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Old 16th March 2006, 11:19 PM   #1
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Default 2 tube questions

A couple questions for the tube gang: I have a number of 6AS5 and 6CU5 tubes on hand. They're evidently electrically interchangeable. Anyone aware of any amp circuits that could utilize these beam power tubes? I'd like to tinker.
Then: there's a couple of guys over on qth.com (ham radio board) searching for some oddball tubes: one guy's looking for 6HU8s..a dual pentode, the other's on the hunt for 6KH8s...a triode/dual power pentode combo. Anyone here able to help?
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Old 16th March 2006, 11:58 PM   #2
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RES shows a price of $37 for the 6HU8/ELL80. $60 is RES' price for the 6KH8/ECLL800.

6AS5 Data Sheet
6CU5 Data Sheet

Those "low" voltage 7 pin mini O/P types might make a reasonable PP amp. Perhaps Hammond 125E O/P trafos would work. Roll the deep bass off at the I/P. Loop NFB is a must in pentode mode to get an acceptable damping factor. Bridge rectifying the O/P of a 1:1 isolation trafo would give you a suitable B+ rail.

Oh yeah, pentodes work best with regulated screen grid B+. I don't know if a VR75 will "strike" on the B+ rail described above. You might have to use Zener SS diodes.
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Old 17th March 2006, 02:33 PM   #3
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Default 2 tube questions

Eli...thanks for the info! Now to start digging throgh my parts tubs.....
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Old 7th April 2010, 05:15 AM   #4
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Default 6as5

I have spent many the hour searching the web for schematics and other arcane tube info, hoping to learn by osmosis rather than work. I recall seeing one screen where someone said that the 6as5 was the worst sounding tube he had ever encountered. I think it was triode strapped.

That hasn't been my experience. I used the Bill Pearl voodoo method to tie the screen to the plate with diodes, electrolytic capacitors and a resistor or two. (There's another thread that dismisses the possibility that the idea can be of any value. Maybe. It sounds good to me.)

The amp sounds great. I use old Japanese full-range efficient speakers, and I can listen to it for hours. (The preamp is even more heretical, using the triode section of a 6x8, which is also generally characterized as useless.)

I think I have a few 6cu5s laying around--if they are essentially the same tube, then I think I will give them a try

Thanks for the post.
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Old 7th April 2010, 08:32 AM   #5
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semiconductor directory by halfin, electron tubes databases, sourcing network here in Belgium:
ELL80 $41
ECLL800 $35

(I'm not affiliated)

Kenneth
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