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RE: PSE 2a3 operating points? 320V @45mA 5K Fine

Hi Andy,

320 VDC P-K at .045A into 5K is not a great compromise op point IMHO.

First of all, its is PSE so you need to drop output trannie Z in half, to 2.5 K or as low as 1.25 K for two tubes in parallel. One Electron makes a UBT-1 which is 1.6 K as I recall, not too bad, not too costly.

Also, the previously suggested op point dissipates 14.4 Watts across the plate, so tubes will last only about 2,000 hours, and degrade continuously.

I would keep the current about 41 to 43 mA. (-49 to -50 VDC self bias) and reduce the B+ to about 245 to 250 VDC P-K, and the tubes will sound less STRESSED THERMALLY. With 10.5 Watts plate dissipation, tubes could last 10,000 hours, five times longer, and sound better.

If you need a matched quad of used 6B4Gs, I have them.

My very first from-scratch, self-designed SE amp WAS a PSE 2A3 using UBT-1 outputs and a 5687 front end, a two stage amp. Forum Member "Electron" auditioned it, a 'long long time ago.

I would think you can do the Rks either way, combined or separate.

I probably would tend to do them separate and use TWO Mills paralleled Rs, closely matched in Ohmic value, for each Rk. This gives you two wire paths, and hopefully a short return path to star ground.

Place your star ground point NEAR the 2A3 cathodes, and use the body and wiring of the Rks to bridge the span between the Ef XFR and star ground. Use the center tap wire of the 2.5 VCT trannie, KEEP IT SHORT, and no hum pot. You should shoot for film caps across the Rks, multiple bypassed as per Marzio and Jelasi in the old Sound Practices article on Building a Single Triode DC Amp. Short simple return paths to ground for DHTs sound superior.

Your amps I know will not be DC coupled, but the Italian boys' Rk bypassing technique, written in 1994, is on the right track.

Have fun.

Jeff Medwin



Edits: 05/26/12 05/26/12 05/27/12

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  • RE: PSE 2a3 operating points? 320V @45mA 5K Fine - drlowmu 17:14:46 05/26/12 (0)

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