Another Project?

[bandersen]

Originally Posted by leadlike

I have an old Heathkit cap tester. There was an online tutorial on how to fix this particular model, and I've never had any issues with it since it was recapped/repaired. Typically, when I test a cap, I test the potential new one going in, and then test the old one going out. In the case of the 240pf cap that was dead in the vertical section, it didn't register as anything on the magic eye tube.

Nice - I should restore mine.

Originally Posted by jeyurkon

Does your set call for a 6AL5? I mean is it on your schematic or the tube chart? The 6AL5 and 6H6 have different pin-outs.

John

I was wondering about that too. A 6AL5 is a 7-pin miniature and a 6H6 is octal

[leadlike]

Indeed those dual diodes do have quite a different pinout. The socket install looks factory, but I'll check the pinouts to make sure the 6al5 is hooked up properly. GE made a fair amount of changes to these sets during their production run, and I could see this being one of them. However, it is on none of the documentation I have been able to find for this set.

[leadlike]

Not too much time to work on this tonight, but I did discover that the plate voltage is pretty much missing from the clipper half of the 6sn7-sitting at about .3vDC when it should be at 11vDC. The voltage is supplied by a 330k resistor, the supply voltage is 215vDC on one side of the resistor and .3 on the other. I've tested this resistor a couple of times, and it always tests at about 340k- a little high, but no reason to shut out voltage like it does. But having a freaky clipper certainly would explain the sloppy sync I am getting....

In other news, I emailed the screenshots that I have been getting of the set to the original owner, who only grew up with it in his house and never saw it running in the fifty years he has had it before giving it away. He was pretty pleased to see it working at all.

[jeyurkon]

I'd be intersted in seeing the sync clipper portion of the schematic if someone could post it.

The grid voltage should probably be about -0.5V. It's usually derived by grid leak from the sync pulse. If the sync pulse isn't getting to it the grid will be too positive and that would give you a low plate voltage.

Or you could have a problem with the 6SN7. It could have a leaky grid. But, in this sense it emits electrons, rather than collecting them from the cathode, so it becomes too positive. You need a tube tester that can check for grid leaks or a special tester like the Sencore LC-2 leak tester.

Not having seen the circuit, I might have said something stupid.

John