View Full Version : Zenith 20CC50 neon bulb replacement.


Electronic M
04-12-2017, 03:59 PM
I'm working on a Zenith 20CC50 chassis right now. There are 2 neon bulbs across the HV reg pot (did not study schematic to follow function) one of them had a lead corrode off at the glass (set spent it's life in a damp basement). All I have is the schematic (no parts specs). I was thinking of replacing it with a neon from one of those $2 neon bulb testers electricians use to see if outlets, etc. are live....Will that work?

I have a spare 20DC50 that may or may not have (ought to check later) similar bulbs I can scrounge if needed.

Notimetolooz
04-12-2017, 07:26 PM
It may be a NE2.

Findm-Keepm
04-12-2017, 11:17 PM
It may be a NE2.

NE-2's have about 30 variants (NE-2A, NE-2H, NE-2J, NE-2M, NE-2S, NE-2V and many "subvariants") - all with different characteristics - most notably firing (breakdown) voltage. NE-2H and A1A's are the most common for indicators, but in Zeniths, I think they are used as a voltage clamp. The firing voltage is chosen to be just above what is needed for the circuit, so they only light/ionize when something is wrong...

Edit: It may also be one of the many "VR" series regulator lamps, like those used in many HP O'scope power supplies.

Anyone with a Sams? Zenith lamps are usually prefixed "100-", IIRC. I've got a box of Zenith neons here somewhere - lemme check in the morning and I'll let you know what I have, Tom.

Electronic M
04-14-2017, 09:38 PM
Well I should not be be surprised this Zenith just came to life with almost no effort, but I still kinda am...

I replaced the bulb with one from my junk box that appears to have closer spaced elements, re-soldered the clipped HO tube screen resistor, jumpered the HV reg socket (more on that below), replaced the focus diode, and cleaned/adjusted controls.

The original HV reg was supposed to be a 6JK6 or 6JH6 but IIRC a 6HZ6 was installed (by previous owners)...The 6Js are designed with pins 7 and 8 BOTH connected to the plate where as the 6HZ only connects one of those pins to plate. The chassis was designed so the damper is effectively disconnected from the fly if the HV reg tube is unplugged...Since the substitute lacked the internal jumper the damper was disabled WITH the reg plugged in...I added a jumper between pins 7 and 8 and the HV came up, and it was easy repair work from there on. That tube sub made it impossible for the set to work as found (possibly why it was found necked in a TV shop basement).

HV is about 22KV max where the schematic calls for 25KV...I'll let that slide for now.

The neons don't light in use so I guess they are an over voltage protection measure. My 20BC50 parts chassis lacked those bulbs so I had to use a randomn one.

It is working pretty darn good now. Once the metal back, a kind member here is sending me, arrives all it will need is an antenna to be complete.
https://c1.staticflickr.com/3/2815/34041267345_cf1205ff6a_z.jpg (https://flic.kr/p/TS7oNv)

DavGoodlin
04-15-2017, 03:18 PM
Good work. I sold one once but the issues were video amps or cathode drive ckt IIRC. Never heard back after I sold it, always a good sign.

This is the last higher end tube chassis, and two more years of hybrid chassis in cheaper consoles after this.

Electronic M
04-29-2017, 01:03 PM
Finally got the metal back on it the other day...It is not on 5 minutes before I move it a bit and the set looses signal..Probably a dirty tuner or loose connection or something stupid.
https://c1.staticflickr.com/5/4182/33500989584_717bd3ed83_z.jpg (https://flic.kr/p/T3nk3G) https://c1.staticflickr.com/3/2856/34301441456_e31a873472_z.jpg (https://flic.kr/p/Ug6Rv3) https://c1.staticflickr.com/5/4187/33532145533_f62fb77c0c_z.jpg (https://flic.kr/p/T681Ce) https://c1.staticflickr.com/3/2812/34301463026_4d2bacb684_z.jpg (https://flic.kr/p/Ug6XUW)

The back was rather rusty when I got it, but I sanded most of it off and repainted it the same color I used on my 15C6Y15 (which is a close match to it's back's original color). It is interesting that despite the back being off a different chassis set all the key stuff lines up, with only some mislabeled/misplaced service controls not matching up.

iong
05-12-2017, 09:24 PM
Came out nice. Glad you were able to use it.
Perry