mkstewartesq
Well-known member
One of my very first builds was the Rangefinder, and I built it per the documentation except that I used an OC42 germanium transistor that Smallbear had already tested to be in Rangemaster specs using specific resistors and bias values. They provided me with the resistors used in testing my transistor. When I did the build, I didn’t realize that it would be best to include the resistor values they used and the general consensus here when I asked about it (my transistor wasn’t biasing properly) was that, as I was so new to building at the time, it probably wasn’t a good idea to desolder anything.
In any event, I’m now about 25 builds later and I need to do some work on my Rangefinder to figure it out a noise issue that has cropped up and also bring it up to my current building standards (e.g., shielded wiring on the jacks). I figured that, while I had it open, I might as well replace the resistor with the one that Smallbear supplied, as I’ve never quite been able to get the OC42 to bias to the proper voltage.
Below is the sheet that Smallbear gave me showing a 62K resistor was used for the Rb value. Am I reading the Rangefinder schematic correctly that I would replace R3 (68K) with the 62K? (They used a 4.3K for Re, but I believe that that’s the 5K trimmer in the rangefinder documentation, so I assume I can just use the trimmer to dial that value in rather than replace that with a resistor.)
(Purely FYI, the noise issue that has popped up after eight months sounds like a charge pump whine but replacing the 1044 with a 7660 hasn’t helped so I’ll need to keep digging.)
Thanks
Mike
In any event, I’m now about 25 builds later and I need to do some work on my Rangefinder to figure it out a noise issue that has cropped up and also bring it up to my current building standards (e.g., shielded wiring on the jacks). I figured that, while I had it open, I might as well replace the resistor with the one that Smallbear supplied, as I’ve never quite been able to get the OC42 to bias to the proper voltage.
Below is the sheet that Smallbear gave me showing a 62K resistor was used for the Rb value. Am I reading the Rangefinder schematic correctly that I would replace R3 (68K) with the 62K? (They used a 4.3K for Re, but I believe that that’s the 5K trimmer in the rangefinder documentation, so I assume I can just use the trimmer to dial that value in rather than replace that with a resistor.)
(Purely FYI, the noise issue that has popped up after eight months sounds like a charge pump whine but replacing the 1044 with a 7660 hasn’t helped so I’ll need to keep digging.)
Thanks
Mike
