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In Reply to: RE: Ok, so how about best use of 27 tubes ???? posted by vinnie2 on July 01, 2015 at 04:01:02
Vinny,Innerstage Trannie and I used it as a input tube of a two stage amp, cap coupled into a UTC A-18 as a splitter trannie, driving grids of P-P 2A3s. I built mine after hearing his amp, in about 1998.
In 1999 I was a guest speaker at a NY Audio Society meeting, where I demoed an improved version of this amp on Norelco 9710Ms. Would do things different in 2015, like, RAISE the 2A3 Rk ohmic value, and... other things. This was my take, on I.T.'s basic circuit, back then. I was "in" to fine tuning grid resistors by ear then.
I still have those A-18s, if anyone needs them.
Jeff Medwin
Edits: 07/01/15Follow Ups:
Ah yes, I remember the grid stopper "debate", none to fondly..
Curious schematic. Why did you leave the cathode resistor of the 2A3s un-bypassed? Are you aware that that can cause distortion if the mu of the 2A3s differ? It was a somewhat common practice in cheap PP amps, but I am surprised that you would use it.
Also, that 7Hy choke in the supply to the 27 has WAY too much DCR ...
Mikey,That was 1996-1998, and I was following Innerstage Trannie in many ways.
I did NOT stay LONG listening with that supply.
Instead, by 1998, I was using two totally separate low DCR power transformers and L1/C1/L2/C2 for each stage. The Ls were the famous ESPEY 3 HY 24 Ohm units, that I introduced Herbie Reichert and JC Morrison to, and which Herbie used in his Flesh and Blood 300B amp.
I THINK the 27's Rk is bypassed Mikey - with a 25 uF non-polar ( ha ha, not today ) and a 0.47 uF film.
Also Mikey, in 1998, I went to EIGHT 5Z3s to rectify the two power trannies, ...'was into low Z DHRs ( directly heated rectifiers) back then. I believe I "blew away" the crowd at the NY Audio Society meeting with my demo on Norelco 9710Ms, everyone there seemd to like it a lot...1999.
Have fun, I certainly am with my new Type 45 SE build these last few weeks. 'Getting better and better sounding as I develop it.
Jeff Medwin
Edits: 07/02/15
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