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6v6 question

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12/13/1999 9:30 AM

6v6 question

It was suggested awhile back that I could put a 5R4 in my Bandmaster Reverb to drop the B+ and run 6V6's in it. I have a friend that had some 6V6's that he had just taken out of his DR and he also had a 5R4 so I decided to try it and see if I liked it. With 6L6WGB's biased at 40ma the B+ was 440. When I stuck the 5R4 in and rebiased to 40ma I got 425v on the plates. So put the 6v6's in and biased them around 25ma and got 437v on the plates. At 30ma I get around 425v on the plates. All bias readings are taken with the cathode resistor method so the ma readings are off by a couple of ma. These are GT6V6HD's so I assume they are Russian tubes and are not supposed to be very good with high plate voltages, however the Deluxe Reverb they came out of is at 450v on the plates with the tubes biased at 23ma. So here is my questions, am I risking my amp (he doesn't care about the tubes, he just put in some RCA's), and which is worse the higher plate voltage at 25ma or the higher disipation at 30ma? At 25ma and 437v I'm at about 10.92W but at 30ma and 425v I'm at 12.75W which seems too high but the plates aren't red. 70% of max dissipation would be 9.8w. If I were to like this set up and it would work, I would get some NOS 6V6's. Anyway I've never used 6V6's before and am clueless so any help would be appreciated. Can I try it out at practice tonight or should I put the 6L6's back in and not even try it?
Thanks,
Blues

12/13/1999 11:00 AM
Andrew	Hmmm...IIRC, the GT6V6HD IS NOT a 6V6 type, really. Just something that GT badged that way. If you get some good NOS 6V6's, or the new 6V6EH's, they whould be fine at the voltages you're seeing (the 25ma/437V combination looks about right to me.) Good luck. Andrew

12/13/1999 2:13 PM
steve m	Andrew is right, the 6V6HD was actually the Russian designation 6P3S (or 6[pi]3C in cyrillic) which is actually a 6L6-family tube, IIRC. Steve

12/13/1999 6:33 PM
John Stokes	Blues, the previous posters have answered your question as to what the GT6V6HD really is. You can run them at higher currents than a real 6V6. If you want to drop those voltages even more, try a 5Y3 rectifier. If you want to use real 6V6s, go with NOS. The 6V6EH is kinda bright and gritty sounding. If that's what you like, fine, but be advised. NOS 6V6s are WAY smoother than the EH.

12/13/1999 8:26 PM
Bill	I've been following this and am wondering, if the GT6V6HD is really a 6L6 type, what is the heater draw?

12/13/1999 10:17 PM

Yo Bill, since the GT6V6HD is indeed a 6L6 family tube, I would guess that the heater current is on the order of 0.9 amps, just like it's brothers.

Pittman did this because at the time, there simply was not a usable (reliable in a DR) 6V6 in production. IMO they should have been more open in their advertising to tell you what the thing *really* was. Water under the bridge at this point. I don't think GT sells the "HD" any longer, and there are reliable 6V6s made today, along with a good supply of NOS from MIL surplus.

12/18/1999 2:28 PM

Hi John,
I recently bought a "supposedly stock" 68 princeton reverb thru the net. Turns out it has a diode rectifier, different pwr xfrmr, and GT6V6HD tubes. Out of curiosity I searched some groove tube sites and found at least one that states that this tube is a 7408. According to the RCA tube book, the 7408 is used in high quality audio circuits and has a filament current of .45 amps.
Do you know if the 7408/gt6v6hd is the same tube, ie can be used interchangeabley? How can I find out for sure? How can I check the actual filament current draw. Thanx Dom

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