Moog Transistor Matcher Questions

[>>>marjan<<<]

Hi Romeo,

> I just finished making a copy of the moog transistor matcher.  I'm powering
> it off +/-15 V, which according to the notes on the diagram is ok.
> 

Be sure to add 10K resistor to PNP matching circuit, similar to NPN.
Otherwise cct shoud work OK. The resistor should go inbetween fixed
pnp's collector and emitter of pnp under test. One list member had
corrected cct, even made npn/pnp matcher. 

> The circuit seems to be getting really hot.  I'm using a BA4558 and it is
> too hot too touch when the circuit is on.  the regulators get really hot on

if it's PNP cct, read above, if it's NPN cct then you must've made a
mistake.

> the power supply, even though only the matcher is being powered.  I checked
> the circuit out and I've assembled it correctly as far as I can tell(I did
> add the resistor that's missing in the moog diagram).  Can this circuit
> really handle +/- 15 V?

I used +/-10V, and +/-9V (two 9V batteries) and it works OK. 

> 
>  I've noticed that the measurements aren't steady at all. Once I turn the
> power on, the voltage reading on the voltmeter seems to drop as I watch.

:) This is very obvious illustration of all the talk about the need for
temp compensation of expo pair. You see how it changes with temperature.
Try to do it in constant temp room, away from open air flow (window,
doors).
Also be sure to use tweezers to pick and install transistors you test as
heat from your fingers heats transistor a bit and you get some reading
that 
quickly changes as heat is dropped. That's how sensitive it is...
I use large plastic tweezers. Once those precautions are taken, you have
just stable reading, enough for our moog filters. While I did use it for
some uncritical expo pair matchings, you'd better go for signal tracer
for more precise expo pair matching.

> I'm assuming that as the transistor heats up more current flows through it,
> lowering the Vbe.  I would assume that the circuit would be stable and not
> subject to much change.

Cct isn't the problem, transistor is.

Cheers,

marjan