# Vintage Dumont 292 Oscillograph

R

#### Rob

Jan 1, 1970
0
This looks to be '40s or so vintage. Plug in and it appears to work
(I can get a trace), have not done much more than that. The power
caps appear to be 2.5uF, 1500V and there are about a dozen of the
paper/wax types used in the unit. Should I replace these right off,
rather than continuing to fool with it? If so, which ones are the
most critical for replacement? I do not have a schematic and limited
knowledge, I could not tell you their function by looking at them. As
far as calibration, I see a single trim pot, is there a generic
approach to calibrating these that someone can explain?

R

#### Rob

Jan 1, 1970
0
This looks to be '40s or so vintage. Plug in and it appears to work
(I can get a trace), have not done much more than that. The power
caps appear to be 2.5uF, 1500V and there are about a dozen of the
paper/wax types used in the unit. Should I replace these right off,
rather than continuing to fool with it? If so, which ones are the
most critical for replacement? I do not have a schematic and limited
knowledge, I could not tell you their function by looking at them. As
far as calibration, I see a single trim pot, is there a generic
approach to calibrating these that someone can explain?

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).

R

#### Rob

Jan 1, 1970
0
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.

A

#### Alan Douglas

Jan 1, 1970
0
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

J

#### Jamie

Jan 1, 1970
0
Alan said:
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
http://cgi.ebay.com/DuMont-1062-Dua...-MILITARY_W0QQitemZ260061984147QQcmdZViewItem

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!

R

#### Rob

Jan 1, 1970
0
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

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?

A

#### Alan Douglas

Jan 1, 1970
0
Hi,
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?

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

R

#### Rob

Jan 1, 1970
0
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
***********************************************************************************
I've tallied up the capacitors:

Miscellaneous
1x .02uF 600VDC paper type (sprague)
8x .1uF 600VDC paper type (sprague)
2x .25uF 600VDC paper type (sprague)
1x .25uF 600VDC can type (sprague)
1x .5uF 600VDC paper type (aerovox, not oil filled)
2x 20uF 450VDC can type (sprague), this is the dual type can, one unit
2 square type w/ the colored dots, unknown values, these go on the
5500 and 30K setting for the Sweep Range

Thinking of using Mallory 150 Series axial metallized polyester for
these, about $1.25 apiece. http://www.mouser.com/search/Produc...Evirtualkey53900000virtualkey539-150224J630LE Filter Caps: 2x .5uF 1500VDC cans (sprague) Thinking of using 940C Cornell Dubilier axial PP film type for these,$8 or so. Mounting might be a problem.
http://www.mouser.com/search/Produc...virtualkey59850000virtualkey5984-940C16P47K-F

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. M #### Michael A. Terrell Jan 1, 1970 0 Jamie said: Ha, I have a Dumont dual trace Solid State scope, M version, i think it covers up to 60 Mhz.. Don't ack me http://cgi.ebay.com/DuMont-1062-Dua...-MILITARY_W0QQitemZ260061984147QQcmdZViewItem 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! 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. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida A #### Alan Douglas Jan 1, 1970 0 Hi, 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.

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

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