Zenith 8-5-463 black dial console. Didn't need; couldn't resist!

[Tubejunke]

My wife texted me last weekend that she saw this radio, but for whatever reason my "old" flip phone wouldn't take the media message with pictures. So I went on dusty, but shines under the dust. Tubes there; speaker there, and the dial is black. $50 firm was the price. I couldn't see how I could go wrong except for the guilt and pain felt of bringing something else into the house.

The interesting part is that the radio was found but never tried out due to a bad cord. I liked the sound of that myself. When it made it to my place the first thing I see is a section of maybe drop cord with a modern 3 prong replacement plug end. Hmmm. Never tried it out.... The older lady's story was that it needed rewiring. I thought it as layman's vernacular. But I have read some Internet posts on Zenith radios of this vintage having bad rubber insulation and some actually having to be rewired. I hope its not that bad when I pull the ultra dusty chassis. It looks from the top as if there is both cloth and rubber wire insulation and the cloth is nice; some of the rubber is nice, and some is gone like coming out of IF cans to grid caps.

The cabinet looks like it will come back to be beautiful. The slats over the speaker cloth are all good (read to be a problem). So it's the typical clean and cap deal I imagine. I may even get lucky and have the thing work as is. I have many table models of that era that work great as is. Being such a potentially nice piece, I want to at least go through the power supply with the darned 6X5 rectifRIER. The picture is just reference. Not mine.

[Electronic M]

Take it from me: the rubber can look fine and be brittle and missing tiny chips in critacal places causing shorts.

I just got a chair-side with that chassis for $25....It only needs a refinish, new dial glass scale and pointer, the preset button escutcheon, and a full electrical resto...

[TUD1]

Nice radio, but 40, 41, and 42 is when Zenith took a slight dip down on the quality. 6X5 recifiers, rubber wiring, and in 42, very cheap tube sockets. Had 'em break on me real bad before. That was for the Loktals, this set has mostly octals, so you're fine on that. You'll want to convert it to solid state rectification. Those 6X5's are a ticking time bomb. Had one short on me one time, thank God I was there to catch it before it took out the transformer. This is a 40 model BTW. The 4 in 463 means 40. 5 would be 41 and 6 would be 42.

[Tubejunke]

OK, so it seems that I didn't do too badly, but my work is cut out for me. Indeed there is only one loctal tube and it's a goner at about 40% emissions. I really appreciate that drawing TUD1. If I interpret it right it looks very simple in that you simply wire in the two 1N4007 diodes' anode where the plates would be; eliminating them (plates) from the circuit. On the other end it's solid state diode cathode to chassis ground. The heater string resistance is in the left in circuit tube for originality.

If I have that right I may just do that on this set and an evidently pretty rare Silvertone set that I have with the 6X5. It's a 4663 model and IF I find them they are super pricey by my standards. I don't know if that says a lot, but I sure don't want to fry it. My beloved Hickok 209 VTVMs use them as well.

Thanks all for chiming in. I see I'm not in this alone as Electronic M is on board. A good man to have beside ya in a radio/tv foxhole!

[dieseljeep]

Originally Posted by Electronic M

Take it from me: the rubber can look fine and be brittle and missing tiny chips in critacal places causing shorts.

I just got a chair-side with that chassis for $25....It only needs a refinish, new dial glass scale and pointer, the preset button escutcheon, and a full electrical resto...

Is that all it needs!

[Electronic M]

Originally Posted by dieseljeep

Is that all it needs!

God only knows, since I haven't opened it up (or powered it) yet. It is missing a couple of tone buttons, and the speaker cone is damaged too...Maybe I should have left it at Goodwill... I can't start work on it for a while. I've still got a Philco cathedral and a 13" color Zenith to fix for paying customers, and some half completed TVs of my own that I paused for the paying work.

I've got an upright console with the same control panel (and presumably chassis) that was built for 25Hz power. The darn thing still worked nicely on original parts, but I recapped it anyway.

[dieseljeep]

Originally Posted by Electronic M

God only knows, since I haven't opened it up (or powered it) yet. It is missing a couple of tone buttons, and the speaker cone is damaged too...Maybe I should have left it at Goodwill... I can't start work on it for a while. I've still got a Philco cathedral and a 13" color Zenith to fix for paying customers, and some half completed TVs of my own that I paused for the paying work.

I've got an upright console with the same control panel (and presumably chassis) that was built for 25Hz power. The darn thing still worked nicely on original parts, but I recapped it anyway.

I haven't seen anything at a G/W store, that even resembles an old radio.
The last G/W, I went to, didn't even have VHS tapes. They must've quit handling them.

[Electronic M]

It's probably the 3rd to 5th pre-HiFi tube set I've got at thrifts in the last ~8 years, and that don't count tube HiFi gear and stuff they wanted WAY too much for.

I got the guts of a late 50's/early 60's stereo RCA at the same place and time as well as an LG flatscreen monitor*. The cabinet was ugly and I could not fit it so I field stripped the thing and re-donated the cabinet.

*It would come on to it's welcome screen and die a moment later. It was the first flat screen I've fixed. One of the lytics went, and changing it fixed it, but somehow it is now in Japanese language mode....At least I can read enough Japanese to operate it.

[dieseljeep]

Originally Posted by dieseljeep

I haven't seen anything at a G/W store, that even resembles an old radio.
The last G/W, I went to, didn't even have VHS tapes. They must've quit handling them.

I made a mistake on my entry. They had one of those lousy repro cathedrals, either a Crosley or a Thomas. Some rediculous price, $12.00 or $15.00. I wouldn't pay 10% of that.

[Reece]

Tubejunke, this may have just been "a slip of the pen," but feel that I have to point it out just to be sure: with reference to replacing the 6X5 with diodes, you wrote:

If I interpret it right it looks very simple in that you simply wire in the two 1N4007 diodes' anode where the plates would be; eliminating them (plates) from the circuit. On the other end it's solid state diode cathode to chassis ground. The heater string resistance is in the left in circuit tube for originality.

Note that the cathodes of the diodes don't go to chassis ground (which would represent a dead short!) They go to the field coil and the + end of the first filter cap.

As to the 6X5 heater, yes, it can be left connected for show, but disconnecting it would give the sometimes feverish Zenith power xfrmr a bit of a break!

[Captainclock]

Tubejunke:
Now what I've heard though is that the 6X5GTs are safe tubes to use in these circuits as they aren't as suseptible to dead shorting, whereas the 6X5G or the 6X5 (metal cased tube) are the ones you have to watch out for. So if you have some 6X5GTs in that radio or can get a hold of some NOS 6X5GTs then you should be able to still use the tube rectifier circuit in this radio yet without having to worry about frying your Power Transformer.

[SwizzyMan]

Everything you need to know about the 6X5. In contrast to ordinary filament-type full-wave rectifiers, the 6X5 is one of a family of heater-cathode full-wave rectifiers. Unlike some large members of the family, there is no connection between heater and cathode in the 6X5 family. Apart from filament/heater burnout, any vacuum rectifier tube has two major vulnerabilities. One is excessive peak inverse voltage, and the other, excessive peak plate current. Both may cause arcs and shorts in any vacuum rectifier.Heater-cathode rectifiers like the 6X5, with no connection between heater and cathode, have a third vulnerability, which is heater-cathode voltage at or near redline. No heater-cathode potential can appear unless the heater is referenced to ground, or worse yet, operated at ground potential (the cathode carries the full B+ potential above ground). Unfortunately, this is the case in almost every application of the 6X5, as it is operated on the heater circuit carrying all the other tubes, a circuit almost invariably tied to ground in one way or another.
The alternative, of course, is a separate rectifier filament winding that could be "floated" without reference to ground, but that separate winding is what designers were trying to get away from in the first place... It was common, unfortunately, for designers to redline many parts (especially tubes) to get the most "bang" out of their products for their invested buck. With the 6X5 being operated at redline (or beyond) in certain radios, there were a lot of bangs. When you redline any tube, you are simply asking for trouble. Redline output and rectifier tubes, and you're asking for BIG trouble. The 6X5 was apparently pushed to redline on heater-cathode potential and/or peak plate current in sets where it is notorious for shorting out, but this was a designer's fault, not the fault of the tube itself (it may also be possible that the tube was originally rated beyond its actual ability to stand up to punishment). The 6X5G and GT are at equal risk of developing a short, it's really how the tube is treated in circuit that affects its chance to short out. 6X5's will last a long time if run comfortably within their ratings, and especially on a floating heater winding. If the heater has no reference to ground, the major cause of a heater-cathode short is removed. The only caveat is that the floating heater winding should be able to withstand full B+ potential to ground in case there is such a short.

[Tubejunke]

Originally Posted by Reece

Note that the cathodes of the diodes don't go to chassis ground (which would represent a dead short!) They go to the field coil and the + end of the first filter cap.

As to the 6X5 heater, yes, it can be left connected for show, but disconnecting it would give the sometimes feverish Zenith power xfrmr a bit of a break!

Thanks for correcting me on this Reece. I really don't know what propelled me to say that except to say that I had been working on an old Zenith "roundie" color tv that I have and I have been watching cathode current on the horizontal output tube. To do that I break the grounded cathode to place an ammeter in series. No excuse really for mixing that up with a rectifier in a power supply. Geez!

Anyway, I have a couple of 6X5GT tubes that I can use for the time being under close watch in these early stages of resurrection. Swizzyman gave a great read on these bad rep tubes. I hope Captain Clock read his post and I can attest to the GTs shorting as the tube that came in this Zenith was a GT with low emissions. I scavenged a couple of other GTs that I had sitting in boxes and threw them in my trusty old Sylvania 140 tester. One was fine and is in the now playing radio. The other gave a sharp flash when I plugged it in and the neon short lamp went full on. Good thing to have a few old tube testers around!

So yes folks this old Zenith radio came to life last night with little more than a dusting out, a rectifier tube and pin cleaning on only a few of the other tubes. The story's not over though. The volume is pretty low; the tuning eye looks completely dead, and all of that neat O Zenith tuning presets or whatnot has to be cleaned and lubed. I'm assuming that they are station presets. The closest thing I have seen to what I see there is in my Transoceanic radios and they are band switches.

[Electronic M]

On one side the buttons are broadcast presets (there should be a band switch position "automatic" IIRC for them separate from the broadcast dial tuning position) and the buttons on the other side (left) should be the tone switches.

[TUD1]

I once had a Philco 6X5GT short out and nearly destroyed the transformer. I caught it just in time.