[Heathkit] DX-40 Keying trouble

[Mike McCarty]

Curt wrote:
> I'm aware that any electronic component, including a ceramic disc cap, can 
> fail.  However would expect either a fail short or fail open, not 
> intermittent.  Intermittents in my experience are active device problems ( 
> tube or transistor ) or poor connections or shorts.  This problem doesn't 
> exhibit with vibration or movement of the transmitter.

I've experienced intermittent everything.

[...]

> in behavior.  With a DVM connected accoss the key ( to measure the voltage 
> on key-up ) the problem disappears.  Disconnecting the DVM causes the 
> oscillator to hang up again.

Now _this_ little item is very revealing. Presumably an additional
10Meg resistance isn't what's causing the issue to resolve, so
it may be that additional capacitance does the trick, but _why_?

This is most intriguing, and I must say that I don't have an
immediate guess at the cause.

Or maybe it is the additional 10Meg in parallel. Hmm.....

> I've ordered the caps, but plan some more voltage measurements and further 
> testing before wholesale change of the disc caps.
> 
> Thanks for all the advice, am surely happy this is a simple rig.
> 
> 73, Curt KB5JO 

Mike
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