Dove right in! Help with RCA 21-D-8628

Originally Posted by Electronic M

You need AC to test the unknown transformer. The UHF tuner may have a 6V heater winding....You can check by looking at the ID numbers of the tubes in it. On most signal tubes made after 1936 the first digit of the tube ID number is the heater voltage...So a 6AG5 is a 6.3V heater and a 12SN7 is a 12.6V heater.

If you use the UHF tuners transformer to power your mystery transformer pull the tubes out of the tuner and if the tuner has only 1-3 tubes don't run it for more than 30second stints as a source for the mystery transformer. Probably still a good idea to use a 1A fuse in series with the connected winding of the mystery transformer....

The UHF tuner (which I suspect is really what collectors call a UHF converter) probably has a small transformer designed to run the heaters of 1-3 tubes...many 5 tube and higher transformers can take a heater winding short for long enough that you'll notice and switch off, but ones designed for fewer tubes are easier to kill.

The UHF tuner has 4 tubes, three are 6s and one is a rectifier. Would that supply the adequate voltage long enough to test?

I replaced three of the four tubes in the tuner for grins and giggles, I think the old caps are still okayish. Where I live you can't even pickup UHF, and the VHF is weak unless you get the right antenna angle, and that only gets you 3 stations! If you turn the antenna just 10° you lose out on 3 CSI's during primetime. Darn.

As to Kevin, I do not yet have a variac. I'll te-test the transformer leads today and see if I did anything backwards. I could be using the multimeter wrong, though I seem to be getting the hang of it.

Both of the elecgrolytic cans register over half their mfd's (or appear to when the meter auto adjusts) which surprised me.

Something happened to this tv that I still can't explain. What caused the transformer to short out, I suspect as has been pointed out that somewhere between low V rectifier and something caused it. If you left the unit on long enough the tubes began to heat, but no sound or picture. Just lots of smoke.

Also, can I use a homemade short check device? The 250 watt bulb in series with a switch, the transformer, and an outlet? Then measure the outputs?