Equipment required:
Variac (verify the output of the variac is close to what the dial reads)
Preferrably 2 Multimeters - one with plunger clips so that they are shielded and have little chance of popping off the leads on the board. the second with standard pin probes.
100k, 2w resistor
USE CAUTION - THE AMP WILL BE AT FULL TILT AND YOU WILL BE PROBING AROUND LETHAL VOLTAGES/CURRENTS
1) After installing the NOS cap/caps that need to be formed, modify the filter board according to the diagram below. Be sure to insulate the center tap wire to avoid electricution:
2) Attach plunger tip leads on each side of the 100k resistor as shown below and connect to the first multimeter. set the mutimeter to VDC:
- forming caps w leads small.jpg (119.68 KiB) Viewed 24255 times
3) Remove all tubes
4) Turn all control pots to 0.
5) Set the Variac at ~90 VAC and power up the amp.
6) Record the voltage reading across the 100k resistor. Using the second multimeter, carefully measure the voltage across the preamp filter, the PI filter, and coupling caps and take note how close the voltage is to the rated voltage. As the voltage drops across the 100k resistor, that voltage will add to the other filter cap voltages.
7) over a period of a few minutes, gradually ramp the variac voltage up to 120 VAC. Check the voltages across the filters listed above to ensure they are not exceeding the rated voltages.
8 ) The procedure should take between 12-24 hours and is complete when the voltage measured across the 100k resistor is below 5 VDC.
9) As the process comes to completion, its likely that the Variac be turned down to avoid exceding rated cap voltages. Any time you cannot be present to monitor voltages, drop the variac to a level that the math says will be safe.
10) After completion, discharge the board and return it to its previous configuration and reinsert the tubes. Check bias and you're all done.
Cheers
