Dallas Rangemaster collector bias

[jswevers]

Hi,


I have a short question related to the bias of the germanium transistors I have put in a Dallas Rangemaster cirquit. I bought this transistor
from Smallbears and the paper with this transistor indicates values
of the resistor that determine a good operation point of this transistor.
With these resistors the collector bias voltage should be between -6.6 and -7.2Volt, for a battery between 9 and 9.2 Volt.  I measure -7.34 V but for a battery of +9.4 Volt. Is this bias voltage OK, or should I change the values of the resistors? In that case, which one ?

Thanks

Jan

[Doug H]

IMO, the best thing to do is to try using a pot as a variable resistor and adjust the bias to find where you like it best. In fact I think whenever I finally get around to building my Ge rangemaster I'm going to install an external "bias control". I have found a lot of interesting sounds by adjusting the bias. Setting it around -7v as in RG's article sounds good, but don't be afraid to experiment. There are other good tones at other bias voltages too.

Doug

[bwanasonic]

should I change the values of the resistors? In that case, which one ?

I use the Rangemaster article at www.geofex.com for reference. The two resistors you twiddle are R2 (nominally 68k) and R4 (3k9), starting with R2.  The Geofex article has all the info you need. I used a 100k trimpot for R2 in my RM build.

Kerry M

[petemoore]

Having the adjustment for bias on the outside of a Ge device would seem kool, setup right [so it sweeps mostly just past the sweet zone on either side ] you can compensate for temperature and tweek with ease the various biasing and related tones...

[joejoe226]

if you are at 7.4v at the collector you are certainly in the ball park.  If it sounds good then go with it.  if not, tweak the R1 resistor.  and certainly check out the geofx.com site.  i just built a rangemaster and couldn't get it to work until I sat down and read the geofx info on rangemasters.