I have a mini 6LU8 amp with the pentodes in pseudo-triode mode. It hits above its miniscule weight. I've been thinking of converting it to Schade feedback mode, with the triode section used to cascode a 2SK117 jfet.
THe link for the original amplifier is here:
https://www.diyaudio.com/forums/tubes-valves/120804-mighty-mite-single-amplifier.html
THe link for the original amplifier is here:
https://www.diyaudio.com/forums/tubes-valves/120804-mighty-mite-single-amplifier.html
Huh! I just looked on Ebay here, and I see them for $5 each.
Are you looking at BangyBang tubes seller maybe? Their listings are like 10x to 20x the price of anyone else's listings. I don't think they are really in the tube business, but I don't get what they are up to. Someone suggested money laundering for South America.
Another tube price shocker seems to be the 10JA5 tubes. I think they have reached extinction. Used to be able to get them from Vacuumtubes.net for $3, but they are out now. Every where else I enquired about them for some quantity I was told the price just went up today to $12.95. I wouldn't recommend building anything with those anymore.
Hello Stenak:
I guess E-Bay is not a good choice for tubes. If that is the best you could come up with. I just check a couple of the tube dealers and the price is less than $10.US. plus shipping.
There are many other very good tubes to choose from. You might even consider a 38he7 with 21v across pin 10/12 for heaters. @smoking-amp has suggested it would dissipate in the range of 15W. Coupled with an interesting drive tube and it should also produce a very nice SE amp.
The exploration is half the fun.
Good luck with your choice.
I guess E-Bay is not a good choice for tubes. If that is the best you could come up with. I just check a couple of the tube dealers and the price is less than $10.US. plus shipping.
There are many other very good tubes to choose from. You might even consider a 38he7 with 21v across pin 10/12 for heaters. @smoking-amp has suggested it would dissipate in the range of 15W. Coupled with an interesting drive tube and it should also produce a very nice SE amp.
The exploration is half the fun.
Good luck with your choice.
Eli's PS looks over complicated for such a simple amplifier.
Here is the simple alternative.
Haven't seen Eii Duttman (or PRR) on DIY for a while. Anybody know what their status is?
Attachments
You seem to have a knack for finding the most expensive tubes on ebay.
I think someone who knows Eli said he was ok, just dealing with family issues, or something like that. No idea about PRR thou.
jeff
As SCD mentioned, the 38HE7 tube is an unexpectedly interesting tube. Probably only found in the US though. Vacuumtubes.net still sells them for $3. Hopefully for a long while yet. Not much demand for them. It has a 10 Watt rated pentode (horizontal deflection) and a big damper diode. On about 80% of the 38HE7 tubes, the two heaters are in series, with 21V for the pentode htr alone, brought out to pins 10 and 12. About 10 Watts of tube heat budget are allocated for the damper htr + diss. The pentode appears to be a trimmed down (plate) version of the 21HB5A tube (18 W pentode). Without the damper section running, the pentode should be good for around 15 Watt Pdiss. If you look at the 38HE7 datasheet, the top 3 plate curves are nearly equally spaced, which is a good indication for linear class AB1 operation. Ie, audio. The triode mode curves for the pentode are pretty decent too, but the screen is only rated for 150V in pentode mode. Should be good for more V in triode mode, but keep the B+ moderate. 38HE7 pics below:
See the 38HE7 DATASHEET for the pentode curves
On the other hand, 6JC5/6JB5 for $5, gives you a 6V6 like tube at 19 Watt Pdiss. Probably more suited to you output xfmrs. And like 1/10 the price of 6V6 tubes now.
,
See the 38HE7 DATASHEET for the pentode curves
On the other hand, 6JC5/6JB5 for $5, gives you a 6V6 like tube at 19 Watt Pdiss. Probably more suited to you output xfmrs. And like 1/10 the price of 6V6 tubes now.
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dynaco 6v6.
What huggygood posted in
What huggygood posted in
- #2
- the url is in the image I loaded.
- radiolamps.ru/articles/pp/tubeamp_95.html
- BTW the soviet 6p6 is plentiful in europe.
- aku-bat.cz/index.php?s=product&id=4812
Just got my drive autoformers form Jack at Electra-Print - I'll have to figure out an appropriate use for them. One circuit he showed utilizing the transformers used a 6J6 with both plates paralleled via 75 ohm resistors, with the transformer driving a 6BX7 dual triode. That schematic is lost to history now that his web site is down.
Back to OP’s thread - @stenak, if you are interested in the Dynaco 6V6 circuit topology, please take a look at this thread. It talks about the “Boffin” amp which is an evolution of the basic 6V6 Dynaco circuit and enhanced by Mona (@Ketje)
https://www.diyaudio.com/community/threads/6v6-pp-ul-bias-point.360543/page-2#post-6359252
https://www.diyaudio.com/community/threads/6v6-pp-ul-bias-point.360543/page-2#post-6359252
Well, I think I'll veer back on topic and post my version of a p-p 6V6 amplifier. It may end up being the stripped-down version using a folded cascode front end and matched output tubes, with a small amount of tweakability to true the bias in.. I just nailed down a a matched quad of Russki 6V6 equivalents on E-pray....