Transistor cases.
With the connections to the control board all taped off so they do not short out to anything (both the bottom row of 10 wires and 3 bias connection wires per channel).
Install the bottom row of transistors starting from the transformer, NPN, PNP, NPN, PNP.
Remove the one wire to the upper left backplane 6-32 screw by removing the securing nut and floating this wire in the air.
Install rail fuses.
Check for infinite resistance between chassis ground and the transistor cases. If not debug. (you will get a reading between DC ground bus bar and these cases, you meter will be charging up the bulk caps)
Connect a ~10K resistor between the output and ground test point on each backplane.
Bring up on DBT and Variac to 60VAC in on the AC input. Make sure all is good and no smoke is coming out. Measure that you have B+ and B- voltages present at the respective test points and B- at PAD12 and B+ at PAD 11 on each back plane board.
Check that you have 0V at the output test point.
Take the Variac all the way up and repeat.
Next, before doing anything else, power the amp down and fully DISCHARGE the bulk caps using a 1K 2W resistor (any value close to 1K will do) down to a level below 1V.
Then you are good to proceed to the next assembly step if this is all good.
With the connections to the control board all taped off so they do not short out to anything (both the bottom row of 10 wires and 3 bias connection wires per channel).
Install the bottom row of transistors starting from the transformer, NPN, PNP, NPN, PNP.
Remove the one wire to the upper left backplane 6-32 screw by removing the securing nut and floating this wire in the air.
Install rail fuses.
Check for infinite resistance between chassis ground and the transistor cases. If not debug. (you will get a reading between DC ground bus bar and these cases, you meter will be charging up the bulk caps)
Connect a ~10K resistor between the output and ground test point on each backplane.
Bring up on DBT and Variac to 60VAC in on the AC input. Make sure all is good and no smoke is coming out. Measure that you have B+ and B- voltages present at the respective test points and B- at PAD12 and B+ at PAD 11 on each back plane board.
Check that you have 0V at the output test point.
Take the Variac all the way up and repeat.
Next, before doing anything else, power the amp down and fully DISCHARGE the bulk caps using a 1K 2W resistor (any value close to 1K will do) down to a level below 1V.
Then you are good to proceed to the next assembly step if this is all good.
Last edited:
