300B PSE battery bias

[Cyprus Martin]

Does anyone have the details/circuit diagram for converting the 300B PSE to battery bias. I've tried looking through the old WAD BB but can't find anything.
Regards
Martin Emmott

[Greg.]

Hi Martin,

I think Max did it. Search for posts by him.

Best wishes,

Greg

[russell allen]

Mine are converted using batteries from RS. I have a couple of spares somewhere if you want the part number I'll look it up, the details and a circuit diagram are on the old WAD forum. You have to lose the feedback circuit but they sound better that way anyhow. This was far and away the best "bang per buck" upgrade I made to my PSE's

Regards


Russell Allen

[Max N]

Hi
The original thread is here
http://www.worldaudiodesign.com/foru...read.php?t=365

There was a subsequent thread which discussed this and other mods for the 300B PSE, here
http://www.worldaudiodesign.com/foru...read.php?t=414

Also, if you don't use feedback, try increasing C4 to 2.2uF, which gives better bass.

Hope this helps

Max

[Cyprus Martin]

Thanks to everyone who came back on this. I actually converted to the battery bias some time ago but I was asked about the details by a friend but couldn't find the details and didn't want to disturb the 300B's now they are working so well.
Max, with regard to changing C4 any suggestion on what are the best 2.2uF caps to go for.
Best regards to you all from a delightfully sunny Cyprus.
Martin Emmott

[Max N]

You could try Maplin KR80B
(I can't find the ones I used from RS anymore)

I take it you like the battery bias mod? I also tried battery bias in Pre-II (slightly better) and in my DAC valve output stage (worse), but in the 300B PSE it was a big improvement imo.

[Cyprus Martin]

Hi Max
The battert bias mod on the 300B made a major improvement. I also changed the ECC83 to a 6SN7 and did the WAD upgrades (but not the DC heater mod on the 300B's). I'm going to change BR1 and BR2 next and then probably put Black Gates in the power circuit.
I've gone over to the CF for my PRE II but use a Goldpoint attenuator instead of the Alps (again both big improvements).
regards
Martin Emmott
(off to Moscow for 2 weeks on Saturday)

[Cyprus Martin]

That should have been ECC82 (that'swhat comes of typing in the dark!)

[Max N]

Hi Martin. Was the move to 6sn7 for the CF a worthwhile change? I know MJ uses them in his Crystal Palace amp, and I see that Andy Grove has used 5687 for the CF in more recent amps.

[Cyprus Martin]

Hi Max
The 6SN7 replaced the ECC82 in the 300B PSE, not a huge difference unlike the battery bias mod but I have always preferred the 6SN7 to the ECC82, a little more mellow and rounded, like a good wine.
The CF mod on the PRE II was also a major step forward, gone was the hum that had mede me give up using it, now it's crystal clear and with a real bite to it.
I'm away in Moscow for the next two weeks and hopefully when I get back the parts will have arrived to enable me to do the mods on the 6AU6 heater circuit.
All the best
Martin Emmott