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Columbia Screen-Grid 8 (SG−8) Receiver
Radio Service Data Sheet
October 1930 Radio-Craft

October 1930 Radio-Craft

October 1930 Radio Craft Cover - RF Cafe[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.

I always attempt to find a photo of the radio whose Radio Service Data Sheets posted here on RF Cafe. However, none could be located for this Columbia Screen Grid 8 (SG−8) radio. It appeared in a 1930 issue of Radio−Craft magazine, so it was manufactured almost 100 years ago. That might explain why there are no images of them available, especially if the SG−8 was not a particularly popular model. There may be, though, examples of this chassis under different brand names, as mentioned in the date sheet. Wexmark Radio and Allied Radio are two specifically given. If you have found this page because you have a Columbia SG−8 (in one of its forms) and are restoring it, please consider sending me a photo for posting.

Columbia Screen-Grid 8 (SG−8) Receiver

Columbia Screen-Grid 8 Receiver Radio Service Data Sheet, October 1930 Radio-Craft - RF CafeThis is a standard radio receiver merchandised under a number of individual trade marks. For instance, Wextark Radio Stores, Inc., of Chicago, distribute this chassis; and so does Allied Radio Corporation, Chicago. Its manufacturers are the Columbia Radio Corp., Chicago, Ill.

The makers of this receiver, in their manual, stress the point that the Service Man should determine whether the radio receiver has a good ground connection and a set of good tubes, before looking further for faults in operation.

It will be observed that the metal brackets (shown dotted in the schematic circuit) supporting the RF chokes Ch1, Ch2 and Ch3, are connected to the cathodes of the screen-grid tubes; approximately three thousand receivers were manufactured with these brackets connected to low-potential end of the tuned secondary inductances; while seventeen thousand more were made with these supports grounded to the chassis. The final circuit, shown in this Data Sheet, was responsible for greatly improved stabilization of the R.F. circuits, at the upper end of the tuning dial.

If oscillation exists, only between 95 and 100 on the tuning scale, changing the RF chokes above mentioned for units having 650 or 675 turns will probably eliminate this tendency, which may exist in a few instances. The reason for this circuit oscillation is that the chokes are designed to resonate at a wavelength just above the upper end of the broadcast band; this results in obtaining more even amplification throughout the tuning band.

Power detection is used in this receiver: Note that the detector is resistance-capacity coupled to the first stage of A.F. amplification.

A defect in the "radio-phone" switching system such as the switch's failing to connect C10 or to open the pick-up circuit, may cause a loud hum.

 

 

Posted November 6, 2023
(updated from original post on 7/29/2016)


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 227 Radio Service Data Sheets as of December 28, 2020.

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RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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