Restoring Firestone 4-A-20

[Reece]

The rubber-insulated wires to the primary of the output transformer were crumbling, so I replaced them with same-colored new wires right at the transformer, with the soldered joints covered with heat-shrink tubing, and the wires bundled out of the way of the 35Z5 with a couple of mini wire ties. Note that this has negative feedback off the voice coil heading back to G2 of the first audio tube. This tends to cancel out some distortion, a nice touch and not expected in such a radio. Also note the shorty 'lytic cap hiding down inside the cardboard tube.

All the caps in, line cord ready, time to plug in the tubes and turn it on. Nothing! Neither dial light nor tubes light up. All the tubes were previously tested good. Suspect bad switch. Get the voltmeter. Nope, line voltage gets through the switch, but it doesn't get to where the line from the radio side of the switch goes, which is to the can of the electrolytic. That wire fastens to a can lug with several other wires and the solder didn't get down to it. I retouched with the iron and reflowed the solder and gave it another try. She plays, and not bad! I got BC stations across the dial, and with a short antenna, a station and some other typical SW noise on the other band, all in the middle of the afternoon. I touched up the I.F's and the RF and ANT sections of the tuning cap, and this turns out to be a hot little radio with that RF stage. Up and down the dial it's full of very listenable signals.

[Jeffhs]

Originally Posted by Reece

I got BC stations across the dial, and with a short antenna, a station and some other typical SW noise on the other band, all in the middle of the afternoon. I touched up the I.F's and the RF and ANT sections of the tuning cap, and this turns out to be a hot little radio with that RF stage. Up and down the dial it's full of very listenable signals.

You won't get much on shortwave in the middle of the afternoon regardless how good your antenna may be, especially on the one SW band your Air Castle set tunes. I would wait until after sunset and preferably after dark before looking for anything on the SW band; this is when most of the shortwave bands perk up and the DX (ham radio shorthand for distance) reception starts rolling in--however, I just looked at the pic of the front of your set a minute ago and saw that the one SW band it tunes is from nine to 15+ MHz. This range includes the 20-meter amateur radio band (which begins at 14 MHz); this band is often wide open in the afternoon, and some good DX can be had, although a lot of the signals you will hear will be SSB (single sideband) and CW (Morse code), requiring an external oscillator, called a BFO or beat-frequency oscillator, to make them readable.

A note on antennas: A short indoor wire antenna will bring in some signals on the SW band, but for the best results an external, outdoor wire antenna at least 50 feet long should be used.

What station were you hearing after you got your Air Castle radio working? There is a time and frequency station in Boulder, Colorado called WWV, that operates on several different frequencies, all with 1 kW transmitters in the shortwave bands, including one (15 MHz) well within the range of the SW band on your radio. The station uses tone signals and a ticking clock, with an identification signal just before the time announcement: "This is radio station WWV, Fort Collins, Colorado, broadcasting on internationally allocated standard carrier frequencies on 2.5, 5, 10, 15 and twenty megahertz, providing time of day, standard time intervals and other related information. . . . Inquiries regarding these transmissions may be directed to the National Institute of Standards and Technology, Radio Station WWV, 2000 East County Road 58, Fort Collins, Colorado 80524." WWV provides exceedingly accurate time signals, so if you want to set your clocks as close as possible to the absolutely correct time, this is the place to find it.



BTW: Your success with that Air Castle radio has me wanting to get into my Zenith MJ-1035 AM/FM stereo radio to see if I can't get it singing as it used to...and should. I was lying awake in bed last night thinking about that, and made up my mind that I was going to pull the chassis the next morning (today) to see what needs to be done. But, darn it, other things got in the way today--wouldn't you know it! Oh well; maybe I'll at least look at the underside of the chassis tonight before I go to bed. I have a feeling that the problem is caused by one of two things: a missing ground on the case of the volume pot, the wiper contact inside the control isn't making contact with the carbon track, or perhaps it's both. As I said in my last post, though, I like working on these sticky problems as long as they don't get too sticky. I honestly don't think this will be too much of a problem to correct, unless the trouble is someplace else other than in the area around that 2-meg volume pot.