Admiral 20X122 restoration project

[Eric H]

Originally Posted by charokeeroad

The picture sequence is backward but this is a restoration I did on a Motorola bakelite cabinet some time back using stain.
I used Red Oak here but I think Red Mahogany would give a truer color match.

http://s1184.photobucket.com/albums/...20Restoration/

That's a nice job, I've used stain with Lacquer on Bakelite but the results are disappointing, Poly makes more sense in this application, replacing Plastic with Plastic!

I'll have to try it on one of my faded sets,

[charokeeroad]

Originally Posted by Eric H

That's a nice job, I've used stain with Lacquer on Bakelite but the results are disappointing, Poly makes more sense in this application, replacing Plastic with Plastic!

I'll have to try it on one of my faded sets,

I looked back on the original thread and refreshed my memory on what I did.
The stain process was simple but the poly was where the trick came in. I finally ended up with an oil based poly in the spray can. For the little extra it cost for the spray can vs brush or air brush it's well worth it. They have figured out the nozel size and pressure right from the start.

[bandersen]

Interesting technique - thanks for sharing.

Maybe we should create a sticky post in the Tech Tips forum for all the bakelite restoration tricks ?

[bandersen]

I finished recapping and popped out the tuner for an overhaul.

It's stamped Oct 5, 1949 which I find a little surprising. I would have thought this model was retired by 1949 in favor of the 24A12 ?

[bandersen]

I've finished the recap and reassembly.


I'll powering it up for the first time later tonight. Right now I have to go get supplies before the snow gets too deep.

[bandersen]

I powered it up with the 5U4 pulled. All the tube filaments are glowing nicely

[bandersen]

I installed the 5U4 and power it up. B+ looks OK, but no sound, raster or HV I'll keep poking around.

[Eric H]

Hi Bob, I'm working on the exact same set right now, this has been one of the easiest sets to get working (you may remember it worked fine with no work done) while at the same time being one of the filthiest chassis.

I noticed the date on yours so I went and checked mine, it's stamped on the opposite end but there it was, Oct 13 1949, just eight days after yours, how many thousands of sets went out the door in between I can hardly guess.

I'll be updating my thread soon with a video.

[bandersen]

This set is proving to be a bit of a challenge, but I'm getting there.

First, I did some voltage checking and found none in the vertical output circuit or brightness control. Turns out I forgot to install a 1.5K resistor.


That got me a raster, but no video or sound.


Next, I fired up a B&K 1077 and injected a signal into the first IF stage. That got me sound and a very unstable, off-center picture.


More investigating turned up a dirty 12AU7 sync tube socket, a bad 6J6 and 6AG5 in the tuner.

That got a me a stable picture, good sound and a decent picture.

Just one major issue remaining. The brightness control has a strange effect in the picture. The screen is dark for the 1st half on travel. Then a narrow window of visible picture. Then it blooms out of focus and gets dim.

Seems like the grid bias voltage must be off, but they check out OK. Might also be the 10BP4 CRT. I recall it tested good back when I started this project, but I'll test it again. I'll try swapping it out with a known good one too.

[old_coot88]

Sounds like the brightness control element has an open or dead spot in it.

[bandersen]

Good idea, but it checks out OK. I perused the troubleshooting section in the Riders service info and found mention of picture blooming. They suggest it could by the picture tube or the 470K resistor in series with the HV lead.

Well, I'm using a 5AXP4 test CRT that I know is good so time to check that resistor. I found it mounted right on the 1X2 rectifier socket.
Briefly it measured around 500K then my DMM went to infinity and stayed there. I then tried a VTVM and got 30M !


I replaced it and viola! Plenty of brightness and no blooming
I recall reading that these resistors can go funky, but never experienced it before.


Just one problem left. While pulling the 10BP4 to install the 5AXP4, the base got hung up in the yoke and ripped out
Doesn't look too bad though. I'll try threading the leads back through and gluing the base on. I've done it before

[old_coot88]

Yikes! Lucky none of the wires broke off where they enter the glass.

[kvflyer]

One thing I have seen before and Bob, you may be the one that posted it, is that you can tack solder some longer pieces of wire on to the existing leads to assist in threading those wires into the correct pins. I have tried to do that with the leads the length that you show and it was almost impossible.

Please keep us posted...

[Zenith26kc20]

If the set has an "iron wire" yoke, be careful with the CRT. The yokes seem to shrink down a bit in size and grab the CRT socket and pull it off when the CRT is removed. If possible, I would put the CRT back in without the base and install the base afterwards. My Admiral did the same thing but it had the copper seal on the CRT base and went to air shortly after. Also, be careful with the yoke. Being tight can make it easy to damage a winding (don't ask me how I know that....).

[Eric H]

The yoke on my Admiral is tight too, warming them up a little with a heat gun or through operation sometimes makes it a whole lot easier to get the tube in/out.