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What voltages for Ampeg R-12-R?

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7/7/2000 3:20 PM

What voltages for Ampeg R-12-R?

Can anyone help me?? I've built the circuit for this beast as found on Joe Piazza's page, and The voltages I'm measuring seem very high (about 450V on the 6V6 plates) I'm measuring with only the rectifier tube in place. (Is this wrong?) The voltages don't agree with those on the voltage chart in Tom Mitchell's book. Has anyone else built one of these, and if so what tranny is suggested? I'm also finding almost no voltage drop from one B+ node to the next. This one has me stumped. Thanks in advance!

Keith

7/7/2000 4:24 PM
Steve M.	Keith, I believe you have to measure the voltages with the tubes in the circuit. With no tubes, there is no current draw, hence the high voltage. When the tubes are in the circuit, they draw current so the voltage goes down. Steve

7/7/2000 7:08 PM
Keith	Thanks, Steve, that was one of my suspicions, but I'm afraid of subjecting my few 6SL7s and 6SN7s to these high voltages. I guess I'll break out the variac... Thanks again! Keith

7/7/2000 11:32 PM

Keith,

I'm afraid of subjecting my few 6SL7s and 6SN7s to these high voltages.

That's kinda what I thought, I'm always afraid to put good tubes into a new/untested circuit I've built. I usually try to keep a few used tubes around so I can put them into the circuit without worrying. Do you have hamfests in your area? One way to get good used tubes really cheap is to go to them, just a suggestion. Also I keep a few Russian tubes around for just such a reason.

Regards,

Steve

7/8/2000 1:00 AM

Keith,
That's about typical for Ampegs. I have an R-12-R that is factory with 7591's that has 495Volts DC on the plates from the factory. You need to measure the voltages with all of the tubes installed because the voltage will be lower with them all drawing current. Find an NOS 5Y3 because the new ones produce higher voltages. Also you could buy some Sovtek 6SL7 and 6SN7 tubes for 5 bucks a piece and save your NOS ones till you get the bugs out. BTW I bought some NOS Sylvania 6SL7 and 6SN7's from a Radio Shack store(they have to order them from their warehouse) for $6.00 per tube recently.

Peter S

7/9/2000 11:31 PM
Keith	Thanks for the heads-up. Actually I have a fairly good supply of 6s*7's, but I gaurd them jealously, since they're all NOS. I bought 3 of each type for $2 each at the Indiana PA guitar flea market in May. Plus I have others that came from yard sales, etc. Again thanks for the info! Regards, Keith

7/11/2000 12:22 PM

It's alive! (and nothing blew up)

I took your sage advice and everything's copacetic. voltages are tamed down, and it's a really low-noise machine. Just a bit of tweaking concerning some distortion at high volumes. Also the reverb send isn't working (The return does work, however). Overall, a really sweet tone, so far. I want to thank everyone here for the fruits of your experience. I'll be sure to share the wealth freely with others. What a great place!!
Regards,

Keith

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