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In Reply to: RE: Questions about 6BG6G amp build (schematic) Grommes 216BA posted by Triode_Kingdom on May 25, 2017 at 07:53:50
Thanks for your advice on this, in particular about triode operation. I have built several amps inc 6L6GB/C and mention them below, but certainly don't expect anyone to dig thru all that. :) The plate caps are sort of the whole point of this build. :)
I once made a preamp around a beautiful cast alloy Vol knob from a 1948 EH Scott amp.Seems like another way to treat screen voltage is with a 15H 40mA choke, instead of resistor. Unfortunately, R is high in those chokes.
I could do screen regulation; I have room for OBx type tube regulator, since I'm doing this old-school. They will handle the current but not sure about 250-300V.
Researching screen regulation on this august site shows lots of fights and opinions. Consensus is rare. But I guess that keeps it interesting. :)
Thx
Edits: 05/25/17 05/25/17Follow Ups:
I don't think a screen choke is useful for push-pull. The simple RC approach has proven to work well. If you want to regulate, a series pair of 0A2 or 0D3 will get you to +300V.
OK, I understand the aesthetics you're after. If I were going down that road, I'd consider the 1625/807. A quad of those has a nostalgic look that's hard to beat.
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Buy Chinese. Bury freedom.
That's good advice - i will keep screen connections simple. Probably can convert to Triode later to see what that's like. I don't think I need a ton of power. My only triode amp (my first build) was w/ EL34s.
Funny you should mention 1625 and 807s - I have good quads of each of those. BUT you have to commit to the oddball 5 and 7 pin sockets; can't plug in alternatives.
I believe those numbers are maximums. That's a lot of juice, will try to stay in the moderate zone.
Datasheets indicate that this tube type is rated for 20W maximum anode dissipation. TDSL shows that as well in the abbreviated specifications. However, TDSL shows AB1 operating conditions with 450V at 116mA idle current. That's over 26W per tube. Operating at full power, or 210 mA, pushes that to 47W.
TDSL shows these same operating conditions for the 6L6 and 6L6GC. In fact, the latter is the only one in this series that can be run at those power levels.
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Buy Chinese. Bury freedom.
Yeah, I knew that current draw was crazy high, but I'll have adjustments to each tube, at least that's the plan. I will measure mA at each tube.
OK, sounds like you've got it under control. Have fun with the build!
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Buy Chinese. Bury freedom.
Sorry, I had forgotten that the 6BG6G is the ST bottle. It's also one of the nicer looking tubes. Guess there's not much reason to use the less common sockets, although the 1625/807 do have a higher dissipation rating. Speaking of which, watch out for the limit if you're building a supply over +400V. The 20W rating will be easily exceeded at higher voltages.
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Buy Chinese. Bury freedom.
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