Unknown Chassis Identified
Part of "Radio-Television Training Association" home-study course
This chassis was purchased at a hamfest. Its original purpose or manufacturer were not known for almost a year. We had surmised that the chassis was part of a home-study electronics course. That guess turned out to be correct. A positive identification was made from full-page ads for the Radio-Television Training Association in the September and October 1957 Popular Electronics. It is labeled as "Public Address System".
The tubes are 5Y3 rectifer, 6V6 audio output, and a 6SQ7 and 6SK7 as preamps. The single control is for on-off volume. The unit does not have an audio output transformer on board. The screw terminal strip on the back is engraved "output" , "B+" and "GRD". Two unmarked screw terminal positions are used for 6.3 VAC. Added pencil marks below the "B+" and "output" screw terminals indicate red and blue which would be correct for the external audio output transformer, probably mounted on the speaker. The tube locations are marked with pencil. The two phone jacks are also labeled in pencil as "phono" and "mike".
The ad shows a speaker next to the chassis. I believe the smaller round object below the speaker is a microphone.
Looking for more info
I had originally assumed that this chassis was part of perhaps a two or three chassis combination training module which used this main piece as the power supply and amplifier. This assumption was based on the exposed B+ on the terminal strip as well as the 6.3 volt terminal points. The other small chassis shown in the ad is the "CW-telephone transmitter" which appears to have a receiver-type variable cap and two tubes or possibly a tube and a plug-in coil. I assume that chassis was powered by this one. In fact, this chassis may have been used as the modulator for the transmitter chassis. Was the "transmitter" a broadcast band "phono oscillator" circuit?
If you have any information on the "Radio-Television Training Association" home-study course or come across a schematic or better picture of the "CW-telephone transmitter" module, please let me know.
The ads do not appear in the 1958 or later issues of Popular Electronics.