Ampeg BA115 Trouble Shooting

[DrGonz78]

Almost forgot to let you all know... The IRFP9140 and IRFP140 mosfets, in this case, are not matching pairs according to the parts department at Loud. The guy I spoke with was really cool and even offered some discounts on the shipping costs. The parts are about twice as expensive than from Digikey. Oh and he recommended a cool site to search for chips.

http://www.findchips.com/

[Bruce / Mission Amps]

Almost forgot to let you all know... The IRFP9140 and IRFP140 mosfets, in this case, are not matching pairs according to the parts department at Loud. The guy I spoke with was really cool and even offered some discounts on the shipping costs. The parts are about twice as expensive than from Digikey. Oh and he recommended a cool site to search for chips.

I used the Mouser parts too... matched or not.
The amp still put out about 90 watts into a dummy load and it cost me like $15.00 repair it, that included the new driver transistors too.
But, I could not really get the bias trim pot to set up where the schem says it should be.... oh well.. it's been out to 3 gigs already and a couple rehearsals.

[DrGonz78]

So I did nearly the same thing Bruce and went with Digikey drivers and mosfets since it was cheaper price to pay.

The amp is now working and that bias trim pot is really sensitive to set the amp to 5mV. I luckily got it set and holding at 6.2mV and decided that is really close enough for me.