Taking a break before the "heater test" to share a few items that I hope are helpful:
First, a friendly reminder about the dangers of mains voltage wiring, even if you have been doing it for decades as I have -
About 15 years ago, I learned a lesson when working with mains circuitry that I had forgotten over the years, until today:
NEVER plug in a piece of gear into the same power strip/circuit as your soldering iron! The first time this happened, I was working on an old ARP Axxe synthesizer. I was working on, and testing the power supply board (For those not familiar, the power transformer and mains connectors are part of the main PS circuit board. I had the synth and the soldering iron plugged into the same power strip. The later model Axxe has an IEC power connector, and the ground wire is connected only to the chassis. I powered the synth down, i.e,
switched the power switch into the "off" position, and, thinking I was safe, picked up the power supply by lifting it up from the bottom of the board in my bare hand. It felt like someone hit me in the arm with a baseball bat. Yes, the outlet was wired correctly. Yes, I checked after I installed that outlet years before. The nearest uneducated guess I could make was that the soldering iron created a low-impedance bridge from Hot to Neutral, and since Neutral and ground eventually connect,
WHAM.
So, today after reinstalling the power transformer, I tack-soldered the hot side of the primary to one lead of the brown 6.3V heater coil, and the other brown lead to the hot pin on the IEC connector. I powered it up with only the rectifier heater and the HV lines connected to the rectifier socket, with no tube. The ground wire on the IEC connector was already connected to the chassis. Voltage readings went well, with 5.9VAC on the rectifier heater line, and some value I forget from one HV line to its center tap. Yes, the soldering iron and the amp were plugged into the same power strip, as I didn't want the iron to cool down (because I needed it for the next step). I was reaching to power the amp off, so I could swap ends of the brown heater leads and re-test, my forearm lights caught the edge of the chassis (it was painted even, but the paint must've been really thin there), and I got a moderately nasty tingle. I powered it off, swapped the leads, grabbed the voltmeter, and... ...nothing. This is what I found when I pulled the fuse out of the holder to check:
Gang, that WAS a 1.25 Amp fuse. I guess the strong tingle was only a tingle because of the brave sacrifice made by the fuse (RIP). So, after replacing the fuse as swapping the leads, I measured the rectifier heater voltage again, and came up with 5.2 VAC, so it was the correct way around, and after making the connections permanent, I brought the amp into the house to test it on a GFI outlet, to see if I had indeed screwed up the wiring. The GFI outlets I installed in the house will trip if you sneeze to hard near them, so I figured I would find out quickly. I plugged the amp in, with the power switch off, and all was well. I unplugged it, turned the power switch on, and then plugged the cord back in (did you REALLY think I was going to touch that amp given the circumstances?), and once again, all was well, and the fuse held, and I rechecked the voltage on the heater winding, with both my elbows WAY away from the chassis. When I test the heater circuit tomorrow, I'll put one lead of the meter into the ground terminal in a vacant outlet, and then probe the chassis. If there's even ONE volt of AC on that meter, that ground wire is coming out. And no, Gordon W, I didn't put the "death cap" back in!
)! The sharp-eyed will note that those are 12AT7 tubes in the front-end sockets. The heater current draw is the same as 12AX7, and no way was I going to plug in any of my good 12AX7s in that thing before it was tested!
