Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: zendragon63 on September 18, 2010, 12:53:34 am
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I got a sack full of tubes given to me recently that maintenence man found in the attic at the church. Most were 6J7's, a couple were 5U4's and this nice pair that may or may not ever has been used. They have 6V6 scribbled on the top of the box and while they look like they could be 6V6's, the numbers do not match to anything I can find. Google gives me a surplus tube site that IDs it as a 'transmitting tube' but that is about it; Franks tube data site yields no match. Any ideas anyone? thanks in advance. Regards.
dennis
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337 is Westinghouse
8255 is October 2, 1955
Dunno why there is a standard tube number but the tube pictured certainly looks like a 6V6.
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Could be the old-style 5881. Or just another 6V6. Is it the same size as 6V6? Or 7591. Which pins are missing? Which pins seem to be the filament pins (check with ohm meter)?
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Those 6j7's might make a nice pentode preamp.
Even if they do have that funny mini cap on top.
Ray
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6J7 does make a nice preamp. I had to make a top cap shield to keep out hum, fabricated from a copper 1/2 inch pipe cap.
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6V6GT will be 1.1875" glass diameter and 2.75" from top of glass to chassis surface. Most 6L6/5881/etc will not be this size.
"All" octals have heater on pins 2 and 7. Apply 5V from a spare recto winding or a wall-wart, expect dim orange glow (here only visible between top of plate and bottom of getter flash). If that seems right, apply 6V through a 1-ohm resistor. AFAIK, the 6V6-types are the only octals to draw 0.45 Amps. With resistor this will read maybe 0.42V.
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Whew, got through the Saturday chores. I was ready to post a response when I saw PRR's--I checked for filament continuity and, sure enough, it was 2 and 7. What the heck I know nothing anyway and I am thinkin 'those big black plates could sound really good', stuck them in a PP 6V6, turned the VVR all the way down and brought it up slowly and-sheesh-they sound pretty good. Very clear, clean and loud more like 6L6 clean though. Idle Ik is 32ma @ 378V so they seem right in the 6V6 ball park. Played them pretty hard for 15 minutes and no problem. So worth every bit I paid for 'em.
In case anyone is interested, that surplus tube site lists this tube at $10 ea and they show an inventory of 1578.
http://www.surplussales.com/Tubes-Sock-Acc/100/TubesListed_100up_5.html
6J7 are certainly sound like candidates for preamp. I need to try it in place of a 6SJ7 I have in my little train amp.
Thanks for the responses guys--I try to be cautious, depending on how little I know and how much potential collateral damage I can cause. Scaredy Cat :grin: Regards.
dennis
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> sure enough, it was 2 and 7. What the heck
That was reckless. "ALL" Octals have heater on 2 and 7. 3A8 (3V filament), 6550 (1.6A heater), 6336 (5A! heater), 50L6 (no harm no foul, but no glow).
There may be an Octal with other heater pinning, but 98% of octal types are 2-7 heat.
Glad it worked for you.
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Well not quite all. 6SN7 or 5Y3 for example.
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That was reckless.
Looking back--oh yeah, no doubt and, if I had toasted the filament windings, I would certainly have felt the sting of impatience. Been known to make more assumptions than I should.
That said, I still appreciated the responses. Regards