1 post / 0 new

410 HD-130, low bias volts and plate, light shocks too

Hello, my 410 HD-130 started lightly shocking me through a mic plugged into a different amp on the same mains and then blew a fuse in my 130. Nearly all the filter caps failed ERS tests. So, I recapped all the electrolytic caps through out the whole amp, replaced the pair of 1KV 3A diodes (D9 & D10) on the rectifier board. The diode change because someone had been replaced one of them with two smaller diodes in series. I replaced the brown drops on the driver board as well. Lastly, I isolated the death cap from the circuit. Tubes all tested good but I swapped the EL34s with a known to be good matched quad set. It still shocks but doesn't pop the fuse.

The amp draws almost 3 amps on high power with standby switch closed (out of stand by). Through a current limiting 250 watt light bulb it glows like a 25 watt bulb. I'm trying to cure the low voltage and what feels like a voltage leak. FWIW the fuse doesn't blow anymore.

Test Points read as follows:
H = 568 VDC
G = 281 VDC
F = 266 VDC
A & B = +43VDC / -43VDC
Y = 0.460V max I can get (biggest amp draw at this setting)
at minimum setting it's cold and current on main AC drops to .5A. The 10 ohm 1 watt resistors on EL34 pin 8 spec out perfect. It's amazing how the bias controls the overall amp's current draw.

The PT failed a ring test with all secondary leads disconnected. With all the secondaries disconnected I could only get to 281VAC on the red lines, which explains the low test point H. So I replaced it with a NOS, original type. Mine is the early style with the stand by switch on the back panel and connected to the PT secondary side. So I didn't have to rewire the main power switch witrh the later PT styles. I don't play it on the low setting so I never cared about the LO setting tone problem. I still have the same issue of low voltage and heavy current draw when pin 8 is set near 460mV or more.

I tried jumpering the power switch but that didn't reveal a switch problem. The voltages are still too low but I'm not sure where to go next. Does anyone have any advice? Thanks