(no subject)

[stormdog]

Electronics friends! Can anyone tell me what this thing hanging off the back end of this transformer is?

Power transformers in VTVMs typically have two secondaries; one provides power for the heaters in the vacuum tubes, the other powers the rest of the machine. Is it related to that?

The yellow wire on the top is set off from the body by some kind of insulator and is junctioned to what looks like a big filter cap, a secondary from the transformer, and the adjustment pot for the triode balance formed by one of the tubes. The red wires are soldered on at the top and bottom of the body and look like they connect to the other set of transformer secondaries and another big filter cap.



Also, yowch!

Comments

[stormdog]

I posted on an electronics forum after knowledgeable friends on Facebook didn't know. In about two minutes later, I had the probable answer! I love the internet sometimes. It's probably a copper-oxide rectifier. This makes sense because the schematics I've seen for VTVMS have a diode for AC rectification right after the power transformer. I was assuming one of the components on the board was a diode, but it's probably this thing.


http://www.rfcafe.com/references/radio-craft/copper-oxide-rectifiers-july-1933-radio-craft.htm

[acelightning]

Huzzah! But how quaint that seems today... an actual rectifier, producing that half-inverted sine wave output, without anything to even smooth the peaks... :-)

But once you figure out what tube(s) you need, and replace that jumpered-around fuse (!), I'll bet that VTVM will actually work!

[stormdog]

I hope so! I'm so excited about working on it. I feel as though I'm healing it; bringing it back to life. And preserving something special.

[acelightning]

Although I'm strongly a neophile, I also understand what you feel. The old stuff is so very different from today's devices, it's a challenge (well, I first learned on the old stuff, so the challenge for me is remembering it). I also know about healing machinery - I found out I was able to "heal" machinery just by touching it, even before I learned any of the theory of how stuff works. (I'm often called a "technomage".)

And you are preserving something special! By some definitions, your VTVM qualifies as an "antique", which puts you in the same position as a woodworker restoring an ornately carved Victorian chair :-)

[stormdog]

I meant to comment earlier. That's a really nice way to think about; being someone who restores an antique. I've had that in mind as I work on it. Thank you.

[acelightning]

Well, the most global definition of "antique" is "anything that's over 100 years old", but there are other definitions as well; for instance, a car is considered an antique if it's 25 years or more old. Electrical/electronic equipment in general, and particularly test gear, should fall into a similar category.

And even if it's not technically an "antique", it's still a piece of technological history. You are a skilled craftsperson, and I admire your drive to restore it to its original operating condition.

[stormdog]

It's hard for me to believe that I'm good at many things. Thanks for the assurance. Coming from someone with a lot more experience, it's really meaningful.

And the new tube did the job! I can easily zero out the meter now! I just have to get a probe set for it now; possibly this one: https://www.ebay.com/itm/Custom-VTVM-Probe-Set-Assembled-B-K-Eico-Knight-RCA-Paco-Meters-More/232269025972?hash=item36145012b4:g:2agAAOSwhQhYxeCS

[acelightning]

From what I've read in your journal, you're good at many things, a lot of which come under the general category of "machinery" - riding and fixing bikes, tinkering with antique electronics and audio gear, keeping cars in running condition, household construction and repair projects - as well as other things like taking care of animals. I was lucky that my father was like that, and taught me everything he could, and also inspired me to consciously learn as many skills as possible. (I'm still learning! I'm slowly teaching myself to play the ukulele...) Acknowledge yourself. Look at what you do as if you were watching someone else do it; what would you think of them? I know I'd be impressed if I watched you work.

And it's great that you found those replacement probes. They always seem to have gotten lost over the years... ;-)

[stormdog]

Thanks for saying that. Reminders help.

...

One website maintainer wrote that he's convinced that there is a giant government warehouse somewhere where lost probes have all been shipped off to languish forever...

[acelightning]

Whenever my self-esteem levels drop to a critical low, I try to remember to think of the people whose abilities I admire, and remind myself that there are a lot of things I can do that I would admire in someone else. That's what helps me!