Admiral 20X11 restoration

[bandersen]

I figure while I have my 20X12 up on the bench I might as well tackle this set too. It's the black set on the left.



It appears to be a very early revision of the 20X1 chassis. It also has quite a few original Admiral branded tubes including the CRT.



When I pulled the knobs off, a few small washers came falling out. I was puzzled for a while - where did they come from ? Finally, it occurred to me that they are spacers between the inner and outer knobs. Without them, the knobs have a tendency to track when rotating one or the other. I have a few Admirals sets with these same knobs, but never found washers before. I suspect they all were lost over the years and never replaced.


It's had some work done over the years. I'd say about half the original caps have been replaced. The two multi-section electrolytics are original though.

[bandersen]

I decided to try something a little different with this project. Instead of shotgunning all the paper and electrolytic capacitors, I'm going to try to reform the electrolytics by powering the set up slowly over several hours. Then, assuming I get some signs of life, I'll troubleshoot the circuits that aren't working properly.

I'm also itching to give my recently restored Solar CB-1-60 a workout

[Electronic M]

I've got one of that model cap checker (someone mounted a new transformer outside the case on mine) that I've been meaning to test/restore. I wonder how it compares to the heathkit C-3?

[Kevin Kuehn]

Is there an EIA code anywhere on the CRT or other tubes, indicating who manufactured them for Admiral? Is that rust on the transformer laminations?

[bandersen]

Originally Posted by Electronic M

I've got one of that model cap checker (someone mounted a new transformer outside the case on mine) that I've been meaning to test/restore. I wonder how it compares to the heathkit C-3?

There are some key precision parts in the CB-1-60 like a big tapped resistor divider and 2% capacitors. I'll post details in the Test Equipment forum in a bit.

I'm not familiar with the C-3, but I do have a Simpson 383-A Capacometer I'll be restoring.

Originally Posted by Kevin Kuehn

Is there an EIA code anywhere on the CRT or other tubes, indicating who manufactured them for Admiral? Is that rust on the transformer laminations?

Here are the markings on some 6AU6s. The CRT base is marked National Video Corp. Chicago, 10BP4 while the bell is stamped "Admiral" and "S". Perhaps it's been rebuilt

Yes, it sure is rust. I've worked on three 20X1 chassis to date and they've all had rusty power transformers. I use a little Loctite Rust Neutralizer on them than some satin black enamel paint.





The reforming seems to be going OK, but I had to use light bulbs of increasing wattage because my cheapo variac died a few months ago. It blows fuses instantly when it's turned on even with no load

[Kevin Kuehn]

I was just curious who sold them tubes. I suppose they may have even taken lowest bids. The 6AU6's are Sylvania (EIA 312).

[edit] 939 is likely 39th week of 1949

Rust converter is good on transformers.

[bandersen]

Thanks for the info
I'm just about up to full line voltage. One can is cool while the other is just a little warm.
While waiting, I did some troubleshooting on my variac and found the problem
Can anyone guess what it was ?

[earlyfilm]

Originally Posted by bandersen

While waiting, I did some troubleshooting on my variac and found the problem
Can anyone guess what it was ?

I have had no experience with Chinese made imitation Variacs, but based on experience with the Japanese imitation species that flooded US in the late 1940's and early 1950's, causes for shorted imitation Variacs in order of probability:


1) Line bypass or wiper bypass capacitor failed

2) Insulating washer on the spring loaded wiper failed

3) Incorrect wiper adjustment allowed the wiper to over extend and an arc melted a bit of solder, which shorted adjacent turns on the winding

4) Carbon wiper brush fell out and the metal holder shorted near turns on the winding


Or, finally, if the fuse blowing is not instantaneous, but takes a couple of seconds, the fuse holder spring.

James

[dieseljeep]

The power cord doesn't look like it was strain releaved very well. Might have gotten pulled real hard and the connections crossed.

[miniman82]

I have the same variac, it blows fuses when trying to power the 525 watt 21-CT-55. lol Other than that, it works well.

[bandersen]

None of the above. The culprit was the cheap AC meter right across the output socket with no protection. The meter coil shorted out.
I clipped it out of the circuit and the variac is working again

[bandersen]

Well, I was able to get a one inch high raster on the original caps. No sound or video though. First, I tested all nine electrolytics - seven are in two multi-section cans. Only the replacement cap in the center of the chassis tested good. Two others had minor leakage. The others were all open.

So I tacked in replacements for the open ones, but now I had no sound or raster! Cleaning the tarnished tuner contacts got me some good sound. but still no HV.

I then got a scope on the hor. oscillator and found it was way off frequency so I rebuilt the whole circuit and the HO circuit too.

Every single paper cap I tested was either very leaky or way off value. Only a few of the more modern replacement caps were good.

Still no HV

Then, while fiddling around with the focus control, I suddenly got a raster back

I got an ohmmeter on it and found it was open Rotating it fully counter clockwise would bridge the bad section and get power going through to some circuits.

I tacked in a temporary replacement and finally got a picture and sound




The vertical height control is maxed out and the picture is still squished so I'll tackle that circuit next.

[M3-SRT8]

So...You ended up recapping it. I knew you would.

60 year old caps are hopeless in my book. Why chance it?

I like that set, BTW. I'd like to find a good one to restore for my collection.

Keep at it, Bob.

[bandersen]

Thanks. I knew I'd recap it too, just curious. I also recorded some video I'll be posting to illustrate how futile it is to try running vintage sets on the old paper caps.
As for the electrolytics, while I'm sure it is possible to reform them in some cases, I've never had any luck and don't really see the point.
Why not just replace them too while the chassis is out on the bench and not have to worry about them ?

After rebuilding the vertical circuit, I have plenty of height


Next up, remounting the restuffed cans.
I also found a number of resistors that were off 100% or more in the video IF which I replaced. So I'll go through an alignment when it's all back together.

[Phil Nelson]

Speaking of Solar cap analyzers, guess what I ran across when straightening up my shop last week?



Let me know if you think it works well enough to be worth restoring. I doubt I would use it a bunch -- my attitude toward 60-year old electrolytics is that they all deserve to die the true death -- but anything with an eye tube warms my heart and I hate to have non-working things piled all over the place.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html