Micromold resistors

[JohnCT]

On another thread (asbestos related), I mentioned running across some weird shaped Micromold capacitors. Well, they aren't.

I finally found four schematics for this Emerson that are all similar, not exact, but close enough to work on the radio.

So these are little bakelite bullets that have "Micromold" printed on the back, and paint dots like the Micromold capacitors have, but they are in fact resistors. The length is about the same as a Micromold capacitor is wide.



These are the only type of resistor in the entire radio other than a big 175 ohm standup for filament dropping purposes.

Every one was bad, without exception, and I don't mean 25 to 30% off either. The ones that weren't dead open were ridiculously high in value.

A 250K resistor read 1.2M, and a 50K read 175K.

Oddly, the paper capacitors are original, they are also Micromold tubular paper caps (never saw Micromold tubular papers either) and every one is perfect. Usually, a .1 uf (for instance) would read .3 or higher as they older and shrink and have leakage, but these .1 caps read .13 or so and show no leakage at almost full rated voltage.

John

[Electronic M]

Those are an older style micamold resistor than the one my 50s Zenith clock radio...they must have changed them over the years.

[JohnCT]

Originally Posted by Electronic M

Those are an older style micamold resistor than the one my 50s Zenith clock radio...they must have changed them over the years.

It's hard to pin a year on this radio as the basic H-5 chassis was made from the early 30s to the early 40s from what I've found, and in many variants.

I've found a couple that had no AC switch, others that had floating grounds (one ground via .1 uf cap). Every variant I saw also had different IF frequencies. I figure the later ones were the 455khz (although there was a 456 as well).

Since 100% of the resistors were either open or 3X to 10X higher in value, I will just shotgun all the resistors along with the caps if I ever run across any more.

John

[Tim Tress]

Those are the Micamold insulated carbon resistors; I have only seen them in 1930s radios. The wire-wound types are a little bit wider and the case has a different design; they were made in two different sizes. Zenith was probably the biggest user of them, and they turn up in other brands as well; Midwest, Emerson, and Stewart-Warner to name a few.

[vortalexfan]

Originally Posted by Tim Tress

Those are the Micamold insulated carbon resistors; I have only seen them in 1930s radios. The wire-wound types are a little bit wider and the case has a different design; they were made in two different sizes. Zenith was probably the biggest user of them, and they turn up in other brands as well; Midwest, Emerson, and Stewart-Warner to name a few.

I have a 1952 Zenith Clock Radio that had some of those in it. It was of the wider variety though in this case.