Restored and old Zenith console radio 7S323 Ch 5714

[walterbeers]

I guess I just wanted to toot my horn about a restoration that I did on an old Zenith console radio from 1938/39. I found it for a friend on CL as he was looking for a Zenith console that has a tuning eye tube, AM and SW. Well he bought it with the idea of me getting it back into operation. We hauled it to my basement shop, and so the task at hand was upon me. Although I have done many radios in the past, I don't believe I have ever worked on one this old. It turned out to be a very tedious and yet a very rewarding project. The cabinet was in reasonable decent shape, (as I am not a furniture finisher) so other than some touch up where the veneer had pulled off, the majority of work was on the electronics. Getting into it, all the old wax capacitors, brittle wires, a dead 6U5 tuning eye tube, made me wonder if it would ever play and tune in stations like it should. (only minor IF alignment was required) Then on top of that I found a dead mouse in it, and it had chewed up a coil and some of the wiring in the preset tuning circuit, and the push buttons for the presets were un-repairable. Luckily my friend found another chassis like it, and bought it also off CL, hoping it had some good parts. I removed the dial plate, took some windex to the front of it (to clean it off) and the markings started to come right off. He got the other chassis, (no cabinet), and it luckily had a good dial plate, coil and push button assembly. The dial cord and belt were obviously rotten, and the original dial glass was gone. After doing research, found it was risky to replace the 6X5 rectifier tube, as they are known to short and take out the power transformer. Speaker was in good shape, only one small hole which some silicone glue took care of. Also the power transformer was good as well. Found a solid state replacement for the 6X5, which worked out great. Did a good cleaning of the chassis, and complete recap. The run down of parts, well lets say it wasn't cheap, but it is now a radio to be cherished. The parts I replaced, well here is a list. The dial cord, dial belt, 6X5 solid state tube replacement, power cord, dial glass, 6U5 eye tube, band switch lever, volume and tuning knobs, dial light bulbs, station tabs, tone tabs, and buttons, grill cloth, and lots hook up wire and contact cleaner. From the other junk chassis, I used the push button assembly, push button tuning coil and dial plate. Finding all of these were a challenge for both me and my friend, but they were available from various sources. Radio now plays great, and sounds as good as a modern stereo, even though it is only mono. I also added a 1 amp fuse for protection, as the unit had no fusing. Without help from my friend Rick, I don't know if I myself could have found all the sources for parts, and also the cash to purchase them. It was quite a challenge and enjoyable to get it going again.

[Electronic M]

Nice work.
I've got the top half of one that is a parts donor for a table set with the same chassis I have on the back burner.
I'm surprised you spent money on a plug in 6X5 replacement! You can replace the 6X5 with a couple of cheap 1N4007 diodes, a terminal strip, and a few minutes on Google to get the 6X5 basing diagram and the schematic equivalency between tube and SS diodes....Just disconnect everything but the heater leads from the original tube (if you want the original to sit in it's socket and light), attach them to the terminal strip, add the diodes to the strip, test, and voila! A safe replacement that is undetectable from above chassis.

It is common knowledge among tube radio collectors that water and normal cleaning agents destroy Zenith black dials. I've heard face grease works well (if your face don't have any ask a teenager to loan you some).

I'd not have gone with LEDs for the dial lights (as a general rule I hate non-incandescent electric light) as the light they cast is a dead give away to the presence of that non-period correct part.

[walterbeers]

We used the LED dial lights, as that is what my friend Rick wanted. Also the copper colored solid state replacement looks neat in the tube socket. Yes, we could have used diodes as well. I understand the SS replacement has the dropping resistor or thermister in it to prevent surge to the filters and power supply. I am amazed how much bass an old radio like that can produce. The most expensive was the buttons, inserts and for the tuning and tone push/pull buttons. At least the IF and RF cans seemed to be ok and intact. I did touch up the 455 KHZ cans, and slight calibration of the dial. Other than that not bad for a radio older than me. (And I"m almost 65). Grill cloth is not the exact same pattern that was with the radio when it was made, but is the pattern for one of the other console models. The one that was in there when I got it was nothing more than an off-white bed sheet.

[Titan1a]

I'm the owner of the aforementioned Zenith. Walter did an outstanding job on the electronics. I did the "legwork" in finding the replacement parts, schematic and etc. It was my insistence that he purchased the solid-state 6X5 rectifier replacement. He was hesitant to fabricate a 1N4007 rectifier adapter and other modifications. I paid the price and it was well worth it.

BTW An antenna is essential to making these radios perform. A simple wire antenna dangled behind the chassis just won't hack it. Try hum, interference and no reception. I purchased and installed a CCrain twin-coil antenna. Granted, it only works on AM (BCB). Obviously, the shortwave bands will require a different (outside) antenna. With four other shortwave radios (Panasonic RF-2200, Zenith Transoceanic 7000-1, Radio Shack DX-160 and Ten-Tec RX-320D, the 7S363 is low on the totem pole and destined for DX on AM and it shines there! 1940's and 50's programs sound neat. This vintage Zenith shows just how good AM used to sound.

[Olorin67]

I don't really see how replacing a 6X5 with diodes is "safer". the 6x5's don't short on their own (except maybe if damaged in shipping) But if a filter cap shorts and overloads them, they can fail and cause a short in the process, taking out a transformer. 5y3 and other directly heated rectifiers would fail in that circumstance also, but they don't tend to short out when they do, acting as a kind of fuse. If you added a quick acting fuse, wouldn't that be safer? if a filter cap shorts with a SS rectifier you'll probably still harm the transformer before the diodes fry, plus without a dropping resistor the B+ would be higher than stock.

[Titan1a]

The indirectly heated cathodes would short frying the power transformer. Installing fuses may/may not prevent damage as Murphy's Law states that a transformer will protect a fuse by blowing first.

[Reece]

In the underchassis view, there appears to be a pot at the far end of the tuning shaft, out beyond the flywheel. What is that control for?

[Electronic M]

Originally Posted by Reece

In the underchassis view, there appears to be a pot at the far end of the tuning shaft, out beyond the flywheel. What is that control for?

Should be volume. Zenith liked to use a single triple ganged knob (volume, tuning, band) back then.

[Reece]

Thanks. I never worked on one of these.

[Schanz]

I love that radio. Congrats.

[walterbeers]

Yes, the pot at the far end of the tuning shaft is the volume control. When I worked on it, I added a 1 amp fuse and holder on the back which should blow in case of a shorted rectifier (6X5 replacement), a shorted power transformer, or a shorted filter capacitor. The problem with using the 6X5 tube is that the filament is tied in with the rest of the filaments of all the tubes, and one side of the filament winding goes directly to the chassis ground, putting over 250 volts between the filament and the cathode in the 6X5 rectifier tube. In other makes and models they used a 5 volt filament (IE 5Y3, 5U4, etc) rectifier with a separate 5 volt secondary, so the filament winding was isolated from the rest of the circuit by the power transformer. Also for your information, the radio draws slightly less than 1/2 amp of power, so I figured a 1 amp quick acting fuse in the power line was sufficient to blow in case of a short, yet would still handle an average power surge that may come from the wall outlet. I saw the radio at my friends "Titan1a's house" and his CCrain twin-coil antenna does a super job of pulling in distant stations, eliminating the hum, interference and buzz associated with all the electronic noise present in today's digital environment. Also the 6X5 solid state replacement contains the surge/dropping resistor which also adds protection in case of a filter capacitor shorting.

[marty59]

As bad as the 6X5's are at shorting, the best design are the X-Plates which are rather sturdy and similar to the design of the miniature type 6X4.

[wa2ise]

One angle would be to run the 6X5 heater off its own filament transformer, and leaving the heater "float" or maybe connect one end to the cathode. Looks like there's plenty of room in the cabinet that you could mount this transformer on teh side of the chassis.

[NoPegs]

Originally Posted by walterbeers

Without help from my friend Rick, I don't know if I myself could have found all the sources for parts, and also the cash to purchase them. It was quite a challenge and enjoyable to get it going again.

Any chance your parts chassis has an intact dial pointer? I'm on the lookout for one for my Zenith chairside restoration.

[walterbeers]

The dial pointer is intact, however the dial plate from the donor chassis was used for restoring the console. I don't have it, you would have to contact Rick, titan1A, and see if he wants to sell it. He also has a decal with the radio station dial, that could be used to restore the dial plate. I'm not sure if it would be the same pointer or dial plate that is used in the chairside radio.