HAMPTONeTMPS: Field calibration of our Tube Microphone Power Supplies
Filament adjust:
Our current TMPS have two independent regulator circuits for the filaments (assuming a dual), allowing fine adjustment of each mic. Once complete, the mics should be labeled and used with the appropriate output on the supply if you want it calibrated as close as possible. In general, they will be very close and interchangable. On single supplies, there will only be the circuit on the left. We set these under load, so they will be very close, but it is always best to verify this under the load of your microphone, especially with tubes like the VF14m or AC701k.
The pictures below show the test points and voltage readings for an AC701 (TMPS2-KM54), as well as the trimpot location to fine adjust them. Be careful not to bend the leads on the power resistors in the post filter, they are raised off the board for better heat dissipation.
To take this one step further, you can calibrate out the loss in the cable, which I have found to be 25-50mVdc, sometimes more with older cable. The measurements below should then be taken in the mic through the cable, right at the filament input to the tube. I chose to take the pictures showing the target value to avoid confusion. So if you want 3.95vdc at the tube, you would adjust the test points below for 3.95+.03 vdc.
*Filaments should be adjusted very close to maximize tube life*
Plate adjust:
Adjust the Plate supply after the filament(s) have been adjusted. There is only one regulator circuit for the plate (hi voltage) supply because the current draw on this supply is less than 2-3mA. The regulator circuit can actually handle 100mA or more. Next to the trimpot in this picture is a zero ohm resistor which is the hi voltage test point. The voltage for this supply was 120vdc. If you are unsure what the test values should be, we will provide those for you.
