EH Scott Radio Enthusiasts

The Fine Things are Always Hand Made

This morning I was doing some cleaning and inspection of the radio tuner chassis of my 1946 Early 800B. The C33 capacitor that has two 20mF sections @ 500VDC  and bypasses the plate load resistors of the two 6J5 audio tubes was still present on the chassis, but had been disconnected. In its place electrically, were two individual electrolytics underneath the chassis. I had visions of re-stuffing the existing black covered C33. I saw that its 3 leads had been cut loose under the chassis. I was able to twist the capacitor loose from its large retaining nut and remove it from the chassis. In the process I discovered its leads were insulated with the notorious rubber insulation of the 1940s that cracks and falls apart when touched. I had to find and remove all the debris generated by removing the capacitor.

I inspected much of the rest of the chassis wiring in the radio tuner chassis and I saw no more components with the rubber insulated wiring, so hopefully this is the only item made that way.

The OEM C33 appears to have been encapsulated with black plastic and although there is a conventional metal chassis mounting ring for a twist-tab type electrolytic present, Scott used a insulated electrolytic that incorporated a threaded bottom shank and a large nut plus a fiber insulating washer were used to secure it to the chassis. I do not see any way to get inside the capacitor to remove its internal elements. It appears to have been sealed with some sort of mastic or tar material which would likely prove almost impossible to remove without destroying the case. Unless some of you have managed to re-stuff one of these and has some suggestions on how to do it without destroying the part, I think I may just re-install it after clipping off the wires. Since there are two individual electrolytics mounted underneath the chassis already, I will just leave them unless they are so old they need changing too.

It will soon be time to replace any paper-foil type capacitors here. This will include rebuilding the bathtub type capacitors with new film type capacitors inside. It will also be a good time to verify resistor values and replace any that are off value. Most of the carbon composition resistors I see look to be 1 Watt rated or better.

Joe

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The rubber wire may have been added by someone performing a repair. I confess to using old AC power cord "zip cord" with the rubber insulation you describe in my misguided youth.

In my recent work on repairing my Scott SLRM, built in 1945, I was surprised to see that it had colored plastic insulated wiring, whereas my slightly older RCH and RBO both have the more old school varnished woven fabric insulated wiring. Seeing the plastic insulation in a 1945 radio was a bit of a surprise. Not to say that plastic insulation cannot rot away. Early 80s Volvo wiring harnesses were notoriously bad in that respect, especially where the main harness including the alternator to battery charging wire ran below the crankshaft belt drive pulley ahead of the oil pan and was exposed to a lot of moisture and salt spray.

The C33 in the picture (from SN 1035 Early chassis) is an original Scott part, you can see the part number, 15B745, on it. I have two other 800B radio tuner chassis (one Early and one Late chassis) and they have the very same OEM black plastic insulated electrolytics that have the fiber washer and nut for retaining them in the chassis. Two of the Early chassis I have (SN 1035 and 1123) have the plastic insulated wiring combined with cloth insulated wiring. The one Late chassis I have (SN 6182) has more cloth covered wiring than plastic covered type. Both the cloth covered and the plastic covered wiring is much to be preferred to the rubber insulation type. Even the Late chassis still had C33 supplied with rubber insulation.

It appears that the only part that Scott Radio Laboratories used in their chassis that had rubber insulated wiring was C33 (at least on the radio tuner chassis). I have not looked that closely at the FM IF/Audio Output/Power Supply chassis yet to check the electrolytics that are present there. I may do that later today. The important thing to note about the two power supply chassis I have is that both of them are of the Early chassis production. The one Late production radio tuner chassis that I have has an OEM C33 with rubber insulated wiring whose rubber insulation is still soft and pliable - go figure.

Joe

I have on occasion encountered the black plastic electrolytic capacitors with the top loose or missing.  The electrolytic capacitors were likely installed from the top then a lid was glued on top.  I have been restuffing aluminum FP type electrolytics by rolling the original over a metal cutting saw blade on my table saw to open them then using adhesive backed thick aluminum foil to seal in the new components.  You may be able to remove the top of the plastic electrolytic in the same manner but using plastic cement to seal the capacitor after restuffing rather than adhesive backed foil.  If you wanted to stay with the character of rubber insulated wire, although somewhat costly, silicone insulated wire comes in many gauges and colors and will not deteriorate in our time frame.

Norman

The way the electrolytic was made was such that the entire top bottom and sides were encapsulated in black plastic. There is no aluminum visible even at the threaded part that the retaining nut screws onto. It appears that the entire case including the threaded part are entirely plastic. I would likely destroy the whole unit if I tried to open it up since the plastic is brittle. I might try this with the one on the Late model parts unit. I will report back on results.

Joe

You should be able to cut it open with a fine tooth hand saw.  I use the table saw because I can get a perfectly straight cut around the can using the fence as a guide.

Norman

On plain aluminum cans I have used a tubing cutter to get a nice clean cut and did the same way you did, used some aluminum tape over the cut area - hard to detect unless someone looks closely. I had enough room inside to reinforce it with a piece of PVC tube and some glue. Thanks for the suggestions.

Joe

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