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Stromberg Carlson 1200 "Dynamtomic" Table Radio (1948)
This model was one of a
series of very popular
"Dynatomic" style radios
from Stromberg Carlson,
beginning with model
1101 in 1946 and
running through 1951
with model 1500. As well
as the standard brown
bakelite versions, there
were ivory painted
models and, in the case
of model 1500HR, a
maroon painted version
This is an ac/dc powered 5-tube radio covering the standard broadcast band. Tubes
used are 12BA6 (RF), 12BE6 (mixer/LO), 12BA6 (IF), 12AT6 (2nd detector/AVC/1st
AF), 50L6GT (beam power). It uses a selenium (early solid state) rectifier and as such
yields the equivalent of 6-tube performance. Certainly, this set benefits from the tuned
RF stage and has great sensitivity and selectivity.

I recently restored this radio. The filter caps were strong and I decided to leave them
be. Normally I would replace these as a matter of course, but in this case there was
not the slightest trace of hum. I did however replace all the paper capacitors. The
radio initially crackled when played and I at first suspected the IF transformers (which
often, for radios of this era, suffer an affliction that has become known as silver-mica
migration disease). However, in this case the problem turned out to be a faulty 50L6
output tube, which I replaced. Nevertheless, I removed the IF transformers, dismantled
them and gave them a good cleaning so as to forestall problems in the future. Some IF
transformers of this period are riveted together and difficult to service, however the
ones used in this model are held together using clips and were very readily
dis-assembled for cleaning.

The IF transformers
Two capacitors, one for each tuned circuit, are formed in the base of the unit from a sheet of mica
having two pairs of silver films deposited on it.  The sheet is sandwiched between four metal
contacts, compressed between plastic forms and held in place by two small clips, the front one of
which is seen in the lower center of the photo to the left. The tiny mica sheet, upon being removed  
was found partially covered with a dark deposit of migrated silver, which eventually would have
formed a conductive bridge between the contacts and caused the transformer to malfunction. I
carefully cleaned this off  with q-tips and gentle scraping, readying the radio for many more years of
trouble-free service!
Stromberg Carlson 1200 Bakelite Table Radio IF Transformer
Stromberg Carlson 1200 Bakelite Table Radio (1948)