[AMRadio] K4KYV monitor scope

Donald Chester k4kyv at hotmail.com
Thu Mar 31 20:19:23 EST 2005

>If you are around, some time ago there was a discussion where you described 
>what you did to your heath kit monitor scope to reduce the hum on the 

I would have to dig up the documentation, but relying on my memory, I recall 
beefing up the HV filtering, rerouting the filament circuitry and replacing 
the magnetic shield on the scope tube.

As I recall, I substituted a separate filament line for the original design 
that depended on the chassis for one side of the circuit.

The piece of tin wrapped around the neck of the tube is worthless is a 
magnetic shield.  I had an old military RTTY monitor that used a similar 
shaped scope tube, and cannibalised the special black anodised magnetic 
shield and managed to shoehorn it in place by relocating some of the 
original scope components.

I got rid of most of the hum that shows up on the vertical trace, and the 
additional filtering got rid of the hum that modulated the brightness of the 

I also modified it to add some astigmatism control, which results in a 
sharper, better focused and better defined image.

The original designers could have done a much better job.  The manual even 
mentions the problem; they pass it off as "insignificent" in a scope that is 
"only" designed to monitor modulation.

Since I use mine only on AM, I pulled out the tube from the two-tone 
generator and vertical amplifier.  That lightens the load on the 
failure-prone power transformer.  I excite the vertical deflection plates 
directly with rf.

Instead of running the rf  feedline through the scope, I use a remote 
toroidal pickup link to  feed the scope some  distance away from the rf 
feedline. I had to locate it on the transmitter side of the antenna relay; 
otherwise the pickup link was inducing an intolerable level of noise from 
the scope into the receiver.


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