Crawls Backward (When Alarmed)

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Hand me my Geraton

Today we delve back into the world of old tube junk. In other words, dig it! Ve gonna get dem filaments glowing! We gonna treat our ears to tone so thick you can cut it with a Hinckel knife...we're gonna...

We're gonna stop using goofy metaphors.

Whatcha see here is a "Geraton" amplifier. I wuz surfing the ol' E*a* and found this. It's a really small amplifier that dates to 1961. My best guess is the intended use was as a PA amp - there are inputs for a phono and for a microphone and there's a mixer section. It's really tiny - and the cage is really cute. IF, that is, cages can be cute. If they can, this one is.

This thing is a transformerless design - more on that later.


This way cool little amp was made by "Special Electronics Company" of Silver Spring, Maryland. This is of interest to me because I am a Maryland native. I am aware of Bendix, located in Baltimore, who made mainly aviation electronics but some consumer radios too. And I have a killer Nems-Clarke communications receiver, also made in Silver Spring. So there were a few manufacturers of electronic junk in Our Little State back in the day when vacuum tubes ruled and electronics were assembled by hand.

I should add that vacuum tubes still rule, but most people think they are obsolete. Bwhahahahaha! More for us, eh, comrades? Dey like solid state, dey can have eet, yes?


You can see the 'mixer' section - a pot to control the relative levels of the inputs. There's an RCA phono jack and an Amphenol mic input on the back panel.

The amp is only about 5 x 7 inches. Really compact. Since it's a transformerless design, they could keep it small. I have to say that a metal chassis with a metal cage and no AC transformer is probably not he safest thing in the world - no way it would go into production today. Potentially hazardous. Not that it stops me from owning these kinds of things. You just have to handle them with care.


Here's the bottom. Untouched since it left the factory in 1961. Pretty well made to boot.

So, vhut ve gonna do ees hook de ting up and see if it:
- Makes good noise (i.e. more or less works)
- Makes bad noise or zero noise (i.e. squeals and hums or sits there and looks at us)
- Goes up in smoke.

To prevent the last thing from happening, we have some protections/methods of sorts. You may have read on old radio sites stuff like "Don't plug it in! It may blow up and take components with it." This is a touchy subject, but I will say this much: one should not just plug in An Old Electronic Device without a few precautions. And I don't recommend just "pluging [sic] it in" as they say on E*a*.

One of the most obvious things first is: check the AC cord. It it's shot or has shorts, it needs to be replaced. The second precaution is to use a current limiter or variac connected to an ammeter so you can determine pretty quickly if there are Problems With The Device. On the far right of my bench I have a GE Variac (the box wit de big honkin k-nob) and an ammeter connected to it (two boxes to the left - the one wit the big meter). I don't have this stuff just cause it Looks Neat (which it does), I have it cause I use it for these kinds of projects.

Quite a few folks on old radio forums insist you should replace electrolytic filter caps before firing it up. I don't. I think if you have taken the precaution of monitoring the current draw, you will be ok. If you start to draw mucho current, choo shut it down. If it's ok, it will come up and the worst thing that can happen is you'll have a lot of hum.

I wanted to blog out (blogout?) how I connect up a New Device on my workbench. I hook up a DMM to the B+ line to monitor voltage. If it's an amp, I connect up a speaker if necessary. I have this way cool Electro-Voice speaker I got at my church rummage sale a few years ago. Excellent for testing old junk. Since our amp has no speaker, we connect this one up.

Next we connect our meter, set to DC volts, to the B+ line. The longer red probe at the top is connected to B+. This amp has a selenium rectifier on the top of the chassis so it's right there to connect to. Probably not the safest thing in the world in terms of design, but there you have it. The black probe goes to ground. Just an FYI, the connections to the left are the speaker terminals and they go to our aforementioned $3 EV speaker.

I have an old Sony AM/FM Walkman I use as an input device for amps. It's nice cause you can tune it to a station and you'll hear it if your amp or whatever is working. Obviously, you wouldn't have do connect this for an old radio. Choo can see I have a bunch o'connectors for any possible variation I might run into!

De output from the Sony goes into our phono input on the ol' Geratron. You can see the dreaded "RCA" or "Phono" connector. Bad design. The "hot" side of the connector is the tip and the ground is the ring. If you plug this into a live device (I know you have!), you'll hear a bad 'crack' 'bang' 'bzzzt,' or similar noise when the ground makes contact. That design dates back to the 1940s and it's still in use today even though it's a poor design.
But I digress.

Now we reach over to our Big Honkin Knob and gradually bring up the voltage on the variac. This meter is connected to the variac and measures AC, or essentially our line voltage. I usually come up to 25 volts for a few minutes, then 40, 50, etc. Most old amps and radios start to show signs of life at around 70 volts or so. It's a real gas to hear one of these puppies come to life the first time - it may have been decades since it's been run. At least it's a gas for me. Your mileage, as they say, may vary.

At that voltage, on the other hand, you will see the first signs of problems if there are any. Since nothing's real hot, and it hasn't run for long, you can shut it down right away.

Here's a shot of the DMM with the AC voltage up to 120 - this is what we have for B+. My guess is this is a tad low. We do have output from the amp - but it's really low in volume. Probably have some leaky caps in there. I would (and will...) replace all the caps, but I like to fire up the device first to get an idea of what I'm in for. Then I can either work in it right away if it's gonna be easy, or I can add it to my growing "to do" collection.

This one is going into the "to do" pile for now.

 
 
 
 

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