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10 hours ago
Hi Steve
Because the Power Scale is not ground-referenced in the kit version you have, you can only use a relay to switch it.
When selecting between power levels in a Power Scaled amp you have to switch BOTH the Power Scale control and the Drive Compensation control. You did not mention the latter.
You can switch the power level as you described. Have the added resistance inline all the time and short/unshort using a relay pole.
The master volume you refer to is a post-PI MV directly wired to the power tube grid-leaks, with the pot-0 of both sections tied to the bias-feed, wiper to grid-stop, pot-X to the coupling cap from the splitter. Since it is a dual pot, each half of the output stage can have its own bias pot to assure hum-balancing. Switching for this requires two relay poles.
Changing the reverb level at the same time requires a fourth relay pole.
Two DPDT relays are required to achieve the switching you desire. Since the Power Scale relay pole is working within a resistive path there should be no noise issue.
Have fun
Because the Power Scale is not ground-referenced in the kit version you have, you can only use a relay to switch it.
When selecting between power levels in a Power Scaled amp you have to switch BOTH the Power Scale control and the Drive Compensation control. You did not mention the latter.
You can switch the power level as you described. Have the added resistance inline all the time and short/unshort using a relay pole.
The master volume you refer to is a post-PI MV directly wired to the power tube grid-leaks, with the pot-0 of both sections tied to the bias-feed, wiper to grid-stop, pot-X to the coupling cap from the splitter. Since it is a dual pot, each half of the output stage can have its own bias pot to assure hum-balancing. Switching for this requires two relay poles.
Changing the reverb level at the same time requires a fourth relay pole.
Two DPDT relays are required to achieve the switching you desire. Since the Power Scale relay pole is working within a resistive path there should be no noise issue.
Have fun
