I just realised, that i set up bias on my FF (+ extra bias 1K pot in Q2 collector) without a bit of thinking :icon_confused:. What exactly is the temperature sensitivity of the Ge transistors like?
Does bias Vc on Q2 go up when the temperature goes up? Or vice versa? Is it better to set the bias below 4.5V Vc-Q2 just to kick it up later with the 1K pot?
Does bias Vc on Q2 go up when the temperature goes up?
To one degree or another, depending on the transistors.
test by Measuring collector voltage while heating a cool transistor with thumb or thumb and forefinger.
Ah of course, thank you, shame on me. :icon_redface:
I always add a Ge-diode between E and B on a Ge-trannie to overcome the temperature problem in a FX box, a additional cooling device for the trannie is helpful too.
When I measure a Ge-trannie I put in in and wait 1-2 minutes before I measure the values. Often the trannie works quite stable after this time and the values won't drift anymore.
JHS
FF is more sensible to changes in Q1 than in Q2. This is because any variation in Q1 will be amplified by Q2. In the case of a FF heating Q1 will increase Q2 collector voltage drastically while decreasing Q1. On the other side heating Q2 will make the opossite effect but less dramatic.
Try this:
http://guitarfxs.tripod.com/soft/biascalculator.zip
mac