[Electrothaumaturgist]

I dunno about any of that. Seemed like some were fully engulfed. Regardless, the procedure is as I described.  

[Arran]

If it's that axial lead electrolytic under the amplifier chassis that you are speaking of, and not the aluminum twist lock can on top, then I would get a larger cardboard tube and make a replica,
I have some that came from those large rolls of Saran Wrap that are 1'' or more across that I acquired, though there are other sources of them such as mailing tubes. You could probably scan the label on the original and make a reproduction, or perhaps slice it open and peel the cardboard away from the cement?
Regards
Arran

[Electrothaumaturgist]

That is an excellent idea, Arran! I was sweating bullets at some points during the process, afraid of destroying the cardboard and not having anything to replace it with. It was touch and go many times. Oh, and , by the by, do they still make those longer carbon composite resistors anymore? The dogbones are easy enough to construct, but those long ones might be tricky to reproduce and paint properly if Ed is going to take that route with those components.

[EdHolland]

Right then!

With the RCA happily restored inside and out, I am at last ready to make a start on this Zenith. The first question is whether to restuff caps and do something authentic-looking with resistors.

The large "radiogram" cabinet is in somewhat distressed shape. Structurally it is sound, but the bulk of it is photo-finish, and this has shrunk and crazed. It is unlikely I will be able to, or have time to do much about that in the near future, as it lives ~300 miles away.

First things are easy-ish:

1) Restuff electrolytics. Whatever they are, axials or twist-lock, there is a way to renew them.
2) Rewire chassis and harnesses to deal with the crumbling rubber covered original stuff.
3) Check resistors against marked values.
4) Decide on the restuff or replace of paper caps.

It may be a week or so before things get going.

Cheers

Ed

[Arran]

Ed;
  I would guess that the larger carbon comp resistors, such as the 2 and 3 Watt ones, would be just about impossible to find new, the 1/4 and 1/2 Watt ones are harder to find, and more expensive then the alternatives. There is one type of resistor that I ran across recently, it's a 3 Watt that is the same size as an old 1/2 Watt from the 1940s, I think that they are metal oxide or some newer material, not wire wound, one of those could be used inside a fake 2 Watt carbon comp resistor I suppose.
Regards
Arran

[jcassity]

late to the show but..... that is a very nice example of OEM works. many people would one day marvel at the assembly line techniques.

[EdHolland]

Right then!

With the antenna back in the trees, I returned to the radio bench and finally touched this one with a hot iron, so we are officially underway.

Yesterday I started taking notes on the audio amp and power supply chassis. Then some exploration. The large 40 mfd +40 mfd twist lock was carefully removed with a view to opening and restuffing when the new caps arrive. I probed a few resistors, which seem within tolerance, and started to figure out the wiring to the harness which connects to the main chassis. The hot lines are rubber insulated wire which is falling apart...

As to the big ecap under the chassis, it is riveted in place. Unless I can slide it free, i will just disconnect it and add a new cap to the tag board.

Good fun!

Ed

[EdHolland]

A little time at the bench today. I removed the cardboard tubed 40 mfd cap, and was able to open it and remove the contents. The parts box yielded something to place inside the can, and I made a new end cap to support the + terminal which was slightly damaged in getting things apart. This will all go back together, the end of the can rolled back and the whole thing placed back in the cardboard tube. I drilled small holes to allow discrete wires from the new caps to be soldered to the external tabs.

I did drill the rivet in the bracket holding the cap to the chassis. A 3 mm nut and bolt will resecure the clamp around the cap. From above, no visible change.

The cap foil and paper were stil moist - it could possibly have been reformed, but this approach is better.

Cheers,

Ed

[EdHolland]

Last night I noticed something interesting when scanning the schematics, getting ready to doze off... A lot of the resistors are marked with M rather than k suffixes. Now I'm darned sure there are not handfuls of 47 Meg and 470 Meg resistors (I can read the colour bands).

Do many other schematics call out values this way?

Oh and aside from the rubber wire, the RF deck is full of paper caps in horrendous locations. I suppose I'll untangle them all and desolder properly, but it is no surprise that many repair men clipped and resoldered to the leads of the old component...

[EdHolland]

Quite a bit of progress today on the amp/PSU chassis. Replaced all the rubber wire in the connecting harness. Also completed the restuff of the large 40 uF under chassis electrolytic cap.

I looked at one of the larger paper caps, and it came apart in a messy sort of way, so I have decided against restuffing them. It also came to light that the parts box is short of a few values needed to complete this job, so I'll order up what is needed.

Lastly, I frightened myself by looking under the main radio chassis at all the caps and rubber wire hiding therein and awaiting replacement.

Cheers

Ed

[Ron Ramirez]

Last night I noticed something interesting when scanning the schematics, getting ready to doze off... A lot of the resistors are marked with M rather than k suffixes. ...Do many other schematics call out values this way?

Yes, there were some companies which listed their resistors in that manner. Keep this in mind: If you see a resistor labeled 47 M on a schematic, it is 47K (47,000 ohms) and not 47 meg. Manufacturers who did this were referring to the Roman numeral "M" (which equals 1000). These same schematics will usually spell out a resistor which is in the megohms as "2 MEG." or "2 MEGOHMS".

I recall Magnavox used to do that. Way back, about 500 years ago, the first radio I ever owned was the chassis and speakers of a prewar Magnavox Belvedere (CR-181). This was in 1974 and I was 14 years old. I contacted Magnavox (they were still an independent company then, this was before the Philips buyout) and they sent me a photocopy of the service manual, free. Its schematic had resistors in the kilohms printed on the schematic as "47 M". I soon figured out they meant 47K! (I seem to recall that a letter I sent to Jim Fred on that subject came back with the reply confirming that.)

[Arran]

Another thing that some manufacturers did, although this would show on the parts list but not the circuit diagram, was to use 1/4 Watt resistors, which probably explains why I run into so many that have drifted upward in resistance over time in certain makes. In many tube circuits 1/4 Watt is just borderline, use at least a 1/2 Watt for replacement.
Regards
Arran

[morzh]

The Airline I have just finished also marks their kOhms as "M" and MOhms as "megohms".

[EdHolland]

Thanks folks. The schematic shows M, Meg, and then just plain numbers for ohms values up to about 2200. I got the gist fairly quickly, and a quick look at the parts themselves obviously tells the story.

[EdHolland]

Busy day on the radio bench today. I peeled open the big 40 uF + 40 uF filter cap, and spent an unhappy while unstuffing the can. Unlike the last one I did, this cap was packed in super tight - it makes me wonder how they got all the gubbins in there! Then some time wondering how to bring the connections out through the base. I thought I had a really good idea, which resulted in breaking out one of the tags. This was put straight, but then time was needed to let epoxy adhesive set.

With that, I pulled out the main chassis, and started to look. Oh dear, that wiring to the magic eye valve looks hideous even on the top side. Out with the notebook and record the wiring details. Accessibility on this chassis is very tricky in some places. Anyway, I found a way to get each wire desoldered, and tacked its replacement on to the end, so that I could pull the new run through. Most lines had to pass through a shield under the chassis, and this was a good way to avoid threading from scratch. All done

Then on to the wiring out to the tone selection switches. This proves to be a bit confusing - how to get to the solder joints in the switch mechanism? eventually I find that the tag board can be slid out from the button mechanism. Time to stop, but these will be rewired next session.

After that, it is paper cap replacement time, possibly also more under chassis wiring.