Vintage Dumont 292 Oscillograph

Just want to add that this would be for learning purposes at the beginner's level, "fooling around" if you will. And yes, I am aware of the dangerous voltages involved even if unpowered (though not much more than that).

I just measured the power caps rated .5uf/1500V. One reads .67, the other .62. Not bad for 60 years. Spot checking other caps (Sprague brand), the worst I find are 50% out of spec, .33 or so when cap is rated at .2. None leak or show shorts, amazing build quality. Made in the USA.

Hi, The Du Mont 292 came out in March 1950. I have the schematic if you need it. The two electrolytic filter caps ought to be replaced. Normally paper capacitors of this vintage are leaky by now, but Du Mont sometimes used Aerovox oil-filled caps which hold up pretty well. I wouldn't run it for extended periods however. Capacitors are cheaper than power transformers.

Alan

Ha, I have a Dumont dual trace Solid State scope, M version, i think it covers up to 60 Mhz.. Don't ack me

Yup, it still works how ever, i did have to change the Trippler in it. I stuck a TV trippler in there wrapped in Tin foil just out side the the cage. it works perfectly! :)

There is one Aerovox, beneath the CRT. I fired it up for awhile, all tubes work and I get some kind of response, but it is not working properly. I can center the spot, but can't move it to the right past the centerline. I connected up the probe and plugged into a socket with no response on the trace. Would it be worth replacing the power caps?

Hi,

My guess is the 0.1 600V caps from the 12AX7 plates to the CRT deflection plates are leaky. If the spot still won't go past center, check the X or Y position pots.

This wasn't a high-end scope, so restoration would be more for its own sake than to get a working test instrument.

Alan

Miscellaneous

Thinking of using Mallory 150 Series axial metallized polyester for these, about $1.25 apiece.

Filter Caps:

Thinking of using 940C Cornell Dubilier axial PP film type for these, $8 or so. Mounting might be a problem.

I also see a few trimmer capacitors.

So, looking at about $30 in caps. Worth it? Tube appears to be fine and I am getting some response when probing household power, but things seem a little out of whack.

Once again, you are completely off topic. This time, you are telling the man who had a book published about old test equipment. Alan is a wealth of knowledge on old test equipment. You should read his book, and learn.

Hi,

You could change a few, in the time base and the coupling to the CRT deflection plates, and see if they make an improvement, before buying the others. The filter caps ought to be changed before you run the scope very much, since they could take out the power transformer if they short. But they'll probably work long enough to evaluate the rest of the circuitry.

In general, scopes of this vintage are only collectors items or suitable for fooling around, which is to say, once you've used a more modern scope with triggered sweep and calibrated vertical and timebase, there's no going back. This particular model was not high-end even in its day. With its gas-tube sweep generator, it's a pre-war design with "modern" (late-40s) 12AX7s in the vertical amp.

Alan