FEATURE AMP -
1947-48 Supro
Here are some photos of two of my old Supro amps. Both share the same circuit, but differ in cosmetics, transformer
manufacturers and grill cloth material. Both have the same tube compliment, 1-5Y3 Full Wave Rectifier tube, 2-6V6GT Beam Power
Amplifier tubes configured in parallel class A, and a 6SL7GT High-Mu Twin Triode preamp tube providing two gain stages to drive
the output section. Both have two inputs, one single volume control with no tone control, on/off switch and fuse holder for the 3 amp
fuse. The earlier Supro sports a Jensen P-8-T permanent magnet 4 ohm speaker and a Jensen output transformer mounted to the
frame of the speaker. Date code stamped on the output transformer is 220737, the volume pot has a date stamp of 304751, so this
is a late 1947 or early 1948 amp Serial number on the Brad tag reads V17741, and the chassis also has a stamp inside reading
14323. The amp has the old cloth type grill that was popular on old radios from the 30's and 40's. It also has a Stancore power
transformer that has a bit more iron and a bit larger than the other Supro power transformer does.
The later Supro has an 8" Rola 4 ohm speaker with marking 285844 and 550-2. The volume pot code reads 340829, so it's safe to
say this one was most likely built less than a year after the one with the stock Jensen in it. This one is serial number V27014, and
has an inside chassis stamping that reads 17834. It features the "newer" grill cover material. It is composed of a wire mesh, alot
like an old screen door has in it, with felt type material embedded in it. This one is chocolate brown in color. The covering on both
amps has the same theme, dark brown on the outsides of the amp, the earlier Supro having more of a tan/brown color in the center
part of the amp, while the later has a darker brown. Both amps have the four post speaker mount set up. (Later models of Valco
amps with 8" and 10" speakers sometimes used a 2 bolt speaker mount set up.) Both the amps also have the output transformer
riveted directly to the speaker frame. I have seen many of these model Supro's with replaced speakers and output transformers,
probably because the old TV/Radio repair guy you took it to back in the ol' days didn't want to drill the old tranny off the speaker and
mount it to the replacement speaker. Most of the replaced speakers I've seen in these amps are 8 ohms, and this really hurts the
tone and volume of the amp. Valco made this model for several other companies as well, including Dickerson, Oahu, McKinney and
also a National version, which was Valco's top-of-the-line brand name.
