On 27/04/2019 11:59, Trevor Wilson wrote:
On 27/04/2019 10:48 am, John Robertson wrote:
On 2019/04/26 4:32 p.m., wrote:
On Friday, 26 April 2019 22:45:21 UTC+1, Dave PlattÂ* wrote:
In article ,
Â* wrote:
Does anyone know anything about these ? I know the basics but there
are details missing from the print,
LIKE THE PINOUT of the CRT !

The service manual is available at HiFiEngine.com (free registration
required to download).Â* The scope-module schematic is on page 62 of
the original and the tube ponout is given.

The scope V901 is "CRT with 13-pin Nixie base", Marantz part number
337-1000.Â* According to one article I read elsewhere, it's originally
a Siemens D3-II GJ.

After all of these years, I wouldn't be surprised if the cathode were
worn out (low emission) or the CRT has become gassy.

From what I hear you would need a SWAT team and a bunch of
automatic weapons to get a replacement CRT.

Â*From what I read, it's well beyond that now... you'd need the services
of at least four demigods, and several falling asteroids to blast one
loose.Â* They're probably mostly in the hands of owners of Marantz
receivers in that series, being preserved against a Time Of Need.

Even people with experience on these things, how many receivers had
built in scopes ? I saw one in another
brand once but can't remember what it was, maybe a Kenwood ? Other
than that only Marantz and then even
very few models.

Some Macintosh tuners had scopes.Â* Mac seems to have used a more
common/popular tube variety (a 3RP series), for which there are still
some used-but-good tubes available and even a few Chinese-build
clones.

Anyway, thanks in advance for anything useful on this matter. It
makes a big difference in the value of the unit.

One guy who wrote, said that he'd sold a Model 19, and had also sold a
new-old-stock replacement CRT he had for it.Â* He got more for the CRT
than for the receiver.

I've been dealing with a slightly similar problem myself... I bought a
CTS service monitor whose scope is working-but-dim.Â* Fortunately it
has a 3RP CRT (like the Cushman and Macintosh systems do) and I have a
local source for a used tube (and there are online sources as well).

I was thinking of trying to cons up a solid-state replacement.Â* I
think one could probably be made by using a Raspberry Pi or similar
processor as a core, hooked to a reasonably fast (audio-speed)
two-channel SPI-based ADC which would sample the horizontal and
vertical deflection voltages (suitably attenuated and centered of
course).Â* The Pi would capture the data, and then draw it to a 2"
color LCD.

shango66 on youtube does some good explanations re CRT emission
problem fixing. Though I don't remember him discussing EHT boosting.


NT


Aren't you going to run the risk of X-Ray production if the EHT is
increased beyond a reasonable point? The link below says 5KV and up
can produce X-Rays:

https://www.nde-ed.org/EducationReso...generators.htm


We have a problem in my industry with 13" colour tubes being over
driven by ignorant people using the wrong HV transformer (from 19"
monitors) and getting the tube into the soft X-ray range...

John :-#(#

**I've had the odd X-ray and, being an inquisitive chap, I usually
examine the equipment as best as I am able. I've never found an X-ray
machine that operates below 75kV.

The lower keV x-rays are not useful for diagnostic purposes, because for
example, 10keV photons would be totally absorbed in your body, (still
very probably damaging your DNA), and basically none of it would make it
through to the cassette with the intensifying screen (fluorescent stuff)
and film, so it does not help with making an image of your innards. So,
to maximise the benefit and minimise the harm, medical x-ray machines
use relatively high voltages and are also required to include a filter
equivalent to a certain thickness of aluminium in the beam path between
the tube and the patient. This filter removes the lowest energy photons
(that are useless and harmful because they would be totally absorbed in
your body) without causing too much loss of the higher energy photons
that are still harmful but are also potentially useful because they have
some chance of passing through you and making an image.

All vacuum tubes will generate photons internally with some energy. Any
photons shorter in wavelength than roughly 300nm can damage your DNA,
and that corresponds to only a few volts on the anode. Whether the
vacuum tube will emit hazardous photons externally depends on whether
the photons can pass through the vacuum envelope of the tube. I would be
quite careful at 5kV or even below 5kV, if there is absolutely no
shielding other than a thin glass envelope. Whilst the tube envelope may
attenuate the x-rays by a large factor, on the other hand the anode
current, tube-to-human distance and exposure time with e.g. a RF
amplifier being serviced, might be much less favourable than in the case
of a medical x-ray. Medical x-rays usually use a few milliamps for a
second or less. Big amplifiers may run several hundreds of milliamperes
for hours. The other thing to be aware of is that many Geiger counters
are very (or totally) insensitive to 5keV photons. Whilst the Geiger
counter may tick furiously with the accelerating voltage set at 40kV,
and fall completely silent as the voltage is turned down to 5kV, that
does not necessarily mean that the x-rays have stopped, it might just
mean that they are now at a wavelength that the counter cannot detect.