Took a peek into the Dumont 241 scope

I couldn't resist and took a peek into my Dumont model 241 scope.
The quality of the workmanship is top notch.
There are lots of components that I am going to need to check out.
Nothing looks like it ever got very hot so I'm hoping the resistor
colors haven't changed much.
There are many flat rectangular devices that I think are mica caps
but I'm gonna need some guidance identifying just what is what. While
I'm waiting for the caps and the inductor for the DeVRY scope I'll
need to start making a list of caps for the Dumont.
There are the ubiquitous paper caps and of course the round can
electrolytics. But there are also some large rectangular cans that I
suspect are also electrolytic caps.
You know, this is kind of fun. Reading about tube circuits and how
they work and then identifying the components inside something.
The power transformer is HUGE. The scope only draws 3 amps at 115
volts so I am wondering if the size is because of the high voltage
needed by the CRT. There is also a really big choke mounted above the
power xmfr.
Looking in the bottom I see that the large rectangular cans are
indeed electrolytic caps. They are being used as filters. There is a
can cap inside the bottom portion that is rated at 3500 VDC.
There is also inside the bottom what at first I though was a little
incandescent bulb. That didn't make any sense to me because it
wouldn't have illuminated anything that could be seen from outside the
scope. So then I thought maybe it was a neon bulb or similar. Removing
it I can see the elctrodes.They look like a hat that has bee split in
half vertically. It must be a neon bulb. But what for?
Cheers,
Eric

 

[Trevor Wilson]

On 13/10/2019 9:19 am, etpm@whidbey.com wrote:

I couldn't resist and took a peek into my Dumont model 241 scope.
The quality of the workmanship is top notch.
There are lots of components that I am going to need to check out.
Nothing looks like it ever got very hot so I'm hoping the resistor
colors haven't changed much.
There are many flat rectangular devices that I think are mica caps
but I'm gonna need some guidance identifying just what is what. While
I'm waiting for the caps and the inductor for the DeVRY scope I'll
need to start making a list of caps for the Dumont.
There are the ubiquitous paper caps and of course the round can
electrolytics. But there are also some large rectangular cans that I
suspect are also electrolytic caps.
You know, this is kind of fun. Reading about tube circuits and how
they work and then identifying the components inside something.
The power transformer is HUGE. The scope only draws 3 amps at 115
volts so I am wondering if the size is because of the high voltage
needed by the CRT. There is also a really big choke mounted above the
power xmfr.
Looking in the bottom I see that the large rectangular cans are
indeed electrolytic caps. They are being used as filters. There is a
can cap inside the bottom portion that is rated at 3500 VDC.
There is also inside the bottom what at first I though was a little
incandescent bulb. That didn't make any sense to me because it
wouldn't have illuminated anything that could be seen from outside the
scope. So then I thought maybe it was a neon bulb or similar. Removing
it I can see the elctrodes.They look like a hat that has bee split in
half vertically. It must be a neon bulb. But what for?
Cheers,
Eric

**It's a kind of vacuum tube zener.

--
Trevor Wilson
www.rageaudio.com.au

--
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On Saturday, 12 October 2019 23:13:39 UTC+1, et...@whidbey.com wrote:

I couldn't resist and took a peek into my Dumont model 241 scope.
The quality of the workmanship is top notch.
There are lots of components that I am going to need to check out.
Nothing looks like it ever got very hot so I'm hoping the resistor
colors haven't changed much.
There are many flat rectangular devices that I think are mica caps

just beware of micamould domino caps, which are actually paper

but I'm gonna need some guidance identifying just what is what. While
I'm waiting for the caps and the inductor for the DeVRY scope I'll
need to start making a list of caps for the Dumont.
There are the ubiquitous paper caps and of course the round can
electrolytics. But there are also some large rectangular cans that I
suspect are also electrolytic caps.
You know, this is kind of fun. Reading about tube circuits and how
they work and then identifying the components inside something.
The power transformer is HUGE. The scope only draws 3 amps at 115
volts so I am wondering if the size is because of the high voltage
needed by the CRT. There is also a really big choke mounted above the
power xmfr.

quite likely a swinging choke psu, a volt reg arrangement of sorts

Looking in the bottom I see that the large rectangular cans are
indeed electrolytic caps. They are being used as filters. There is a
can cap inside the bottom portion that is rated at 3500 VDC.

might make the EHT supply dangerous
Ah, 1948. Probably is a killer EHT supply.
https://www.oscilloscopemuseum.com/oscilloscope-dumont-241-s1431.html

There is also inside the bottom what at first I though was a little
incandescent bulb. That didn't make any sense to me because it
wouldn't have illuminated anything that could be seen from outside the
scope. So then I thought maybe it was a neon bulb or similar. Removing
it I can see the elctrodes.They look like a hat that has bee split in
half vertically. It must be a neon bulb. But what for?
Cheers,
Eric

Neons were used as zeners. Their main downside was the need for much higher voltage to strike. If not designed around the result would be a major Vout spike - but soft starting the output is fairly trivial.


NT

 

[Phil Allison]

et...@whidbey.com wrote:

----------------------------

I couldn't resist and took a peek into my Dumont model 241 scope.
The quality of the workmanship is top notch.
There are lots of components that I am going to need to check out.
Nothing looks like it ever got very hot so I'm hoping the resistor
colors haven't changed much.
There are many flat rectangular devices that I think are mica caps
but I'm gonna need some guidance identifying just what is what. While
I'm waiting for the caps and the inductor for the DeVRY scope I'll
need to start making a list of caps for the Dumont.
There are the ubiquitous paper caps and of course the round can
electrolytics. But there are also some large rectangular cans that I
suspect are also electrolytic caps.
You know, this is kind of fun. Reading about tube circuits and how
they work and then identifying the components inside something.
The power transformer is HUGE. The scope only draws 3 amps at 115
volts so I am wondering if the size is because of the high voltage
needed by the CRT. There is also a really big choke mounted above the
power xmfr.
Looking in the bottom I see that the large rectangular cans are
indeed electrolytic caps. They are being used as filters. There is a
can cap inside the bottom portion that is rated at 3500 VDC.
There is also inside the bottom what at first I though was a little
incandescent bulb. That didn't make any sense to me because it
wouldn't have illuminated anything that could be seen from outside the
scope. So then I thought maybe it was a neon bulb or similar. Removing
it I can see the elctrodes.They look like a hat that has bee split in
half vertically. It must be a neon bulb. But what for?

** See schematic.

https://stevenjohnson.com/oscilloscopes/dumont-241.pdf

The scope is AC coupled to the plates and so uses passive trace positioning.

Vertical BW is about 20Hz- 2MHz and the triggering looks a bit primitive.

There is a nice mag shield on the CRT and it IS built like a brick shithouse.

I have a 3 inch CRT scope with similar specs, better triggering, calibrated H and V plus amplified trace positioning. Built with all new parts, when I was still at high school, using saved up money earned from a holiday job in 1970.

It still works, with the original CRT and few new valves - only 5, mini 9 pin types.



...... Phil