[Penthode]

I had a chance to work on the CTC5 today. I am methodically going through the chassis. I traced the 25Hz power supply and this is what I found.

The main chassis transformer was exchanged for a filament transformer only. The box on the chassis is indeed a transformer with 3 secondary windings: two for the 6.3v strings and 5v for the rectifiers. Note the Montreal factory substituted the unique Canadian Robertson head screws to hold the main chassis transformer.

The auxillary chassis has a whopping 20 pound transformer for the B supply only. The auxillary chassis also has a big filter choke and a pair of 80mfd 450v electrolytics which parallel with the 80mfd filters on the main chassis.

The 25Hz transformer will run cool at 60Hz and the extra filtering should make the B supply really clean.

There is evidence of the history of the set's manufacture. The date codes on the main chassis run from the 20th week of 1956 through to the 39th (the latest I could find on a component). The auxillary chassis electrolytics are dated December 1956 so the set's delivery was probably early 1957.

I was amused by the somewhat sloppy modification in one regard: some of the added connections were not soldered! The wire that attached to the rear socket for the primary of the B supply transformer was not soldered as was the B transformer lead that attached to the 5U4 rectifier plates. The connection to the 5U4 actually is burnt from arcing. I suspect the previous owner must have found the set unreliable hence it appears it was not used much. All of the receiving tubes, including the 6CB5 Horizontal Output and the 5U4 rectifiers appear original.