converting an MR501 monitor into a "Huntron Tracker"


I have a heavily modded MR501 with almost all the controls removed. it's the same one shown on as being part of a receiver system. looking at the MR501 manual, it struck me that it does not use the 25VAC winding internally, so I could use this drive to make it into an XY component curve tracer like a huntron tracker easily, since it is already an XY monitor. The AC winding appears to float, so I think it is safe to do this, but any feedback about TM frame problem issues is appreciated.

you can see this uncommon plug-in here on the tekwiki:

For some reason, I am in TM500 mode this month, so I thought I would try and do something with this unit as I work through all the other ones I have sitting around. this idea has been in my head a long time ever since I bought this unit. I hope it can be workable, as space is wickedly tight inside the MR501. I am happy to share my results if anybody is interested in them. It looks like the same thing could be done with an SC501.

all thoughts appreciated.
all the best,
walter (walter2 -at-
sphere research corp.


Sounds like a very interesting use for this plug in. I would like to hear and see more as the project progresses.

Michael Lynch
Dardanelle, AR

Ed Breya

Sounds like a good use for it, but if internal space is very limited, it may not be possible to fit the extra parts needed. The biggest issue would be the series power resistor(s) that set the test current range(s). It depends on how much juice you want to be able to supply. If the mainframe pass transistors are uncommitted, you can use them to make a synthetic variable power resistor. This would take some extra circuitry, but at least the power dissipation would be in the mainframe rather than the plug-in, and it could be more compact overall.

Another option may be to build a separate plug-in to go with it, to provide the test sources, with more available options from its windings and transistors, and panel space. Of course, this takes up a full slot, so it's not as compact or "cute" as it would be to squeeze a simple tester function into the original unit.



The AC winding appears to float, so I think it is safe to do this, but any feedback about TM frame problem issues is appreciated.
There are separate 25VAC windings to each TM50x slot, and they do indeed float, which is what makes PS503s floatable, and why series PS503s work. I do this all the time: I have three PS503s in series delivering up to ~120VDC end to end, and I earth either at the extreme left or bang in the middle, depending on whether I want single or dual supply rails for the DUT. So in the single-rail configuration the RH PS503 is floating by at least +80VDC.