reverse bias temp stabilization on a MKII?

[foxfire]

i tried a few searches without much luck. i don't know that i was using the right words and i would just try it out on my breadboard but i'm in the middle of moving so i'm without my parts bins. anyway my question is whether it is worth putting reverse bias diodes on Q1 and or Q2 of my MKII? i've the bit on this over at http://www.geocities.com/sunsetstrip/studio/2987/britface.html and over at http://fuzzcentral.ssguitar.com/3knob.php. so think i have agood idea of what it does. just not not where it's worth implementing this little trick?
rylan

[mac]

In my experience I notided that Ge diodes are unpredictable like Ge transistors. Some leak more than others, some are more sensitive to temperature than others, etc.
You need to find one that works.
In a MKIII the bias point varies if you change the diode.
I had best results using a Ge transistor of the same kind instead of a diode.

One thing I never tried is a thermo-resistor. But again, finding one with the right temp coefficient is a trial and error thing.

mac

[foxfire]

In my experience I notided that Ge diodes are unpredictable like Ge transistors. Some leak more than others, some are more sensitive to temperature than others, etc.
You need to find one that works.
In a MKIII the bias point varies if you change the diode.
I had best results using a Ge transistor of the same kind instead of a diode.

One thing I never tried is a thermo-resistor. But again, finding one with the right temp coefficient is a trial and error thing.

mac

thanks for the tip. do you think it's worth the time/parts to do this in a MKII? i have the room for it but, if the general conciseness is that it's over kill then i won't waist my time/parts?
rylan

[aron]

Rylan, try it and let me know if you get it to work well.

[foxfire]

i will but, it's gonna be a bit before i get finished with my move and am able to get back to my breadboard. i was hoping to finish up my layout in the interim but, i guess even that can wait really...
rylan

[mac]

Both diode and thermo resistors depend on the transistors being used, so there is no general rule.
There are another options:
1. the rock face, which uses an opamp and a LED/LDR to correct deviations from 4.5v due to temp. Works fine, but I recently posted that the opamp also might look the guitar signal like a change of bias. If this is the case it will try to set the collector at 4.5v.  Could have some effect on sustain.
2. the bias pot and a small external voltmeter is the best option to me.

mac

[foxfire]

yeah i'm just gonna keep the bias pot external. i don't have that much germanium laying around so i try not to "waste" it. when i have the time and my work area back together i'll play with it some more on the breadboard. thanks for the suggestions.
rylan