[ARC5] A hardly relaxing oscillator

[Kenneth G. Gordon]

On 2 Feb 2015 at 7:24, mike Kana wrote:

> Hi all - Im doing some referb on a modified reciever (12V filaments) - when
> spinning up the 12V (!) dynamotor that came with the radio, the neon bulb on the
> audio transformer lights up and the audio has a loud oscillation - reminds me of
> the old 'relaxation oscillators'.

Sounds to me like the bypass capacitors on the dynamotor are open, AND 
that the dyno is not properly grounded to the receiver.

You will have to remove the end-bells and look carefully at the capacitors 
you will find connected from each brush to ground, and/or across the 
armature.

> I figure the new caps might fix the
> issue

Well, not if you mean the caps in the receiver....although C-16A/B/C is the 
main filter for everything coming OUT of the dynamotor. Even so, they only 
catch what's left after the filters on the dyno itself take care of the BIG 
spikes.

> but has anyone run into this before?

Yes, of course...

Ken W7EKB