Re: MR501 HT Success!



Would love to see pictures. Could they be posted to

George kd6new

On Jul 20, 2019, at 6:54 PM, walter shawlee <@walter2> wrote:

Well, 5 resistors and a rotary switch did the trick, I now have a variable range "huntron tracker" up and running in that modded MR501.

it is currently in "ugly" prototype stage, literally held together with some tape, and running on an extender cable but I wanted to be sure before cutting the panel that the idea was workable with no surprises. I still have to tweak some gains to prevent traces falling off the screen, but I have great performance from low voltage to about 10Vfs, and easily within the range of all the controls.

I can send some pics to anybody interested, the process was very simple:

1. attach twisted pair to rear 25VAC wining on 13A/B, run that to a small pcb with the range resistors.
2. remove rear connector X/Y connections on 16/17 for re-use.
3. remove the vertical gain pot from the front.
4. install 3 pos rotary (min. grayhill) in its place, run to pcb to select input voltage from divider pcb..
5. add vertical current sense 1K resistor across the vertical input.
6. connect common and horiz input to the pcb.
7. cable BNC for sample input.

now I have to add a BNC to front, thankfully the shell goes to ground/circuit common, or an insulated BNC would be needed. using a BNC to mini-grabber cable makes testing a snap.

there is a bit of end trace distortion (most visible on circular cap traces) due to other rectifiers sharing the same core transformer as the test winding. very minor issue, but interesting to see how loads affect the primary transformer reflected back to the line.

I looks very usable, certainly more so than the raw MR501 I started with.I will provide better pics and info once it's finished.
all the best,
walter (walter2 -at-
sphere research corp.

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