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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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Old 21st April 2015, 11:55 PM   #58
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I was wondering George if you've tried torturing or know anything about the reliability of the Tung-Sol reissue tubes:
www.thetubestore.com - Tung-Sol 7581 (6L6GC) Audio Tubes

I have some old production tubes that would work in my son's Fender but I was wonder what of new production might be the best.

I've read a few good things about them but otherwise don't know much about them.
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Old 22nd April 2015, 05:30 PM   #59
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Originally Posted by tubelab.com View Post
I set out to perform the autopsy, and found that the patient was still alive. I had yanked the power cord to the oscillator by mistake. The amp is still alive even with the exploded cap. There is this messy goo all over the PC board and all of the parts. I changed the cap, wiped up the goo put in some more of the Sylvanias and cranked it up again. OK it works, makes about 2.2 WPC and still sounds good, but this is BORING, and I got a box full of tubes to test.

What's next..... After thinking for a few milliseconds, it became perfectly obvious. I needed to answer the question. You know the question that I always ask. How much power can you get out of this thing. Well, even I know that exploring the upper limits will require gome glowing tubes, but I don't need any more exploding capacitors, and I need some more knobs to turn, so its time for fixed (adjustable) bias. No more resistors in the path to slow down the flow of POWER. Speaking of power, I am going to need some more. So I wired up the big Fluke. Now I can go to 550 volts and 300 mA. The tubes are not going to like this! I jumped the cathode resistor, and connected the bias terminals of the power supply up to the grid resistors.

At first I was running both channels, but I only have one bias knob, so I pulled one tube and decided to wire the remaining tube in UL mode. I put in one of the better looking Sylvanias and cranked it, and cranked it and finally just turned the power supply all the way up.

Thats right a 6V6 with 550 volts of B+, 535 volts across the tube. I decided to ignore the glow and set the bias for the best power and lowest distortion. Would you believe that a 6V6 can put out 10 watts at 3% distortion, 11.6 watts at 5% distortion, and 17.2 watts when driven to maximum power. The bias current was 100 mA. this means a static dissipation of 53 watts, minus the output power! Remember this is a 6V6 in SE! You must know what the tube looks like! As I said before, good Sylvanias are tough tubes.


George, I'd like to have a little of all your knowledge just to be able to make this kind of experiment ...... amazing !!!
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Old 29th April 2015, 07:38 PM   #60
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Quote:
I was wondering George if you've tried torturing or know anything about the reliability of the Tung-Sol reissue tubes:
I haven't tried any, since I tend toward cheap tubes. They are made in the same factory as Sovtek, EH, and Mullard reissues, so I can assume similar quality.

Maybe 6 or 8 years ago I got offered a box full of "previously auditioned" Russian tubes for $10 each. All were Sovtek, or EH branded and had the TubeStore matching stickers on them. Most were matched pairs.

I stuck 4 of the Sovtek EL34's in a Marshall 100 watt amp, and they were still alive when I sold the amp 2 years ago.

I stuck a pair of EH KT88's in my original "Industrial" SSE. That amp runs the tubes hot (and the Hammond power transformer hotter) at 100 mA and 430 volts each. After several years of near daily use, they are still in there, but have lost their cool blue glow.

None of the other tubes have died, but they haven't seen heavy use. I believe the TubeStore screens and matches their tubes to weed out the duds, but I don't know anything about their process.
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