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Tutorial/tips on restoring vintage electronics

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rvmeush:
There is a thriving community of folks interesting in bringing vintage electronic equipment back to life.  Often this equipment has laid around, unpowered for decades.  I've seen some debate about the use of variacs to gradually re-power this equipment, as well as techniques for dealing with old components that may not have aged well.   I'd like to get Dave's thoughts on working on some of these old gems, perhaps with a project to restore a specific piece of equipment.

c4757p:
I don't think Dave cares much for vintage electronics. Not to speak for him, but I'm pretty sure I recall that he tends to think of them more as obsolete annoyances than anything. I like vintage stuff, but I can definitely understand that view.


--- Quote from: rvmeush on March 28, 2013, 12:05:34 am ---I've seen some debate about the use of variacs to gradually re-power this equipment, as well as techniques for dealing with old components that may not have aged well.

--- End quote ---

Ugh. I hate that method - so hamfisted. "Don't turn it on, take it apart!" I always open things up and carefully inspect for shorted resistors, open-circuit resistors, open tube filaments, conductive debris, etc. I even check that the tubes are the right type - I've seen one example where some dumbass must have thrown a random tube in an empty socket to make it look complete, but it was a completely different type that would have stuck the B+ straight up the filament. Then every single aluminum electrolytic capacitor gets removed from the circuit and tested for capacitance, dissipation factor and leakage at full rated voltage, and every non-aluminum large capacitor (oil, etc) gets replaced without question. Then the device is turned on.

When I feel something behind my car tires, I don't back over it real slowly so it doesn't damage the paint, I get out and move it.

[/rant]

krivx:
Variacs can certainly be useful for testing mains-powered equipment. Often you can't tell if any active device has failed until you apply power, and slowly increasing the supply voltage while monitoring the current drawn can prevent any further damage.

Radio Tech:
Being a vintage restorer myself, Variacs are completely useless at bringing up old equipment. Old dried out caps will blow now, or later. A variac will not fix these.

I agree with c4757p, take it apart and inspect and replace the obvious. Starting with an overall inspection with a schematic. Then start with the power supply. That is where the first big bang is produced.  If you just go for broke and plug it in, and fry the transformer, well you now have vintage parts.

c4757p:

--- Quote from: krivx on March 28, 2013, 12:36:12 am ---Variacs can certainly be useful for testing mains-powered equipment. Often you can't tell if any active device has failed until you apply power, and slowly increasing the supply voltage while monitoring the current drawn can prevent any further damage.

--- End quote ---

With tubes, they are useless. What kind of tube failure will cause it to draw way too much current, but not show up during pre-power tests? It's pretty much either "this shorted to that" (always something I check for), or "doesn't work at all". With either very high B+ or tiny signal tubes, an air leak can cause arcing, but you can see that by the color of the getter flash. And if it's semiconductor-based, it's not uncommon to see a circuit that will fry itself when undervolted, so the variac is right out.

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