Tube DIY Asylum

Right , Steve. Here are a few additional considerations:

97.115.102.119

This Post Has Been Edited by the Author

In Reply to: RE: Almost a Leak 20 posted by SteveBrown on May 26, 2009 at 12:47:21

You have it figured out: the amp design is strongly influenced by the classic Leak Stereo-20 and the Mullard 5-10. I did extensive A/B listening tests with a number of various circuit configurations using the P-P EL84 (both ultralinear, and T-C) before finally arriving at this configuration.
Since this amp is triode-mode only, I have chosen the Mullard specified lower current specs for class-A operation of a triode-connected EL84: 24/25mA per tube. This way the EL84s are operating FAR below plate dissipations ratings, and so last a long-long time while also sounding just great. I advise against using the higher resting currents associated with ultralinear operation as it's totally unecessary with triode operation, and IMO, does not sound as good.
Also: A 12AT7 is a "drop-in" replacement for the 12AX7 invertor in this circuit. It only draws just a tiny bit more current, and so no componet values need changing. I personally use 12AT7 invertor tubes in my unit these days.
Also: I know the circuit, as shown, has much more sensitivity than really needed. Nonetheless, there is a good harmonic complementarity between the 12AU7 input stage and the rest of the circuit, and deleting it will unfortunately diminish some of the sense of presence, and the amp will then sound a little less open. Your might as well try it both ways, and see what you think for yourself.
Also: On the Triode Electronics "Dyna-Clone" Z-565 OPTs: These things are real "detail" monsters, and reproduce a very good sense of speed and openness too. IMO, They are a real bargain, and happen to actually be manufactured in the U.S.A. I did experiment with the less costly Hammond units for this application --decent in some ways, but the Triode-Electronics units bested them in every way I could discern by a considerable margin.Yes, there are more exotic and expensive P-P EL84 OPTs out there, but likely on a continuum of rapidly diminishing returns beyond the excellent and affordable Dyna-Clone Z-565s.
On the little 150-Henry Hammond choke: Well worth the $10 cost, as it provides great LF PS isolation for the input stage which you will immediately hear.
enjoy!
-T.M.

Edits: 05/26/09 05/26/09 05/29/09 05/29/09

Follow Ups:

RE: Right , Steve. Here are a few additional considerations: - SteveBrown 16:06:35 05/26/09 (4)
- Very interesting! BTW: I'd be sure to ... - Thom_M 16:28:33 05/26/09 (3)
  - RE: Very interesting! BTW: I'd be sure to ... - SteveBrown 05:10:47 05/27/09 (2)
    - RE: Very interesting! BTW: I'd be sure to ... - SteveBrown 06:12:21 05/27/09 (1)
      - Steve, Interesting results. Question: what is the value of your .... - Thom_M 10:02:56 05/27/09 (0)