Admiral 26R12 restoration
 

Yeah! Another Admiral restoration project :drool:

This time it's the console on the left with a 21B1 chassis run #2.

http://farm7.staticflickr.com/6012/5...4a94ff83_z.jpg

It's a bit more primitive than the run #14 chassis I just restored. For example it lacks the couplates and gated AGC you'll find in the later runs. Also, it's not copper plated, but luckily, it's not rusty - just very dirty. It also has the original metal back.

http://farm7.staticflickr.com/6143/5...f6624af0_z.jpg

Someone added crappy casters at some point. I'll be removing those.
http://farm7.staticflickr.com/6133/5...4c3fce3d_z.jpg

Here it is up on the workbench.
http://farm8.staticflickr.com/7161/6...b4363917_z.jpg http://farm8.staticflickr.com/7029/6...d9621075_z.jpg

Original owner ?
http://farm8.staticflickr.com/7030/6...55c234ef_z.jpg


I found evidence of many old repairs under the chassis.
http://farm8.staticflickr.com/7020/6...9307a69e_b.jpg

First, I popped out the 5U4 rectifier and power it up. All the tubes lit up and I get what I expected on the secondary.

The flyback and yoke resistances check out OK too.
http://farm8.staticflickr.com/7143/6...c0e30056_z.jpg http://farm8.staticflickr.com/7168/6...9d87cce1_z.jpg

Uh-oh! Bad vertical output autotransformer :tears:
I was hoping I could find a break near the output lead and repair it. Nope.
http://farm8.staticflickr.com/7175/6...6b51fbd4_z.jpg http://farm8.staticflickr.com/7151/6...9982eb2f_z.jpg

Uh-oh! Bad vertical blocking oscillator transformer :tears:
http://farm8.staticflickr.com/7018/6...efe8f6ed_z.jpg

Not to worry. Videokarma member kvflyer (AKA Don) to the rescue :banana:
The new transformers on the right just arrived in the mail and measure good.
http://farm8.staticflickr.com/7012/6...bfba1d6d_z.jpg

I'm almost done recapping and replacing many out of spec resistors. So many in fact, there won't be many original parts left in this set!

There are also many ugly old repair attempts. The horizontal oscillator and output circuit is a good example. Several resistors have been replaced with ones of very different values. A couple capacitors have been tacked in that aren't even on the schematic. Worst of all, the HOT cathode has been shorted directly to ground bypassing the 47 ohm resistor and filter cap.
http://farm8.staticflickr.com/7010/6...6f2727e0_z.jpg

Here it is cleaned up.
http://farm8.staticflickr.com/7172/6...09fb59de_z.jpg

I've been testing all the mica caps with a Simpson 383A Capacohmeter. So far, they're all still good.
http://farm8.staticflickr.com/7002/6...1813718f_z.jpg

The big 3K candohm power resistor is burned out.
I wonder if this 15W aluminum housed resistor will do if mounted properly ?

http://farm8.staticflickr.com/7156/6...295b04ff_z.jpg

Bob,

I am very fortunate that my 26R12 was not hacked up like yours. Actually, when I bought it working from a guy about 20 miles from here, he told me it worked. He had quite an assortment of what I would call "Desirable" sets. Anyway, it did work so it was just a matter of replace caps, test, replace caps, test etc. I was lucky that all coils and transformers were good.

Just FYI, it worked fine for about 2 hours and then I heard a "POP" and the vertical collapsed to about half. I was not able to make it bigger with the height control (clue #1) but the vertical linearity did work. Voltages did not change whilst rotating the height control (more confirming clue #2). I tried lots of stuff and was unsuccessful so I put it down.

One of the guys, I think Dennis, at ARF suggested "tin whiskers" on the height control. Removing, cleaning the outside and the problem was gone. Lesson learned by me, remove controls, clean the outside a well as the carbon track and reinstall.

I have an NOS RCA 16TP4 in mine. Not aluminized so it isn't super bright. And I think I found out why it was NOS in the box for so many years. There are about three spots on the face where the phosphorus is missing. Factory defect. But you really have to look for them so, "No Worries Mate!".

Sorry if I hijacked your thread. It is nice to follow this thread...

Not at all - comments are most welcome. This CRT is not aluminized either so I expect it will be quite dim compared to the Silverama CRT in the last set I restored.

Wow, that set sure had a lot of "issues." With all those hack repairs, maybe that's why they put casters on it :D

Fabulous work as usual, Bob.

-Clark

Great thread so far Bob :yes: - Lucky about getting some replacement vertical transformers, in all my TV adventures over the years I've only come across one that had an open circuit vertical blocking osc transformer. By the way I keep noticing that speaker on its front at the back of your bench, just curious as to why it just sits there? Is it one of those things that you keep meaning to move and forget about :D I have things like that on my workbenches..:yes:

LOL - could be :) I confirmed that the sets current owner has tile floors so I'll be putting felt pads on the bottom. I just hope the holes drilled for those casters didn't crack the bakelite.

This set sure has been rather interesting to work on. I'd say the oddest "repair" so far was the addition of an extra 470 pF mica cap into the horizontal oscillator circuit where none belonged.
It the one turned around so no color dots are showing. I assumed that one of the originals must be bad, but, nope, they're all good.

http://farm8.staticflickr.com/7011/6...a0cab9aa_z.jpg



I got around to checking all the tubes last night and was surprised to find there all quite good except for one. The 6AC7 video output tube shows a short on the plate so I'll replace it.

Ah, that's a field coil speaker for an Admiral 20X1 chassis. I've been working on 3 of them in between these 21B1 Admiral chassis so I just left it up there for convenience. I really should put it somewhere safer though. I'd hate to tear the cone :sigh:

When I have a speaker, now the first thing I do is to tape a piece of heavy corrugated cardboard cut to the exact size to the speaker over the front. Of course, it is easy to drop those needle nose pliers or screwdrivers just at the wrong time. They always seem to find the backside of the speaker. :D

kvflyer wrote: the first thing I do is to tape a piece of heavy corrugated cardboard cut to the exact size to the speaker
So do I, to avoid the great sorrow experienced more than once! :cry:

Yes, we (unfortunately) learn from experience don't we? :tears:

OK, the speaker is safely stored away ;)

I restuffed the electrolytics, finished recapping and installed the replacement vertical transformers.
http://farm8.staticflickr.com/7148/6...b47b4636_b.jpg


http://farm8.staticflickr.com/7142/6...3108ffff_b.jpg

The tubes have been installed and it's ready for a 1st test. The tubes wit green tape test OK, but just into the good range.
http://farm8.staticflickr.com/7158/6...e13f53cc_b.jpg

What kind of a tool do you use to peel open the bottom lip of those electrolytic can caps? I've tried a couple different things and always end up botching things up. That and I usually slip and I poke myself with whatever tool and get real angry. :D

Yea, what kevin said. I'm just as sick a' skewering myself as him....Also you do a neater job than me and I'd like to do as neat of a job as possible especially considering that I'm going to be getting a CTC-4 soon...

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.
http://farm8.staticflickr.com/7147/6...7c91779f_z.jpglickr

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 :banana: Those relacement vertical transformers are working just fine :yes:

Barely any sound though :scratch2:
http://farm8.staticflickr.com/7027/6...9bb6946e_z.jpg

After a little investigation, I discovered a broken antenna lead. Fixing that helped a little.
http://farm8.staticflickr.com/7161/6...aa790c91_z.jpg


Then, I tried rocking each tube in it's socket and, bingo!, a 6AL5 wasn't making good contact. Plenty of sound now :music:
http://farm8.staticflickr.com/7015/6...1ddd1da6_z.jpg

Next, I hooked up a better signal source. The picture is pretty good, but rather dim. Not surprising really for an original CRT.
http://farm8.staticflickr.com/7173/6...d397a0f1_z.jpg

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 :)
http://farm8.staticflickr.com/7172/6...b2edfdbf_z.jpg

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.:scratch2:

Kenosha?

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

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

I guess he posted it here too. Great stuff.

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

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

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 ?

Using the notes mbear2k posted, I was able to completely eliminate the retrace lines :)
http://farm8.staticflickr.com/7161/6...bd5390347c.jpg http://farm8.staticflickr.com/7011/6...c484e3580d.jpg

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.
http://farm8.staticflickr.com/7015/6...2d948c0bea.jpg

The signal at the preceding stage (horizontal oscillator) looks correct so I'm not sure where it's coming from.
http://farm8.staticflickr.com/7028/6...a902c24f2f.jpg

Otherwise, the set is playing fine, just a little dim and washed out. I may try rejuvinating the picture tube :scratch2:
http://farm8.staticflickr.com/7171/6...cde55feb3a.jpg

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.
http://farm8.staticflickr.com/7175/6...7972fd7810.jpg

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.

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 :screwy:

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.

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

http://farm8.staticflickr.com/7168/6...5d9cf709f0.jpg

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 :tears:
http://farm8.staticflickr.com/7155/6...2621531ded.jpg

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.
http://farm8.staticflickr.com/7157/6...0fc7337fe9.jpg

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.

http://farm8.staticflickr.com/7148/6...9f7bbea553.jpg

You too huh? I seem to be having a run of high resistors lately...Maybe they're conspiring against us? :naughty:

And so the resistance movement has begun!!!!!!:smshot::jawdrop::pistols::uzi:

LOL.

I'll get those resistors in line! :whip:

As for the IF alignment, I tried two different sweep generators and what I'm seeing just doesn't make sense. The gain is lousy and the response curve is nothing like it should be. I'm starting to think I might have a bad coil or cap in there somewhere. I still have the set I just restored with the same chassis so next I'll compare them side-by-side.

I also cleaned out the HV cage. Pretty nasty in there.
http://farm8.staticflickr.com/7175/6...5a575eaa88.jpg http://farm8.staticflickr.com/7150/6...732b37e069.jpg


Terrible idea to put the AC power plug so close to the fylback :no:
Amazingly, the fuse is actually the correct 1/4 Amp. I usually find one more like 10 Amps :rolleyes:
http://farm8.staticflickr.com/7007/6...58c28a908a.jpg

The porthole Zenith that I have (still in queue) had exactly that! A 10 amp fuse in the Horizontal circuit. Needless to say, the flyback looked like a burned pork chop. I was lucky to find an NOS Merit thanks to one of the guys on ARF.

I remember reading one of the production changes in the chassis series was including that fuse to satisfy U/L requirements.

Wow!

I would imagine, from the factory, that the wires were dressed a little better than that! At least I hope so. Does the other duplicate chassis look the same in that area?

Anyway, I zoomed in via flicker. The outer flyback coating looks like it is completely "punched through!" Are you sure the outer windings are 100% OK. Did you test it with your EICO flyback and yoke tester? I think that you said that you had... It wouldn't have taken much more abuse before that flyback ended up as toast!

I slid some heatshrink tubing over the AC wires and pushed them out of the way. It seems to be OK. I've had the set playing a few hours with no HV problems. I should melt some new wax over it just to be safe.

Here's a production run #5 chassis (this set is run #2). Copper plating, but same bad design.
http://farm8.staticflickr.com/7029/6...07826d6e31.jpg

Finally, by production run #14 they had the sense to relocate the AC plug.
http://farm8.staticflickr.com/7166/6...9485d48f42.jpg

I hope you have decided against rejuvinating the CRT for now. You could easily kill it. I've got a CRT rejuvinator/tester, and have never used the rejuv feature with it. I've never seen a rejuvinated tube that lasted more than a few months at the most.

Your set is looking fantastic! I'm really enjoying the progress you are making!

Bruce

Thanks. No, I'm not going to rejuv. this picture tube. It's very watchable if you dim the lights a little.

My Sencore CR70 has an auto-restore and several rejuvinate functions. I've only used them on CRTs that were really weak. It helped a little - couldn't say for how long though as I don't play my sets that much.

I received my filter parts over the weekend and finally had a chance to try it out tonight. Here's where I wired it in.
I'll do a neater job once I'm done tweaking it. I figure I can use one of the unused damper socket lugs for a tie point.
http://farm8.staticflickr.com/7152/6...f0de32602d.jpg

It definitely reduces, but doesn't eliminate the ringing. I'll try tweaking the capacitor value to reduce it even more.
http://farm8.staticflickr.com/7166/6...83ce0a5cdb.jpg

Unfortunately, the bars are still there but not as bad as before I think.
http://farm8.staticflickr.com/7173/6...ee28eb2c68.jpg

I also tried several different 6W4 and 6AX4 damper tubes with little change.

I re-read those Admiral servicing notes more carefully and discovered that the filter must installed inside the HV cage not under the chassis. I'm not sure if that affects the circuit or it's a safety issue, but I went ahead and moved it. I mounted a terminal strip to an existing hole and soldered in the components.
http://farm8.staticflickr.com/7023/6...916d8725_z.jpg

I also tweaked the capacitor value. I figure the ripple is a harmonic of 15,750 Hz. The closest to what I saw on the scope are 173 and 189 kHz. A little experimenting found that 189 kHz was correct so I went with about 5900 pF in parallel with the 120 uH inductor.

Unfortunately, while mucking around in the HV cage I managed to snap off a flyback lead. I melt back the wax a little and managed to solder it back on then coated it with corona dope. Seems to work fine after 10+ hours of playing.
http://farm8.staticflickr.com/7034/6...fb2d078a_z.jpg

Then on to cleaning out the tuner and going through the alignment procedure.
I found this date stamped inside the tuner.
http://farm8.staticflickr.com/7013/6...9d7d9fbe_z.jpg

Here's the IF response.
http://farm8.staticflickr.com/7166/6...d4dab639_z.jpg

I spent a lot of time fighting with the focus coil, centering lever, ion trap magnet and yoke. It's not perfect, but certainly better than what I started with.
http://farm8.staticflickr.com/7035/6...9a7040e8_z.jpg

Here are a couple screenshots. You can see how the bottom right-corner bends up a little.
Another issue is an occasional hiss / crackle in the audio. it sounds just like a HV leak, but I can pull the HO tube and the hiss remains :scratch2:

http://farm8.staticflickr.com/7009/6...5c46b4dc_z.jpg http://farm8.staticflickr.com/7174/6...1f450cff_z.jpg