Classic Hifi Care

I found this, and, it contains tubes I have never heard of.

https://detroit.craigslist.org/okl/ele/ ... 70744.html

Bill

That radio does have a different tube complement. The 18-volt tubes are those low heater current types developed just before everything went solid state. The 50- and 20-volt tubes are higher filament current types. So there must be two heater strings, since this appears to be a hot chassis set. The 20EZ7's are TV tubes. The 50HK6 and the 50C5 are both output tubes. Interesting set.

I wonder why they used two different output tubes? It's stereo! I wonder if they were looking for different separation in stereo sound, or, something?

Bill

I was wondering exactly the same thing. I wondered why there was just one 50C5 output. And then I looked up 50HK6, and it's also an output amplifier. Very odd. But it's a handsome little bugger.

Chris Campbell

Bill, do you have your RCA tube manual handy? If so, look up the 20EZ7. That might tell us why they used different output tubes. Maybe one for FM detector and one for AM? Will a 50C5 sub for the 50HK6?

The 50C5 is a beam power tube, and, the 50HK6 is a power pentode tube. They do not list to interchange. Pins 5 and 6 are different between the two.

As far as the 20EZ7 goes, my tube book wasn't very helpful. I did find this on line for those of you who understand this.

http://www.nj7p.org/Tubes/PDFs/Frank/04 ... /20EZ7.pdf

Bill

The 20EZ7 appears to be a 6EU7 with a 20 volt heater, pinout is similar but also a stereo audio preamp, used in similar-vintage radios. The second 20EZ7 may be for the FM MPX 19 kc amp and 38 kc doubler. I have not seen one in a TV, though it might be part of a combo's amp chassis.

I can't speculate why two different tubes are used for audio power outputs. Maybe one can handle an external speaker load better. While price is at the upper end of price range, if anyone here decides to get it, Ill send a schematic since its probably in my Sams library.

This particular radio was made by Arvin Industries of Columbus IN, as noted by the 132.xxxx. I had an Arvin-made Sears clock radio with that same dial (and also occasional silver mica disease) and it really did sound fantastic, out of one 5x7 oval speaker. It also used the 18FX6, 18FW6, 50HK6, etc.

I thought I remembered a TV one time that used a 20EZ7, maybe in the vertical circuit? As vertical oscillator and vertical output amp, maybe? A small Silvertone TV, if I remember right. I never thought about the Multiplex circuit, that makes sense now. It 's an interesting circuit for a radio.