Restoring Firestone 4-A-20
 

Matt of matt_s78mn kindly sent me this radio just for the cost of shipping. I love radios that need a lot of work because you get to solve so many problems. First was a crop of tiny tiny black spiders that came with the set! I put it in a garbage bag with some paper towels soaked in starting fluid (ether) and sealed it up overnight. That got all but one (Super Spider!) that I found on the bench but I quickly blotted him/her out.

http://i177.photobucket.com/albums/w...restone010.jpg

The cabinet was in rough shape but the chassis appeared to be all there. I decided to work on the cabinet first since this is an AC/DC set with no rare/expensive parts like a burned out power transformer to impede restoration, so I figured it would be easy.

The cabinet was wobbly and loose and some of the side veneer was coming off. The top had veneer damage and I considered repairing that but the plywood of the top was delaminating so I decided to make a new one. A couple of whacks inside with a hammer handle and the old top came off. I reglued the set in a number of places: I think you can see five clamps in one of the pictures.

http://i177.photobucket.com/albums/w...somegluing.jpg

http://i177.photobucket.com/albums/w...eregluingB.jpg

I ordered some walnut veneer for it from Rockler so did not mount the top yet as it would be easier to veneer with the top loose. There are some control decals so I took pictures and notes on them and will make my own replacement ones. I stripped the topless cabinet and it looked eminently restorable. The speaker baffle board was delaminating so I made a new one from plywood and painted it black. The reverse paint on the glass dial scale had some big scratches and alligatoring in the paint so I cleaned the front of it and the back very carefully as best I could, scanned it, and put it away safely. I'll deal with making a reproduction later. To be continued...

Wow - that's quite an undertaking :thmbsp:

I'll be watching how you tackle that veneer with great interest. I have some sets that need the same work done.

(Pictures had temporarily disappeared but they are back.)

In between if the weather gets colder or raining and less conducive to cabinet work I'll work on the chassis. The speaker cone looks great: to keep them that way I always fasten a piece of cardboard over them to keep from sticking my fingers through the cone.. The tuning cap was dirty so blasted it well with CRC Electronic Cleaner. Five of the six tubes test good. They are mixed brands with the sole Firestone Air Chief 35Z5 probably original.

http://i177.photobucket.com/albums/w...egroupB029.jpg

The 500K volume control had been replaced at one point but in order to get a split splined shaft the tech sort of kludged together the shaft off the old control onto the body of a build-a-control (think that's the name) where you can install your choice of shaft type. He didn't have the right part and made do.. The mechanical connection was iffy at best. J-B Weld to the rescue and the control works as it should.

http://i177.photobucket.com/albums/w...earchassis.jpg

The chassis is really crammed tight: they could have increased the size of it by an inch or two in both directions and made it much easier, and cheaper for them (and me) to wire. The chassis is lost in the cabinet with plenty of room all around it. As such I knew I was going to have to replace some components not in the neatest way that I would have liked to. Doing it perfectly would mean yanking some of the coils and I didn't want to do that. Look below: the filter can terminals are buried just behind the volume control. They had to build this thing in layers.

http://i177.photobucket.com/albums/w...egroupB011.jpg

http://i177.photobucket.com/albums/w...egroupB010.jpg

Since real estate under the chassis is so tight, I also decided to restuff the topside can. This took a little more heart surgery. Lots of fun making a drawing of where all the wires go and then getting the can out. Since this won't show I just hacksawed the base off the can. Funny: the guts pulled out of the can actually smelled like a cow barn. The can is isolated from the chassis with a phenolic mounting wafer and has a cardboard sleeve over it. It all went back together nice and easy. Note that the can looks original but is a shorty inside a taller outer sleeve. Odd. You can look down inside the open top tall sleeve and see the can top down in there.
http://i177.photobucket.com/albums/w...restoneCan.jpg

Wow that's crammed!

Given that the new caps will be a lot smaller it should look a lot cleaner under neath.

I enjoy watching your restoration progress. Sorry about the spider infestation!

Re: spiders: how could you know? They were really tiny little buggers just hatched out, smaller than pinheads. No big deal. Maybe I should have kept SuperSpider and bred him/her up to eat more bugs.

You horrible awful person, you...Spider MURDERER !!! (grin) Can't wait to see this beauty brought back from the dead ! Good show !

Now you got me worried: big spiders chomping at me in nightmares, aaaaarrrgghhhh!!

Yard work today, more later on the radio.

I was not going to say anything but it looks like you have a snake in there too ;-)

That area under the chassis by the volume pot sure is crammed..and all those paper caps too! You'll be making quite a roadmap to get every component back to it's proper place!

I restored a Philco 40-115 that was not only crammed but had the dreaded crumbling wire in it too. I started the process from one end and worked my way to the other..

It was a fun project and it's a good player! The cabinet needed some minor attention (thankfully)....that's where my skills need to improve..

I'm glad you're taking this one on..it will be nice!!

Since it's a six-tuber (AA5+1) and no three-gang tuning cap, what are they using the extra tube for?

I like working on transformerless radios for the same reason: no worries about power transformers, many of which are very difficult to find today for vintage radios. I have three transformerless vintage sets in my collection right now -- all Zenith: H511, MJ1035, C845. I don't know if the MJ1035 counts as a "transformerless" set, since it uses a filament transformer wired in parallel with two series filament strings; however, the B+ is derived from the AC line.

I also have a question about filter caps. My Zenith MJ-1035 has a very loud 60-Hz AC hum which I am sure is caused by the 3-section power supply filter capacitor going sour (if it is, it wouldn't surprise me since this radio is 45 years old). Would it be possible or practical to replace just the "guts" of the original filter cap with modern, smaller caps? I know you're doing just that with your Air Castle set, but I'm wondering if it is even cost-effective to undertake the same project on a much newer radio. Also, I wonder just how I'm going to be able to get at the terminals on the 3-section filter, as they seem to be blocked by at least one layer of underchassis wiring. I have visions of having to disconnect dozens of wires, components and such just to get to the capacitor. Of course, if I can work from the top of the chassis and remove the capacitor's innards at that level (leaving the underchassis wiring as it is), it will make the repair a lot easier.

BTW, I know all too well what you mean regarding working on radios with problems. I like working on those as well, but when the problem is very difficult to find, then the job starts grating on me. My Zenith MJ1035 is a case in point. The radio works extremely well from an RF sensitivity standpoint, as it will pull in stations for miles around using just a 6-foot length of wire on the antenna terminal. However, the audio is extremely weak, and I think the volume control may be open. I can tell the radio is pulling in signals, as the stereo FM indicator light illuminates on just about every station the set picks up (most of the FM stations in my area, 35 miles from downtown Cleveland, broadcast in stereo).

I haven't done much with the radio lately, but I might power it up later today to see if it is still working at the level I just described. I notice that the case of the volume control is supposed to be grounded (such a ground is shown on the schematic diagram), but on my set the ground is missing; therefore, my first step in eliminating the loud hum I mentioned will be to re-establish that connection. It wouldn't surprise me if that eliminated or at least minimized the hum. I'd like to avoid doing anything with the filter cap unless it is absolutely necessary because, as I mentioned, it is likely to be a very involved and messy job with all that wiring directly in front of the terminals, looking directly at the bottom of the chassis. I can't help wondering what Zenith's R&D guys had in mind when they designed the MJ1035 this way--did they think the filter would probably last at least 50 years (!), so they made it darn near impossible to replace if or when the cap goes bad? After all, we VKers know it is more a question of when, rather than if, a filter cap will fail, especially in very old equipment. If Zenith's R&D boys thought the filer caps in these radios would last forever, they were very sadly mistaken, although I haven't read much here in this forum regarding replacement of filter capacitors in any of Zenith's high-end tube radios of the 1940s-'60s, including the MJ1035. Were the caps in Zenith's higher-end sets meant to last years or decades longer than those in the company's cheaper sets, including small AA5 table models? I'm asking this because my Zenith H511, now 59 years old (!), is still working very well and still has its original 3-section filter cap--no noticeable hum yet. Were the caps better made 60 years ago than they were by the 1960s? Another example: My late grandmother had a Sears Silvertone table model radio made in 1936. The radio, long gone by now, still worked well 40 years later, with its original filter caps. The only thing wrong with it, and I mean the only thing, was that the power cord was bad and needed to be replaced, as the insulation was crumbling and there were bare spots, making the cord a safety hazard. The set was unceremoniously discarded shortly after my grandmother died, and the cottage the radio was in (her summer getaway) was sold; the new owner of the place obviously didn't know or care beans about antique or vintage radios or even had the germ of an idea how much that particular radio would have been worth today.

However, again I wonder. Were capacitors made to last decades in the '30s? :scratch2: If so, their quality has really taken a nosedive in the last seventy-plus years, as the small filter caps and other underrated components used in today's electronic devices often go bad within a year or two, if they last that long.

Phew, yard work all day, mowed, trimmed, blower, went and bought and planted a few tomato, pepper, and eggplant plants, dug out some weeds along a fence, and am now cleaned up and collapsing in front of the magic television/typewriter.

Rollei35guy, I killed the radio snakes, too. No longer required. I've got something to say about that, too: the snakes were on the power cord leads. Notice that the self-grommeted hole for the power cord is right back of the first audio tube, one of the most sensitive spots for hum pickup. When I put my new power cord on, I used a UL knot inside the rear chassis apron and then twisted the two leads and routed them around the side of the chassis passing the 35L6 and the 35Z5 until reaching the switch and the terminal on the rectifier. You want to keep your AC power wiring away from audio inputs. The cord I used was polarized so I put the hot lead on the switch.

marty59, yeah, it's really tight working in there. I took plenty of pictures and made myself sketches. I have another radio, an RCA 28T, almost finished, that was full of crumbling yellow rubber wiring. I had to replace 99% of that and some was in really tight places. Big 8-tube table set with push-pull audio. Had to unfasten a scary-looking unobtainable-if-you-screw-it-up shortwave coil and swing it out of the way at one point. Work around a multi-gang band switch sweatin' coconuts.

On this Firestone, there is a 3-gang tuning cap, just not visible in my picture. The first tube in line is a 12SK7 and it's the RF amp. It's only used for the broadcast band, however; is out of the circuit for short wave.

Jeffhs, some of the wet electrolytics from the '30's if they haven't been abused by a short somewhere, or if they haven't dried out, may still work OK. Ditto some of the big paper caps used in the late '20's for filters before electrolytics became more common/cheaper. I've heard it was because of the good paper they used. Supposedly later on, the paper used was prone to deteriorate.

However, wax dipped paper caps and of course the infamous black beauties eventually become leaky. The thought was that wax was impervious to moisture: it isn't. But the ceramics that Zenith liked to use fifty years ago, and orange dips when they came along and "yellas" that we use a lot now should be a lot more reliable than the old wax firecrackers. No paper in 'em.

All that being said, it's a crap shoot as to when a paper or electrolytic cap that has been playing merrily along decides to die. I've had them do that right in front of me and maybe some of you guys have, too. Was playing one chassis while working on another and the working set all of a sudden sputtered and maxed out on hum and I yanked the cord. Paper cap underneath had puked its waxy little guts out. Once had an electrolytic pop, too, and hum went right up to the top. It's best to replace them.

If there's room on top of the chassis to somehow cut the filter can open and scoop out the guts, you could restuff it with new caps. You can't solder to the terminals that come up through the phenolic wafer, though; they're aluminum. You have to drill a hole or holes in the wafer and run your wires down and solder them to the terminals underneath, which are normal tinned terminals staked to the aluminum stubs. It would probably be easier, which is what I do when possible, to mount a terminal strip under the chassis and put the new electrolytics there, leaving the old can in place for looks. The terminal strip doesn't have to be right by the old can if there's no room there.

Back on the job, replaced the paper caps and this opened up a lot more breathing space. It was tough making some of the connections: terminals were buried and full of wires, so I resorted in a lot of cases to making "squibs," or whatever you want to call them, where you curl the wire from the new cap into a spiral to slip onto a stub from the old cap left on the terminal and solder it. If you're making a lot of these you can make a tool which is just a piece of wood or dowel about 1/2" in diameter and about 6 or 8" long, with a couple of brads stuck into the end of it. The wire is guided around the central headless brad by the other brad offset from the center. I'm too lazy to make a tool so I just loosely curled the wire from the new cap around the wire from the old one (so I know it will fit over the stub from the old one.) Finally I use pliers to stack the coils together and then snip off the end sticking out. On the right is circled an example of one of these connections. The big blob of a terminal carrying the stub of the old cap is original. I wasn't going to dig into that Gordian Knot...

http://i177.photobucket.com/albums/w...estoneSqib.jpg
I ohmed out all the coils just to be sure because some of them are wound with "hair" wire. All but one checked OK. The one open coil is shown below in before and after condition. This coil is wound on a machine and there is no way to rewind it perfectly. The way I checked it was to connect an ohmmeter to one coil terminal and then probe along the side of the coil windings with a fine sewing needle alligator-clipped to the other ohmmeter probe. I found continuity about a third of the way in from the outside. Nothing to do but unwind the coil to find the break.

http://i177.photobucket.com/albums/w...foreafterA.jpg

I made a sketch showing where all the wires connected and then pried out the mounting clip and removed the coil from the chassis. I put a box on the floor and carefully started unwinding the coil, allowing the wire to pile up loosely in the box. The fine wire was enamel-coated and also served with a thin (probably cotton) covering, so if there was a break anywhere it was going to be hard to see because the serving tended to hold any break together. Every few layers unwound I stopped and carefully scraped to bright copper in the wire and tested looking for continuity. Finally about a third of the way in I found the break, sure enough with the cotton holding it together (like a "green stick" break.) I scraped the wires, twisted them, and soldered them back together.

Then I started rewinding the coil. I tried to do it as neatly as I could by hand but hoped for the best. I had a light-colored wax candle going and every now and then I'd drip some wax onto the coil to hold it. Finally got to the end and reinstalled it and wired it up. It ain't pretty but ought to work, because this coil is in the plate circuit of the RF amp and serves to transfer the signal to the next stage. I'm guessing that maybe a plate current surge popped the wire, or just the hand of fate. It is not a tuned coil so the fact that the inductance and Q may have changed by rewinding it should not matter much. Cross fingers.

Here's the chassis with its new "yella" caps.

http://i177.photobucket.com/albums/w...pedcropped.jpg