Sentinel Model IU-355P -- One-of-a-Kind

BY MARVIN HESS

WEB EDITION

Radio purchases made in flea markets, yard sales, and estate auctions frequently contain a surprise or two. Marvin Hess's find proved that to be true. (Editor)

I was late arriving at an estate sale, but as luck would have it, a tube portable was still there for sale. It was a Sentinel portable radio, shown in Figure 1, and it looked very good.

Figure 1. The Sentinel Model IU-355P portable radio.

When I got home, I opened the back to check the inside. The inside label read, "Model IU-355P," as shown in Figure 2 (see print version). To my surprise, there were transistors in the radio, not tubes! See Figures 3 and 4.

Figure 5 (see print version) is the chassis layout for the Model IU-355P and shows the location of where the tubes would have gone. The rod antenna and speaker also are shown.

However, the chassis is not a worked-over tube chassis. Someone had very professionally formed a new chassis and stamped out holes for the transistor sockets, the IF cans, the speaker, and all other components generally in the same place as on the chassis layout for the tube radio. The volume control and variable condenser are positioned to use the original holes in the case.

Figure 3. This view of the professionally made chassis.

The work is most professional. The chassis has all the appearances of an engineering development model. The placement of the ceramic trimmer capacitors on the rear apron of the chassis also suggests that this radio was not a production model. I can only assume this was a lab-built model that got out in the trade somehow.

My Model IU-355P is a very neat transistor radio built into a Model IU-355P tube radio cabinet.

(Marvin Hess, 204 Queensway Rd., Elma, NY 14059)

Marvin Hess, an Amateur Radio operator licensed as W2WKU, is the director of the Quarter Century Wireless Association. He is the vice president of the Niagara Frontier Wireless Association.

Figure 4. A Raytheon CK722 transistor and socket.