-
•Restoration of a Colin B. Kennedy Model 20 B console radio
-
•built in 1929
-
•AM broadcast band receiver with external phono input
-
•The following additional information is provided:
-
•summary of restoration
-
•service manual and schematic
-
•e-mail thread on antiqueradios.com
-
•Summary of the restoration (see schematic and photos):
-
•This radio is so old that it is not a heterodyne receiver. It is a TRF receiver. Truly ancient technology that is very interesting.
-
•The wires are so old that they crumble in your hands if you try to bend them in any direction, so i had to try to stay away from the wires whenever possible.
-
•The parts inside are so old that they are nearly un-recognizable! The resistors look like inductors except that they were painted and the capacitors were made up of all sorts of different shapes. Some appear to be purpose-built for this radio.
-
•Patent numbers adorn everything. This has much to do with the highly contested radio intellectual property battles that were occurring back in the 20’s and 30’s.
-
•Before I powered up the radio I opened it up and noticed a few really nasty looking old paper capacitors. I replaced all of the paper capacitors, the power supply capacitors, and the Sprague ‘Midget’ coupling capacitors (one of which had, what appeared to be, bubbles coming out of the ends of it).
-
•I left the capacitors that de-couple the RF section tubes as-is. These capacitors are built into metal boxes. They have three-terminals each. These caps turned out to work.
-
•I did not have to replace any of the resistors. The strange looking resistors held their value over the past 80 years. I did find that the cathode bias resistors in the RF section were not the same value as indicated on the only schematic that exists for this radio (see pdf below).
-
•The audio output stage was different than the schematic. My radio uses a single-ended pentode output rather than a push-pull triode output (see pdf below).
-
•I did find a bad type 227 triode. The filament was intermittent, causing a sort of flickering appearance inside of the tube.
-
•I replaced the cloth power cord with a 3 terminal grounded computer power cord. I grounded the metal chassis for safety. I also placed a 3A fuse in-line with the hot wire.
-
•After all of this restoration, the radio worked the first time I turned it on!
-
•This radio is very reliable and sounds absolutely wonderful.
-
•There is a phono input on this radio that is not RIAA compensated. The audio is passed through un-filtered. I wired up my Ipod to this phono input connection. Old jazz classics from the 30’s and 40’s sound live through this old radio! Much better than through my hi-fi stereo. I think this is because the 1929 radio has a limited audio frequency response, so it cuts out the noise and junk that you would otherwise notice while playing a vintage recording on a modern hi-fi stereo system.
-
•This radio also works great for listening to talk radio pod-casts.
-
•This was a great project, very rewarding, and I am having lots of fun listening to it every day.
-
•I plan to throw a party on this radio’s 100’th birthday! Coming up soon in 20 years.
-
•I want to thank everyone at antiqueradios.com who chimed in on our discussion about the flickering 227 tube, thank you.
Press
Engineering Notes
-
-
Briefings (slide shows)
-
G. L. Charvat, “Repair and Restoration of Antique Radio Equipment,” MIT Haystack Observatory, October 21, 2009.
-
The author is not responsible for any injury or death that may occur due to working on antique radio equipment. Antique radios are dangerous because of the high voltages inside of the radio equipment. Do not work on antique radios unless you have proper training or experience. Serious injury or death can occur. These briefings are for reference only.
