This is a battery radio, which on the surface sounds simple but in practice will definitely not be. Even though it's a couple years younger than my Philco cathedral, it's technologically closer to my ancient Fada Neutrodyne. The Fada is a TRF and this Airline is a superheterodyne, but they both run on "battery" power. That's not just DC, that's (in this case) three different voltages: 2 volts for the tube filaments (that's the A battery), 90 volts for the tube plates (the B battery) and -7½ volts for the grid bias (the C battery). Oy.
The A and C voltages aren't a big deal—I could make those up from flashlight batteries; but coming up with a 90V source is another thing. There are two particularly interesting websites about making battery eliminators: one is from Phil's Old Radios, which is the one I used (the ABC eliminator near the bottom of the page); the second site is this one from Ronald Dekker. There's more if you're willing to wade into a Google search.
Back to the radio. It's also different than anything else I've got (I'm not complaining about that). It's a four-tube wonder: one 1D6 mixer, one 32 IF amp, one 32 first audio amp and one 33 final out. The 32s are tetrodes, which you just don't see very often; the 33 is a pentode. All of them were chosen, it appears, because they're power misers.
I don't have much info on this yet so no interesting background. NostalgiaAir has the schematic from the Ryder Perpetual Troubleshooter's Manual. Brian McAllister has a nice scan of various Airline schematics, and there's an old website from "Herb" that has a photo of the radio with its cabinet.
All I've got is the chassis. Picked it up (as I get many of my projects) from a thrift-shop website. I knew this was an old Monkey Ward Airline but that was it. I thought I'd identified it as a farm radio but when it arrived I turned out to be very wrong. Happily the model number was stamped boldly on the chassis, which saved me a lot of poring through old Ryder and Beitman books hunting for it. The bad part is that I'd thought I could run it off a 32V laptop battery. Noooooo.
It's just arrived, so I'll check it out over the weekend. The tubes are inexpensive (under $10 each from TubeDepot.com, even the 32s!) and as expected they test Good (if they were $50 1L6s, they'd all be weak or dead). The caps look original. The face is actually in good condition, though the plastic backing is disintegrating (it's hard to see in the photo, but there are two dirty-yellow discs that form the face; the front disc has dial markings, the rear disc appears to just be some sort of facia); and hooray! it has all three knobs.
I'll have to come up with some kind of cabinet, a speaker and (of course) the power supply. That missing speaker is going to be a PITA: you know you're screwed going in when the official service docs say "speakers cannot be ordered; defective speakers must be repaired."
Update as of May 2013: the old man (in spite of my help) made up a battery elminator A-B-C power supply based on Neil Sutcliffe's device. The main page is at Phil's Old Radios website, and the schematic is here. My version of it is the gray box on the left side in the photo.
We made a couple modifications to the original plan on the schematic. I chose a little larger transformer than the Hammond 229A12. We made the B- and C+ a common ground. But the big thing we did was add an LED meter that the old man bought as a small lot from eBay cheap, and he's been putting them on everything. The meter is connected internally to read the voltage of the A and C supplies,depending on the position of the toggle switch. The A and C supplies are both variable via pots (you can't see them in the photo, but they're on either side of the switch). B+ fends for itself (~90V).
So now the electrical work begins. Initially, I couldn't get it to do much of anything beyond an initial pop of sound as I turned it on.
The Old Man was out to visit and took a look at it, and quickly determined a couple things. One is that the on/off switch on the front wasn't engaging ON fully.
What's happening is that there are two plastic sheets, one on top of the other; the upper sheet is the frequency dial and there's a hole cut out
to show the On/Off position. The plastic sheet underneath has a green area and a red area. The sheet is attached to the ON/OFF shaft and rotates with it. When
the set is ON the red area shows in the cutout (red because you're drawing battery power, I assume); when the set is OFF the green area shows (green because you're not
pulling any power). The lower sheet was catching on something (still is, actually) and wouldn't let the switch fully engage, so you have
to help it along. There's a fix to this but I'm not sure what it is at the moment. The plastic is already brittle and I don't like
handling it any more than I have to. I'll probably end up warming it with a heat gun and try to bend it a bit. Which means I'll
likely end up having to photograph it and print up a new one to replace it when I break it.
Once it was running we determined that the audio out was good but there's a problem upstream. I was given the task of
recapping it. No problem—I've done a fair amount of recapping. I know how to do that.
The adventure began with something new. This radio has three caps I'd never seen before; they were all held by a metal strap in the center and riveted to the chassis (they're visible in the photo above). The Old Man recognized them as double-caps, similar to multi-stage filter cap canisters. Each end of the cap is one lead and the strap connects to a shared wire in the center, which is common to the two caps. So I had to be careful, when replacing them, to replace each with two caps and connect them correctly.
The annoying part of this, and I didn't realize it until later, was that the caps aren't symmetrical; i.e. one end might be a 0.05µF and the other a 0.01µF,
rather than have each end be a 0.05µF and another be a pair of 0.01µFs.
Got the recapping done. Now I'm stuck again. I lost the audio out. Zip. Nada. I'm measuring 14V B+ on the plate and verified that my p/s is putting about 90V, so either I screwed up one of the cap replacements or there's some other break or short that happened during the recap.
I know there are people who relish this as a challenge—I have no idea how those people at all.
After what seemed like an eternity, in reality a couple weeks, I was able to restore the audio out without having to call The Old Man for help. Amazing what happens if you actually light the filaments. It's one of those things I understand but don't understand. I understand the part where I found the battery rheostat was connected to the A- and the other side to nothing. So once I hooked the other side to ground, the filments (obviously) lit up and I got audio.
What I don't understand is how this ran when the Old Man was fussing with it two weeks ago, because I know for a fact that neither of us had touched the rheostat. So I dunno. Maybe it was temporarily tied to ground and I disconnected it and forgot. Or gremlins did it. That's the most likely answer.
So I'm back moving again. I get noise tapping the grid on the 2nd detector, so the problems (I'm sure there are multiple) are somewhere in the RF section.
I do have one lead. There's a tiny broken wire that's part of the antenna coil section. The wire comes in from the top of the chassis and it's bare. I've been looking but I can't see any obvious evidence of the other end of the break, so I'm not 100% sure where it goes. The problem is compounded by the fact that the above-chassis part of the wire is hidden under a metal shield (the Antenna Coil section on the schematic), so I can't trace it. Taking off the can will require drilling out the pop rivets, one of which is mostly inaccessible.
Oh well. Tomorrow. At least I feel better with the audio debacle done. I was very discouraged that all this time and effort, and I still can't troubleshoot a relatively simple radio. If I can't get this thing to run, how can I even look at the Hallicrafters?
And then it went to hell again. I decided that since I had audio, I'd try to peak the IF section which might make it easier to troubleshoot the RF detector problem upstream. This machine's IF is 465 KC, don't ask me why. So I set the generator to 465, checked it with the freq counter, began injecting signal and peaked the IF. Really brought it up.
Then I decided to try the RF. I took the bare wire and wound it around the nearest terminal on the coil, the place I thought was logical for it to go because it wouldn't stretch much farther and I couldn't see any broken spots. I fired up the machine, and thought I was getting a station when I was touching the grid of the 2nd detector. The full-body antenna? Tried injecting an RF signal from the generator at the antenna input but couldn't get anything. Couldn't get anything from the grid of the converter.
And then—a metallic ting sound, which I had heard before when I lost audio, when I was turning the chassis on it's side or tapping tubes. I figured something crapped out again. So tap-tap-tap, rattle, turn over chassis...
repeat ad infinitum over a week, also looking for breaks, shorts, arc marks.
Nada. Nothing. The audio is dead again. I know the speaker and the output transformer are okay because I can make noise fussing with the wires, but I can't get anything upstream. Not a peep.
So I'm stuck again. I'm guessing I blew out a tube filament from having it spend too much time sideways while running, though I'm not sure at all. They all pass the test on my EICO 625, but I wonder.
What annoys me most is not that I have none of these tubes on my shelf: it's that they're such oddballs that if I buy extras, I'll likely never use them. It's not like buying a 50C5 where you know it'll end up being used somewhere or another. I'll have to find another radio with a similar tube compliment.
So the project is suspended until new tubes come, or I come up with some other idea of what's wrong. But so far I've come up blank.
Tuesday Afternoon or really evening. A consult with The Old Man, who suggested cleaning and tightening the pin-contacts (for lack of the proper name) of the sockets, because the old, low-voltage tubes were known for making intermittant contact; at 2 volts and little current, a little oxide buildup or an iffy contact would shut them down. So I hosed them down with contact cleaner, pinched them a little from underneath with the long-nose pliers, and plugged the tubes back in. And NOISE!
Touched my finger to the grid of the 2nd detector and once again, picked up what was probably KLAA 830 kHz, with additional stations in the background; my left hand isn't very selective.
- Whew - That's a load off. Plus it saved me $25 in tubes.
The bad part is that now I have to figure out where that broken wire goes...
Sailor on the Seas of Fate. So it hasn't been like a rollercoaster—it's like bobbing up and down on the waves in a small boat. More fussing with the radio and the audio died again. I threw in the towel and called The Old Man for a conference. He was skeptical of my tube orientation theory (that something's shorting because the tubes aren't meant to be sideways) but finally agreed that one or more, probably the 33 output tube, was intermittant and bad. So I called in my order for replacements. Hopefully they'll be here next weekend.
Later I got an email from him suggesting I try them in the tube tester in the same orientation where I'm having trouble (sideways—when I have the set on its side so I can work on the under-chassis). Did that when I got a chance and the 33 seems fine. Plugged it back in and the set worked. Huh.
Next step: the wire. After a conference with poring over the schematic and a hard, hard look at the chassis, I decided that the "broken wire" is really the gimmick capacitor.
So—put the set back right-side up, plug her in and—dead.
I won't drag this on any longer. One culprit is a bad connection on the A- lead. The A- goes from my battery elminator to one side of the battery-compensating rheostat, and I'd touch the wire accidentally and the set would die or come back to life. So I resoldered it to make a better connection. Later on I'll bundle the wires together (since they all enter the chassis through the same access hole) and add some sort of strain relief.
Meantime, the machine still doesn't like being tipped on its side. For whatever reason, pulling the 33 out and doing the emissions test in the EICO seems to bring the set back to life. Though it still sputters and coughs and carries on.
Spent some time trying to see if I can get it to pick up a signal properly from my generator. Yes, I believe, but it is faint faint faint. The RCA puts out a big signal and ought to overwhelm it, but obviously it isn't (the B&K isn't so powerful. I can just barely perceive the tone among the white background noise). I've decided to wait until the new tubes come. I'll swap them in and see if it behaves any better.
June 2013: Salting Away
The tubes made no difference. I finally realized, again, that the problem is bad connections on the filament pins on the 33 output tube. So yet another squeeze, and some contact cleaner, and it's running.
But now the faint tone I had been getting from the signal generator is gone. It's weak but I can't figure out what's doing it. I'm slow, low and out of ideas, so this project is going to get mothballed. Maybe the Old Man will be able to figure it out.
Halloween 2013: The Gremlins Are Still Alive and Well
The Old Man was out to look it over. Beyond finding one wiriing mistake of mine (not a destructive one, I just soldered one of the replacement caps across two ground points), it's still and uphill pull. I'm torn: I was happy to see that it did all the same things to him that I had to me: kicking in and out at the slightest touch, alternately noisy and dead, etc; but the downside is that I didn't learn what was wrong with it and how to fix it. He did find a break in the local oscillator coil and fixed it, but still no go. The problem appears to be somewhere in the front end. He thinks the LO isn't oscillating.
But the gremlins in his garage are in mine as well. My RCA signal generator was intermittant, which turned out to be a problem with the miserable car-radio-antenna-cable. I'm going to convert the thing to use BNC plugs. Luckily I had the BK 970. This is why you need all the test equipment you can get.
Then the scope was being a PITA. It needs a clean and calibration and going-over by someone who does it for a living.
So there we are. Still not running, and going back on the shelf for another round some day.
Current status: on the shelf; needs cabinet, more electrical work.