Another RCA CT-100 discovery B8001599

[ARC Tech-109]

Personally I'd rather stay true to the original design despite the 56 watts of heat given the rarety of replacement parts in the chain. An open resistor is far cheaper than a smoked transformer or buckled plate when a redesign goes haywire. Just my two sense

[dtvmcdonald]

In my CT-100 I stared at the low voltage cage for days before deciding what to do.
I love the look of those huge orange selenium rectifiers.

But I also noted that the chassis mount can electrolytics were soldered down.
I decided that unsoldering all of them would be dangerous. Cutting them
all off near the base to restuff would be difficult and risky too.

So I decided to rebuild the whole B+ power supply with modern caps, 5 watt
silicon diodes, several fuses in various places, and large old-style Ohmite series 210
tapped (adjustable) resistors to drop voltages. In my
case the original ballast was OK and was left in series with the new Ohmites.

It put all those on an epoxy circuit board and mounted it in the cage.
I used the usual chassis clips to space the resistors at various distances from the board.

I set the line voltage with a Sola regulator transformer and a Variac ( permanently
mounted ... I inherited about 50 Variacs from a scrapped chem teaching lab)
so the filaments were exactly 6.3 and then adjusted the resistors so that the various
B+ voltages were exactly as Sams specified.

The fuses saved the 15GP22 from its first two arcs, as it got gassier and
gassier. But the third one, while it did blow the fuse, was fatal.

[Penthode]

Originally Posted by dtvmcdonald

In my CT-100 I stared at the low voltage cage for days before deciding what to do.
I love the look of those huge orange selenium rectifiers.

But I also noted that the chassis mount can electrolytics were soldered down.
I decided that unsoldering all of them would be dangerous. Cutting them
all off near the base to restuff would be difficult and risky too.

So I decided to rebuild the whole B+ power supply with modern caps, 5 watt
silicon diodes, several fuses in various places, and large old-style Ohmite series 210
tapped (adjustable) resistors to drop voltages. In my
case the original ballast was OK and was left in series with the new Ohmites.

It put all those on an epoxy circuit board and mounted it in the cage.
I used the usual chassis clips to space the resistors at various distances from the board.

I set the line voltage with a Sola regulator transformer and a Variac ( permanently
mounted ... I inherited about 50 Variacs from a scrapped chem teaching lab)
so the filaments were exactly 6.3 and then adjusted the resistors so that the various
B+ voltages were exactly as Sams specified.

The fuses saved the 15GP22 from its first two arcs, as it got gassier and
gassier. But the third one, while it did blow the fuse, was fatal.

I have stared at this set's power supply and haven't decided anything yet. I would like to keep it original especially if the selenium rectifier are good. I have generally had no problem with the seleniums unless there was a B plus short. But the fuses are there for protection.

I was thinking of fitting a 50W wirewound resistor in the ballast tube. But 41watts? I wonder if the resistor would survive? Maybe remove the seleniums and use the space to mount some old style porcelain 100w Ohmites?