Anniversary amp caps

[amh]

Hi gang.

I'm thinking about recapping a 9442, it's coming up on 20 years old now, and I am not sure about some of the components. The electrolytics are easy, I'm going to replace them with a descent quality cap, such as the Panasonic FM series. Nothing fancy or esoteric. There are however some caps I am not sure about. These would be the small silver can types, axial leads, with clear shrink wrap. Small values in the parts list, and high voltages, 630V typicaly. They do not have a polarization marked on the PCB board like the electreolytics do. Question, are these polypropylene film caps? Do they have a life span like the electrolytics do? The parts list does not specify cap type, just values.

Anything else I should consider while the amp is "up on the rack".

Thanks for advice guys.

[bfish]

I have a few Anniversary amps, but haven't yet felt the need to replace the 'lytics yet, but 20 yrs is about where I draw the line. I'll probably do them all when I have the first failure. Don't let that stop you though, if you have the time and ambition, it's good piece of mind.

Haven't been into one for awhile so I checked the schem. The low values of those 630V caps suggest other than 'lytics, as does the lack of polarity as you noted. Run the label #s through Mouser's or Digikey's parts search for verification of type if you want.

'Lytics are unique in their lifespan and primary failure mode (destructive short). Unless subjected to V or temp beyond ratings, the worst other types usually see is mild value drift.

Before you button it up, run the simple bias and offset adjustments detailed in the manual. Verify correct fusing, and clean as needed. If the thermal compound for the power transistors is dry to the crumbly point, apply new compound (and mica spacers if you have them).

[amh]

Thanks for the tips bfish. When I get home tonight I'll try one of the parts referencers you mentioned. Never dawned on me to verify correct fuses, I will do that. Guess I ASSumed they were right

I have several of these amps as well, and I do occasionally check bias and offset. These are nice, solid amps, just want to keep them fresh and purring along.

Thanks again!

[bfish]

You're welcome.

Yeah, fuses do little good if they're wrong. After finding lots of 15-20A AGC car fuses and the occasional blown one wrapped in cigarette pack foil, I always check. Having bought a huge asst at a TV shop auction years ago, I usually even zip tie or tape a spare somewhere handy.