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RE: Choose: 300b SET or 2a3 PP?

Posted by shane. (A) on May 25, 2012 at 00:09:10

In Reply to: Choose: 300b SET or 2a3 PP? posted by andy evans on May 19, 2012 at 06:26:27:

Andy,

I really think implementation is the key..

I have PP 2A3 the OPT are Onetics and the drive stage is filament biased 01A DC to 71A IT coupled (Onetics Lv2) SE to PP grid.

Also, three stage DC coupled 01A -71A- PSE 2A3 into One Electron UBT.

Both amps are essentially the same in their input/driver which should make comparison more meaningful. In addition the parts count is low; nickel input transformer and filament biased input/driver, no bypass caps on any of the stages, nor any high value resistors. The PSE output stage has merely two 10R in the cathode cct to form a faux CT which then is referenced to the driver B supply. I've not seen simpler.

The main difference between the two amps, is the IT in the PP amp, and of course the operation of the two output stages. (SE v PP). The power supplies for both amps is external, and the same. The primaries of the different output stages also load the tubes equally for the SE and the PP (6k6 for PP and 1k3 for PSE 2A3).

Sure, I'm not using 300B's. But the power output for both the SE an PP stages are the same also. I built them this way to get a more accurate representation of SE v PP.

The output tubes are either Sylvania Bi plate or JJ 2A3-40. Yes, I did run the JJ at 300B like op point and preferred them that way in PP but for some reason not in PSE.

The PSE amp is better in most ways. The loudspeakers are Duntech 90dB 4ohm. I thought PP would have had the edge in this regard, and expect the same differences to be more pronounced with more efficient speakers. PP is wider in its delivery, PSE is much deeper, more organic and natural, more detailed. PP is still nice, but again, the PSE is a better amp to me.


Of course YMMV,
Shane

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