Crawls Backward (When Alarmed)

IconProjects, musings about guitar builds, guitar repairs, vintage tube amplifiers, old radios, travel, home renovation, and other stuff.

Triplett 3434a Sweep Signal Generator Restoration - Pt. 2

I'm going to recap the Triplett signal generator. The filter caps are in one of the Mallory cans typical of this period (1960s I believe).

So I need to remove the large blobs of solder that are on the chassis and the can's mounting tabs.

For that job, I use my 175-watt Weller soldering iron, aka 'Big Bertha.' And some soldering wick.

I do clean and tin the iron for every use, but it still gets dull in between uses. So I clean it with a soldering cleaning block and tin it.

Over the years, I've used a variety of tools to cut open filter cans - hacksaw blades, kitchen knives - but now I think I've found the best tool for the job.

This is a flush-cut saw I got from Stew-Mac. It's designed for cutting braces, dowels and other similar things on guitars. It has a very thin kerf (I measured it at .012 in or .30 mm), which is ideal.

Mine is an older model - they now have a newer one which is probably even better.

Here I am cutting the can.

The saw is very sharp and made quick work of the thin aluminum can.

I forget how easily these things dent.

I've written before about this process, so this time I'm just showing the highlights. You can search to find more.

But it really isn't rocket surgery.

Usually the innards of the can are dried up and just slide right out.

But this one was still together and took more work. I wound up using a screw extractor and it came right out.

Here's the extractor. This one is 1/2 inch (about 12 mm). The threads are left-hand.

Drill a pilot hole into your broken fastener, then drive this into it and turn. Since the threads are left-hand, it will turn the fastener (or can capacitor innards...) to the left as you drive it in.

If you work on old British cars, you will need this eventually.

You can see how the innards came right out.

It's a capacitor on a stick!

With the can empty, we can put modern caps on the base, and run wires down through holes in the base. Then solder to the appropriate terminals.

A lot of people won't do this. I like it because it's easy, sort of fun and keeps the original look from the outside. In a lot of gear, there just isn't enough room to put discrete caps under the chassis. And even if you can, it generally winds up looking sloppy.

Sure, you can buy new production cans. But if you keep a decent stock of electrolytic caps on hand as I do, it's easy to take 15 minutes to get the can out, open it and put new caps in. Better than ordering an expensive can and waiting a week for it to show up, too.

Just my opinion. Once you do one, it's like eating peanuts. You can't stop.

Then we use epoxy and put the can back together.

You can also paint over the seam if you want to make it look more original. I did not, but I should have. Doh.

Here's the can reinstalled.

Nice solder blobs, huh?

Bertha does great, but boy, when you are holding that iron upright like I was here with your hand and head over it, it gets really hot!

I put a note on it to indicate it was serviced.

Aside from the filter cap, there are only 4 other caps to replace. They're all in the audio frequency circuit - it generates a fixed 600 Hz signal.

Here are 3 of them - the new caps are yellow modern poly. They replaced old paper foil caps.

The fourth is an electrolytic on a terminal strip.

I also straightened out that dent where the sweep output jack is.

Turns out the aluminum panel is so soft that I could bend it by putting a connector on the jack and just moving it sideways.

The dent probably happened the same way in reverse - a cable was plugged in and took a hit and the panel got bent.

I still needed a few taps with a hammer to get the panel perfectly aligned.

Next I'll put a proper 3-prong grounded AC cord on.

 
 
 
 

Post a Comment 0 comments:

Post a Comment