Admiral 26R12 restoration

[bandersen]

I too have a few scars on my left hand from various tools slipping. Here's what I'm currently using. I start off with the pocket knife.
If that can pry up a little section, I move on to the small screwdriver. If not, I use the pliers. Note they do not have serrations so they don't chew up the aluminum all that much.
lickr

[bandersen]

I powered the set up slowly and all seemed OK so I went for full power. I was really surprised to see a distorted image. A little control tweaking and I got a stable image Those relacement vertical transformers are working just fine

Barely any sound though


After a little investigation, I discovered a broken antenna lead. Fixing that helped a little.



Then, I tried rocking each tube in it's socket and, bingo!, a 6AL5 wasn't making good contact. Plenty of sound now


Next, I hooked up a better signal source. The picture is pretty good, but rather dim. Not surprising really for an original CRT.


I switched to a dead channel and I have vertical bars similar to the last set I restored with the same chassis. This time there's one pronounced stripe and several faint bars.
I'll do some troubleshooting over the weekend. All in all, a very successful first power up

[Eric H]

43-08 54th st
I wonder if this is where it originally resided?

http://maps.google.com/maps?q=43-08+...270.12,,0,0.05

[dieseljeep]

Originally Posted by Eric H

43-08 54th st
I wonder if this is where it originally resided?

http://maps.google.com/maps?q=43-08+...270.12,,0,0.05

Could be Kenosha, Wi.

[Eric H]

Originally Posted by dieseljeep

Could be Kenosha, Wi.

Kenosha?

N.Y. was the only one I found with a 43-08 in the address but then this is sixty years later.

[Kevin Kuehn]

Originally Posted by bandersen

I switched to a dead channel and I have vertical bars similar to the last set I restored with the same chassis. This time there's one pronounced stripe and several faint bars.
I'll do some troubleshooting over the weekend. All in all, a very successful first power up

In case you haven't seen this yet over on ARF... mbear2k posted a link to a scan of his Admiral notes from Rider. Take a look at page 4. Still no value for the RF choke, but maybe it's the same as L405 used eleswhere in the circuit? It does identify the three componets being available as a combined filter(part #A34596).

http://www.oldtubes.net/library/free...ures-hirez.pdf

[Kevin Kuehn]

I guess he posted it here too. Great stuff.

http://www.oldtubes.net/library/free...uble_Cures.pdf

[bandersen]

Thanks for the link. Adjusting the drive got rid of the line but I still have the faint bars.

[bandersen]

Originally Posted by Kevin Kuehn

In case you haven't seen this yet over on ARF... mbear2k posted a link to a scan of his Admiral notes from Rider. Take a look at page 4. Still no value for the RF choke, but maybe it's the same as L405 used eleswhere in the circuit? It does identify the three componets being available as a combined filter(part #A34596).

Hmm. I don't see L405 in the parts list for the 21B1 chassis.

It says the RF choke is part # 73B8-3. I checked in my Thordarson cross reference, but it's not listed.

Does anyone have a cross reference guide for other suppliers like Merit or Stancor they can check ?

[bandersen]

Using the notes mbear2k posted, I was able to completely eliminate the retrace lines


I also put a scope on the horizontal output tube's grid and saw this.
There's some ringing in the waveform that most likely accounts for the vertical bars on the left.


The signal at the preceding stage (horizontal oscillator) looks correct so I'm not sure where it's coming from.


Otherwise, the set is playing fine, just a little dim and washed out. I may try rejuvinating the picture tube

[bandersen]

A little web searching pulled up this thread describing exactly the same problem and some solutions: http://www.antiqueradios.com/forums/...p?f=3&t=108670

I put my scope probe near the yoke and found really pronounced ringing.


I flipped though some 21B1 schematics and found the last revisions which did include that filter as part of normal production. No values given though so I'll have to experiment.

[Kevin Kuehn]

Originally Posted by bandersen

A little web searching pulled up this thread describing exactly the same problem and some solutions: http://www.antiqueradios.com/forums/...p?f=3&t=108670

Thanks for posting the ARF link. I hadn't read that one before, that was some very informative reading. Now if I could only remember all this stuff I read for more than a couple days, I could be like smarter

[bandersen]

Yeah, lots of good info in that thread. I took a closer look at my scope snapshot and estimate the ringing frequency at roughly 180kHz just like Tom noted. I see what chokes I have on hand and try to cobble together something with that resonant frequency.

[bandersen]

I used the capture mode on my scope to analyze that ringing more closely and it's definitely around 180 kHz.



Here's a schematic of a later production run showing the damper filter and unknown inductor L406.
That mystery value might be revealed in Riders Vol #13, but those pages are missing from my copy


Knowing that it's a 0.0068uF cap and 180kHz I pulled them into a resonance formula and got about 115uH. I rounded up to the next standard value - 120uH and ordered a few.

I hope it does the trick.

[bandersen]

Something else I'm working on is the washed out picture. At first I thought it might just be a worn out CRT, then I got a scope on the 6AC7 video output tube.
It turns out the signal on the grid is about 33% low and so is the output going to the pix tube. Now, I'm going through the IF stages hoping to boost the gain.

As with every Admiral I've worked on lately, most of the resistors are way off value. This 1K resistor is measuring almost double that.