IM-5217 FET Replacement Suggestions

[John H. Klingelhoeffer]

I have a well-worn IM-5217 Utility Solid-State Voltmeter that has been having
some zero drift problems.

On looking into this, I'm finding that the input N channel JFET is EXTREMELY
temperature sensitive - enough that the meter needle ungrounded with no input
goes from 0.3V to > 1.5V when I walk from the air conditioned house into the
outside warmth when on the 1.5VDC scale!

I have a bunch of JFETs in the junk box, but none of the original 417-241
Heath parts.  The instruction manual says this crosses to an "EL131".  That
proprietary part number does not show up in any of my 1970s or 80s cross
reference guides nor has an internet search been productive.

I suppose I will go ahead and use one of my junk box 2N3819s on this
application and see if they will work.  They only cost a buck apiece at Radio
Shack to replace them.  However, I'm wondering if an RF JFET is really
appropriate in this application, or if I need a low-noise, low-frequency
device?  I also have several National Semiconductor dual NJFETs that are rated
more for instrumentation than HF/VHF use.   I figure since this is a balanced
circuit, that I will probably replace both JFET's to minimize any Idss
differential changes over temperature.

Any comments on replacements and potential problems?  Thanks in advance.

John...
WB4LNM

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