Idea for Ge Bias Stabilization

[Bill Mountain]

I just picked up my first Ge transistors to try out some vintage fuzz circuits.  As I always do, I've been thinking about how to use them in more designs.

One could certainly argue that unless you're building a vintage circuit, Ge's are useless.  I would agree.  But this quest is more "what if?" than academic.

In the past I have run JFETs at higher voltages (24V and up) to help mitigate the bias variances.  With a large supply, Vgs and such become less important.

This led me to wonder what characteristic of the Ge transistor allows the bias to shift.  If we knew just how much or little the Ge bias can shift, I was thinking that with a high enough V+ we could compensate for any variances regardless of temperature (this is where I'll point out that I don't understand leakage and how it can be effected by increasing voltage).

There is also the possibility that I don't know what the hell I'm talking about.  There is also a certainty that with super high voltage it wouldn't clip anyway and then the point of using a Ge becomes moot.

But...MOJO!!!

Full disclosure:  I have been studying and building for a while but stayed away from Ge for all the right reasons.  I still don't understand leakage so I need to get a handle on that before I start building.  But...common sense aside.  I have dreams of a treble booster that sounds good anytime, anywhere, and any temperature (Ge not required).

[digi2t]

I have dreams of a treble booster that sounds good anytime, anywhere, and any temperature (Ge not required).

ROG Omega.

Like you said.... Ge not required.

[dwmorrin]

This led me to wonder what characteristic of the Ge transistor allows the bias to shift.

From my RCA transistor manual: "the operating point for a particular transistor is established by the quiescent (dc, no-signal) values, of collector voltage and emitter current."
So, change the collector voltage (this is the voltage at the collector, not the supply voltage) or the emitter current, and you'll get a bias shift.
That's a pretty wide field to cover.
Beta is what changes with temperature, and that directly affects the emitter current, which will affect the collector voltage.
Feedback of some type is needed to counteract the shift.
An external emitter resistor gives feedback one way, and a shunt feedback resistor from collector to base gives feedback another way.

[dwmorrin]

In the past I have run JFETs at higher voltages (24V and up) to help mitigate the bias variances.  With a large supply, Vgs and such become less important.
If we knew just how much or little the Ge bias can shift, I was thinking that with a high enough V+ we could compensate for any variances regardless of temperature.

I think if you survey most common Ge transistors, you'll find that they are not capable of withstanding high voltages.  This is one of Ge's big drawbacks.  Can't handle high idle power dissipation either, so you're quite limited in your high V+ theory... but I do love the theoretical idea!

[Bill Mountain]

I have dreams of a treble booster that sounds good anytime, anywhere, and any temperature (Ge not required).

ROG Omega.

Like you said.... Ge not required.

It's definitely leading the pack.

[Bill Mountain]

In the past I have run JFETs at higher voltages (24V and up) to help mitigate the bias variances.  With a large supply, Vgs and such become less important.
If we knew just how much or little the Ge bias can shift, I was thinking that with a high enough V+ we could compensate for any variances regardless of temperature.

I think if you survey most common Ge transistors, you'll find that they are not capable of withstanding high voltages.  This is one of Ge's big drawbacks.  Can't handle high idle power dissipation either, so you're quite limited in your high V+ theory... but I do love the theoretical idea!

Thanks for the comments.  You pretty much answered all of my questions.

[akc1973]

I have dreams of a treble booster that sounds good anytime, anywhere, and any temperature (Ge not required).

ROG Omega.

Like you said.... Ge not required.

100000+ The Omega is *the* treble booster. Love it!