2 tube questions

electronjohn · 16th March 2006, 10:19 PM

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?

Eli Duttman · 16th March 2006, 10:58 PM

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.

electronjohn · 17th March 2006, 01:33 PM

Eli...thanks for the info! Now to start digging throgh my parts tubs.....

briansdad · 7th April 2010, 04:15 AM

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.

kavermei · 7th April 2010, 07:32 AM

semiconductor directory by halfin, electron tubes databases, sourcing network here in Belgium:
ELL80 $41
ECLL800 $35

(I'm not affiliated)

Kenneth

16th March 2006, 10:19 PM	#1
electronjohn diyAudio Member Join Date: Jan 2006 Location: minnesota	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?

16th March 2006, 10:58 PM	#2
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	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. __________________ Eli D.

17th March 2006, 01:33 PM	#3
electronjohn diyAudio Member Join Date: Jan 2006 Location: minnesota	2 tube questions Eli...thanks for the info! Now to start digging throgh my parts tubs.....

7th April 2010, 04:15 AM	#4
briansdad diyAudio Member Join Date: Oct 2004	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.

7th April 2010, 07:32 AM	#5
kavermei diyAudio Member Join Date: Jan 2005 Location: Lokeren, Belgium	semiconductor directory by halfin, electron tubes databases, sourcing network here in Belgium: ELL80 $41 ECLL800 $35 (I'm not affiliated) Kenneth __________________ Never send a human to do a machine's job. --Agent Smith


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