On 27/04/2019 3:46 pm, John Robertson wrote:
On 2019/04/26 6:59 p.m., 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. I recall reading some years ago that
X-rays begin to be a problem at around 20kV. That said, I would
imagine a small tube like the one fitted to the Model 19 (which I also
own, BTW) would operate on a potential of around -500 Volts or so. WAY
lower than 5kV.
I wish you were right about 75KV being the minimum voltage to generate
X-rays,
**Read what I wrote. Particularly this point:
"I recall reading some years ago that X-rays begin to be a problem at
around 20kV."
but the article suggested otherwise. I'd agree that anything
under 1000V is likely to do anything other than shock you - I've found
nothing so far to challenge that assumption.
**I've never heard of any issues surrounding X-ray production at
potentials as low as 5kV. And at the several hundred Volts on a Model 19
tube, there is zero chance of a problem.
The problem with video game repairs with using a 19" flyback on a 13"
tube is the tube is then working at upwards of 25KV, which the specs on
the tube say is dangerous. The maximum safe voltage for these 13" tubes
was around 20KV.
**Sure. Colour picture tubes are a known source of X-rays.
An interesting paper on 6BK4 tubes being driven (60KV) to give off
X-Rays, but it appears they would also generate X-Rays at voltages found
in colour TVs:
http://www.belljar.net/xray.htm
Later 6KB4 tubes had leaded glass it seems.
Well, that is enough time spent on X-Ray production for now. sure looks
like under 1KV is quite safe, and over 20KV it gets interesting.
**Which is pretty much what I said.
--
Trevor Wilson
www.rageaudio.com.au
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