Hi Matador,I'm using the mic as a test load, plugged in, I'm getting 130vdc with the trimmer backed out all the way? The heater is perfect, and the bias is at .032 measured at xp1 pin on the mic, bias trimmer is also backed out all the way?
Finished build and ready to test.Question; Does it matter which red wire from transformer goes to pin 5 or 6 on Xlr.Same with blues wires to txp 1 or 2. They're labeled + and -If so how do you tell?
You really need a test load to set B+ and bias: put a 180K resistor between B+ and ground right at the 7-pin cable jack on the PSU.
Quote from: Matador on March 11, 2013, 01:36:31 AMYou really need a test load to set B+ and bias: put a 180K resistor between B+ and ground right at the 7-pin cable jack on the PSU.Thanx Matador,Ok, i put a 182k(closest i had) resistor across B+ to ground, i adjusted B+ to 120v, and the heater is good at 6.3v, but i get 0 action out of the bias trimmer?? Any ideas?T
I reflowed everything, i very carefully checked all product placement, it all looks A OK.So here's what i've got now, i replaced the 5k bias trimmer for the heck of it, and as i was doing it i realized the stock wiring has pin 4(bias pin) jumped to ground at both mic and psu 7 pin xlr's(I believe that's for the stock cathode config??). I clipped those and now i have a properly adjusted -1.0v bias, 6.3v heater, but I still cannot get 120v out of the B+, its 130V B+ and the trimmer is backed off 100%? any ideas how i'm screwin up this time?thanks T
Chunger & MatadorHope this is not an issue ..High impedance isolation teflon pins being soldered straight to pcb!!well this is supposed to isolate high impedance from pcb isnt?
Ok, I know i'm a newb and all, but i tried everything i could think of and have been told to try, Matadors instruction to put a 180k resistor as a dummy load allowed me to get the proper B+ voltage. But then with the mic plugged in, and using 2 different tubes, i have not been able to achieve the proper b+ of 120v. I started to trouble shoot the mic next, and what i found seems impossible. R15 and R14 250m resistors read DEAD! Nothing, nada, zero, no continuity what so ever, open! I just got a new fluke 87v, and i thought i was doing something wrong, till i broke out the old MM and the same thing, no reading? Would r15 and r14 being dead, and a break in this circuit cause the voltage to stay up around 130v with the B+ trimmer turned all the way counter clockwise? Other 200m to 500m resistors test fine? I've been spending way to much time on this, so i ask, am i crazy or missing something?thanxT