Transistor biasing

[paulS]

Hi
    I read the article regarding the dallas rangemaster at the GEO site and I have a question about biasing the transistor. It is a PNP Germanium  transistor( gain is 84) and to bias he suggests replacing Rb with a 100K pot and Re with a 10K pot, then set beginning values to 68K and 3.9K. Ok this far no problem, but it is the measurement I am having a problem with. He states between the collector and ground there should be -6.8 to -7.2 volts, my reading is positive and it is reading +2.8 volts. WHERE AM I GOING WRONG? I have used his circuit but added a 3pdt switch for true bypass utilizing the PNP negative ground layout at General Guitar Gadgets, Is it the negative ground wiring??  Anyway hope someone can shed some light here.

Paul

[R.G.]

It is the negative ground wiring.

If you have the most negative point in the circuit being ground - that is, zero volts - then everything else must be more positive than that, right? So you can't bias anything more negative than ground.

I don't care for negative ground wiring on nominally positive ground wired old PNP circuits. The theory says it's fine, it can always be done. However, I personally have run into situations where I could NEVER get a negative ground conversion to work. And I'm not a beginner at this.

There are two kinds of people who've done negative ground conversion circuits - those who have had bad problems with negative ground conversions, and those who have not yet had a problem with it.

[vanhansen]

After reading this, and looking at that article again, and another schematic (the one from Aron's list), I think I goofed big time on mine.  I took the schematic that Aron has listed on the schematics page and converted it to NPN.  BUT I think I goofed up, even though it works.   

Everything on the schematic is as-is, except for the transistor now being NPN and the eletrolytic caps being flipped around.  But it still works.  Did I do it right?

[vanhansen]

Ohh, nevermind, I didn't goof.  My brain wasn't working right when I read all this.  See, this is what happens when the weather goes from 80 degrees one day to 30 the next.        My RM is fine.