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Old 17th June 2008, 01:03 AM   #51
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Quote:
Originally posted by vinylkid58
BTW, AES wants $1.00 each to select specific brands. I hope the GTB's are as robust as the GA's, cause that's what I'm looking for.
Here's what I've tried so far:

6BQ6GTA (Sylvania black plates) -- Run these with a cathode current of 55mA, and they red plate obviously. You can see the glow under normal lighting.

6BQ6GTB (Sylvania black plates -- control grid radiator wings) -- No glow with the cathode current as high as 70mA when viewing in the dark.

6BQ6GTB (RCA Grey plates -- no grid wings, slightly taller plate structure) -- Run at 70mA in the dark, these show a trace of colour. No glow when operated at 55mA.

6BQ6GTB (Realistic Lifetime -- factory seconds of unknown origin) -- Same as the RCA grey plates.
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Old 17th June 2008, 01:55 AM   #52
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Quote:
Originally posted by Miles Prower

6BQ6GTB (Sylvania black plates -- control grid radiator wings) -- No glow with the cathode current as high as 70mA when viewing in the dark.

6BQ6GTB (RCA Grey plates -- no grid wings, slightly taller plate structure) -- Run at 70mA in the dark, these show a trace of colour. No glow when operated at 55mA.
What sort of plate voltages are we talking about here, more than 350V?

Not sure I'm lucky enough to get Sylvania black plates, but I'll ask anyway (you never now). There are a few Westinghouse GTB's available locally, not as cheap, but no shipping cost.

Thanks,
Jeff
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Old 17th June 2008, 01:59 AM   #53
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^^^^

Vpp= 350Vdc
Vsgsg= 150Vdc
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Old 3rd July 2008, 04:30 AM   #54
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Well, inspired by this thread, I took advantage of a sale at AES and grabbed a couple dozen 6BQ6s at just under a buck each- all are RCA, GTB flavor. They look kinda small next to some of the beasties I've been playing with lately. I also took the opportunity to nail down some more 6LR8s, one of my favorite tubes of the moment. The 6BQ6s will wait around for a while until I figure out an appropriately nefarious use for them. Projects in the works:

1) 6CD6GA screen drive SE with Hammond 125ESE output iron - This was my first-ever tube amp, but got stalled on the bench while I worked on other stuff. The finishing concept is quite different from the citcuit I started... The monster is sitting at my job waiting for a couple of ground wires, then I'll fire it up.

2) JFET-6LR8 hybrid push-pull ultralinear - stalled on the bench waiting for me to match the input JFETs and buy the output iron - probably Hammond 1620.

3) 6LR8 triode-connected SE using Hammond 125CSE output iron - waiting for me to do the rest of the cabinet work (holes for jacks and such, and some crackle paint). I found out the hard way that winter is not the best time for crackle paint.
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Old 3rd July 2008, 05:41 PM   #55
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Quote:
I also took the opportunity to nail down some more 6LR8s, one of my favorite tubes of the moment.
So did I, but there were only a few left. Too many people are reading this! I have been using 6LU8's but the 6LR8 is the same tube with a few less pins on the bottom. I also have a single tube "spud" amp, haven't finished optimizing it yet.

I got some more of those $0.98 6BQ6's. I have some P-P experiments in mind.

Quote:
Better get 'em now while they're still cheap because they ain't stayin' cheap.
They said that they have "a lot" and they aren't selling. Stan told me the same thing.
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Old 3rd July 2008, 06:53 PM   #56
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Quote:
Originally posted by tubelab.com
They said that they have "a lot" and they aren't selling. Stan told me the same thing.
I'm dumb enough to buy just about anything for a dollar, but I haven't grabbed any of the 6BQ6. Yet. I guess I need to know there is some easy place to plug them in before I'll jump.
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Old 3rd July 2008, 09:19 PM   #57
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I guess I need to know there is some easy place to plug them in before I'll jump.
I usually tell people to be prepared to experiment whenever you wander from the beaten path. You won't find too many schematics for unusual tubes, and you certainly won't find any commercial equipment to just plug and play. If and when schematics for these, or any other uncommon tubes show up, people will start buying them, and the prices will go up.

Miles' schematic looks like a winner, but you would still have to build it. I have successfully made them play in a Simple SE, but they were operating above the published maximum ratings. I got some coming, but I have no way of knowing if I will ever find a realistic operating point for SE use, or when that may happen. I got them for eventual P-P experiments.

They also have some other uncommon sweep tubes for small money, but I resisted the temptation. I have far too many tubes already. The 6GV5 for $1.80 looked good too, and don't forget my old favorite the 6AV5GA for $3.75.
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