[Hallicrafters] HP VTVM's

[Mark Shaum]

> Does anyone know if the screw on tip piece and diode from a HP 410B AC 
> probe
> will fit a HP 410C?
>
> David C. Hallam
> KC2JD

The earlier 410B used the 2-01C tube. Later 410B's (and the 410C used the
EA-53 tube which is "almost" the same thing. (Isn't that always the way)

Unfortunately, the EA-53 is a little longer and this makes it a challenge to
mount the 2-01C in a probe designed for the EA-53. Also, the top contact of
the EA-53 has a spring loaded tip that probably results in a more reliable
connection in the probe and may be one of (the?) reason(s) for the change.

Also, the 2-01C is a 5.0V filament while the EA-53 is a 6.3V filament. The 
filament adjust pot in
the 410's has a wide enough range to take care of this part of the problem.

Anyway, if your probe has the 2-01C, then replacement is easy. If you have
a later unit with the EA-53 in it, you may need to do some "adjusting" to
get the 2-01C the work. No one has stated for sure that the diode
characteristics of the two are identical, but I assume if they are not that
the internal adjustments in the meter are adequate to take care of them.

73! - Mark K9TR
http://www.qsl.net/k9tr