Should i bother restoring a zenith?

[old_coot88]

Lacking a meter, at least get #44 bulb to dip the K current. Is there a RS store near you?
The dip point is very sharp, and if the coil is off dip, the current can be dangerously high and you'd never know it, even if the tube isn't red plating yet.
You're right about letting moisture cook off to see if the hiss goes away. But get the K current dipped first.

[Tubejunke]

Originally Posted by old_coot88

Lacking a meter, at least get #44 bulb to dip the K current. Is there a RS store near you?
The dip point is very sharp, and if the coil is off dip, the current can be dangerously high and you'd never know it, even if the tube isn't red plating yet.
You're right about letting moisture cook off to see if the hiss goes away. But get the K current dipped first.

I agree 100% on getting that current right. My Simpson meter should do the job fine. Or if I chose to use a bulb, isn't a #44 a standard pilot lamp bulb for vintage radio and TV? I need a source for a few of them, but I never would have thought about Radio Shack. I wouldn't think anyone would know what a bulb is that works there frankly! LOL! Again, thanks for REAL words of wisdom and good advice. It would be easy for many to overlook such an issue, but since I have addressed a real issue with replacement of the broken coil (which was floppy like a slinky), I may as well do the job right.

[kramden66]

I never knew how important that cathode current was till I started working on my set and then was given the advice to make sure its ok , it was at 220 or 225 or something like that , I'd have to check my notes but it running like that was causing the fly to get hot after a while , now that I have it running at 200ma the fly doesn't get hot , I don't even think it gets warm , if it does its so low that it is tough to tell and is negligible , so get that bulb hooked up or even better the meter and make sure its not high , I was told I could probably take mine lower but the schematic shows 200 and the instructions say no higher then 210 , I didn't want to go to 180 as was suggested because the proportions are just barely right now , if it gets reduced anymore the only way a circle will still be a circle would be to adjust so theres is a gap at the top and the bottom and I don't want to do that.

is this cathode current issue important for the black and white sets too I wonder .

mike

[old_coot88]

The H output tubes in color sets (like 6JE6, 6JS6 etc.) are run at their absolute heat limit with no 'headroom' for overcurrent. That's why it's imperative to dip the current. Highest 'safe' current would be around 210 ma, with 200 preferable for good longevity. Much below 200 and you start getting width and regulation issues.
Tubes like 6KD6 etc. are beefier by design and can take more overcurrent, a requirement with the feedback-type HV regulation used in some Admirals.

B&W sets normally don't have these issues since the HO tubes run with adequate 'headroom'.

[old_coot88]

RS still lists the #44 bulb..
http://www.radioshack.com/product/in...ductId=2102798
Incorrectly listed as "flashlight bulb".
Also listed is #47 which is more commonly used for dial lights, and is half the current. Cat.# 272-1110

These are foreign sourced junk but better than nothing.

[Tubejunke]

I think I will use my Simpson 260 on this and go ahead and make a permanent and eventually fused connection point. Sounds simple; break the conductor grounding the cathode pin and run two pieces of wire to put the ammeter in series with the circuit.

I have a digital meter with the current fuses blown out of it, so I suspect someone without training in properly using a meter got a hold of that one and checked some amperes in parallel. I was on another thread last night and someone was talking about checking current with a volt meter hooked in parallel. There are quite a few fundamentals of using meters that perhaps we should do another thread on. I think it would be a good thread where the right people could explain the often superior nature of the analog meter. An elaboration on the further pros of the VTVM would be good too.

[Tubejunke]

Also, I got a chance to evaluate types of capacitors on this (for my collection) newer set. I wanted to see what I might immediately want to remove as far as commonly known to fail types like bumble bees for instance. I didn't see any of those. Mostly I saw the old reddish brown drops which I hear are ok in most cases. The paper-foil is what I think needs to go and what I saw was several black plastic coated paper caps. I wonder if these are as bad as the bumblebee type, or even remotely as bad.

I think for now I will leave the multi-section cans alone as they are pretty tough old parts and sometimes I think they might be better than what you get from China. Anyway, what about those black beauties?

[kramden66]

if in doubt check those black capacitors for leakage if you have such an instrument to test them, wouldn't hurt to replace them, they could be causing your color issue too.

as far as electrolytics go i've given up on trusting 40 year old or more electrolytics even multi section , I do have one set running on one original electrolytic in a multi can , its a 58 zenith and the reason is its a 475 volt cap , I didn't have any 500 volt ones to put in so I chanced it and it seems to be holding up , its tough to test the voltage because the set can only be removed by disconnecting the tuner with the two plug in plug out connectors running to the tuner and I really didn't want to remove the tuner just to test the voltage on that one electrolytic just to see if it has a higher then 450 volt running voltage and running wires from it would have been a pain too , down the road I may just replace it , its in the focus circuit.

awaiting the post that tells us the cathode current.

[Tubejunke]

Originally Posted by kramden66

awaiting the post that tells us the cathode current.

Bad luck with meters lately. My digital junk has the current fuses blown. It was that way when I got it. I just forgot to get some more. Then yesterday I got out the Simpson analog; meter of choice and the batteries are dead.

Worry not, I will get this done eventually.

[Tubejunke]

Originally Posted by old_coot88

The H output tubes in color sets (like 6JE6, 6JS6 etc.) are run at their absolute heat limit with no 'headroom' for overcurrent. That's why it's imperative to dip the current. Highest 'safe' current would be around 210 ma, with 200 preferable for good longevity. Much below 200 and you start getting width and regulation issues.
Tubes like 6KD6 etc. are beefier by design and can take more overcurrent, a requirement with the feedback-type HV regulation used in some Admirals.

B&W sets normally don't have these issues since the HO tubes run with adequate 'headroom'.

I want to clarify this procedure before I go further as it keeps being mentioned, but I'm not seeing specific connection points for the meter or bulb. I am assuming that if I read the schematic and find the cathode connection then I can simply break the circuit at the solder terminal and connect one lead. The other lead should be going to chassis ground. Is there something that I am missing or is this OK?

[old_coot88]

Originally Posted by Tubejunke

...I can simply break the circuit at the solder terminal and connect one lead. The other lead should be going to chassis ground. Is there something that I am missing or is this OK?

Yup you got it.

[Electronic M]

If you use a bulb then inserting it between the top cap and the lead that connects there is a better idea as a series cathode resistance from the bulb could throw off the grid bias.

[old_coot88]

Originally Posted by Electronic M

If you use a bulb then inserting it between the top cap and the lead that connects there is a better idea as a series cathode resistance from the bulb could throw off the grid bias.

This is true. But the 4V or so dropped by the bulb would be negligible and probably not noticeable except for a slight width reduction. For convenience doing 'dip checks' in the field, we put the bulb in the plate lead, using a little made-for-purpose adapter.

[Tubejunke]

Looks like pins 4 and 10 will be the two potential places that I can break the connection and run two wires out to an eventual fused terminal. Then I can easily monitor this in the future by opening the two wires and placing the amp meter in series.

I saw a video where a guy showed two ways of checking the current on the tube. He was lucky enough to have some adapter that was made just for the purpose of cathode measurements. Also, he took measurements off of the much more easy to access plate cap, but he specifically used a stand alone milli-ammeter and stressed the dangers of doing it that way due to the extremely high pulses present there. Not sure why the old stand alone meter was any better to use than a normal analog meter, but that is what he used.

[Tubejunke]

Originally Posted by old_coot88

Lacking a meter, at least get #44 bulb to dip the K current. Is there a RS store near you?
The dip point is very sharp, and if the coil is off dip, the current can be dangerously high and you'd never know it, even if the tube isn't red plating yet.
You're right about letting moisture cook off to see if the hiss goes away. But get the K current dipped first.

I did it. I ran the two wires and connected my Simpson meter. At first the current was about 210 or even more. I was surprised at how much I turned the slug to get what I consider to be a small reaction, but I was able to get it down to about 200.

What I battle now (maybe moisture related) is some corona arching, or really more of a hissing. You can see it inside of the rectifier. This gives an interference of course on the picture which by the way is stable and linear. Sound is good. Just missing color now and the hissing. I have more than once been tweaking the efficiency coil or the HV adj and made the hissing go away, but it comes back every time.

My final concern is heat. I'm not used to color sets, and I don't know what is an acceptable amount of heat to have coming from the fly and the power transformer. In a perfect world they should stay cool, or cooler than other things like tubes. I kept shining a flashlight into the H.V. cage and looking at the fly for signs of melting wax or plastic. The metal around the cage was warm to the touch. I wish I had my laser temp gun from work! Now the power tranny was to me hotter than I prefer one to run, but then again I know these color sets pull a lot of current from the wall. I could put my hand on the power tranny, but after maybe 30 seconds it was getting a bit too warm. None of the lytic cans were warm at all, so that's good.

There was one of those brownish/reddish drop caps over in the horizontal section that to me felt slightly warm. I hope it was actually. Maybe it has something to do with my hissing. Oh, and there was one bumblebee in there. Need to get that out quick.