arp filter parts?

[Joachim Verghese]

Dear Doctor,

First of all, thanks for visiting my website, it's good to know
someone finds it useful.

> I have the following question: 
> looking at the 4012 filter, 4014 balanced modulator and the 4023
> filter I see these transistors beginning with TZ (the TZ-81 and
> the TZ-581). What are they, are they still obtainable, and can
> you get replacements?

The TZ trannies used to be made by Sprague (are they called Allegro
these days?), but I reckon they stopped making them years ago.

Electrically speaking, almost any low-noise device will work in
place of a TZ, just check the pin layout. Mechanically, the TZs
came in a pretty big case, one that you don't see often these
days. The nice thing was that the case was formed such that you
could use a cable tie to force the flat surfaces of two devices
together for thermal contact. Try doing that with TO-92s. :-)

Myself, I use 2N5087/2N5089 or ZTX109C/ZTX214C devices a lot
(although I don't remember if the pin layout is the same as
that of the TZ-81/581).

Well, Seasons Greetings and all that, everybody.

-joachim