Hi Tony,

Thanks for the informatioin about the SFB modification and also for the good
suggestions.

If you can produce the original circuit, I would be most interested.

Thanks and 73.

Mike, K9AZS
----- Original Message -----
From: "McCloskey, Anthony" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, May 16, 2002 7:32 AM
Subject: Modifying the sympson 260 multimeter


> Hi All:
> I saw Mike Garrett's post about the sympson 260 meter modification and
> thought I might help.  The chopper circuit used by SFB in its 260
> modification used a unijunction transistor for the oscillator and a
chopper
> transistor who's number I don't remember at the moment.  It also used a 4
> lead audio amplifier made by motorola.  I Think all of these parts are
> obselete at this time, but the circuit could gbe modified using modern
> parts.  A fet llike the mpf102 could be used for the chopper and either a
> transistor oscillator or even the 555 timer would work for the oscillator.
> The lm386 would work well for the audio amplifier.  I think I have the
> circuit for the old meter reader, so I'll try to dig it up and put it on
the
> list.
> In the sympson, the meter was removed and it was replaced with a resistor.
> I think the simpson used a 50 microamp meter, and it was removed and a
1500
> ohm resistor was put in its place.  The chopper circuit was connected
across
> this resistor.
> The chopper circuit was mounted in the area formerly occupied by the
visual
> meter.
> Another method that was used was to leave the visual meter and build the
> chopper circuit in a separate box.  Then the chopper circuit was connected
> across the terminals the terminals of the visual meter.
> I dont remember which issue of btp the article was in.
>
> Tony McCloskey, WA3CAO
>