finally,a zenith rectangular!

[sampson159]

its not too bad, the tuner recap.alignment should fall into place.a little tweaking here and there.thats the part i enjoy!the chassis is 20cc50 on mine.its very cold in the garage,so i didnt stay out there too long.

[DaveWM]

I was working on my zenith out the garage, darned if it was not one of the coldest days on record down here. You think you are safe from that in central florida, not this time.

Did you get a chance to test the CRT?

[sampson159]

crt is a sylvania rebuild.it tests as follows red 9.6,green 9.7,blue 9.6.looks very strong.this set when finished should rival my xl100 nib.that table model like mine is most desirable to me.i like it a little better.but i am very happy with this one and while cleaning my bedroom,i found a 6jh5 in a zenith box.i forgot that i got a box of ho tubes and regulators at an auction for 2.00.63 tubes in all and i have one!a christmas miracle to behold!

[ctc17]

20cc50 is not all tube? Just the deflection and maybe the audio and tuner?

[sampson159]

didnt count the tubes but it has more than 8.tuner has 2 tubes.

[old_coot88]

Regarding the snowy pic problem, have you checked the ant. input (balun) coil(s) for continuity? Occasionally these get zorched by the transient from a nearby lightning strike. It doesn't have to be a direct hit. Also, is there by any chance an 'RF AGC' control in addition to the regular AGC pot? Bill(oc)

[sampson159]

thanks,bill.it does have that control.i missed it.as far as the coil,yes it does happen and it doesnt have to take a big hit either.i will pull the tuner later today and have a look.i really appreciate all the information.as i have always said,the best techs in the entire world reside in this forum!

[DaveWM]

indeed, I had a zenith with a smoked balun. One of the coils was literally burned up, I ended up rewinding it with some 22ish gauge magnet wire, I suppose I should have used some litz but thats all I had on hand. I guess the smart thing to do would have been to just remove the balun and hooked up a 75 coax lead right at the end of the balun, but I was not exactly sure about that.

[DaveWM]

could I just put the coax at the junction of the 10pf and 8pf

[sampson159]

15 tubes in the chassis.my christmas find,didnt fix it.my tube tester is on the fritz so i am back to sqare one again.i may need the 3dc3.it has full vertical and horizontal,but when there is scene changes,the screen will darken and loose focus.certain scenes will make it go completely black.adjusting the brightness will bring it back.

[DaveWM]

I would start with a HV prob on the CRT anode, just to see where you are.

Make sure its the HV, I was reading up on some zenith issues, on HV there is a .22uf and 200 ohm (IIRC) resistor in the cathode circuit of the 6HS5, check those out. The VDR is always suspect.

IF the HV is holding steady then suspect the video out tube (12bh7 i think), if there is a problem there it could be biasing the CRT to cut off. My book mentioned some diodes in the video driver transistor circuit that could open or short causing excess or no brighness.

but it sure sounds like HV reg and the VDR to me, I had the exact same prob (CRT would bloom and could be recovered with constant adj to the brightness), it was the VDR, you could see the anode voltage jumping around 5k up and down, and the HV adj would not bring it down below 27kv with the screen brightness turned down.

The problem I found with the VDR's (they can be got new from talon and moyers) is they are not all the same, BRAND NEW, I ended up paralleing two and it finally worked.

My guess is back in the day when the VDR's were new and not NOS, you would put one in and it would fix the prob, 5 min fix, but now with VDR's not being what they should be its more like pin the tail on the donkey as far as it fixing the problem, hit or miss.

Hopefully in your case its a tube (the HV recifier or HV regulator), if not the .22 or 200 ohm resistor, if those check AND the HV is still to high (and jumps all over the place) with the HV control having little effect on bringing it down, then I would just try subbing in some high value resistors (like 2 meg to start with) for the VDR. There is a term strip behind the 6HE5 that has the vdr connected to it, you should be able to get some jumpers on that and bring it out to the back of the TV, this would let you try different resistors (or vdr's if you get some).


One last thing, check the resisor that goes from one side of the pot to the ground on the HV, make sure it has not driffted high. that would cause a Low HV, I just got thru a zenith that had that happen (it was a roundie with a shunt tube 6bk4). Main thing is to get that 6he5 the correct bias so it can track the fly and load it down to the correct voltage, that keeps some reserve so when the beam current goes up, the HV will not drop.

welcome to the HV woes club...

[old_coot88]

Back in the day, that blooming problem in Zeniths was invariably caused by the 6HE5 (/6JB5) regulator. The tube would test good but fail in use, and the only real fix was to sub it. That's not to say that after all these decades, some other components in the reg. circuit might have drifted, which was not the case "back in the day". Bill(oc)

[sampson159]

mine uses the 6jh5/6jk5 regulator tube.i still think this is the issue.the screen will go dark and the horizontal and vertical will increase also.need a sub for 3dc3.i have plenty of good 3a3 s,too many.for some reason,i just cant get a zenith to stay together.my rcas are great,but the zeniths!

[ctc17]

The thing will bloom to a point then the HV rectifier filament will extinguish and it will sit in a half way state. When you decrease the brightness you remove the load and it reheats.
I have seen these do this if the setup was wrong or if there was something off in the horizontal circuit. Lack of horizontal capacity like a weak HOT or the reg tube loading the circuit down will cause it for sure.
You can run that set with the regulator tube out. You may have to jump two of the pins together to get b+ to the damper.

Have fun with this one. These can be some of the toughest to fix problems.

[old_coot88]

My first plan of attack would be to get a known good regulator tube from someone who can verify that it's good in use. Of course checking component values would be on parallel track while waiting for the tube. Bill(oc)