I would guess that the bright spot is where the beam rests after drawing
the face and is waiting for the next refresh trigger.
My own scope clock draws each face once every 20mS (16.66mS in 60Hz
land) synchronised to the mains. If a particular face takes, say, 8mS
to draw then the beam is parked somewhere and left blanked for the
remaining 12mS (in this example) waiting for the next face refresh
trigger. So if the beam is left on for the waiting period then it will
appear as a very bright spot at the parked position. You'd have to
investigate the software you're using for what triggers the face drawing
and what happens in the waiting period.
Grahame
On 27/11/2023 22:50, Max DN wrote:
I'm attaching the voltage divider that I am using and the one that I'm
going to try using values calculated assuming 0.5mA current draw
(which I understand makes sense for this CRT).
Sharing this useful website to calculate resistor values using
parameters from the datasheet, it is starting to make sense now!
https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1946/12/page45/index.html
Blanking pin currently disconnected (still waiting for an
optocoupler). I wonder whether that will fix the bright spot (of
course it will fix the smears on the display).
@ gregebert - I may find this latest update useful
Il giorno lunedì 27 novembre 2023 alle 09:28:02 UTC Max Di Noi ha scritto:
Ok, I managed to make some improvements by changing some resistors
on the voltage divider, I'll post my new layout later.
Much better now, although I need to better understand how to
calculate resistor values as at the moment I don't know current
draws by each crt pin.
I get a very bright spot on the clock image, I don't know if
that's because I have not connected the blanking circuitry yet or
overvoltage on A1 (I'm waiting for an optocoupler, hopefully it
arrives this week).
Picture attached. Getting there.
-------- Original message --------
From: 'Grahame' via neonixie-l <neoni...@googlegroups.com>
Date: 26/11/2023 11:21 (GMT+00:00)
To: neoni...@googlegroups.com
Subject: Re: [neonixie-l] Scope Clock with 3LO1i
Hi
£55 is expensive - you should be able to get them for £30.
Have you tied the deflection plates to A2 for testing purposes or
left them floating? They should be tied to A2.
Can you turn the brightness pot down to fully extinguish the dot?
If not you need to be able to.
Grahame
On 25/11/2023 18:28, Max DN wrote:
@Grahame
Thanks for the suggestion. I didn't know about CV2302 DH3-91, I
see Langrex is selling it for £55 on eBay.
Yes, my voltages were off. I have made some changes:
Cathode is now -350V to ground
A1 is +30V above cathode
A2 is +150V above ground, that is +500V above cathode
I'm having some problems with Grid voltage, I'm guessing...
@gregebert
This is the pinout I'm using:
Pins 1-14 heater
Pin 2 Cathode
Pin 3 Grid G1
Pin 4 A1 (focus anode)
Pin 5 n/c
Pin 6 Grid G2
Pin 7 X1
Pin 8 X2
Pin 9 A2 (acceleration anode)
Pin 10 Y1
Pin 11 Y2
Pin 12 Grid G3
Pin 13 n/c
Pins 3-6-12 are all internally connected, other than on mine 3 is
no longer soldered on the grid.
Pin 3 or 6 or 12 (Grid) is connected to -525V (that's 40V above
-485V negative voltage doubler in Cathode Corner's schematic),
still not good (pic attached). I connected a few resistors in
series 500k, then 1M to bring voltage down up to -250V, with not
much difference. So it's clear I don't understand how to connect
the Grid pin!!
I did find a schematic here (suggests to reduce max negative
voltage rail to -300V):
https://www.catahoulatech.com/index.php?product=KIT-0001
https://www.catahoulatech.com/products/KIT-0001/OscilloscopeCrtDriverData.pdf
I also find something else that is exactly what I'm trying to do.
It's using different POTs and +350V vs -350V (whereas I'm using
+250V and -485V)... Schematic attached.
Il giorno sabato 25 novembre 2023 alle 10:07:25 UTC Grahame ha
scritto:
Hi Max
https://threeneurons.files.wordpress.com/2015/05/3lo1i.pdf
gives the normal operation acceleration anode A2 voltage as
500V (WRT cathode) and the focus anode A1 as 0 to 50V. Your
voltages are higher, especially the focus anode voltage.
Hence the green splat rather than a dot.
My experience with this tube and the 6LO1i which is the
slightly larger rectangular version is very poor. The
phosphor literally turned grey, then black and the light
emission faded over a couple of months in use. It wasn't that
the phosphor burned with the image but the phosphor greyed
uniformly. Most odd. Might have it been a bad batch of tubes?
IIRC someone else has seen this effect.
If you want a small tube then look out for a 1CP1 or DH3-91
or CV2302 would be my suggestion.
Grahame
On 24/11/2023 22:49, Max DN wrote:
Hello,
I managed to successfully build a scope clock almost
entirely based on Cathode Corner design using CRT 3RP1A.
I happen to have a 3LO1i (I know it only lasts for 1000
hours...) and I tried to modify the voltage doublers to use
my circuit with this CRT but I'm not too sure about the
correct voltages. At the moment I have:
Grid: -480V; HTR2: -380V; HTR1: -384V; HTR1-HRT2: 6.3VDC;
CATH: -384V; A1: -248V; A2: +200V
However I cannot get a small green dot, only a wide green
shade, picture attached.
I'm sure I'm doing something wrong with the voltage divider.
Any suggestions please?
Thank you,
Max
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