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Old 01-05-2018, 01:10 PM
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bandersen bandersen is offline
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Admiral 26X56 restoration

I found this set on the local craigslist about 5 years ago. It's an Admiral 2656 circa 1950/51 with a metal cone 16GP4 CRT. It's complete and in good condition aside from a broken off control door which I have since replaced

It was sitting in the basement of the house it had been in it's whole life. The house was being sold and it had to go. The seller had grown up with it and remembered watching it years ago when something popped and the screen went dark.





The CRT tests on the weak side and the 5U4 looks well used.


HV rectifier plate cap lead is broken off as this picture taken 5 years ago shows. Wish I had remembered that when I started working on it last weekend

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Last edited by bandersen; 01-05-2018 at 01:24 PM.
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Old 01-05-2018, 01:26 PM
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Here it is up on the bench.






I popped out the 5U4 rectifier and powered it up. All the tubes lit (or so I thought) and got around 600 VAC on the secondary :thumbsup:



This cap is the only evidence I've found of old repairs. Not sure what it's doing at that point. There is only a 0.047 shown on the schematic - not a 20uF

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Old 01-05-2018, 02:34 PM
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I put the rectifier back in and slowly power the set up over about 20 minutes. As B+ increase so did the hum in the speaker. B+ should be 300 but measure less than 200 with plenty of ripple. Turns out the main 60uF filter cap was open. I cut it loose and tacked in a new one. That killed the hum but still no reception. Cleaning the tuner and wiggled some tubes and got some clear audio

Eventually, I rediscoveredd and repaired the broken HV lead. HV was pretty weak but at last I managed to get a raster.


I also rejuvinated the CRT which was testing very weak. It's up into the green now, but the raster isn't very bright.

Replacing the horizontal output tube and tweaking the horizontal drice helped a little. I noticed B+ was still well below 300 though. Replacing that tired 5U4 and a couple more electrolytics got it up where it should be. HV is also close to spec.


Gradually, the image got better and better.


Replaced a few weak IF tubes and played with the flaky contrast control and got a decent image. Sync is non-existant though.



Worked on the sync circuit and found the 12AU7 was dead.


This set had the shortest 6SN7s I've seen. Assuming that's even what they are. No markings on them at all!


Replacing that got me solid sync but victory was short lived...
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Old 01-05-2018, 02:56 PM
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I was tweaking the horizontal drive trimmer cap to get rid of that annoying line when the image started to fade. I smelled something burning too and turned the set off immediately. I sniffed and poked around and it seemed like one old paper cap near the HOT was warm. I powered it back up to troubleshoot and the drive signal on the HOT grid was fine, but 0 HV.

Time to examine the flyback. I grabbed a DMM and found intermittent HV winding readings. Sometimes infinite. Sometimes fluctuating in the k and M ohm range.

Let's take a closer look.


Ugh. Found a 14 A fuse in the 0.25A holder


Poked around and would briefly get the correct resistance on the HV winding giving me hop it's not fried. The fine wired had some green corrosiion so I unsoldered the end and slide off the spaghetti tubing.

After a couple flexes, the wire broke off. I cleaned it off near the wax and tacked in a temporary bridge.

That restored solid continuity. I'm going to clean out all the dust, replace the fuse and splice in a proper repair. Then fuly recap the horizontl circuit before another power up.

Worst case, I think I can dig up a replacement flyback.
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Last edited by bandersen; 01-05-2018 at 03:00 PM.
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Old 01-05-2018, 07:43 PM
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Nice set Bob Im sure it will come out right.
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Old 01-08-2018, 02:30 PM
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I did some work inside the flyback cage over the weekend. First I cleaned out all the dust and this removed this cap which did not look original. I'm thinking it was added to increase the width ?
I also installed a correct 0.25A fuse.


Then I carefully spliced in a new HV lead using teflon coated, silver plated wire. Very nice stuff to work with if you can get some. I then used some Super Corona Dope to insulated the repair.


Alright! Back in business
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Old 01-08-2018, 02:45 PM
Tom9589 Tom9589 is offline
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If that "extra" cap which you removed was connected between the damper plate and cathode, it was definitely used to increase width. They used to sell a device which was sandwiched between the damper tube and its socket. It had a small cap which connected between the plate and cathode of the damper. It worked well for a customer who had limited funds to pay for TV repair.
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Old 01-08-2018, 03:33 PM
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Good to know. I have full width now so I assume whatever was causing width issues has been repaired. Probably a leaky paper cap.

I've been taking these screenshots with the brightness and contrast at 100% in a dim room. It also takes a while to get an image from a cold start.

Time to replace that weak picture tube.


I removed the metal hoop around the screen and loosen up the yoke support. THe CT started to slide out but the base got hung up in the yoke.
Luckily, I've been in this situation before and knew an old trick - heat up the yoke. One option is to run some current through it. I opted for a heat gun. A few minutes later I had it out.

The chassis looks a little strange now.


I popped in a 5AXP4 test CRT and, wow, what a difference. Very watchable with the controls far below max. I'm optimistic the spare, rebuilt 16GP4 CRT I plan to install will work well too.


However, I did notice a strange issue. As I decreased the brightness, it dimmed more on the sides than the center.

You can get it down to where there is just a think strip visible in the middle.

I'm thinking the HV doorknob cap way be bad or there is some ripple in the power supply. There are still a few old electrolytics left. I'l tr replacing them first.
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Old 01-08-2018, 03:43 PM
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Quote from bandersen's post: "Ugh. Found a 14 A fuse in the 0.25A holder"


Who on earth would install a 14 amp fuse to replace a 0.25-amp one? Needless to say, this is a disaster just waiting to happen.
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Old 01-08-2018, 04:27 PM
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I'm sure you took the focus magnet off when you installed the test CRT.
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Old 01-08-2018, 05:08 PM
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I did indeed This set uses a tapped focus coil. A wirewound pot is shunted between the tap and one leg.

That brings up another issue. The focus control is only responsive for about 25% of it's travel. I suspect there is a break inside. I'll pop it open and attempt a repair. If I can't, I might have a spare from a scrapped Admiral chassis.

The tricky part is remembering where my box of salvaged controls is I need to get serious about sorting and organizing since I moved almost a year ago!
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Old 01-08-2018, 07:05 PM
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Quote:
Originally Posted by bandersen View Post
However, I did notice a strange issue. As I decreased the brightness, it dimmed more on the sides than the center.

You can get it down to where there is just a think strip visible in the middle.

I'm thinking the HV doorknob cap way be bad or there is some ripple in the power supply. There are still a few old electrolytics left. I'l tr replacing them first.
I believe that there is a bad electrolytic capacitor for the video output cathode bias that is bad. i've seen this before. if the doorknob capacitor is failing, there would be HV issues, but from what i see of the pics, this is more like a problem with the video output stages. i would venture to say that a total recap of the set will fix the problem.
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Old 01-08-2018, 07:08 PM
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Quote:
Originally Posted by bandersen View Post

The tricky part is remembering where my box of salvaged controls is I need to get serious about sorting and organizing since I moved almost a year ago!
I wish you good luck on finding them soon, I'm still waiting for you to find me a width control for my 20A1 chassis :-).
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Old 01-09-2018, 12:22 PM
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Quote:
Originally Posted by robert1 View Post
I believe that there is a bad electrolytic capacitor for the video output cathode bias that is bad. i've seen this before. if the doorknob capacitor is failing, there would be HV issues, but from what i see of the pics, this is more like a problem with the video output stages. i would venture to say that a total recap of the set will fix the problem.
You were close. There is no cathode bias cap on the 6AC7 video output tube, but the problem was a filter cap. While investigating, I was surprised to see that the filament ground wire on pin 2 wasn't soldered. It also appears to have Glyptal (red insulating varnish) paint on it Weird. It must be making good enough contact because the tube is warm. I cleaned off the gunk and soldered it securely.


I then went hunting with a scope and found a huge 200V triangle waveform at around 15.75 kH on the B+ boost rail. The old 20uF cap still wired in must be dead. I temporarily tacked in a new 22uF and viola - problem solved.




I have a few more old caps to replace then I'll check the alignment before installing a new 16GP4.

Normally, I would do a shotgun recap but I find it can be fun and instructive to do it in stages too.

One other thing I've noticed in this and other 1950 era TVs is a weird assortment of resistors. Also some in series or parallel to get the needed value.

They must have really been hurting for 1K resistors. A bunch are actually 1.2K and here are two 2K in parallel. They even used a dogbone.


I thought this was a ceramic cap at first, but no, it's a 2.2 M resistor.


I figure the big demand for consumer electronics and the Korean war was causing shortages.
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Last edited by bandersen; 01-09-2018 at 03:23 PM.
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Old 01-18-2018, 09:56 AM
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Finished replacing all the caps and loads of out of spec resistors. The audio output stage was especially bad with one resistor being 10X high. Set is playing very well now. Definitely no need for an alignment.

Still need to repair or replace the focus coil then I'll try installing a new 16GP4. Also going to try a vertical retrace suppression modification.

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