, this is the first of these I've had opened up, and I was measuring voltages and noticed that the screen is basically at the same voltage as the plate (even a touch above on occasion). Should I step up the 470 ohm resistors to get a little voltage drop? I have a set of RCA blackplates to go in it, and even though they can supposedly take the abuse, I'd like to make sure that it's safe to run that way. Usually on every amp I work on the screen voltage is a bit below the plate voltage, and I thought this was necessary. Insight?
Also, anyone familiar with this circuit could fill me in on typical issues to be addressed would be great...Thanks....