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The unit uses a 6X4 dual diode for the power supply rectifier. As I was doing the final cal and buttoning things up, something started to go snap snap zzzt.

After tracing things down and measuring everything, I found that the pins for the 6X4's plate and cathode were shorting together in the tube socket itself. The socket is one of those cheap dual-layer wafer sockets, and it apparently has some carbon buildup inside the wafers. It has a minimum value of 60 ohms from plate to cathode (tube removed.)

Just goes to show you that anything can fail on an old device. I've never run across this problem before, but now it's something I'm going to be checking for. Once I get replacement parts, I'll drill the old socket out and look at the wafers to see if I can spot the problem.

The unit uses a 6X4 dual diode for the power supply rectifier. As I was doing the final cal and buttoning things up, something started to go snap snap zzzt. After tracing things down and measuring everything, I found that the pins for the 6X4's plate and cathode were shorting together in the tube socket itself. The socket is one of those cheap dual-layer wafer sockets, and it apparently has some carbon buildup inside the wafers. It has a minimum value of 60 ohms from plate to cathode (tube removed.) Just goes to show you that anything can fail on an old device. I've never run across this problem before, but now it's something I'm going to be checking for. Once I get replacement parts, I'll drill the old socket out and look at the wafers to see if I can spot the problem.
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[–] • 1 pt

lol That's what I meant.

If you replace it, don't expect it to be as durable as the old one.

[–] • 1 pt

The only thing I can replace this particular part with is a new old stock one. That type of socket hasn’t been made for a long time.

I was hoping I could use one of my good ceramic RF sockets but nooooo Heath had to use ones with oddball mounting centers.

[–] • 1 pt

If you need help with sourcing tubes you can contact Paul (Mr Carlson's Lab) on jewtube.

[–] • 2 pts

Just talked to the guy at hamtubes.com, he's still kicking. He's going to be at Fort Wayne in a couple weeks.

[–] • 1 pt

Antique Electronic Supply has a good selection at decent prices, hamtubes.com has great prices but I haven’t heard from him in a while.

For the most part I pick them up at shows. Ohio is odd in that there are many hamfests in this state, and with The Dayton Hamvention every summer I usually stock up on my needs.