Keepin' it vintage (blackface Princeton Reverb)

[glebert]

I recently got a 66 Princeton Reverb project. Chassis only, looks like it sat in a barn for 30 years. All parts look original except a poor 3 wire conversion that needs to be redone. I don't have extensive experience with really good vintage amps so could use advice in proceeding.

So far the only thing I've done is bring it up partway on the variac with a LBL (no tubes installed) to see if the PT was kicking AC voltages, which seemed good. I was thinking I should take some time and try to reform the caps to the extent possible. I didn't know if I need to reform each individually or I can do a bit of "all at once." If doing all I was thinking it would make sense to use a solid state rectifier temporarily (on variac and LBL) so that I could get low and controlled DC voltages. I think (but could be wrong) that the tube rectifier doesn't "turn on" until the voltages are significant.

Also, the 18k dropping resistors need to be replaced, one is missing and one is broken. Seems the original were carbon comp but I noticed that on Rob Robinette's site he shows them as metal oxide. Is that considered a necessary safety update? Don't even know if I could get that value/size in carbon comp.

Will disconnect death cap that is still in place. Wires from convenience outlet to power switch look discolored, like they got pretty hot, but ohm out OK. Should those be replaced?

Thanks in advance for any advice.
Greg

[The Dude]

My thoughts, in no particular order:

1) It's a 50+ year old amp. Just recap it.
2) I don't see any reason to test with a SS rectifier if you are on a LBL.
3) Metal oxide or carbon comp? I wouldn't spend a second worrying about which. They are not in the audio path. Either would be fine.
4) Yes, do remove death cap and add grounded AC cord.
5) If the wires to the convenience outlet are burnt and appear to be unsafe, replace them. If they are just slightly discolored, I wouldn't worry about it.

In general, make it work, make it safe, make it reliable. That's my $.02.

[Chuck H]

Well the way you paint the picture I think the whole amp is toast. Not worth the effort. But I need a project right now so I'll give you fifty bucks plus shipping... As a favor.






What Dude said.

[gui_tarzan]

There are so few parts in there replace the caps and obviously bad parts. Make it safe. Enjoy it!

[g1]

Agree that if you want to reform, you should ideally use SS rectifier. Very easy to cobble together a plug in type from a bad old tube and some diodes. Then you will always have one for test/troubleshooting purposes in other amps.

[Helmholtz]

Reforming works best with full supply voltage and current limiting.
I've had good success with using a low wattage (40W max) bulb limiter in front of the amp.
Bulb limiter limits current and lamp brightness shows progress.