Ampeg BA-115 Bass amp

[Cal57]

Hello I have ampeg ba-115 bass amp that has blown the drivers and outputs and a resistor at r31, I dont have a schematic but looks like one output is irfp9440 and the other is irfp140 with drivers Je350 and je340 dont have any idea on the resistor as its destroyed if these part #'s are correct any suggestion as to where to get them or if there is a sub for these. Thanks in advance......Cal

[Enzo]

IRFP140R and IRFP9140R.

The drivers are MJE340 and MJE350

R31 is 220 ohm as are the other three resistors in series with the drivers. The FET gate resistors are 47 ohm. If the FETs burnt, then the gate resistors are suspect. Change them no matter what.

These parts are generic. The little MJE340,350 are stock Moto (now ON Semi) And if the exact IRFP numbers are not in stock at Mouser, something reasonable could be subbed. Mouser will even usually cross them automatically.

DO NOT USE the NTE stuff. Get real parts.

[jimmyjazz]

My BA-115 blows the power supply fuse on power up.

Nothing looks fried.

Should I pull the fets (Q2, Q5) and ohm 'em out to see if they are blown?

do something else? Test the drivers too (Q1, Q4)?

I have schematics and know my way around tube amps.

thanks for any help or recommendations.

[52 Bill]

I'd suggest checking the output first and then the power supply diodes/bridge.

[jimmyjazz]

Thanks Bill. I'l check them tonight.

[Enzo]

No need to pull them, just see if they check shorted where they sit. If they do, THEN pull them. There is nothing in the circuit that can make a shorted part appear not to be.

[jimmyjazz]

The outputs are blown. Dead short.

Where do you buy these things?

Mouser lists them as OBS, can a sub a IRFP140A for a IRFP140R? IRFP9140PBF for the original IRFP9140R?

Here is a link to the IRFP9140:
(http://www.mouser.com/Search/Product...%252bQYw%3d%3d?

Thanks again for your help.

[Enzo]

Pb is the symbol for lead in the periodic table of elements. When you see PBF after a patr, it means it is "PB Free" - in other words no lead in it, lead free. This satisfies the current ROHS rules for Europe.

The PBF version of the parts drops right in for the older version.

Yes, you can make those subs.

[jimmyjazz]

Thanks again Enzo. the RoHS compliance makes sense. I know a lot about this.

[jimmyjazz]

Just a quick follow up. Replacing the outputs and drivers fixed the amp.

Thanks to all for the help.

[Enzo]

Here is the BA115 schematic, so I can retire my email address.

[mfratus2001]

thanks for schematic!

I just started on a fried BA-115... one resistor was a mystery.

I used IRFP240PBF and the IRFP9240 complement. Got them from Newark.

Thanks again, Enzo.
Mike.