Crawls Backward (When Alarmed)

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Filter Can Restuffing for Valco Amp - Completion

I got the new capacitors from Mouser and I'm going to restuff the can. Glad I measured them and ordered more or less by size. This is the smallest can cap I've done and everything was a tight fit.

I've written about this before, but here is is again in case you missed it the last go-around.

Drill some small holes in the base of the can. One for each of the positive tabs and one for ground. It's a good idea to do some planning beforehand, especially for the ground hole.

In the past, I've said something like "thread the positive leads through their respective holes near the tabs." Here's a picture. This is the first capacitor's positive (+) lead being pulled through. I just bend it and wrap it around the tab. It will get soldered later when it's back in the amp and everything is being reconnected.

Here's that planning I mentioned.

I'm putting a 22 uF cap in the first section. Originally, the can had 10 uF, but modern caps are so much smaller that I was able to double the capacitance. I think 10 uF is pretty skimpy.

So we have the 22 uF cap with its leads going through the base of the can. You see one of the 10 uF caps (there are 2) lying next to it while I figure out exactly how it will go above the first cap.

The leads won't reach on their own, so I solder a piece of component lead onto them so they'll reach. When I build or work on stuff, I save clipped-off leads for this very application.

Here are all three capacitors installed.

The bottom cap - the 22 uF one - has its ground lead running through the can's bottom to one of the ground tabs. Then I ran a wire up toward the other 2 caps' grounds and soldered them together. So we have all of the grounds running to one point.

The positive leads run down through the bottom of the can and connect to their respective tabs. See the green heat shrink? That's covering those leads.

You may say, "Mr. Crawfish Man, why don't you just tie the grounds to the can itself?" That's a good question. The answer is that the can is aluminum, and hard to solder to. So I just use a tab instead. I also like the idea of just one ground point.

A final test run to make sure it all fits.

This one was fairly tight, as I mentioned, so I used some electrical tape to hold the cans together and doubly insure nothing could work loose and touch the can by accident. Not something I usually bother doing, but this was a little different than usual.

Mix up some JB Weld and put some on the mating seams on the can. Reminder to self: you are now out of JB Weld. Get more.

Line the can top and bottom back up and gently clamp the can in a vise to dry overnight.

If your cut was clean, and you've lined the seam up well and you clean up the excess epoxy, the seam will not be visible from a distance.

Congratulations! You've saved a vintage Sangamo capacitor can from extinction.

There's one more electrolytic capacitor I'm going to change before I fire up the amp. This is the first section cathode bypass on the 6SL7 preamp tube.

You can see the old cap alongside the modern Sprague I'm replacing it with. The Sprague is rated for 50 volts versus the 25 of the original, yet it's still much smaller.

Good thing I made a layout drawing of the filter cap connections, huh?

I also put a modern 3-prong grounded AC cable on the chassis. I don't like the way the AC line has to run across the amp, so I raised it up out of the way as much as I could.

Here's the reconnected filter cap in the chassis.

Couple of notes here: the blue arrow shows the grid (signal) line to the output tube from the preamp tube. I'm eventually going to move that coupling cap (red one on the left) over to the output tube grid. I'll also run a shielded line here instead of an unshielded wire.

The way this is wired leaves it open to pick up hum and noise. You'll see it runs right across the amp under the high current filament lines off the transformer. It's just poor wiring layout.

The other change I'll make is at the green arrow. This is the 6 volt filament line for the preamp and power tube. It's not dressed properly - it should be a twisted line. Easy to correct, and again, it's an anti-noise measure.

 
 
 
 

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