Admiral 20X11 restoration

[bandersen]

Originally Posted by Phil Nelson

...Let me know if you think it works well enough to be worth restoring. ...

Absolutely! I mostly use it to test mica caps. It's nice to know if the originals are really bad before trying to try down replacements with oddball values.

I think this is the first time I ever bothered to test electrolytics. It was interesting to see how much better new caps test compared to vintage ones.

[Phil Nelson]

Micas, OK -- I will give it a whirl. Just found a decent 20-page manual online, too.

Nice job on the TV, by the way. My first Admiral is still languishing in the back row, but I'll get to it some time before next summer.

Phil Nelson

[VintagePC]

If memory serves, the main issue with the old EL caps is the electrolyte tends to dry out. Most had a paste of water and borax(?), and the water would slowly escape or be driven out by heat as the caps got warm. Initially, of course that would be from the tubes, but as they lose efficiency, the caps start producing their own heat as well...

There was a note a while back here where someone said that oil-filled caps were rarely bad; with water-based caps, since the innards are rarely damaged, you _should_ (in theory) be able to re-hydrate them and have them work again.

[Electronic M]

Originally Posted by Phil Nelson

Micas, OK -- I will give it a whirl. Just found a decent 20-page manual online, too.

Nice job on the TV, by the way. My first Admiral is still languishing in the back row, but I'll get to it some time before next summer.

Phil Nelson

Could you please link that manual. I'd love to read some info on it to get me fired up enough to fix mine.

Tom C.

[bandersen]

Originally Posted by Electronic M

Could you please link that manual. I'd love to read some info on it to get me fired up enough to fix mine.

Tom C.

I've created a new Solar CB-1-60 thread in the test equipment forum.

You'll find a link to the manual and parts list there.

[Electronic M]

Thanks! Spotted that thread first, and read all but the linked pages (I'll read those soon).

[bandersen]

I received some salvaged controls courtesy of grimer today. They came well packed in electrolytic peanuts

Unfortunately, this focus control is bad too. Not totally bad though. I get the correct 0 to 1,500 ohms on one leg through the full rotation. The other leg is open so there's probably a break very near that lug.



The original focus control in my 20X12 had failed too! I'm starting to suspect a design flaw

Time to investigate. I carefully popped open the one that originally came with this set by prying back metal tabs. Sure enough - there's a definitely break about 20 turns from one end.

This resistive (nichrome wire?) is a pain to solder so I wedged in a scrap of copper foil plated with gold. It seems to work OK, but there's a noticeable "bump" when the wiper goes over the damaged area. Luckily, this control isn't adjusted much and the damage is near one end.


I'll pop open the one from grimer too and try to repair it. Whichever works better will end up in the set.

[bandersen]

Yep, the control from grimer had a break is almost exactly the same spot! Once again, a gold plated copper shim did the trick

[ha1156w]

That's a pretty ingenious solution to that problem. I'll have to remember that trick. I suppose one would also be able to limit the travel of the wiper by putting a block of some plastic superglued to the inside of the control.

[pearsonk]

According to Sams, the focus control in later production units was 4w/1350 ohm. Early was 2w/1500 ohm.
So, you might want to put in a 4 watt pot. I have had the 4 watt burn out
also. I have found 4w/1500 ohm ww focus controls from other sets of the same
brand as used in the Admiral, and been able to remake a good control.
Your solution looks good.

[bandersen]

I do have just one spare of those 4W variety. It's noticeably beefier and I'm going to use it in my 20X12. I'll use one of these 2 watters in this set and hope it holds up.

[mbates14]

youtube vids?

[bandersen]

I finished a total recap and replace many out of spec resistors.
I added a 220 ohm resistor to one leg of the focus pot to compensate for the shorted windings in the damaged area.



The linearity is pretty good.
The horizontal is off a little (squares on the left are wider than on the right), but the linearity adjustment coil doesn't have much of an effect.


Here's a multi-burst bandwidth test at 0.5, 1.5, 2.0, 2.5, 3.58 and 4.2 MHz.
Curious that the middle bars (2.0 MHz) are less distinct. I suspect the IF has a pronounced double hump response.

Originally Posted by mbates14

youtube vids?

part 1
part 2

Still working on part 3. It will cover alignment.

[bandersen]

I finished with the alignment. Here's the video IF response before and after.
It really wasn't that bad to begin width. The service info calls for the peaks to be within 30% of each other. I tweaked the coils to equalize the height, but the only way to get a flattop is to kill the bandwidth.

My scope is set for 1 MHz / div so the bandwidth at 50% is about 3.2 MHz just as the service info calls for.

I suspect the IS was a design compromise to fit the chassis into a relatively small cabinet. The Admiral 20A1/20B1 stagger tuned chassis I've restored previously perform better. Then again those sets use a split chassis with plenty of room for more complex circuits.



The picture is prrety good except for some faint diagonal interference lines.

[Nuke]

Bob - You have a nice clean chassis a couple of pictures back. How did you get it that way?