Ge transistors with heatsinks.

[col]

One of the first pedals I built was the 'Easy Face' (mix of Si and Ge trannies) which usually sounds good but which is very temperature sensetive and changes tone if used for too long. The Ge transistor I used was one of those with the big heatsink with a hole drilled through it. Is this behaviour normal? I have considered changing it for one of the more usual 'top hat' type transistors but should the heat sink really make any difference? It is the only transistor I have used with one.
I have built other Ge circuits and used a temperature stabilising Ge diode in the circuit. I might have to do that here.

Col

[Paul Perry (Frostwave)]

A heatsink won't change the temperature sensitivity, it will just take longer for the transistor to come to room temperature. (of course, it's different if it is a power transistor carrying a heavy load, but for a fuzz, there isn't significant self-heating).
Back in the days of early ham radio, people sometimes made little thermostatically controlled "ovens" to keep frequency-determining crystals at a constant temperature. I guess we could do that! We could even keep it BELOW ambient, thanks to the magic of peltier cooling slabs. Better swap the little 9v battery for an auto storage 12v lead acid one, though 

[jmusser]

Would the temperature stabilization germanium diode work for this application?

[Fret Wire]

Would the temperature stabilization germanium diode work for this application?

It will work only to a degree, just like it only works to a degree with any other Ge tranny. The diode temp trick isn't perfect, but it does give a Ge fuzz more temperature tolorance before it starts to crap out. Nor will it make up for unstable/high leakage Ge's.

For 9v FX, treat the AC 128/01, or other heatsinked Ge, the same as you would any other Ge. The heatsinked units were intended for higher voltage operation. For fuzz's, they're all the same: if they're stable, low leakage, and in the right gain range, they're good.

[jmusser]

Good to know. I kind of thought it was the ultimate band-aid for the temperature degredation problem concerning germaniums. I had always wondered if something like a Fuzz Face would benifit from a 2 1/2" X 2 1/2" muffin fan, and vent ports across from it, especially if they were heat sinked with a copper strap type heatsink? I found a couple of the SB type germaniums in an old beat up radio, that used a 1/4" copper strap around it for a heat sink, that had about a 3/4" "flag" of the copper strap sticking off of it. That seemed like a really neat idea. These were the basic AC128 style straight sided can transistors.

[Fret Wire]

That would work fine, but it's more complicated than a fuzz needs to, or should be. The ge diode trick works for most situations. Some add an external bias pot to compensate for temp. Just add the diode, bias it up properly, and if it ever does succumb to temp, two taps of your toe can switch off a ge fuzz and switch on a si fuzz.