[Penthode]

Last night an electrolytic died in my RCA CTC-5 Whitby shortly after switching it on. I had reformed all the electrolytics and replaced all the paper capacitors when i restored the set in 2012.

The capacitor that died was a Canadian made Mallory on the 25Hz subchassis! The additional subchassis weighs about 35 lbs And contains a massive B supply power transformer, choke and two 80ufd 450v capacitors. The additional filtering was to help minimize the 25 Hz ripple.

The set itself was manufactured in Camden NJ and must have gone by Montreal for the modification. I found that the modification was not well done initially: I found the power lead to the chassis interlock socket was never soldered. It had been like that for over 55 years and there was signs of arcing. Amazing as it must have been bothersome although the set had low hours and I expect the original owners gave up on it.

The Camden capacitors are all Sprague and were very healthy when reformed: the leakage after careful reforming was below 100 uA at full rated voltage. The Mallories were much more leaky at about 1 mA at full voltage. I was tempted to replace them in 2012 but as they did not get warm in operation, I decided to give them a chance. The set subsequently has had a fair bit of use over the last 9 years so I won't complain.

The short took out one of the 5U4 rectifiers and a 15 amp household fuse and nothing else. As you can see the auxillary B supply and the replacement chassis mounted filament transformers are massive and escaped unscathed.

From the photo, the replacement capacitor is in the short can (the old can cut open and restuffed) and it's original companio for testing. After running the set for an hour, it is fine. However I think I will restuff the other Mallory as I have now no trust in it and it may fail in the next 5 to 10 years.