[JMS] Variarm Update

[Niel Wiegand]

Might a transformer cause a steel chassis to vibrate...either via 
magnetics or just the physical vibration of loose transformer laminations?

This vibration would couple into the rest of the ECO as 60 cycle FM 
modulation.

National probably used this reasoning in the HRO Sr external power 
supply design.

Niel - W0VLZ



Paul Christensen wrote:
>> "Mr. Wilson, the circuit diagram for the Variarm ECO came out of QST magazine from the 40s, not his design."
> 
> For anyone interested, the original QST article is titled: The "Variarm 150" and was authored by Henry Rice, W9YZH.  See the January, 1941 issue, pp. 8-11; p. 74.  This quote from the article is especially interesting:
> 
> "The absence of all transformers ensures vibrationless operation without the necessity for resorting to a separate power supply unit."  I'm not sure what he meant by "vibrationless," but it's possible he was referring to hum modulation where the 60 Hz line frequency beats with the oscillator and results in a "fuzzy" CW tone when demodulated.
> 
> Any other guesses?
> 
> Paul, W9AC
> 
> >