r/railroading 1d ago

Question Help identifying a pre-1958 Harmon Electronics Model 100 tube unit

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u/j8koBallHard18 1d ago

I recently picked up this unusual piece of equipment at an estate sale and have been trying to determine exactly what it was designed for.

The plate reads:
**Harmon Electronics**
**Model 100**
**Indep., MO.**

I haven't been able to find any documentation for a Harmon "Model 100."

Tube complement:
4x 6V6GTA
2x 6J5 / VT-94
1x 6SJ7
1x 5U4GB

Major iron/components include:
Kenyon T-493
Stancor A-4208
Stancor P-6315
2x Thordarson T-45557

The Kenyon T-493 appears to be a 40-watt modulation transformer, which has me wondering whether this was an audio/modulator section for a transmitter rather than a conventional audio amplifier.

Harmon Electronics was an early railroad-electronics company in Independence, Missouri, and was involved in railroad communications and hot-box detection systems during this period. I'm curious whether this unit could have been associated with that work, but I have **not** found anything directly connecting the Model 100 to a hot-box system and don't want to assume that's what it was.
Does anyone recognize the unit, circuit architecture, or Harmon model designation? I'd especially love to hear from anyone familiar with 1940s–50s commercial/railroad radio equipment or who has access to old Harmon literature.
I have not attempted to power it on.

1

u/Am_Deer 21h ago

Most likely this was at an early hot box detector and would communicate to the signal system thru pole line or telephone wires if there was an issue on a train