DavidC wrote:Yeah, the connection of the pins are correct. 1K cathode resistor indeed connected to the center tab of heater. The thing is I disconnected the B+ connection to the plate while I did the test with just the rectifier power up and the arching occurred. Any possibility of power transformer problem?
Any chance rectifier heater and 300B filament heater are connected together - both are 5V after all, sure you haven't soldered both valves heaters to the same winding? Stranger things have happened
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
Yeah, the measurement came up to 100ohm across the 380 HT tabs. I finally nailed the problem. It's in the power transformer. Somehow the 5VAC for the 300B filament and the 5VAC for the GZ34 is shorted internally, causing the GZ34 shorted to the ground through the 300B cathode resistor. I managed to switch the 300B heater supply to another 5VAC tabs and the amp is working now. I couldn't understand how the two winding got shorted internally. I'd used this transformer previously and the two windings were working perfectly.
I got this from a local surplus store. I used it for a while in another amp and junk it aside for a few years. Recently I reused it for a new amp and encountered this issue.
