Restoring The Admiral Model 20X1 B/W Television Set

I found this Admiral 20X1 at a local auction house. Looking it over it appeared to be in pretty good condition, no cracks in the Bakelite case and only the usual amount of dust a set this old would collect over the years. One of the auction house workers said they had plugged it in but it didn't appear to work. I didn't exactly want to hear that, plus a sniff at the rear of the set gave a lingering smell of something burnt, but never the less I decided I would bid. I wondered if I would have any competition, however only one other person seemed somewhat interested, so I got the set for less than $75. Now if only there aren't major problems that can't be resolved.

Technical Data

Trade Name:   Admiral
 
Manufacturer: Admiral Corporation Chicago, Ill.

Model Year:   1949
 
Type Set:     Television Receiver B/W

Tubes:        Nineteen

Picture:      10-inch Black & White

Tuning Range: Channels 2 thru 13

Cabinet:      Bakelite Console - Brown


The chassis is transformer powered utilizing a 19 tube line-up. Electro-magnetic deflection is used on the picture 
tube. The speaker is of the electro-dynamic type with the field coil used as one of the two filter chokes in the LV 
power supply. The tuner is of the turret type.



Tube Line-up:

V1   6AG5.....1st RF Amp          V11  6AS5.....Audio Output  
V2   6J6......Mixer/Osc           V12 12AU7.....Sync Amp-Sync Sep 
V3   6AU6.....1st Video I-F       V13 12AU7.....Vert Osc-Vert Amp
V4   6AU6.....2st Video I-F       V14 6SN7......Horiz AFC-Horiz Osc
V5   6AU6.....3nd Video I-F       V15 6BG6......Horiz Output 
V6   6AL5.....Video Det.-AGC      V16 5W4.......Damper 
V7   6AU6.....Video Amp           V17 1X2.......HV Rectifier  
V8   6AU6.....Sound I-F           V18 5U4.......LV Rectifier
V9   6AL5.....Ratio Detector      V19 10BP4.....Picture Tube    
V10  6SN7.....AF Amp/Sync Clipper

The unit is housed in a Brown Bakelite cabinet measuring 32 1/4 inches high, 16 1/4 inches wide, and 17 inches deep. I can't vouch for any truth in it, but I have been told that this is the largest piece of Bakelite ever cast.

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The Restoration

As I did not have a schematic diagram, I decided the first order of business was to get the Bakelite cabinet cleaned. The knobs and four screws holding the chassis were removed and the chassis slid out of the cabinet. The bezel and glass were also removed. The cabinet, bezel and glass were washed with a solution of water and mild soap. A vigorous rub-down with Novus plastic polish brought the shine back to the Bakelite. A final polishing with brown wax shoe polish finished it off and made it shine up quite well.

The chassis was dusty but no corrosion or rust. A quick going over with the air compressor and brush removed most of dust and a close inspection showed things to be in very good shape.

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A query on one of the antique radio forums yielded the promise of a schematic. Meanwhile, I looked over the chassis being mindful of the burnt smell, but finding nothing unusual I decided to bring it up on the variac to see if it would show any signs of life. All of the tube filaments lit up except for the 5U4 rectifier. I pulled the 5U4 rectifier tube and discovered that the key-way had been broken off and the it had been incorrectly inserted in the tube socket. After inserting the tube correctly still no signs of life, that is when I discoverd that the speaker field coil was open, thus no B plus voltage. I substuted a choke in place of the field coil, temporarly connected a PM speaker and the set showed promise with sound but no raster.

Bringing the tip of a screwdriver blade close to the top cap of the 6BG6 horizontal output tube should produce a voltage arc if the horizontal circuit is working, but no arc was observed. Without the horizontal oscillator circuit working, there would be no high voltage on the picture tube. A look under the chassis revealed a blown fuse in the horizontal output circuit. Replacement of the fuse resulted in HV but still no raster. Hmmm...do I have a picture tube with no emission? Then I spied the ion trap on the neck of the tube and with a little adjustment the tube sprang to life with a nice bright raster.

With rabbit ears attached, a few adjustments and the set received the three local stations with quite a good picture.

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While waiting for the schematic to arrive via U.S. mail, I decided to proceede ahead and replaced all of the electrolytic and paper capacitors.

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The schematic arrived so time to check voltages against the readings in the voltage chart. All voltages check out well within tolerance so now to hook up the generator and oscilloscope and do a bit of alignment. Since the set is playing so well I suspect that only a touch up will be necessary. Going through the alignment procedures proved that to be the case and a slight improvement was noticed, especially with the tuning of the audio.

This set uses inter-carrier audio instead of split sound audio. The TV signal carries both the video and audio signals. At some point the audio and video must be separated and detected separately. In split sound, the audio portion of the signal is taken off just before the video Intermediate Frequency amplifier chain where it is amplified and detected in the audio IF stages. In inter-carrier audio, the audio signal is amplified along with the video signal in the video IF circuit, the sound being pulled off at the end of the video IF chain. This eliminates a stage or two of separate sound amplification, saving on tube and component count.

A good going over of the chassis with a damp rag, a few Q-Tips and the chassis came out looking quite clean.

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Finally the problem of the open field coil had to be resolved. I began removing the outer layers of insulation around the coil and discovered that the connection between one of the external wires and the small field coil wire was broken where they were orginally joined. This was resoldered and the outer insulation replaced and new wire from the speaker to the plug was installed as the old wiring was pretty frayed. A new speaker board with new grill cloth replaced the old board and cloth, the chassis installed in the cabinet and the restoration is complete. It is really a pleasure to see a fifty-seven year old television perform again, especially when watching videos of Jackie Gleason, Abbott and Costello, Bob Hope, and a Bogie and BaCall movie or two.

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