[AMRadio] K4KYV monitor scope

Gary Schafer garyschafer at comcast.net
Thu Mar 31 22:18:32 EST 2005

Donald Chester wrote:
>> 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 trace.
> 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 trace.
> 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.
> Don K4KYV

Thanks Don!
Now I need to find some 1600 volt caps for the high voltage. I thought I 
knew where to get them but can't seem to find them now.
Anyone have any idea? .15 mfd or greater at 1600 volts.

Gary  K4FMX

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