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1821 tube full wave rectifiers replacements & tolerances (Philips 747a radio)

Some time ago I bought a Philips 747a which I knew was missing the rectifier(1821).
The rest of the components looked to be present & as the cabinet & general internal aspect was in good condition I thought it worth trying to get up & running again. However in looking for a direct replacement I found a couple of suggestions for suitable alternatives for the 1821 which got me wondering. If a direct replacement with an identical spec. isn't available what are the acceptable differances that can be safely allowed if one cannot get the originally specified part? What are the rules for determining any allowances? 
I think I will be lucky as there sems to be a few 1821's advertised, but a couple of them seem a little expensive. The only thing I am aprehensive about is buying one that says "tested" but dosent say if the test revealed it was a dud or not so any advice on a reputable source would be appreciated.
Many thanks.

lapatnet's picture


I have this Philips radio: Philips 456A Prelude  (
The rectifier type AZ1. I think if your set have individual heat coil for the rectifier can use the AZ1 valve. Make a socket converter.


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