Admiral 421M

21" screen, 1952
click image to enlarge

This set uses chassis 21Y1.  That's an AM radio between the two larger knobs.  There's also an input for a turntable, but connecting one to this set is not for the faint of heart:  to plug it in requires removing the back and reaching deep inside where the RCA jack is hidden (larger combo models using this chassis had the turntable built in).

Tube Complement
RF amplifier   1   6BQ7 
mixer/oscillator  1   6J6 
video IF amp  2  6AU6 
3rd video IF   1  6AG5  
video detector   1  1N64  crystal
video amplifier   1  6AC7 
gated AGC   1  6AU6 
audio IF amp   1  6AU6  
ratio detector   1  6AL5 
audio amp/AVC   1  6AV6 AM radio detector
audio output   1   6V6GT 
sync sep/clipper   1 12AU7 
sync inverter   ½  6SN7GT 
sync discriminator   1  6AL5 
horizontal osc   1  6SN7GT 
horizontal output   1  6CD6G 
damper   1   6W4GT 
vertical osc   ½  6SN7GT 
vertical output   1   6S4 
B+ rectifier   1   5U4G 
HV rectifier   1   1B3GT 

AM subchassis:

converter            1   6BE6  
IF amplifier            1   6BA6 

Restoration notes: 

Now that I've amassed a collection of vintage sets large enough to meet the threshold of being a 'serious collector', I can look back and say that the year I really began to collect seriously was 2005.  That year I rented a U-Haul to bring to the Early Television Convention swap meet and brought it home filled with sets.  This is one of them.

I almost restored this set in fact if I had had a CRT tester at that time I definitely would have chosen this set over the one I did work on.  That set turned out to have a tube with a heater-cathode short, while the Admiral's tube tests like new.  I had never had the back off in seven years, never even plugged it in.   Soft-starting with a variac produced no sparkles, sizzles or also revealed no signal whatsoever from the radio or the TV.  But there was a bright, nearly full raster on the screen at full line voltage, which meant all systems go for a recap!

The Admiral's tube is mounted to the cabinet rather than to the chassis.  While the chassis was on the bench I tracked progress with a TeleMatic Telecheck, an 8XP4 CRT in a box with built in yoke and speaker. 

I replaced only the first two filters and three or four paper caps in the horizontal section before powering up again.   Mysteriously enough, this time there was strong reception on channel 4, with audio coming in loud and clear and diagonal video that was obviously a sharp picture if only it would sync, instead stubbornly slanting to the left no matter which way the horizontal hold was turned.  Working through the sync circuit and gradually replacing caps seemed to make little difference.  Eventually the vertical was solidly synced, but the image was still slanted to the left and slowly wandering one or the other direction sideways.  Finally I came to C308, a .047 cap that couples the video amplifier output to the sync separator.  With this capacitor replaced, the picture sprang instantly into frame. 

sudden death

I have in the past done shotgun recaps of TV sets and fortunately doing so never resulted in catastrophe, but it's a practice I would never recommend and probably will never return to after lessons learned from working on this set.  I had actually been proceeding in gradual steps, powering the set up again after each of the old can electrolytic capacitors was replaced with a strip of new caps.  After  the last can was bypassed, the next power up produced no picture, quickly determined to be the result of no high voltage.  I had no more than a couple of minutes to ponder this dilemma before the audio suddenly faded and disappeared to silence.  Where I had had good picture and sound before, now I had nothing.

There's no more discouraging note to leave things on, but I decided to sleep on it.  The next day I decided to concentrate on the radio, which had not worked at all up to that point.   Testing showed that the 6BE6 was very weak;  the 6BA6 turned out to be broken, its pieces held in place by the retaining clip.  Replacing both these tubes brought the radio back to life.  The TV audio likewise turned out to be a 6AU6 that picked the absolute worst possible moment to spontaniously flatline in emissions;  replacing the 2nd IF tube brought the TV sound back loud and clear.   But the screen was still dark.

Despite not more than one capacitor section having been disconnected at any time while I was installing replacements, I checked and rechecked my work to be sure I had not miswired anything.  In fact wiring up that set of capacitors was not the only thing I had done at that time:  I had also tested a couple of tubes, namely the rectifier and the horizontal output tube.  The consultation I sought for the problem suggested various voltage checks which promptly led to the grid of the HO tube where I saw a curious sight...

That's funny, aren't capacitors supposed to have more than one lead?  Embarassed  Apparently the lead was already hanging by a thread when I started this project and removal of the tube from its socket was enough disturbance to finally break it off.   This marks the first time I've ever had to replace a mica capacitor.  I knew it was only a matter of time, but I hardly expected it to be brought about by such a weird failure. 

A more gratifying milestone is the first attempt--and first success--at dial restringing.  No, not of the radio fortunately... 

The selector switch is inside of a concentric shaft, the outer part of which is unmarked but turns out to be a cord-driven tone control.  The original dial cord had snapped.  It is a rather inconsequential adjustment and could have been set to a pleasing value and simply left there, but I thought it would be valuable practice as I work my way up to radios like my Airline 62-1100, which has been kept out of the restoration queue by an unstrung dial.  The "dial cord" here is actually 30 lb test fishing line.

With Admiral's reputation in mind, this TV was chosen as a "piece of cake" project after a string of extra-challenging restorations.  In spite of the broken cap lead snafu, it pretty much lived up to its reputation for sensible design and solid, no-nonsense build.  A singular exception to this is the radio portion.  As its performance was flawless after tube replacement I considered leaving it alone, but ultimately decided to recap as long as the chassis was already on the bench.  While the tubes can easily be reached from underneath (as can IF adjustments if alignment were ever necessary), the entire subchassis must be removed to gain access to the rest of the components. 

This entails disconnecting all the wiring and the removal of the tone control string (if it isn't broken) so that the unit will slide free of the long selector switch shaft.  It's a rather thoughtless design, especially compared to the rest of the chassis.

The picture is razor sharp with perfect geometry.  Likewise the sound is truly hi-fi from the full-range 10" speaker.  No wonder the old school techs swear by Admiral:  easy to get working and a great performer when finished.

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