Originally Posted by FishHead
Finished but not Finished.
v+ to Grnd: 26.5 vdc
All screws turned clockwise until clicking.
Ta2R to grnd: 20+ VDC Final value not seen as power button mashed.
Ta2L to grnd: 20+ VDC Final value not seen as power button mashed.
Tb2R to grnd: 20+ VDC " " "'
Tb2L to grnd: 20 + VDC " " "
Pretty Leds light nicely. No smoke. No solder bridges seen. No hot electronic smells (I mash the buttons when 20 VDC arrives).
Thanks in advance.
Well, TA2R to GND and TA2L to GND set the tube bias. Turning the RA5 trimmers all the way clockwise is not going to accomplish anything but increase your frustration when you try to bias the tubes.
As for the Diamond Buffer bias, the measurement is TB2R to TA2R and TB2L to TA2L, not to GROUND. All you're doing is repeating the measurement of the tube bias by measuring those test points to ground. Please refer to this page to review what we're trying to bias:
In the case of the buffer, all the test points provide is a measurement across the the RB10 and RB11 resistors. Either one can be measured to set the bias. All four resistors are 2.2 ohms. So, if you measure in mV (you cannot measure milliAmps in this instance), you only need to divide by 2.2 to get the mA of bias through the circuit. Again, though, you are not measuring to ground when biasing the buffer - only the voltage across the resistors connecting the complementary output transistors in the push-pull arrangement.
So, please and carefully - set your probes in TA2L and TB2L, turn the power on, note the mV reading, and turn the power off. If it's less than about 40mV, then that's OK. Set the probes in TA2R and TB2R and turn the power back on. If it's less than about 40mV again, then turn the power off. You're OK and need to turn your attention to biasing the tubes. Refer to this page again:
P.S. Nice stone table, btw. Also, your work looks very good. I'm sure once we verify the correct points to measure, you'll be able to get it up and running in no time.
Edited by tomb - 9/12/10 at 5:14pm