A year ago I bought a rather rough looking Drake L4B at a hamfest. It was without PS but had 2 3-500 tubes with globes. It seemed relatively intact and unmolested except for some rust on the cabinet from sitting in a humid midwest garage for a number of years. I gave 2 Benjamins for it. I thought the tubes were at least worth it. I had planned to remove the tank and use it for an AM transmitter.
Well I just could not do it. I did not want to tear it apart. I had the tubes tested in a known good amp and found out one is just fine and one is gassy. So not a good of a find as I thought -
The power supplies for these are hard to find and expensive when you do find one. I could easily drop 4 Benjamins or more. So it sat.
This spring I started helping a guy make some PCBs. He said he could take that amp and get it working well with a PS he had. So I shipped it to him and he fixed it up nice! New paint, grounded grids, soft key upgrade, etc. Ran full power with his tubes.
So - what to do about a PS...
See attached. I am taking a Antek 8T650 and a Harbach doubler board and making a power supply to run the 3-500 at 3500V. Hammond makes a enclosure that looks almost identical to the L4-PS enclosure. I think this will work FB with my single tube. Perhaps it may even have enough current to run two if I decide to drop more Benjamins on one. Transformer is a 800VA unit that makes .62A on the secondary. Pretty close to the OEM supply. I think it will drive one tube just fine at 3500v @ 400ma.
I will let you guys know when I fire it up.
On edit - running Duncan's amp PS program, using the actual winding resistance of the transformer, I think I will be ok. The output voltage is estimated at 2800V at 560ma with a 5K ohm load. Running the load as constant current with steps of 400ma and 800ma, it will make 3200V@400ma and will do 2800V@700ma. I think it will sag if I drive it to full power with 2 tubes. With 1 tube this might just work FB!
John