1935 GE Model A-53 AM/SW Tombstone Radio
 

Hello everyone this past weekend I picked up at one of my favorite antique shops near me a 1935 GE Model A-53 AM/SW tombstone radio that needed some work done to it (it was missing the power cord, had a blown out flexible Resistor R-11 a 450 ohm 1W Flexible Resistor, some bad capacitors a bad tube and an incorrect rectifier tube).

I've got the radio completely recapped but dummy me forgot to order a replacement resistor for the blown out Flexible Resistor, which I would assume a 470 Ohm 1 Watt Flameproof resistor would work in place of the old flexible resistor?

Thanks for your help.

I can't see why a 470 ohm, 1w resistor wouldn't work. It's in the cathode circuit, of the audio output circuit. The rectifier tube can be a 5Y3, 5W4 or another 5Z4.
I have one just like it! It's a strange non-AVC superhet, with the volume control that isn't in the detector circuit.

Well, this one had a 5U4GB in it in place of the 5Z4 Rectifier tube, and all of the tube substitution books I have show that the 5Y3 and the 5W4 are not substitutes for the 5Z4 tube, and neither is the 5U4.

Is it common for those old flexible resistors to just blow apart? I'm asking because this resistor's outer cloth shell was completely disintigrated and all that was left was the resistor's wire element which then shorted to the chassis and left a burn mark on the chassis where it shorted to the chassis! :thumbsdn: :smoke:

Also as for the replacement resistor I did come across in my parts stash 2 270 Ohm 2 watt flameproof resistors that I tied together in series to make a 540 Ohm 2 watt resistor (the original resistor had no tolerance markings listed so I figured that that would be close enough.

the original 6A8 tube (this radio had all metal cased tubes which were brand new at that time) was completely dead according to my tube testers (I tested it on my Knight Model 600 Tube Tester, my Sencore Mighty Mite VII Tube Tester and on a B & K Model 606/666 Tube Tester and all three of them tested the tube as bad/zero emissions), thankfully I had a NOS 6A8GT tube that I was able to stick in there, hopefully it won't affect the performance of the radio with it not being a metal cased tube like the rest of the tubes.

You said this radio doesn't have AVC or a standard Volume Control configuration, how does this radio perform compared to others in your opinion? I like to use these radios for Night Time DX'ing.

The 5Z4 is a real odd-ball tube! The first ones looked like a ballast tube, with a perforated metal housing and two sealed capsules in it. They only made it for a short time, as they were failure prone. The newer 5Z4's were like a metal 6F6. As I stated, the 5Y3 has a 5volt 2amp heater and the same pin-out. The 5U4 has a 3amp heater and too much current for the power transformer.
Regarding the flexible resistor, they all crumbled after so many years. I would use two resistors to equal a value closer to 450-470 ohms.
When DXing with a TRF or a non-AVC superhet, you have to have the volume control set to max, to have the sensitivity to seek out distant stations.
If the radio squeals or motorboats, you might have to use a tube shield on the 6A8GT.

Well it seems that this radio may not work with an unshielded 6A8 tube in the set as the radio just hums/motorboats really badly when fed a signal from my signal generator or any other kind of signal and unfortunately I don't have any tube shields that are large enough in diameter to fit over an octal tube and short enough to go over a 6A8GT tube so that the gridcap can go over it... :sigh:

when I have the original 6A8 metal tube in the radio it doesn't do anything (no audio or anything) but then when I turn off the radio I can hear my signal generator coming through loud and clear and undistorted (no hum/motorboating), which tells me that they wired this radio up so that it could only use metal cased tubes I think... :scratch2:

As for the resistors, I already have the 2 270 ohm 2 watt reistors installed in the radio, and I don't really want to have to go back in and remove it and reinstall new ones again as it was a pain in the butt to install them the first time around, is there any sort of problem with having a resistor that's 70 ohms higher than the original? The original resistor as I said previously didn't have any sort of tolerance listing listed for it in the Rider's Service Data which usually means its at least 20% tolerance or more, and 20% of 470 is 94 ohms which means that 540 Ohms is well within the original specs... :scratch2: :thmbsp:

If your crafty you can make a temporary shield out of aluminum foil to use till you can find an appropriate original...

I was able to jury rig a tall octal tube shield by cutting it down so that it was the appropriate height and it still seems to be having issues with motorboating when a signal is applied to it with my signal generator, it basically just hums like mad when a signal is fed through the radio, either through the grid of the 6A8 tube or through the antenna wires, and the hum goes away when you tune away from the signal, and also the hum gets louder or softer depending on how you adjust the gridcaps on the 6K7 and 6J7 tubes, any ideas as to what might be going on here?

Did you ground the tube shield with as short of a wire as possible?
Also, was any component drastically relocated in the convertor or IF circuit?
The servicing instructions state that the set could be unstable under certain conditions.
Maybe you have to wait until you can obtain a metal 6A8. :sigh:

That statement usually pertains to carbon resistors! Wire wounds are usually pretty close. The flexible ones are wire wound. :scratch2:

Sounds like there might be a 'floating grid' condition with the 6A8. That's when the DC path to the control grid is open (like an open in the RF coil or bandswitch). What resistance do you measure from the grid cap to ground?

(Since there's no AVC bus, the coil ties directly to ground according to the schematic.)

I have since removed the series 270 Ohm 2 Watt resistors and replaced it with a 270 ohm 2 watt and a 180 ohm 2 watt resistor in series to make a 450 Ohm 2 Watt resistor.

The only "alterations" I made to the IF and converter circuit was replacing the grid cap wire leads for the 6A8 tube and the 6K7 tube because the wire leads for the wire leads were dry rotted and had exposed wire.

Other than that when I replaced old capacitors and resistors I put them back where they were originally in the circuit (I completely unsoldered each capacitor from their respective tie points and soldered the new capacitors back in where the old ones connected originally).

The only components I relocated were the two 8 MFD electrolytic can caps that were bad (the ones on top of the chassis), I disconnected the components from the old capacitor leads, and then took a terminal strip with a blank mounting tab (mounting tab with no terminal attached) and soldered it to the terminal on the old can cap that way the components and the new capacitor was isolated from the old cap but was mounted in a convenient spot.

I reattached the wires/components and the new capacitors to one of the isolated terminals on the newly attached terminal strip and attached the negative lead of the new capacitor to the chassis just like the old ones were, and I made sure that the leads from the new capacitors were as short as possible.

The only other thing I can think of is that maybe when I installed the new wire leads for the grid caps on the 6A8 and 6K7 tubes I might of made the leads too long, but it was kind of hard to know how much lead to use especially on the 6K8 tube's grid cap lead because I had to go from under the IF can to the top of the 6K8 tube which is about 2 inches, and I think I may have cut about 3 inches of wire lead because I wasn't sure how much I needed for sure and I didn't want to cut myself too short.

Could having too long of grid cap wire leads cause the issues I'm having?

Its 5.5 Ohms from the 6A8 Grid Cap to chassis ground.

Is that what its supposed to measure, or do I have the aforementioned "floating grid" issue you spoke of?

In a self-biased output tube circuit, it's best to be close to the original cathode bias resistor. It'll save a distortion issue, later on!
You seem to get some, not-to-common sets to repair, restore! :scratch2:

It's definitely not floating. A few (or several) ohms sounds right. Floating would be infinite resistance.

Well I figured out what my problem was, my one replacement filter cap that I installed to replace one of the old can caps on top of the chassis didn't have a good solid ground connection to the chassis, so I unsoldered the negative lead from where I had soldered it to the chassis, roughed up the metal chassis in the area where the negative capacitor lead was to go and then resoldered the negative lead to the chassis (that solved the incessant humming noise issue)

and the issue with the extremely distorted audio when being fed a signal from the RF Signal Generator, was because the grid cap for the 6J7 was grounding itself out (the grid cap wire lead had apparently lost enough of its rubber insulation inside the shielding sleeve that the shielding sleeve was causing the grid cap wire to ground out against the shielding sleeve, so I took and replaced the grid cap wire lead and BAM! the radio started working properly!

The only problem I have now is that the volume control seems to have some "dead spots" in it because it will go from completely silent to blow your ears out in a quarter turn and then I think the speaker might have some issues because the audio comes out completely distorted and barely audible at about quarter volume or a little less, and when you turn it up to about half way the sound is so distorted that you can barely hear what is being said on the radio.

Just thought I would give a little update on this radio.

OK So another update:

I DID have this radio working fine last night, but then when I went to install a permanent power cord onto it tonight (instead of the temporary one I had on last night for testing purposes) I went to fire the radio up after installing the new permanent power cord and wouldn't you know it the radio went back to humming like a son of a gun again! :sigh: :thumbsdn:

I checked all of the ground connections and they were fine, I checked all of the electrolytics and they were fine, and I even checked the 6J7 tube's Grid Cap wire shielding and that was fine so I don't know what to say about this thing! :no:

Any ideas as to what to check next? Because I'm starting to run fresh out of ideas on this thing...

You probably have to remove the volume control and have a look inside!
IDK if the volume control is a log or a linear taper. Also, the schematic shows a 250ohm resistor in series, but the parts list shows that the resistor is part of the control. Some experimenting is needed!
Re: the next entry problem with the hum, maybe the 6J7 or the 6F6 has an H-K short.
Sure is one for the books.

I cannot for the life of me imagine how just changing the power cord would cause a very loud 60-Hz hum as you are describing; after all, the power cord itself should not have any effect whatsoever on the audio output. If the radio had been working up to now, the only thing I can come up with is a heater-cathode short in one of the audio tubes. Given this radio is very old (pre-WWII vintage), that would not surprise me in the least. Vibration from moving the chassis could have caused such a short, especially if the tube were about to develop an H/K short eventually.

I would not operate the radio in its present condition if it does not have an AC line fuse (it is my understanding that most pre-war radios did not have such a fuse, which all too often led to very serious trouble if a tube were to develop an H/K short or a filter cap would short the same way). The house fuse might blow in case of a shorted tube or filter capacitor, but I wouldn't count on it.

Well for sure I did swap out the 6F6 tube and the 6J7 tubes for known good tubes to check the H-K Short theory and of course it still has that nasty hum to it even after swapping in known good tubes.

I ohmed out the volume control pot just to make sure it was still good and it was only measuring 1 ohm all across the pot no matter where the volume control knob was set, which tells me that the volume control pot has failed and is perhaps what is causing my humming problem, because the volume control is grounded to chassis using the left side terminal and goes to the kathode of the 6A8 tube from the middle and right side tap of the volume control pot.

Is there any way to test this theory by somehow taking the volume control pot out of the circuit?

I think I figured out what happened, I think the volume control pot is what's causing the radio to hum, because I think the volume control pot (which was already sketchy when I had gotten the radio going) finally went to "pots" (pun intended) when I attempted to clean the volume control pot with contact cleaner to see if I could restore the volume control's functionality again (because as I had mentioned before the volume control pot when it was working before it apparently finally failed would cut in and out depending on where the volume contol was rotated.)

Does any one on here have any known working volume controls with a built in power switch that they could send me?

I don't think there's too many volume controls of that value around! :sigh:
Check it with all the leads disconnected and see if it reads the same.
Remove it from the chassis and look inside.
All kinds of strange goings on with that set.

OK Will do.

I've seen non-AVC superhet radio circuits, but that one is a real gem.
I repaired the one I have or had, but I just replaced the bad caps and never realized that the set was that strange! :thumbsdn:

I located that chassis in my collection. I'm not sure if I have the cabinet, so I don't want to part it out.
It sure is a strange beast!

how is yours wired up?

I think the same, but I'll look again to look at the connection. :scratch2:

Here's a picture of the underside of my radio, is there anything that looks out of place here compared to yours?

I had a look at the schematic and the 5000 ohm volume control seems to vary suppressor grid voltage on the 6K7 IF tube.

That volume control pot looks like a replacement and a wire-wound control.
The one in my chassis is smaller, possibly the original.

Looks like it also ties to the cathode and to the 6A8 cathode. So applying varying positive voltage on the cathodes equates to varying neg. voltage on G1s (control grids).

Well I'm not sure about the volume control and whether or not its original or not because its the same exact volume control pot as what's in my Philco 116B which is from 1936 and unfortunately it has developed the same "sticking" power switch issue as the power switch on my Philco 116B has.

The volume control/power switch pot on this radio is a CTS (Central Telephone System) Type T Power Switch/Volume Control Pot, which seems seems to be a trouble proned volume control/power switch pot, because actually come to think of it this humming issue is exactly what my Philco 116B did which I thought it was bad filter caps but now thinking upon it I'm now wondering if it wasn't maybe a bad volume control pot, which I'm now wondering if that's not the case here...

CTS by the way has a plant in Elkhart, Indiana which is not too far from where I live, which is actually where the two aforementioned pots were made.

I had acquired late last year, more or less the sister set to this radio the RCA 5T and that thing when I first acquired, would blow the breaker for the circuit my workshop was on in my house, (and he told me that's all it did for him as well, and that was why he was selling it).

It was because the previous owner of the set a fellow antique radio enthusiast/collector had at one point replaced the original cloth cord with a modern lamp cord but he didn't wire it up right, which was why it was blowing the breaker, and it took me a few months of studying the Rider's Manual and the old RCA Red Book service diagrams for this radio to figure out that the wiring diagrams for the switch on this radio on those manuals (or at least the Rider's anyways) were written incorrectly and had the "dummy terminal" on the Power Switch marked in the wrong spot which is I think why the previous owner had issues with the wiring of the RCA 5T I am currently writting about.

Anyways the RCA 5T I just got going is a great performing set, its super sensitive and selective and the SW band on it picks up stations like its nobody's business (I was picking up the WWVB time stamp signal @ 5 MHz, I was picking up many Religious Stations on the SW band, and I was even picking up Radio Havanna out of Havanna, Cuba on it!

Anyways my point is that some of these old radios are super easy to repair and troubleshoot and some of these radios are a pain to troubleshoot even using the best troubleshooting skills one has to offer.

Actually calling the RCA 5T the "sister radio" to the GE A-53 is kind of inaccurate because the 5T is a vastly superior radio to the GE A-53 in many ways including the fact that the 5T has a great performing AVC circuit, whereas the GE A-53 lacks any sort of proper AVC circuit.

A little update:

I think I may have found a replacement switch/volume control that might work on this radio, someone gave me an old junker Philco Model 60 Cathedral Radio from the same time period as this GE is from (1936) and it also had a CTS Model T power switch/volume control assembly in it, the volume control pot on this switch/volume control is a 500k Ohm (.5 Meg) pot and I was wondering if this might be a viable replacement (even though this radio's original pot was 5k ohms) would the 500k vs. 5k make that much of a difference in how this radio performs?

Any help in this matter would be appreciated.

Thanks.

Well Unfortunately I think the radio's power transformer got fried because when I tried turning it on the pilot light wouldn't light up (the bulb is still good), and the power transformer was really hot to the touch and the Kill-a-watt meter was reading over 100 watts and the rectifier tube was the only tube that was hot to the touch, the rest of the tubes were stone cold.

So I think this radio unfortunately might be toast. :sigh:

The 500K pot is strictly an audio pot. It won't control the bias on those tubes.

When testing a radio transformer, always remove the rectifier tube first before applying power, in case the set has a B+ short, electrolytic or other component.
Either the PT is wasted or the short was robbing the 6V heater circuit.
Try it again with the watt-watcher and the 80 tube removed.

How long was it run in that condition?

It actually has a 5Z4 rectifier tube in it, but either way, I removed that tube from the radio, plugged it in turned it on, and sure enough I heard a well pronounced sizzling noise coming from the transformer, so yes I definitely think the transformer is bad. :sigh:

I have a power transformer on the Philco 60 that I could check to see if its still good or not, and if it is I might be able to swap that into this radio, because the Philco 60 is a very similar chassis design to this GE (2 band radio, AM and SW, similar tube count as well, and same tube voltages).

The the radio wasn't on that way very long, I turned it off right away as soon as I saw it wasn't working and felt that the transformer was getting hot.

what do you guys think?

I got lost in the dialogue!
What transformer is damaged? The one in the GE A83 or the one in the Philco?