bjt

[acebaker]

I'm looking for a replacement for Vishay/Siliconix smw20p10 and smw45n10 has anybody found them and repaired an old Orion Cobalt amp with them, Thanks.

 

[Perry Babin]

Those are FETs, not BJTs.

I don't have a known good sub.

 

[twilliar]

in the 1994 Siliconix, the smw20p10 is crossed to the IRFP9140 and the smw45n10 is crossed to the IRFP150
Both can be found through Mouser

 

[acebaker]

Bjt

Thanks Perry. I just figured because it was an old amp they were BJT's. Thanks Twilliar for that info. I found someone who has these but I figure something newer would be better and they want a lot of pesos for them. While i'm here how do you guys feel about using Higher UF and slightly lower voltage Pwr supply only caps on a PPI Art A200? its got 4 caps, all 85c 1000uf 50v

 

[Perry Babin]

Unless the PPI engineers were completely incompetent and didn't use enough capacitance, more will do nothing.

 

[twilliar]

Maybe a higher temp capacitor to allow more room for temperature derating? But then again it goes back to the engineers.

 

[acebaker]

caps

Thanks for that guys. I asked because another tinkerer said using caps rated at higher voltages increased the ESR. He used lower voltage caps on the PS supply of an A400 than came with it. With only 2 PS caps and two Output theres not many options here. At least its a lot easier than re-capping a later powerclass amp with its bazillion caps.

 

[Perry Babin]

A higher voltage rating typically lowers the ESR. That can be good where there is high ripple current but that's typically only on the primary side and not generally an issue (engineers used what was needed). Where it is a problem (like on some of the early Rockford amps - BBQ pit style era?) you will repeatedly see all of the primary filter caps blown. There, you will see that Rockford used 63v caps where 16v caps would have been good enough if ripple current wasn't an issue.

Unless you have a real reason to change the part from what the engineer thought was needed, use the same value (higher voltage doesn't hurt but isn't likely needed). They are rarely wrong.

 

[acebaker]

caps

Thanks Perry just looking for ways to improve things if I have to change them anyway. What about the temp rating? It came with 85 deg but would 105 be better?

 

[Perry Babin]

Some amplifiers are tough on primary side caps and 105C caps are sometimes used there. On the secondary side, 105C caps are rarely any better.If 85C caps fail on the secondary side, there is likely another problem (like when drivers fail in class D amps).