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previous: Stan Bailey Just plopped a couple of SF, s in t... -- 1/25/2000 3:57 AM

Re: Wow, what a difference!

1/26/2000 11:55 AM
lion	Re: Wow, what a difference! Hi Stan! Sorry for the delayed reply – I’ve been very busy and haven’t been able to monitor the Ampage BB for a couple of days. If you’r still interested I’ve put up a schem: http://www.dizz.dk/mosfet2.gif In my amp the PT has no seperat bias winding, so as you can see, I’ve modified the original bias circuit off the PT sec to a 3 branched parallel config: bias-/V- source supply/+ drain supply - as suggested by RG. I originally set out to get +100/-100V for the MOSFETs - in order to be able to replace them with a 12ax7 – in case I got haunted by the solid-state ghosts –but there’s nothing but sweet sweet tube tones from the amp, and I’m very pleased with the result. In the final adjustments I led myself to believe that I could detect (maybee I’m just fooling myself) a slight improvement with a increased drain voltage - >150V (and the outputwaveform looked a little cleaner on my scope too with the volume maxed?) so I settled on the +170V. Thanks once again to all who contributed and made it possible for me to do this mod. Lion

1/26/2000 11:55 AM

lion

Re: Wow, what a difference!

Hi Stan!

Sorry for the delayed reply – I’ve been very busy and haven’t been able to monitor the Ampage BB for a couple
of days.

If you’r still interested I’ve put up a schem: http://www.dizz.dk/mosfet2.gif

In my amp the PT has no seperat bias winding, so as you can see, I’ve modified the original bias circuit off the PT sec to a 3 branched parallel config: bias-/V- source supply/+ drain supply - as suggested by RG.

I originally set out to get +100/-100V for the MOSFETs - in order to be able to replace them with a 12ax7 – in case I got haunted by the solid-state ghosts –but there’s nothing but sweet sweet tube tones from the amp, and I’m very pleased with the result.

In the final adjustments I led myself to believe that I could detect (maybee I’m just fooling myself) a slight improvement with a increased drain voltage - >150V (and the outputwaveform looked a little cleaner on my scope too with the volume maxed?) so I settled on the +170V.

Thanks once again to all who contributed and made it possible for me to do this mod.

Lion

Replies:

NL Hello lion,I wired this up ... -- 1/27/2000 6:55 AM
todd hepler Let me ask the Inevitable question : -- 1/28/2000 4:18 AM