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In Reply to: Lynn Olsen designs vs. others posted by KurtP on March 11, 2007 at 16:33:40:
I built a 6H30PP interstage 2A3PP with LLs. I liked it but you really want to use the highest quality interstage trannies. After I replaced the LL1660 with a nickel interstage I found the sound was lifeless before. Probably it is more critical than OPT.I stepped into the deep end of (parafeed) SE ... no turning back for the time being.
Follow Ups:
Replacing Lundahl interstage transformer with UTC HA-107 was a big improvement. Permalloy cores are inherently more linear than silicon steel. They may be not the best choice for output transformer due to saturation issue, but for interstage use they are unbeatable.HA-107:
15+15 K primaries
45+45 K secondaries
20-20,000 Hz 3 dB
Pmax 200 mW
No unbalanced DC
Weight about 4 lbThe core in these transformers is supermalloy (or hypermalloy, as UTC called it). It is 80% Ni alloy annealed in hydrogen atmosphere to achieve the highest mu (about 20,000 compared to 10,000 of 45% Ni permalloy and 5,000 of silicon steel). High permeability allows achieving the same inductance with fewer turns, thus decreasing stray inductance and winding capacitance. HA-107 has two layers of shielding, external mu metal and internal copper. Separate windings allow independent biasing of output tubes.
The Amity/Karna designs rely on a shared cathode resistor with a dual triode PP topology. Assuming the triodes are perfectly matched, I will get no DC imbalance.What kind of real world triode-triode matching can I expect (lets assume JJ ECC99 for now), and what will a "no DC imbalance" transformer allow me to operate under?
Or would I be better off with separate cathode resistors, one of which is adjustable?
HA-107 will take 1-2 mA imbalance in the primary. My driver circuit is a pair of 45 with a common cathode resistor. I matched tubes as best as I could, and then compensated for the remaining difference with additional small resistor in one of the cathodes. Due to drift, there could be 0.5 - 1 mA unbalanced current, but I did not notice any deterioration.
With regards to both the Raven and Amity/Karna, what manufacturer and parts would you recommend?
You got an answer. UTC is a great choice, probably the best for PP. LL winds the same coils also on amorphous cores, that would be an other choice. Tribute or AE in Europe are other choices, they use also amorph cores. Japs are utterly expensive.I picked up a very different beast... the EXO173PPS Ni by Mike at Magnequest. You wont have anymore a PP into PP amp as it works with a SE driver ... but as I said I stepped into the SE world.
If I may, I would suggest you to have a look at the Seth schematics on MagneQuest site just to have a different view on PP amps (it comes with a full and detailed tutorial as well)
http://www.magnequest.com/diy_lessard_2a3pp.htm
A similar schematic was used also by SunAudio
http://www.meta-gizmo.com/Tri/RRM/sun.html
and in almost all the Sakuma PP amps. For example this parafeed interstage splitter
http://www10.big.or.jp/~dh/work/8005.html
Don't ask me to explain why I preferred ni cores ... I can't live without now. That's a fact.
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