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12.10.199.11
In Reply to: RE: Harman Kardon TA5000X output transformers posted by Triode_Kingdom on May 06, 2016 at 05:55:42
Time honored and very well proven are the Williamson and Mullard styles. As Mullard style is more forgiving of O/P "iron" weaknesses, I lean in that direction.
An updated version of the H/K Cit 5. should work out very nicely. The "5" used 7581 "finals".
Eli D.
Follow Ups:
Most HK amplifiers (other than Cit II and V) use a different topology than the designs you've mentioned. They employ a Cathodyne phase splitter attached directly to the output stage. In this regard, they're similar to Dynaco. Even then, they differ in that the power amp block uses a triode, rather than a pentode, ahead of the splitter. I much prefer a Cathodyne to be followed with a buffer, but I'm not going to change this when I rebuild the A500. The feedback network is more complex than many, and IME it works extremely well with the HK iron. With NOS 6L6s, I measured 0.4% THD at 20W and less than 0.1% THD at 5W. Those numbers indicate to me the 6L6s are at home in this design, and I'm hoping to do a little better in the final build. My intent is to create an all-octal amp, so the 12AX7 and 12AU7 will be replaced with a 6SL7 and 6SN7 respectively.
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Buy Chinese. Bury freedom.
Go for it!
I made the suggestions, thinking more voltage gain than OEM would be needed.
Just in case, I'm uploading the Cit. 5 schematic and an alternative voltage gain setup. The 12BY7 is going scarce and I think the available stock should be saved for already existing units.
Eli D.
"I made the suggestions, thinking more voltage gain than OEM would be needed."
Funny you should say that, because I thought the same thing. However, with 6L6s in place, I measured 27W output with slightly less than 1/4V RMS input. It was this result that made me realize a 6SL7 could be subbed for the 12AX7 and still have sufficient gain.
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Buy Chinese. Bury freedom.
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