10-11-2013, 10:16 PM
Those voltage readings look much more reasonable. The B+ voltage is still a bit high, but this might be a result of todays higher line voltages. The AK schematic specifies a 110V AC line voltage, so you might want to use a bucking transformer or run the set on a variac.
It still appears that one of the 6K7's or the 6A8 is causing the positive grid bias on the AVC line. In normal operation, there should never be a positive voltage on the grid caps. The schematic voltages don't show polarity, but the 5V indicated on the 6K7 grids should be -5V, which would be typical when receiving a station.
You can disconnect one grid cap at a time and see which tube is causing the positive voltage. A gassy tube will produce a positive grid voltage and throw off the bias on all the remaining AVC controlled tubes. The positive grid bias is causing excessive plate current, which results in the higher than normal voltages across R3, R6, R10, R11 and R12.
It still appears that one of the 6K7's or the 6A8 is causing the positive grid bias on the AVC line. In normal operation, there should never be a positive voltage on the grid caps. The schematic voltages don't show polarity, but the 5V indicated on the 6K7 grids should be -5V, which would be typical when receiving a station.
You can disconnect one grid cap at a time and see which tube is causing the positive voltage. A gassy tube will produce a positive grid voltage and throw off the bias on all the remaining AVC controlled tubes. The positive grid bias is causing excessive plate current, which results in the higher than normal voltages across R3, R6, R10, R11 and R12.
