Bremer-Tully Model 7-70 and 7-71 Radio Service Data Sheet
January 1930 Radio-Craft

January 1930 Radio-Craft

[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

January 1930 was very shortly after the major stock market crash in October of the previous year, so a lot of people suddenly were not motivated to buy unnecessary creature comfort items - like radios. Many of the smaller manufacturers were forced out of business accordingly. Fewer and simpler designs seemed to dominate the surviving market for a couple years as the economies of the world slowly recovered. America was not alone in the financial doldrums. Just about the time things were rolling along merrily again, a short-tempered little guy with a funny mustache decided he wanted to rule over all of Europe, starting a war that would eventually cause nations to dedicate manufacturing facilities and materials for radios (and many other things) to weapons production. Non-military radio production was suspended from 1942 through 1945. After that, electronics for all manner of entertainment grew exponentially. The photo of the Bremer-Tully Model 7-70 radio was found on the RadioMuseum.org website. It looks like a very basic tabletop configuration.

Bremer-Tully Model 7-70 and 7-71 Radio Service Data Sheet

This receiver includes three stages of tuned radio-frequency amplification, neutralized in the "Counter phase" manner. To test this part of the circuit, a continuity tester is used to check the connections which include, (in the circuit V1, for example), L2N, C5, and a few turns at the grid end of L1S. The "micro-mikes" or neutralizing condensers C5, C6 and C7 are located at the right of the respective tube sockets.

The procedure of balancing a receiver using the Counterphase neutralizing method will be described. Usually it is convenient to use a vacuum tube with one of the filament prongs shortened so that the filament circuit is open when the grid, plate and one side of the filament are making contact. Now, tune in a loud signal, adjusting all tuning controls very carefully for exact resonance. Replace V3 with the special tube. (Always start with the R.F. stage next to the detector). Retune all controls until maximum volume is obtained. The "micro-mikes" are now adjusted. The best tool for this purpose is a piece of bakelite rod which has been shaped to a screw-driver edge.

Posted October 17, 2023
(updated from original post on 10/28/2016)

Radio Service Data Sheets

These schematics, tuning instructions, and other data are reproduced from my collection of vintage radio and electronics magazines. As back in the era, similar schematic and service info was available for purchase from sources such as SAMS Photofacts, but these printings were a no-cost bonus for readers. There are 255 Radio Service Data Sheets as of April 30, 2025.

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