Muntz M-21
   

12" screen, 1949

click on image to enlarge


"They were lousy TV sets!"--Grandpa Roper

Muntz had been out of the TV business for about 15 years when I came across a 1949 advertisement for their sets in a book.  When I asked my grandfather about the sets Mrs. Muntz wouldn't let Madman Earl give away, the above was his response.   He didn't elaborate, but years later I learned exactly why and how the company earned its reputation.

This table model is among the very first for sale by Muntz.  As the legend goes, its chassis was designed by process of elimination.  Earl Muntz began clipping parts out of a good (Admiral...?) TV chassis until it stopped working, determining down to a piece the absolute minimum number of components necessary for a television set to operate--then put the design into production.  By the time this set hit stores the first Muntz chassis design was found to be too basic and so had been modified and the tube count increased--to 15. 

 


Tube complement
RF amplifier    1 6AG5  
oscillator/mixer  1   6J6 
video IF amp   3 6AU6 
video detector  1 1N34 crystal
video amplifier  1 6AU6 
sound IF   1 6AU6 
detector/amp  1  6T8 
audio output   1 6AQ5 
sync limiter/DC rest   1 6AU6 
horizontal osc/output   1 6BG6G 
damper   1  6W4GT 
vertical osc/output  1 6SN7GT 
B+ rectifier   1  5U4G 
HV rectifier    1   1B3GT 

A picture's worth a thousand words

On the left in the picture above is, by industry standards of 1949, a simplified TV chassis using only 19 tubes (there are two LV rectifiers, so it could have been made with 18).  Compare the simplified Wilcox-Gay chassis at left to the Muntz chassis on the right.  Yes, it's complete!

In studying the Muntz schematic, I believe the common story about its design is partly urban legend.  I certainly see no design cues from Du Mont or Philco, sets cited elsewhere as guinea pigs for Muntz experimentation.  The combination sync and DC restoration circuit was apparently adapted from the circuit used in the 3" Pilot TV-37.  The simple "stacked" B+ scheme using just the audio output to supply proper voltages to RF/IF stages without the use of dropping resistors, plus presence of a power transformer and rectifier tube (along with other similarities) suggest Muntz may have started with an Admiral 19A11 chassis and scaled it up to work with a larger tube. 

While the exact source of his design inspiration is a matter of debate, Muntz' determination to use the absolute minimum number of components based on that design is hardly in dispute.  


Born on Halloween

For a specific example of Muntz-style engineering, let's start at the very beginning (a very good place to start) where the sets's B+ line connects to the rectifier filament.  Imagine Mr. Muntz examining a set with a conventional LC filter consisting of, say, a 40 mfd input capacitor followed by a choke and then a second 40 mfd cap.  He might think to himself "that inductor is expensive, so why not just snip it out and paralell the capacitors?"  And that's exactly what he did.

The other major section where Muntz threw conventional design wisdom out the window was horizontal scanning.  Even a simplified set of the time typically used a twin-triode oscillator tube and a dual-diode tube for frequency stability along with a damper.  The Muntz M-159 chassis deleted all these tubes, leaving only the now self-oscillating output tube in the cage with the high-voltage rectifier.  That was  sufficient to sweep a 10" tube, but the damper was added back in for the next chassis, the M-169 used in my set. 

The 6BG6 tested weak and would not lock to the proper phase.  Fortunately--and ironically--this set is far more forgiving than some when it comes to hand selection of tubes, so it was easy to find a 6BG6 it was happy with.


??

With a shorted IF tube, a converter with low emission and high voltage rectifier with nearly zero emission, it is nothing short of a miracle that the set exhibited any signs of life at all as found.  In fact it was trying very hard to work with those hollow-state handicaps and all its original paper and electrolytic caps.  The bit of paint-by-numbers work pictured above was not part of the original circuit, rather it is a modification that must have been done when the set would already have been considered quite old.  It was apparently added to eliminate retrace lines.   I returned the set to its original circuit because the mod eliminated DC restoration of the video.



There is no fine tuning knob.  It's a further miracle that the set was tuned spot-on for the cable box in my living room.  On the bench I fiddled with lots of adjustments, fine tuning included, and after the finished set was moved into the living room again, the tuning was so far off that the screen was black.  To access the fine tuning, you have to remove the decorative panel behind the knobs.

 

 



For the record, Muntz are not lousy TV sets, at least the ones of this set's generation.  True, the RF modulators we connect them to now provide essentially laboratory conditions versus the antennas of days gone by, but I've seen sets with a lot more parts give a lot less impressive performance under the same conditions.  For those who loathe the Muntz philosophy let's just put it this way--they work a lot better than they deserve to. 

 Laughing



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