Zenith Console combo

[DaveWM]

stopped by my tube guy, checked all the tubes on a 539 hickok, turned out the HV regulator tube was very weak (and yet looked brand new). I hope that helps resolved the regulation problem.

Today I replaced 3 resistors on that chroma amp tube, while checking the other tubes he thru in the syn/noise/agc tube, two color demodulators, a new audio tube (6z10), a 2 IF tubes (one shorted, the other very weak), and an RF amp tube (again very weak).

I also replaced the focus rectifier stick.

Cleaned the chassis top, inspected the ground stakes (two were cracked) and resolded.

Cleaned all the gunk around all the term strips/tube sockets, cleaned the tube socket pins (small nylon spiral brush and cleaning juice). cleaned all the tube pins (brass brush). Cleaned all the plug in sockets (hue/color, convergence, yoke) cleaned the CRT socket (sprial brush). Wiped off all the sticky goo from the wires (yoke, CRT, speaker).

inspected the bottom for any componets that may have been moved after working on the resistors, and transporting the chassis.

Cleaned up the fly back plate (dust, general nastyness) careful not to work behind it where you cant see the fine wires.

Still need to give the pots a quick shot of cleaner/lube, that is all the pots on the chassis front, and the volume pot.

the Thermistor is busted, every set I have seen has a busted thermistor. I have a CL90 but not sure if the rating is correct. Will do some checking and see.

[DaveWM]

looks like the CL-90 specs out at least to the cold resistance (120@25c) and since its in the B+ it should be fine current wise. I have used them on other things, but that was on the primary side of the power tranny to soften the blow to the power switch (fisher 400).

so the thermistor is in, but its getting late so I will have to wait till prob Sat to reinstall the chassis and see how it goes. wish me luck...

[batterymaker]

Sounds like you're almost done. So close I can taste it...

[ctc17]

The adjustment on the front labeled brightness limiter should really be 'bloom limiter'

[DaveWM]

whew.. lots to report

voltage regulation was not happening, I check the voltage at the grid and the cathode, should be 350/360 (-10v bias) was more like 375/300 or -75, so the shunt tube was completely cut off, not loading the fly at all, so no regulation. I checked everything there was to check but the VDR, no joy.

since there is no specs on the VDR I decide to just replace it. I found on that was suppose to be a cross, put it in, bingo regulation. I was able to get the grid voltage up to about 340 so a little low there, and I need to keep the HV set as low as it will go, that gets me to about 25kv.

I am going to check a couple more resistors and the boost voltage (yes replaced the focus diode that supplies the 900v boost that drives the regulation). I thought I checked them but will check again. I have another zenith set to compare to. there is a voltage divider in the fly cage that gets the focus voltage down from 5kv to the 900v so I will look there again. but at least its in the ball park now.


after I got it installed another problem popped up, color hum bars. Now it was fine before I pulled the chassis so I really doubt anything went bad.

after a few careful looks I found a rather large disc cap that seemed pushed down and possibly having a lead touch where it should not.

this is the only thing I really dont like about point to point wiring, esp with open bottom chassis. you have to be REAL careful about how you handle and transport the chassis.

anyway I moved the cap and the color hum bars are got, thank goodness.

I really like what zenith did on some of there 50's era tube sets, where there was a metal bottom plate. this not only shielded from EM radiaition, but prevented just this kind of problem, AND the chassi was much stiffer so less flexing and possible damage from that as well.

getting late so I will reinstall later in the week, but getting real close now.

Oh I also replaced some resistors that had gone out of spec on the chroma amp tube, that helped with the weak color (had to have the color turned all the way up).

Not too far to go

[old_coot88]

Originally Posted by DaveWM

...after I got it installed another problem popped up, color hum bars. Now it was fine before I pulled the chassis so I really doubt anything went bad.... anyway I moved the cap and the color hum bars are got, thank goodness.

Colored hum bars can be caused by residual ripple in the degauss coil. It could be an intermittent in the auto-degauss circuit. Might try wiggling stuff in that area if the problem shows up again. Bill(oc)

[DaveWM]

it's ok now OC, I found a cap (large disc) that had gotten moved and looks like one of the wires had come into contact with some it should not have. I repositioned the cap and the color hum bar is gone

I just hate when I create a problem. Needless to say I will just be that more careful when handling the chassis. I think the prob happened when I was transporting the chassis in the back of the SUV. I had a soft blanket to set it on thinking it would cushion it, but I think what happened is the chassis just settled down and the blanket pushed the caps up into the chassis.

next time I will set the chassis on a hard surface and then put that on a cushioned surface so I don't bounce it around.

I figure this was a rookie mistake, I will not repeat it.

Thanks for the heads up I will keep that in mind if it happens again (looking around the degausse).