Maestro Fz-1a

[JasonG]

Hey guys
I have gotten a good deal on a Maestro FZ-1a and the only thing it needs is one trasistor. I have put in some of the ge tranneys I have but they just dont do it for me. Can you guys tell me whitch Small Bear tranny would be right for it and if you think I should chang out the caps.
          Thanks
             Jason

[gez]

It's not that simple as it relies on leakage current to get the bias right.  I've built a few of these and to me the make/type of trannie, even gain wasn't that crucial - leakage was!  Here's a post I made earlier on in the year which 'might' be of help (everything is subjective):

I've built a few of these, all 1a (the ones with the 1.5V supply). I tried out a lot of different transistors and it didn't seem to make much difference so long as they're Ge.

What does make a difference (more than gain in my opinion) is the leakage of each transistor, as it's leakage which biases each device into conduction. I didn't test specifically for collector-base leakage, instead I used RG's circuit as outlined in his fuzz face article to test for both gain and leakage.

For Q1 I'd recommend using a low leakage device (the ones giving best results measured between 58uA and 120uA in my tests). If the transistor is too leaky virtually all the supply appears across the emitter resistor, clipping the signal on +ve swings resulting in a constricted, muffled sound. If you're too lazy to do all that measuring just stick a trannie in there and if the emitter measures somewhere between 0.4 and 0.6V it should sound sweet.

For Q2 you need a slightly higher leakage (my results were between 100uA and 220uA). If leakage is too low the transistor biases towards cut-off, collector current is too low and gain is pitiful, resulting in hardly any fuzz. If leakage is too high it biases towards saturation and the fuzz sounds constricted again. There's a definite 'sweet spot' for collector voltages between 0.75 and 1V with the 'attack' pot set for max fuzz.

For Q3 you can get away with higher leakages (188uA - 367uA for my results). Best results were to be had with the collector measuring between 1.25 and 1.28V. This is the only stage where I found gain made any difference (though only slight) - the higher the better.

Wear rubber gloves when handling the trannies as finger heat will totally distort all measurements. It's best to wait a few minutes to allow the circuit to settle in before making measurements (keep a book on standby).