Crawls Backward (When Alarmed)

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Our '42 Amp Comes to Life!

I hooked up a voltmeter to the B+ line and connected a signal generator to the input and brought the amp up slowly on a variac.  You can see that process on some other posts, such as this one about my Geraton amplifier.

While I was doing that, I took some voltage readings off the output transformer, since the connections are above the chassis and uninsulated at the moment.  I was getting a correct reading on one side of the OT, but not the other.  So I shut it down and started investigating.

What I found was one of the small gauge (maybe about 28 ga or so?) wires on the input side had broken right near the connector.  I took a picture to illustrate - the green arrow points to it.

Fortunately there was enough wire left that I was able to solder it back on the terminal.  This isn't uncommon; I've fixed guitar pickups the same way.  Sometimes the stress of being moved around or being soldered is enough to break those fine wires.  Note that they are covered with lacquer usually, and you'll need to scrape that off with a hobby knife to expose the bare lead.

With that cured, I hooked it back up and ramped up the voltage, and it works!  We have test tone!

In the past, I used a little Walkman-type radio, but this time, I have new toy, comrades!  I've wanted one of these for years and finally got one recently.  It's a Hewlett-Packard 200CD audio signal generator.  This is the kind of thing that radio or amplifier manufacturers or engineering-type folks would use in the 50s.  A real classic and way cool looking to boot.  Basically you can generate audio frequency tones with it.  I set it for 600 Hz and ran it to the amp's input.  When I heard the tone, I knew the amp was working. 

There are of course, modern generators, but they have transistors.  This one has tubes, so it sounds better, and you can also use it as a small space heater.

 
 
 
 

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