Hi all
Quite a lot of years ago there was a topic posted here that went on for some time but never reached any conclusion as to the cause of the problem...unfortunately the exact problem I think I'm having right now. I wonder if any of you have encountered this and with fresh insight perhaps shine light on the cause? I've done a fair bit of investigation so far but I'm loathe to really get stuck in and start pulling the thing to bits without at least a better likelihood of being sure where the problem probably lies. Some basics - in NON storage everything is perfect and ALL diagnostics pass OK. In this respect there is zero problem. I re-calibrated it all about 18 months ago and have loved this scope for many years. PROBLEM - In STORAGE mode everything seems a bit mixed up. Channel 1 displays a trace but the amplitude is half or less of the real value. Channel 2 is similar but probably a quarter of the real value. Switching to BOTH it looks like there is only one trace but actually they are both overlaid on top of each other and it is not possible to separate them at all. Putting a sine into 1 and a square into 2 then the resulting waveform is an odd hybrid of both but not in the way 'add' would do that. Similar strange things happen with the amplitude also and all the other issues are a combination of this general characteristic. With the 4 wire connector going to channel 2 on the storage board removed and grounded appropriately leaving only channel plug connected watching a sine trace in store mode as I write it is just 20% of the real value but but does keep expanding to around 50% every now and then. The post from years ago seemed to point to U2101 on the storage board that both channels go to first but I'm not sure. Someone actually said it was that chip mixing up the signals but never gave evidence as to why that was so. Those chips just do not exist anymore so if it is then it's game over. I de-soldered mine and put it in a socket so I could take it out easily if I needed to. Is it an issue with the vector board perhaps? That's a pain to get to so I'd like a good idea the issue might be there before I go that route. Finally, time measurements are NOT affected. So, if you've got this far reading I thank you and if anyone has any thoughts please do share, I'd be very grateful. Cheers.
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It is a cute little scope, but very low bandwidth,
something like 10MHz. Its HV transformer suffers
from the epoxy disease that affects 547 scopes.
They are quiet, not having a fan, and the plugins
contain all the deflection circuitry (as I recall).
I used to like them quite a lot back in the day, for
audio work.
The storage functions are finicky.
-Chuck Harris
Stephen wrote:
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Hi all, and Happy New Year 2021,
Is a 564B a good grab, is it desirable at all?
It¡¯s not considered a 500 series, right?
56x family I suppose...
Thanks ?
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Re: Slightly OT: How can I dissolve Potting Compound?
Dennis the 26 cm Spectral tubes are the most popular, used in physics labs
These use 5 kV open ckt current limited transformers and run at 5 - 20 mA.
The optical spectrum is dependent on gas mix, and temperature and not on tube current or voltage.
The best lamps are "hollow cathode"
Jon
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Re: Grid Bias Adjustment on 475A
The mesh is an electrostatic lens that magnifies the
limited vertical and horizontal deflection to fill the
viewing screen area.
This is done to allow a lower deflection plate voltage on
a fairly short CRT.
The mesh lens is the magic sauce that allowed tektronix
to abandon vacuum tube deflection amplifiers for solid
state, and to break the about 50MHz bandwidth limitation
tube amplifiers imposed.
The downside is the mesh lens adds thickness to the trace
that would have been avoided with a longer CRT or a higher
deflection voltage. It also adds some spurious ghost
images on the screen at high intensities.
The mesh bias places the lens at a voltage where it won't
adversely affect the electron beam (attract it, deflect it,
reflect it, distort it...)
-Chuck Harris
Jeff Dutky wrote:
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So I've measured everything EXCEPT the high voltage levels (waiting on an HV probe).
R1396 and R1399 feed the second grid on pin #8, the schematic says they should see +50 V, and I measured +50 V
R1398 feeds the astigmatism grid, schematic says the range should be -8 V to +110 V, I see that range, the original setting was +40.82 V
R1330, R1329, VR1329, C1329, and CR1329 feed the mesh and all meet at a node on one of the ceramic terminals, according to the schematic that node is supposed to be -150 V, but I measure -110 V. The -150V level is supposed to have (if I am reading the schematic correctly) a sine wave superimposed with a range of 300 mV peak to peak, but what I see when I hook the scope up to the common node on the ceramic terminal (rather than the opposite side of CR1329, which I think is high voltage) is only 150 mV peak to peak, and not very sinusoidal.
So the mesh voltage is low (high?) and its AC signal looks wrong. Maybe one or more of the passive components is failed (which I can check pretty easily, with the power off, by lifting the legs attached to the ceramic terminal), but it might also be a problem with T1320, which I guess is on the opposite side of the board? I have an HV multimeter probe coming on Tuesday, so I'll feel better about checking the high voltage stuff then.
I don't really understand what the mesh is doing in this CRT. Is the mesh bias really a good candidate for the symptom I'm seeing?
-- Jeff Dutky
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Hi all, and Happy New Year 2021,
Is a 564B a good grab, is it desirable at all?
It¡¯s not considered a 500 series, right?
56x family I suppose...
Thanks ?
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Re: How to clean Helitrim potentiometers?
Hello perhaps you are confusing Helipot a multiturn precison 3,5,10,15 turn potentiometer with internal 1 turn pcb mounted trimpots or single turn controls?
If you can pr¨¦cis your questions with photos of the pots or reference to the schematic part number or function you can receive better answers.
In general every old instrument can benefit from exercising every switch and control, use of contact cleaner or renew
Sealed pots that are blue and square are Bournes ModPot, lubricant with syringe or spray tube down the shaft and on the edges of the sections.
Bon Chance
Jon
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Re: font/typeface for Tektronix binder spines - was Re: [TekScopes] Push button font
I'm sorry I arrive pretty late in the conversation. There are online tools to identify fonts, with easy yes/no questions. I used one once to find which font was used on Philips instruments (for a Python GUI I designed to control a PM5192 generator). Can't find the site any more though... There are sites where you can upload an image and they find what font is used but I haven't tried them, for example (from a Google search results) : Nicolas ________________________________ De : [email protected] < [email protected]> de la part de toby@... <toby@...> Envoy¨¦ : samedi 2 janvier 2021 17:59 ? : [email protected] < [email protected]> Objet : font/typeface for Tektronix binder spines - was Re: [TekScopes] Push button font On 2020-12-14 9:04 a.m., toby@... wrote: On 2020-12-14 12:17 a.m., Chuck Harris wrote:
I'm pretty sure it is something put together
by Tektronix's graphics department.
Yes, and I don't think it's consistent either; after all, it spanned
several decades. It would probably be possible to find a suitable free
bold, compressed font that resembles it.
Turns out I have considered something suitable for binder spines before: View/Reply Online (#146250): /g/TekScopes/message/146250I also took a shot of my own shelf with some sample setting: /g/TekScopes/album?id=258709Of course Fjalla isn't the _same_ font as any of the binders, but the binders aren't consistent either, so it might help someone get close to the original look. You could also try horizontal scaling as desired (I couldn't do that in GIMP?!) --Toby --Toby
-Chuck Harris
snapdiode via groups.io wrote:
Cough, cough... Can someone perhaps identify the font(s) used on the plastic CombBind spines of the manuals?
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Re: Slightly OT: How can I dissolve Potting Compound?
Dear Dennis: We worked on arc and gas lamp ballasts since 1970s.
Then designed and manufactured 12 kV HV modules, in 1980s..1990s.
The encapsulant is a very high solids epoxy, specially cured.
We used heat and mechanical picking to disassemble.
The components can be damaged by the depotting process, so it is a destructive diagnostic but you will not revive the PSU.
Especially susceptible is the transformer insulation, it will be contaminated in the process.
Better idea is to replace with a new one.
Finally the laser supply and spectral lamps have very different performance, eg lasers DC with HV ignition pulse, spectral can use current limited AC similar to a neon sign transformer.
If you have a small neon transformer, try that on a variac.
If you PM me the specs and exact model of tubes, I may have an off the shelf supply I could send to you.
Happy New Years,
Jon
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
HI
Please,Larry,add me to the list.I am located at Spain.
Regards.
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
I would also be interested in a set of the boards, please add my name to the list. I am in Dublin, Ireland so I am aware that shipping will be somewhat more than the nominal amount suggested. I am happy to provide payment up front via PayPal friends and family. My thanks to Jared for the detailed engineering that went in to this, and for being willing to share it with the community, and to Larry for making a group purchase possible.
kind regards,
Peter Mulvey.
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Thank you to everybody!
I have enough information to attempt a transplant.
I'll post here the outcome
Giovanni
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Re: Slightly OT: How can I dissolve Potting Compound?
Hi Dennis, On Sat, Jan 2, 2021 at 06:18 PM, Dennis Tillman W7pF wrote: I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I believe it's not worth the effort, I'd personally build a new one using instructions from Sam's Laser FAQ: You'll find wealth of information on this site, it's amazing (even I contributed with my unusual Argon laser specimen). Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. I have no experience with spectral tubes but from your description it appears they work in the same way as a HeNe laser tubes do. Therefore a matching HeNe power supply will work for sure, but to my recollection the values you stated are much lower than the usual for HeNe tubes. These start with approx. 5-15kV and work (steadily conduct) at approx. 1-2kV. So to use an off the shelf HeNe PSU I'd try under-powering it (in therms of voltage) and/or increasing the ballast resistor. I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don¡¯t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I
have. The PSU needs to be matched to the particular tube you're using, my experience with HeNe tubes is the following: - High voltage for initial start has ample tolerance, it just needs to be able to start the tube. It is universally implemented as a diode-capacitor ladder multiplier so you can add elements until you get it high enough. Capacitors are normally small as you don't need excessive energy to kick-start the tube (e.g. CRT HV power supply can deliver orders of magnitude more energy than HeNe HV starter). - Ballast resistor and working voltage need to be fairly matched. The flicker you experienced with the other PSU is exactly the symptom of a mismatch. The ballast resistor cannot counter the intrinsic negative impedance of the working gas tube and the resulting runaway results in tube shutting down. The flicker is due to HV start occurring in a random loop. You can safely try to increase the ballast resistor and see if that improves the situation. This helps with aged HeNe tubes when they start flickering at end of life, sometimes ballast needs to be increased as much as threefold. The ballast resistor needs to be low enough to supply enough current through the tube to maintain plasma, but also high enough to limit the current. - The working voltage of a traditional transformer based PSU can be adjusted using a variac. Since in your case you most likely need to go down with the voltage, I'd say variac approach will give you ample headroom to match the HeNe PSU to your tubes. HTH Best regards and Happy New Year, Nenad Filipovic
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Re: Slightly OT: How can I dissolve Potting Compound?
Supposedly a 50/50 mix of formic and acetic acids will do the trick but I've never tried it.
DaveB, NZ
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Dave Daniel Sent: Sunday, January 03, 2021 21:59 To: [email protected]Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting Compound? My approach to this sort of problem (I¡¯ve done it twice in the past thirty or so years) has been to use an Xacto knife to cut the potting compound away. I never did find a solvent that seemed to work. DaveD On Jan 2, 2021, at 21:18, Dennis Tillman W7pF <dennis@...> wrote:
I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I
would appreciate any suggestions on what works to do this. I¡¯m
guessing it may be epoxy. I stuck the tip of a hot soldering iron in
it for a few seconds without much effect.
When it was working it turned out to be perfect for powering gas
filled Spectrum Tubes. These spectrum tubes (smaller versions of neon
signs) filled with a variety of gasses are an excellent source of
spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.
Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas
in the spectrum tube conducts the voltage across the gas drops (250V
to 450V for
example) and unless you limit the current (to a few mA) it will
destroy the tube. Can anyone can point me to a source of information
on how to determine the proper voltage and current I need to power
these spectrum tubes? Is there a web site or group devoted to Spectrum Tubes?
Something happened to the inverter and it stopped working. The input
is now open. The inverter is a black potted brick 3¡± x 1?¡± x 1¡±. The
ballast resistor has continuity so that is not the problem. The
original label on the inverter is partially destroyed so I can¡¯t tell
what its initial high voltage output was or what it current limits at.
All I do know is that it was made by Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.
I wrote to the company that took over the company that took over Laser
Drive Inc. asking if they could tell me the output voltage and
limiting current but I didn¡¯t receive a reply.
At this point I am hoping if I can remove the potting compound I can
figure out what went wrong with it.
I have a different, bigger Laser Drive Inc. potted inverter which is
powered by 115VAC. It puts out 2350VDC at 6.5mA. This causes the
Spectrum Tubes to flicker. They do not run continuously. I am guessing
that this because 6.5mA is more current than the tube can conduct. The
amount of current the tube draws increases in proportion to the inside
diameter of the tube but I don¡¯t know much about this matching the
power supply to the tube. All I do know is the one that went bad seems
to be an ideal match for the spectrum tubes I have.
Battery operated (DC input) inverters are much more desirable than AC
input inverters for this application because the AC rectification and
poor filtering shows up on the output DC as significant ripple causing
the amplitude of each spectral line to be blurred.
Dennis Tillman W7pF
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Re: Slightly OT: How can I dissolve Potting Compound?
My approach to this sort of problem (I¡¯ve done it twice in the past thirty or so years) has been to use an Xacto knife to cut the potting compound away. I never did find a solvent that seemed to work.
DaveD
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On Jan 2, 2021, at 21:18, Dennis Tillman W7pF <dennis@...> wrote:
I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I would
appreciate any suggestions on what works to do this. I¡¯m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.
When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.
Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?
Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3¡± x 1?¡± x 1¡±. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can¡¯t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by
Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.
I wrote to the company that took over the company that took over Laser Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn¡¯t receive a reply.
At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.
I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don¡¯t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.
Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.
Dennis Tillman W7pF
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Re: A question from the unwashed relative to: I built a TM500 mainframe tester...
Just a thought:
I wonder if there are TM500 modules which are particularly picky on correct functioning of the mainframe.
Such a module would
- use all or most of the interface
- show malfunction immediately, like no display, no output or such
- ideally does only use 1 bay
This would permit quick checking of mainframe slots, if you're sure the module is fine.
cheers
martin
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Re: Slightly OT: How can I dissolve Potting Compound?
I guess the point I was getting at but missed, was that it was labeled as containing acetone, but nothing else.? I try to stay away from beauty products (they wouldn't help me- hahaha!), but when it was being tossed out, I said "Acetone? I'll take it!".? Now I know better.
-Dave
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On Saturday, January 2, 2021, 11:02:31 PM PST, Roy Thistle <roy.thistle@...> wrote: On Sat, Jan? 2, 2021 at 10:31 PM, Dave Seiter wrote:
nail polish remover can have weird stuff in it
Yup. Some nail polish removers use acetone. Some removers use ethyl acetate or MEK or both. Remember MEK is used in the "glue" that plumbers use to solvent weld together plastic pipe.... in other words... it softens (and would dissolve) the plastic.
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Re: Slightly OT: How can I dissolve Potting Compound?
Also xylene. Be careful of MEK, it will dissolve rubber gloves.
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On 1/2/2021 11:02 PM, Roy Thistle wrote: On Sat, Jan 2, 2021 at 10:31 PM, Dave Seiter wrote:
nail polish remover can have weird stuff in it
Yup.
Some nail polish removers use acetone.
Some removers use ethyl acetate or MEK or both.
Remember MEK is used in the "glue" that plumbers use to solvent weld together plastic pipe.... in other words... it softens (and would dissolve) the plastic.
--
Richard Knoppow
dickburk@...
WB6KBL
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Re: Slightly OT: How can I dissolve Potting Compound?
Dennis,
A chemist friend once told me to try Dichloromethane. I have successfully
unpotted two assemblies using this.
First, it is nasty stuff, I put the part and the Dichloromethane in a glass
jar with a tight fitting lid and left it outside in the sun. The jar was
about half full and completely covered the part. If anything happened to
the jar, it would just spill into the driveway. I did this in a reasonably
warm part of the year. It would boil from the heat of the sun, condense at
night, and do the same the next day. A tight fitting lid contained the
liquid for months.
Second, it is slow. I unpotted a motorcycle voltage regulator and a 7904 HV
multiplier. In both cases, it took over a month.
Third, it will eat anything plastic. It doesn't know the difference between
potting compound and the plastic case of a diode or transistor.
Fourth, frequent investigation can get you info. On day 10, a transistor
may become partially visible, make note and move on. On day 15, a diode may
become visible, and the transistor from day 10 might be just the metal lead
frame and die. Looking every few days will yield new info. If you catch it
at just the right time, you can make electrical measurements of the
partially exposed leads.
For the 7904 HV multiplier, all the ceramic caps were stripped of
insulation but the leads and conductors were still there. The output
resistor was still measurable, as was the low voltage feedback diode, which
was the mystery for me at the time. I was even able to carefully measure a
diode and a capacitor before the leads fell apart.
It just depends on how desperate you are. As others have suggested,
purchasing a new one would be far easier. And there will be no chance of
repair, just the possibility of capturing a schematic and mechanical
details.
Tom Bowers
PVH Engineering
"
"
Dennis Tillman W7pF via
<> groups.io
7:18 PM (4 hours ago)
to TekScopes
I need to dissolve the black HV potting compound........ "
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On Sat, Jan 2, 2021 at 11:31 PM Dave Seiter <d.seiter@...> wrote: I've found that nail polish remover can have weird stuff in it (besides
the obvious dyes and fragrances) that pure acetone doesn't. Last summer I
poured half a bottle into the plastic tub of a cheapo ultrasonic cleaner,
and it immediately started attacking the plastic. The thing is- I've used
pure acetone in that tub many many times and it's never touched it.
-Dave
On Saturday, January 2, 2021, 09:09:47 PM PST, Roy Thistle <
roy.thistle@...> wrote:
On Sat, Jan 2, 2021 at 08:38 PM, Jim Ford wrote:
MEK is really nasty stuff and a precursor to
Gasoline is worse, but...
MEK is listed as a precursor... but a lot of industrial chemicals are
precursors... and despite being listed... it produced, and used in vast
quantities, in the U.S.
Model airplane "glue" (actually solvent welding, not gluing) has it,
plumbing "glue" has it (dido of welding plastic pipe)... it's used in a lot
of products sold to the public.
If plumbers and kids can handle it... well...
It's not "particularly good" at dissolving the black epoxy potting
compound, after it's cured... but, depends which epoxy was used... and
given a long time... it might dissolve it.
Acetone works better. (But, don't tell your wife of the horrors... or she
might have nightmares after she does her nails.)
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Re: Slightly OT: How can I dissolve Potting Compound?
On Sat, Jan 2, 2021 at 10:31 PM, Dave Seiter wrote:
nail polish remover can have weird stuff in it
Yup. Some nail polish removers use acetone. Some removers use ethyl acetate or MEK or both. Remember MEK is used in the "glue" that plumbers use to solvent weld together plastic pipe.... in other words... it softens (and would dissolve) the plastic.
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Re: Slightly OT: How can I dissolve Potting Compound?
On Sat, Jan 2, 2021 at 06:18 PM, Dennis Tillman W7pF wrote:
Helium-Neon laser inverter power supply
Hi Dennis: I couldn't remember... but finally did. There is the defacto go to FAQ... for "gas laser tube nuts" called "Sam's Laser FAQ" ... there is good bit of information about He-Ne laser power supplies, et. al. (No relation to the schematic service, for T.V. repair... and not a quack [ is/was a prof. and has a PhD, if that precludes that sort of thing.] ) Gas discharge laser tubes are similar to "spectrum discharge tubes" ... at least the spectrum tubes I'm familiar with. There's several scientific supply houses, in the U.S. that sell those spectrum tubes (but, I think they are all made in China.) The tubes I'm thinking of are about a foot long, have cold cathode electrodes on either end, and are made of glass.
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Kevin
Jean-Paul
Peter Mulvey
Giovanni IZ5PQT
Martin