|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
98.180.144.93
In Reply to: RE: Is there any real benifit sonically between class A, AB etc... posted by Tre' on June 26, 2016 at 16:33:14
Hi Tre'
I will have to concede that it may be hard to find an indirectly heated power triode with the beautiful curves of a 300b but I doubt that it has much to do with directly heated vs. indirectly heated. A 12AX7 has some very nice curves. Granted it is not a power triode but it is indirectly heated.
I'm guessing that power triodes were largely being displaced by pentodes and beam tetrodes as indirectly heated tubes were getting more common.
Phil
Follow Ups:
Interestingly the EL 509 and EL 519 tubes when the screens are driven(Berning BA150 and Melos amps)exhibit extremely good triode curves. The Melos amps were rich class AB amps, about 25 watts class A with loop feedback. The Berning was almost pure class B with variable feedback(it sounded best with no feedback). Both companies' amps were excellent sounding.
"A 12AX7 has some very nice curves. Granted it is not a power triode but it is indirectly heated. "
Yup, the 6sn7 at 14ma 200vdc plate is just about as linear as anything gets but none of the indirectly power tubes come close to the DHTs.
Well.......maybe the 6a5. It's build just like a 2a3 with a W filament but in the 6a5 it's a heater with a tiny cathode tube around it.
I think that indirectly heated power tube is just as linear as it's 2a3/6a3/6b4g cousins.
So i guess the answer to the question is, it's in the physical layout of the way that they are made.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Interestingly, the 813 power pentode is VERY linear when strapped as a triode but it is a directly heated pentode...so there is that directly heated thing again.
Perhaps direct heating is more uniform on the filaments and as a result of a greater uniformity of heating the result is greater linearity??
"Perhaps direct heating is more uniform on the filaments and as a result of a greater uniformity of heating the result is greater linearity??"
I understand what you're getting at but.....
The electrons don't go from the cathode/filament to the plate.
They go from the cathode/filament to the electron cloud and then from the cloud to the plate.
So i think that alone means there is uniformity regardless of structure differences but I don't know!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Well, it is not a static system, unless there is no signal applied to the grid, and so I can imagine emission densities higher in areas where the heating is more efficient and uniform and the extraction therefore being smoother and more linear when it is directly heated.
Just trying to think about it mechanistically as if i were an electron being emitted :).
I could see also maybe that a direct heated filament is hotter towards the center of the length of wire and maybe then the electron dispersion is different...there might even be some literature on this somewhere (probably too old to be on the web though). I bet some old East European tube guys have some idea.
OK,
Check out these monsters. I have some of these and some UTC output transformers.
If I can stay on top of the grass long enough, the plan is to make a pair of class A push-pull amps with these tubes.
Phil
Harder to find but the 6337(not 6336) tubes were beautiful, relatively high power triode output tubes also. And they were jus beautiful to look at.
Yeah, those curves aren't bad but still not a match for a 45 or a 2a3.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Nonetheless, the 6C33C can be used to make a VERY good sounding amp. Perhaps the advantage of having far less windings in the output transformer outweighs a bit of non-linearity from the tube itself. Afterall, the output tranny is a big source of non-linearity in many tube amps.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
yeah I recall asking a friend who built PP triode amps how good thee 300B was one day and was surprised when he said he'd give it a B+ saying he preferred the 2A3 a lot.
A big part of the 300B rep I believe came from the Western Electric 300B which was built so well because it was designed to be buried in the ground for long distance amplification and forgotten for 10 years.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: