1937 Emerson Mini-Tombstone Radio Model AU190, in a Unique Transparent Green-Yellow-Brown Swirled Catalin Variety, in Mint, Serviced and Working Condition

In a Nutshell
Emerson's Famous 1937 Mini-Tombstone Radio AU-190 in Green-Brown Swirled See-Through Catalin, Serviced and Working

Introduction:
The documented colour variants of this 1937 Emerson mini-tombstone radio AU190 as well as its very similar younger sister BT245 are marbled alabaster/yellow, marbled onyx/green, marbled walnut/brown, marbled tomato/red, and marbled lapis lazuli/blue, with collector's prices increasing along the list. The differences in value between the green-brown and the red-blue versions are small and depend on condition.
Catalin ( "the Gemstone of Modern Plastics") was produced around 1930-50 in opaque, translucent and transparent forms. The only truly transparent catalin radio known is the 1937 Kadette K-25 Clockette in unmarbled clear teal. It sold as part of the Mark Woolley collection at a Bonham auction on Dec.19, 2007 in New York (lot 5050 in ref.1) for $28'800 including buyer's premium and taxes, about four times the pre-auction estimate. The green marbled version of the Kadette K-25 is transparent too as can be seen at the virtual catalin museum at catalinradio.com (ref.2). Comparing these pictures with the ones of my radio below shows that both radios are made from the same green-yellow-brown swirled transparent catalin. The regular green version of the AU190 some time ago sold for 3050$ on eBay (Item 200192426916).
Catalin casting was an art, performed by skilled and experienced workers (part of the reason why in 1942 production by the American Catalin Corporation of New York (70% market share) was stopped). Mixing different colours and mixing them while casting was a creative act and resulted in individual cabinets, which can be easily tracked due to their unique fingerprint-like patterns. The cabinets for the early AU190 were produced by the Fiberloid Corporation of Springfield, Massachusetts, which called the material "opalon". My Emerson tombstone is either a new so far unknown transparent species of this radio or an example of the green version with an extremely rare anomaly in translucency (click on thumbnails 15 and 16 to see animations) . But it is not only possible but in fact quite probable, according to the very worth reading article by Ed Lyon (ref.3) about the Marblette Corporation, that the cabinet was made by Marblette, which would nicely explain the similarity with the green Kadette Clockette cabinet, made probably by Marblette too. Ed Lyon argues that the extreme color variability of the Emerson tombstone cabinets may have been the result of "poor process control at Marblette"; collectors should applaud them for that.

Additional information:
ref.1: http://www.bonhams.com/cgi-bin/public.sh/pubweb/publicSite.r?sContinent=USA&screen=catalogue&iSaleNo=16088
ref.2: http://catalinradio.com/i-2886078-kadette-k25-26-27-28-clockette-marbelized-green.html
ref.3: http://radioatticarchives.com/features/lyon_marblette.htm
ref.4: http://www.nostalgiaair.org

About my radio:
The cabinet has no cracks, chips or scratches. I have polished it by hand to remove the waferthin alcohol surface layer, normally building up on catalin. When polishing I discovered about five hard-to-see microscopic bubbles left over from production (see pict.31). It reminded me at finding a flea in a piece of amber collected at the Baltic Sea, when I was a kid.
The original speaker cloth was damaged and the dial lens had yellowed. Both have been replaced, but are still there and go with the radio, if wanted (pict.25). The chassis has been electronically serviced, all tubes tested, no condenser had to be replaced. The resistive wire line cord had been cut, and I replaced it with a normal (transparent too) cord. This replacement has to be done with extreme care, not to overload the radio with too much heat. Details under techies below. Finally I custom-made a transparent back plane from 0.08" thick plexiglass (lucite), in order to enhance the radio's see-through sex-appeal. Its holding screws as well as the 4 feet are original. Please e-mail me (Kris) for any questions, ich spreche Deutsch, je parle Français.

For the techies only:
Several smaller size AA5 (All American 5-tube) radios of the late 1930's used tube sets with a high (compared to later designs) 0.3A heater current, the heater voltages of which do not add up to the line voltage of 125V. The voltages of the Emerson AU190 tubes (see table below) add up to 68V (2x25 + 3x6). Two 6V dial lamps dimmed to 4.5V each are connected in series bringing the voltage up to 77V. The missing 48V were dropped in an extra resistive wire in the line cord (145Ω, see pict.34a), thus taking about 15 Watt (or about 40%) heat out of the radio. The butterscotch AU190 for sale too, has even the 2x40Ω surge limit resistors bypassing the dial lights buried into the cord (pict.34b).
Often this resistive cord is either deteriorated or cut, and has to be replaced, if the radio is wanted to work again. Simply replacing the cord by a regular one would overload the tubes and shorten their lifetime and causing tube burn to the catalin. Replacing the missing 145Ω by a resistor inside the radio would increase its power consumption by 60% and again cause heat problems. The clever way is to either implement a capacitive voltage dropper (pict.34 c) or to rectify the heater current (pict.34 d), in both cases dropping the RMS heater voltage without generating too much extra heat. A capacitive dropper would need a condenser of about 25μF, which if chosen as an electrolyte condenser, is reported to cause long-term problems, even when properly protected by additional diodes (pict.34 c). This leaves as the only practical solution a rectifying diode dropper (pict.34 d), which however still needs a dropper resistor of 38Ω, generating about 3W heat. I chose to connect two diodes in series, in case one fails, and to also use a number of diodes in series as efficient surge current limiters, instead of resistors or a Zener diode. All diodes are cheap type 1N4007. The radio worked fine for several hours using this solution.

Here are the specifications:

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