Transformer companies were a particularly fertile source, especially for the smaller, simpler rigs. Thordarson offered a few, Meissner sold the "Signal Shifter" VFO/low-power transmitter; Utah had a cute little 6L6 job (and I think one or two larger ones) and a couple of other firms got in on the multi-company (and higher-power) "All Star" transmitter kit. Stancor was right there, too, with a whole range of transmitters from flea power through at least several hundred Watts, both CW (Morse) and AM (Voice).
The Stancor 10P was either the smallest or the next-smallest, with a 6J5 crystal oscillator driving a 6L6 final, modulated by another 6L6. An '80 did the power supply honors and the whole thing was so cute as to be very nearly twee:
Only 10-¾" wide, 6-½" tall and 6-¼" deep, it weighs in at a remarkable 14 pounds. This one came my way at a reasonable price thanks to good luck (and recognizing what it was) at one of the large auction sites. It arrived with fairly complete provenance, tracing it back to the original owner through the late W2WHW, who was the last boatanchor-fan ham to own it before me.At some point before it graced his hamshack, it was heavily modified with the intent of curing interference to analog television; this was a big problem in the 1950s but was mooted by improvements in TV sets and, ultimately, by digital TV. So I can do what it appears from his notes that '2WHW had planned, and gently return the little transmitter to as close to original condition as possible.
It is always handy to have a schematic; this one has had the original white-on-black scheme inverted for more cost-effective print-out. Even more information, including a full parts list, may be found from K7JRL. (Who has a very results-oriented website, an excellent resource!)I have most of the passive components on order from Antique Electronic Supply and will be posting updates as the project proceeds.
What is the function of SW1 in the transformer secondary? Is that the T/R switch?
ReplyDeleteYes - the normally-closed key jack keys the transmitter in AM mode and the switch in the CT of the plate transformer turns the B+ off and on.
ReplyDeleteYou don't need it in CW mode, since the cathodes of both oscillator and RF amp are keyed.
Three transformers and a choke in the PS - all Stancor, I expect, and no wonder it's 14 pounds.
ReplyDeleteR17 is interesting. Bias adjustment for a carbon microphone?
Exactly! Tapped off the cathode self-bias resistor, an old trick but a good one.
ReplyDeleteThe abundance of profitable transformaerage in even a low-power rig like this was perhaps the main reason outfits like Stancor, Utah, Thordarson, etc. offered them; that and building goodwill with likely repeat customers. Most of them did the same thing with PA/hi-fi amplifiers.
I still have a Atancor 10P. It was my dad's first transmitter as a 19 year old ham in 1942. I got my general in 1954 and he made me communicate at first via CW only, using the little Stancor 10P.
ReplyDeleteBill Smith W0BCD