Uniquely American

[David Roper]

The model number is known actually, it's American Television 2001A.

I've had this set for about four years. In the time since I acquired it I have learned that American Television was headed up by mechanical TV pioneer U. A. Sanabria, whose Western Television had manufactured the Visionette, Empire State and other 45-line triple-interlace TV models back in the mechanical days. In the 50s, his sets were variously branded American, DeForest and DeForest-Sanabria.

It came to me with the base whacked off of the CRT (the cathode lead came off with it, snapped flush with the glass), a condition which kept it in the back of the to-be-restored queue until I recently acquired an 8" test CRT. I did not, however, acquire a schematic. Instead I traced out my own. In doing so I discovered just how unusual this set really is.

There are four distinct B+ lines, only one of which comes off the conventional source. It measures about 365 volts. There also is a 425 volt boost line--nothing unusual about that as it serves the vertical sweep section, except it also provides focus voltage for the CRT. Another source is the rather unconventional 150 volt line, a circuit which leaves a guy such as myself scratching his head wondering what's missing, as this line has no apparent source. But the fourth B+ line is really something else. Trace it back far enough and it does connect to the main B+ which accounts for it measuring within a couple volts of 365. But this fourth line, which provides plate voltages for several tubes including audio and video output, first passes through the flyback and yoke.



So the process was: trace the circuit, rub my eyes in disbelief, confirm that what I drew is in fact how it's wired, move to next circuit, repeat.

With its sparse count of 17 tubes on top of the chassis, I was always skeptical of how well it would work. Once I got a got a look underneath the chassis I was skeptical IF it would work. I'm very pleased to report that, for all the set's eccentricity and economy of parts, Sanabria was no Muntz.



That's an off-air capture using rabbit ears (for close to the last time)

The set shows absolutely no retrace whatsoever. Even when running on an RF modulator it is not the least bothered by white/hi contrast scenes and has as minimal sync buzz as any set I've restored.

The next step is to determine whether the CRT is salveagable and, if not, where I might find a good one.

[zenithfan1]

Awesome! Thanks for sharing David. Great job on the restoration! I bet there's not many of those sets around now. That's a keeper for sure.

[wa2ise]

The audio output tube is providing the 150V source, via its cathode. This effectively puts the audio output in series with the IF strip, in a sense the plate current gets used twice. Instead of burning power thru a dropping resistor to get the 150V, the audio output circuit becomes the equal to that dropping resistor.

[AnalogDigit]

That is a way cool set!

[Dan Starnes]

Great info and very cool that it will live again.

[Eric H]

What CRT does it use?

[Sandy G]

Wonder why it was designed/made the way it was ? To get around the RCA patents? Try to save a bit on mfg/parts costs? Just for the hell of it ? Kewl save/resto, in any case !

[David Roper]

Originally Posted by Eric H

What CRT does it use?

I still am not sure. The printed tube location chart says 20DP4A but that's crossed out and 20CP4A written underneath. Neither can be correct because the tube has electrostatic focus. My best guess is that it's a 20HP4 but I have been unable to locate a number on it anywhere.

[stromberg6]

VERY cleanly drawn schematic! I wish they were all that easy to decipher. Nice, basic, straightforward design did/should provide excellent picture and sound. Definitely NOT a Muntz!
Best of luck!
Kevin

[David Roper]

Thank you very much for the compliment. If it were not so basic I would not have attempted drawing it. But as for straightforward...? lol, At least in my admittedly limited experience there are a few design features I had not seen.

Today I placed a call to Moyer about the availability of a CRT; they'll call back when they've checked.

[David Roper]

They checked. They had one. After two years of hemming and hawing about shipping it, I took the chance and it arrived safe and sound, yay! It's now in the set and at the moment I'm too pooped to do a proper update to the American TV page on my website, but you can watch a new video here.

As always, the humbar is a mere camera artifact and it really looks much better in person. There are some quirks owing to the way it was constructed and I'll get into those when I do the update

Speaking of updates, I did do one for the Muntz set I picked up at the ETF convention a couple weeks ago which turned out pretty nicely if I do say so myself.

[dieseljeep]

Originally Posted by wa2ise

The audio output tube is providing the 150V source, via its cathode. This effectively puts the audio output in series with the IF strip, in a sense the plate current gets used twice. Instead of burning power thru a dropping resistor to get the 150V, the audio output circuit becomes the equal to that dropping resistor.

Just about every large manufacturer of TV sets did that. If the set used a 6W6 or a 6AS5, 6BF5. They refered to it as "stacked B+". The tubes would short real easy, if overloaded.

[old_coot88]

Fascinating stuff, David. I was particularly intrigued by the Muntz with the self-oscillating HO tube and would sure dig seeing the schematic. Presumably sync was by direct injection of the sync pulse(?).
Also be interesting to see how he achieved the proper sawtooth waveform. Could the HO circuit possibly have incorporated an NE-2 to make it into a relaxation oscillator? (Early 'scopes used gas-discharge tubes as relaxers to make the horiz. sawtooth.)
Bill(oc)