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  #16  
Old 02-28-2017, 11:27 AM
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I think you guys are referring to the coil on the plate of the damper tube ? It doesn't appear to be adjustable.


I have a nifty SECO HC8 cathode current monitor I can use.
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  #17  
Old 02-28-2017, 12:17 PM
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This is the 25LC30 circuit everyone's been woopin' and hollerin' about
Looks like you could add in your own horizontal efficiency coil.

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  #18  
Old 02-28-2017, 12:45 PM
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Thanks. Looks like I have the simplified design. I'll see about adding that in when I pull the chassis. Wouldn't be surprised if there's space for the extra components.
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  #19  
Old 02-28-2017, 08:20 PM
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Quote:
Originally Posted by bandersen View Post
Thanks. Looks like I have the simplified design. I'll see about adding that in when I pull the chassis. Wouldn't be surprised if there's space for the extra components.
Get rid of the R35, while you're at it. It's a common failure item and not needed. 1500 ohm, 1 watt.
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  #20  
Old 02-28-2017, 09:14 PM
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Get rid of the R35, while you're at it. It's a common failure item and not needed. 1500 ohm, 1 watt.
Isn't that suppose to act as a current limiter in the event something goes terribly wrong?
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Old 02-28-2017, 09:30 PM
dieseljeep dieseljeep is offline
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Isn't that suppose to act as a current limiter in the event something goes terribly wrong?
Zenith engineering recommended eliminating it. It was the subject of a thread, quite a while ago.
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  #22  
Old 03-01-2017, 12:42 AM
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At first, I thought you found the very same model I have, only realizing that mine has a wood cabinet with its front legs consisting of extensions of the front face of the cabinet continuing to floor level.

I had been working on it, after gathering a new tube for every tube except the 21FJ (which tests good), but there had been a lot of nonstandard work under the chassis, and something went "pop" one night I was testing it out.

It's quite compact for a color roundie with legs. I think I can say with certainty that it is the only color roundie that has ever been transported in a Prius.

Last edited by Robert Grant; 03-01-2017 at 12:48 AM.
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  #23  
Old 03-01-2017, 09:38 AM
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Originally Posted by dieseljeep View Post
Zenith engineering recommended eliminating it. It was the subject of a thread, quite a while ago.
Robert Goodman also says to get it out of there.(Zenith Color TV Service Manual,Vol I,Tab Books) Same book Bandersen showed us earlier. Robert mentions a couple different situations, which at first impression leads one to believe he's talking about two different resistors, however there only seems to be that one 1.5K associated with the HV?

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  #24  
Old 03-01-2017, 10:58 AM
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Thanks for the info. It'll be interesting to see if that resistor has been removed or jumpered.
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Old 03-02-2017, 01:49 AM
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Yep, my resistor popped under that rectifier. The socket was also burned which is why there was an annoying hissing before the repair which was replacement of the socket and jumping the pins where the resistor would have been. This is a good thread! It's making me think of working on mine again.
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Old 03-06-2017, 11:39 AM
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I got a copy of the Sams I'm itching to pop the back off this set, but I've got a ton of post move stuff to do first including setting up a new workbench.

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  #27  
Old 03-08-2017, 10:00 AM
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I popped the back off last night and took some more pictures. I like how the back is held on with clips rather than screws. Very easy to get on and off.



So far I see a mix of bumblebee and maroon caps.
I assume the bumblebee are paper inside and should be replaced but what about the maroon type ? Are these plastic film and generally OK or should I shotgun them ?


Also any thoughts about the missing x-ray shielding ? Would some galvanized or aluminum sheet metal be sufficient ?
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  #28  
Old 03-08-2017, 02:27 PM
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The Maroon Elmencos can stay - they are film, just like an Orange Drop. RCA and Zenith loved them - I've never seen one go bad.

As to shielding, any ferrous metal will work - I've used perforated (1/16" holes) metal before - came straight off of an old Phase Angle Voltmeter. Also, make sure you have the 6BK4C regulator, or a 6EL4A. They are the regulator tubes with the longer anode that provides the optimum X-ray protection. Of note, patented by a female RCA engineer!!
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  #29  
Old 03-28-2017, 02:52 PM
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Thanks for the tips. It does have a 6BK4C/6EL4A installed

A friend stopped by over the weekend and we organized the basement a little. It's not much of a workbench, but this card table is a start


After getting his Farnsworth radio working, I figured why not take a whack at this Zenith?

Doug said he had tried powering it up and there was no B+. I hooked it up to a Sencore PR57 so we could monitor the current draw and turned it on.

The tubes lit up but no B+. I gave the circuit breaker a couple nudges and viola - power. A few moments later, the tell tale crackle of HV and a raster



That was quickly followed by a lighting show around the CRT anode lead. I moved some wires out of the way and that mostly tamed it.

Now we still have an analog OTA LP NTSC station on channel 6 and it's very handy for testing. Try as we might, we got nothing.
There was some noise and static as we changed channels, but no hint of reception. So I dug into the tuner to swap out the tubes.

While doing so I noticed some bits of wire dangling from what I think is a CRT grounding wire


Anyway, after some cursing I managed to get the two tuner tubes swapped out. The dial lamp is out too, but I'll save that for another day.
Is partially visible in the bottom-right. Is there any easy way to get at it ?


That did the trick! We had great sound, but a horribly out of focus picture. The focus control had no effect.


Seemed like the obvious thing to do was replace the 1V2 focus rectifier. Bam! We had a sharp, bright image, but no color.


A little control adjust took care of that Not bad for basement reception of a low power station using a scrap of wire for an antenna!


The HV arcing happened a few more times while swapping the tubes so I wedged in a gob of HV putty.
That helped a lot but there is still the occasional hiss and whiff of ozone.
Seems to me the HV cup and anode wire are a little on the skimpy side. I'll be replacing them eventually.


All in all not bad for a first power up. Don't recall ever having a set come back to life so well just by replacing a few tubes.
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  #30  
Old 03-28-2017, 03:04 PM
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That is a Zenith for you!
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