Date   

Re: 7904 excessive shadow/flare

Chuck Harris <cfharris@...>
 

Hi Dennis,

At the relativistically slow speeds that exist in a CRT,
even one as nifty as a 7904, there isn't going to be much
(if any) interaction between the nucleus of the aluminum
atoms and the electron beam. You need a heavier particle.

The interaction is going to be between the electrons in the
aluminum atom, and the electron beam.

Secondary emission comes in three varieties:

a) true secondary emission, where you stuff in one electron,
and another (the emitted electron) leaks out.
b) inelastic reflected primary electrons.

c) elastically reflected primary electrons.

The three sorts have drastically different energy levels:

The true secondary emission electrons are in great abundance,
and have energy levels around 1 ev.

The inelastically reflected secondary emission electrons are
much less frequent, and have energy levels ranging from 2-30ev.

The elastically reflected secondary emission electrons are
primary (from the beam) electrons, and have high energy levels
(30 ev or more).
They are also in high quantity.

I would expect that the halo we see when we turn the intensity
up high, and a glowing circle of area appears around the beam
are the type a) and b) secondary emissions. They are fairly
low energy, and as such lift off of the surface, and get pulled
right back by the anode's attractive force.

I would expect that the moving halo that dances across the
screen at a multiple of the sweep rate would be the type c)
elastically reflected primary (beam) electrons, and are of rather
high energy levels. They take a relatively long path before
the attractive force of the anode voltage can pull them back
to the screen.

They also appear at approximately equal but opposite angles
to the primary (beam) electrons... like a billiard ball hitting
a bumper.

-Chuck Harris

Inspired by the IEEE Radio Engineer's Handbook.


Dennis Tillman W7PF wrote:

Hi Chuck,

I don't think the electrons recoil from the nucleus at a precise angle. Rather, they scatter over a range of angles which causes the halo to be wide and indistinct but the halo clearly has the shape of whatever waveform is being displayed. The 7904 Was a huge breakthrough when it was introduced. Only a few years earlier the 547 was the flagship of Tek's product line and it was capable of a very impressive 50MHz. Before 10 years passed the 7904 was capable of 10 times the speed of the 547. But the writing rate of such a fast scope was going to suffer from that speed so they boosted the HV to compensate.

The real solution comes a few years later when Tek puts the Micro Channel Plate onto the 7104 CRT. The 3dB point of that 7104 CRT is above 3GHz, and the MCP made it 10,000 times brighter than anything that ever came before.

On a side note: The unit used to measure the probability of an electron striking a nucleus is the BARN. A barn (symbol: b) is a unit of area equal to 10−28 m2 (or 100 fm2). Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is also used in all fields of high-energy physics to express the cross sections of any scattering process, and is best understood as a measure of the probability of interaction between small particles. A barn is approximately the cross-sectional area of a uranium nucleus. The origin of the unit barn is whimsical: during Manhattan Project research on the atomic bomb during World War II, American physicists at Purdue University needed a secretive unit to describe the approximate cross sectional area presented by the typical nucleus (10−28 m2) and decided on "barn". This was particularly applicable because they considered this a large target for particle accelerators that needed to have direct strikes on nuclei and the American idiom "couldn't hit the broad side of a barn"[2] refers to someone whose aim is terrible. Initially they hoped the name would obscure any reference to the study of nuclear structure; eventually, the word became a standard unit in nuclear and particle physics.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: Saturday, June 29, 2019 7:16 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7904 excessive shadow/flare

Hi Dennis,

The mind pictures your description makes are compelling:

I can see the angle the beam impinges on the screen causing the electrons to reflect at the equal but opposite angle, and the "wind" of the PDA catching them and dragging them back down to again splatter on the screen: further to the left when the beam is left of dead center, dead center when the beam is centered, and further to the right when the beam is right of dead center...
giving the appearance of a fuzzy magnified version of the original sweep.

One should be able to calculate the distance the electrons bounced from the screen by measuring both the distance from screen dead center of the original spot, and the distance from screen dead center of the flare.

Pretty wild, Mr Tillman!

-Chuck Harris

Dennis Tillman W7PF wrote:
Hi Chuck and Max,
I have a more complete answer about the cause of the halo / flare after speaking to my friend. He designed the vertical deflection plates of the 7104.

A very important consideration with CRTs 30 or more years ago was their photographic writing rate since photographic film was the only way to capture fast transient events for further study. Photographic writing rate could be increased by raising the accelerating voltage of the CRT. Faster scopes, such as the 7904, required higher HV to transfer enough energy to each electron in the beam since the beam was sweeping across the CRT at faster sweep settings in the 7904.

Inside the CRT the electrons ae accelerated by the HV field. The first thing they strike is a very thin conductive aluminum layer. The aluminum is so thin most of the electrons pass through it and strike the phosphor where they excite the electrons in the phosphor atoms causing them to emit visible photons. The purpose of the aluminum layer is to draw off the charge which would otherwise accumulate on the phosphor layer and repel the beam of electrons.

Unfortunately, as the electrons in the beam are passing through the layer of aluminum there is a small chance some of them will encounter a nucleus. When that happens the electron is repelled (scattered at a random angle) with some force back out of the aluminum layer and into the vacuum of the CRT. It quickly begins to feel the pull of the HV field again and it starts accelerating towards the aluminum again, but it is no longer part of the original focused beam of electrons. It can be scattered fairly far from the original beam by the nucleus it hit. These back scattered electrons are now accelerated toward the aluminum some distance away from the main beam and in a completely unfocused form. This is what is causing the halo/flare you are seeing.

The halo / flare is the same shape as the main focused beam but it is fuzzier and removed from the main trace on the CRT.

Dennis Tillman W7PF




Re: 7904 excessive shadow/flare

 

Hi Chuck,

I don't think the electrons recoil from the nucleus at a precise angle. Rather, they scatter over a range of angles which causes the halo to be wide and indistinct but the halo clearly has the shape of whatever waveform is being displayed. The 7904 Was a huge breakthrough when it was introduced. Only a few years earlier the 547 was the flagship of Tek's product line and it was capable of a very impressive 50MHz. Before 10 years passed the 7904 was capable of 10 times the speed of the 547. But the writing rate of such a fast scope was going to suffer from that speed so they boosted the HV to compensate.

The real solution comes a few years later when Tek puts the Micro Channel Plate onto the 7104 CRT. The 3dB point of that 7104 CRT is above 3GHz, and the MCP made it 10,000 times brighter than anything that ever came before.

On a side note: The unit used to measure the probability of an electron striking a nucleus is the BARN. A barn (symbol: b) is a unit of area equal to 10−28 m2 (or 100 fm2). Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is also used in all fields of high-energy physics to express the cross sections of any scattering process, and is best understood as a measure of the probability of interaction between small particles. A barn is approximately the cross-sectional area of a uranium nucleus. The origin of the unit barn is whimsical: during Manhattan Project research on the atomic bomb during World War II, American physicists at Purdue University needed a secretive unit to describe the approximate cross sectional area presented by the typical nucleus (10−28 m2) and decided on "barn". This was particularly applicable because they considered this a large target for particle accelerators that needed to have direct strikes on nuclei and the American idiom "couldn't hit the broad side of a barn"[2] refers to someone whose aim is terrible. Initially they hoped the name would obscure any reference to the study of nuclear structure; eventually, the word became a standard unit in nuclear and particle physics.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: Saturday, June 29, 2019 7:16 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7904 excessive shadow/flare

Hi Dennis,

The mind pictures your description makes are compelling:

I can see the angle the beam impinges on the screen causing the electrons to reflect at the equal but opposite angle, and the "wind" of the PDA catching them and dragging them back down to again splatter on the screen: further to the left when the beam is left of dead center, dead center when the beam is centered, and further to the right when the beam is right of dead center...
giving the appearance of a fuzzy magnified version of the original sweep.

One should be able to calculate the distance the electrons bounced from the screen by measuring both the distance from screen dead center of the original spot, and the distance from screen dead center of the flare.

Pretty wild, Mr Tillman!

-Chuck Harris

Dennis Tillman W7PF wrote:
Hi Chuck and Max,
I have a more complete answer about the cause of the halo / flare after speaking to my friend. He designed the vertical deflection plates of the 7104.

A very important consideration with CRTs 30 or more years ago was their photographic writing rate since photographic film was the only way to capture fast transient events for further study. Photographic writing rate could be increased by raising the accelerating voltage of the CRT. Faster scopes, such as the 7904, required higher HV to transfer enough energy to each electron in the beam since the beam was sweeping across the CRT at faster sweep settings in the 7904.

Inside the CRT the electrons ae accelerated by the HV field. The first thing they strike is a very thin conductive aluminum layer. The aluminum is so thin most of the electrons pass through it and strike the phosphor where they excite the electrons in the phosphor atoms causing them to emit visible photons. The purpose of the aluminum layer is to draw off the charge which would otherwise accumulate on the phosphor layer and repel the beam of electrons.

Unfortunately, as the electrons in the beam are passing through the layer of aluminum there is a small chance some of them will encounter a nucleus. When that happens the electron is repelled (scattered at a random angle) with some force back out of the aluminum layer and into the vacuum of the CRT. It quickly begins to feel the pull of the HV field again and it starts accelerating towards the aluminum again, but it is no longer part of the original focused beam of electrons. It can be scattered fairly far from the original beam by the nucleus it hit. These back scattered electrons are now accelerated toward the aluminum some distance away from the main beam and in a completely unfocused form. This is what is causing the halo/flare you are seeing.

The halo / flare is the same shape as the main focused beam but it is fuzzier and removed from the main trace on the CRT.

Dennis Tillman W7PF




--
Dennis Tillman W7PF
TekScopes Moderator


Re: 7904 excessive shadow/flare

Chuck Harris <cfharris@...>
 

Hi Dennis,

The mind pictures your description makes are compelling:

I can see the angle the beam impinges on the screen causing the
electrons to reflect at the equal but opposite angle, and the
"wind" of the PDA catching them and dragging them back down to
again splatter on the screen: further to the left when the beam
is left of dead center, dead center when the beam is centered,
and further to the right when the beam is right of dead center...
giving the appearance of a fuzzy magnified version of the original
sweep.

One should be able to calculate the distance the electrons bounced
from the screen by measuring both the distance from screen dead center
of the original spot, and the distance from screen dead center of the
flare.

Pretty wild, Mr Tillman!

-Chuck Harris

Dennis Tillman W7PF wrote:

Hi Chuck and Max,
I have a more complete answer about the cause of the halo / flare after speaking to my friend. He designed the vertical deflection plates of the 7104.

A very important consideration with CRTs 30 or more years ago was their photographic writing rate since photographic film was the only way to capture fast transient events for further study. Photographic writing rate could be increased by raising the accelerating voltage of the CRT. Faster scopes, such as the 7904, required higher HV to transfer enough energy to each electron in the beam since the beam was sweeping across the CRT at faster sweep settings in the 7904.

Inside the CRT the electrons ae accelerated by the HV field. The first thing they strike is a very thin conductive aluminum layer. The aluminum is so thin most of the electrons pass through it and strike the phosphor where they excite the electrons in the phosphor atoms causing them to emit visible photons. The purpose of the aluminum layer is to draw off the charge which would otherwise accumulate on the phosphor layer and repel the beam of electrons.

Unfortunately, as the electrons in the beam are passing through the layer of aluminum there is a small chance some of them will encounter a nucleus. When that happens the electron is repelled (scattered at a random angle) with some force back out of the aluminum layer and into the vacuum of the CRT. It quickly begins to feel the pull of the HV field again and it starts accelerating towards the aluminum again, but it is no longer part of the original focused beam of electrons. It can be scattered fairly far from the original beam by the nucleus it hit. These back scattered electrons are now accelerated toward the aluminum some distance away from the main beam and in a completely unfocused form. This is what is causing the halo/flare you are seeing.

The halo / flare is the same shape as the main focused beam but it is fuzzier and removed from the main trace on the CRT.

Dennis Tillman W7PF


Re: 7904 excessive shadow/flare

unclebanjoman
 

Thanks again Dennis,

It is always worthwhile to review these things.

So we can say that the halo/flare effects is to both the dome/expansion mesh and the secondary emission, right?

Max


Re: 7904 excessive shadow/flare

Craig Sawyers <c.sawyers@...>
 

I have a more complete answer about the cause of the halo / flare after speaking to my friend. He
designed the vertical deflection plates of the 7104.
Dennis Tillman W7PF
I thought the secondary emission halo was a pretty well-known and understood mechanism. But maybe that
knowledge dropped off the perch with the passage of decades ;-)

Craig


Re: 7904 excessive shadow/flare

 

Hi Chuck and Max,
I have a more complete answer about the cause of the halo / flare after speaking to my friend. He designed the vertical deflection plates of the 7104.

A very important consideration with CRTs 30 or more years ago was their photographic writing rate since photographic film was the only way to capture fast transient events for further study. Photographic writing rate could be increased by raising the accelerating voltage of the CRT. Faster scopes, such as the 7904, required higher HV to transfer enough energy to each electron in the beam since the beam was sweeping across the CRT at faster sweep settings in the 7904.

Inside the CRT the electrons ae accelerated by the HV field. The first thing they strike is a very thin conductive aluminum layer. The aluminum is so thin most of the electrons pass through it and strike the phosphor where they excite the electrons in the phosphor atoms causing them to emit visible photons. The purpose of the aluminum layer is to draw off the charge which would otherwise accumulate on the phosphor layer and repel the beam of electrons.

Unfortunately, as the electrons in the beam are passing through the layer of aluminum there is a small chance some of them will encounter a nucleus. When that happens the electron is repelled (scattered at a random angle) with some force back out of the aluminum layer and into the vacuum of the CRT. It quickly begins to feel the pull of the HV field again and it starts accelerating towards the aluminum again, but it is no longer part of the original focused beam of electrons. It can be scattered fairly far from the original beam by the nucleus it hit. These back scattered electrons are now accelerated toward the aluminum some distance away from the main beam and in a completely unfocused form. This is what is causing the halo/flare you are seeing.

The halo / flare is the same shape as the main focused beam but it is fuzzier and removed from the main trace on the CRT.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: Wednesday, May 22, 2019 9:11 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7904 excessive shadow/flare

The 7904, because of its very high anode voltage, and its mesh lens is one of the worst scopes in existence for reflections and flare inside of the CRT. But I like it anyway.

-Chuck Harris

unclebanjoman wrote:
No, the artifact is visible with any type of signal.
It also appears using the signal standardizer. I used the latter today to perform some calibrations on my 7904 and I was very irritated by this halo / flare effect.
With sweep rates of 0.1-0.5 sec and no signal applied is clearly visible the usual "globus" leading/lagging the spot.
Already with moderate brightness the artifact is visible.

Max



--
Dennis Tillman W7PF
TekScopes Moderator


Re: Stuck outer case of 429

Richard Solomon <dickw1ksz@...>
 

Go down to Harbor Freight and get
a Dent Puller. You may need to repaint
the case later, but better than destroying it.

73, Dick, W1KSZ

On Fri, Jun 28, 2019 at 9:46 AM Merchison Burke via Groups.Io <merchison=
yahoo.co.uk@groups.io> wrote:

You will have to either (1) straighten out the dents before attempting
to remove it or (2) destroy the case as Tektronix cases fit very closely
at some points along the chassis.

I recommend that you spend the time to CAREFULLY, straighten out the
dents before attempting to remove the case.

On 2019-Jun-26 10:33 AM, Jeet D wrote:
Hi all!
I bought a 492 SA (used & non-functional, ofcourse ????) but due to some
dents on the outer case, I'm unable to slide it out completely. Seems like
those dents are catching something somewhere. It slides out about half way
but then gets stuck. I've tried a few times to slide it out with increasing
force but have given up after about 3-4 tries. Any suggestions on how to
get past this first obstacle and remove the case completely would be much
appreciated and thanks.
-Jeet




---
This email has been checked for viruses by AVG.
https://www.avg.com





Re: Stuck outer case of 429

Merchison Burke
 

You will have to either (1) straighten out the dents before attempting to remove it or (2) destroy the case as Tektronix cases fit very closely at some points along the chassis.

I recommend that you spend the time to CAREFULLY, straighten out the dents before attempting to remove the case.

On 2019-Jun-26 10:33 AM, Jeet D wrote:
Hi all!
I bought a 492 SA (used & non-functional, ofcourse ????) but due to some dents on the outer case, I'm unable to slide it out completely. Seems like those dents are catching something somewhere. It slides out about half way but then gets stuck. I've tried a few times to slide it out with increasing force but have given up after about 3-4 tries. Any suggestions on how to get past this first obstacle and remove the case completely would be much appreciated and thanks.
-Jeet



---
This email has been checked for viruses by AVG.
https://www.avg.com


Re: 485 parts needed

Colin Herbert
 

Have you tried the usual places?

Sphere in Canada and Qservice in Rhodes (Greece). You are likely to need the Tektronix part-numbers to make searching easier. Part-numbers can be found in the Service manuals.

It can sometimes bear fruit for unobtainium parts to look for a non-working scope with the parts that you want on eBay. There are also common parts between various scopes - the Common Design Parts lists are your friend here. We all need parts-donors from time to time.

Good Luck, Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of n9llo via Groups.Io
Sent: 28 June 2019 13:44
To: TekScopes@groups.io
Subject: [TekScopes] 485 parts needed

I’m going to get an old 485 fixed up and I need some parts. If anyone has any of this stuff for sale please get back to me here or n9llo at aol dot com.
Volts per div knob x2
Variable volts per div knob and shaft
Channel input BNC connector
Small gray ac/gnd/dc knob


Thanks for looking
Chris W9RP


485 parts needed

 

I’m going to get an old 485 fixed up and I need some parts. If anyone has any of this stuff for sale please get back to me here or n9llo at aol dot com.
Volts per div knob x2
Variable volts per div knob and shaft
Channel input BNC connector
Small gray ac/gnd/dc knob


Thanks for looking
Chris W9RP


Re: Stuck outer case of 429

Chuck Harris <cfharris@...>
 

Look for, and mark all of the deep dents.

Slide the case until it jambs, and note which
dent it is hung up on.

Take a small hammer, and tap, tap, tap... very
lightly... around the rim of the dent that is
blocking the cover. Lightly! If you can see
the results of your tapping, you are hitting it
too hard. How hard? A small brad into a pine
board would go 1/4" per tap is how hard.

The idea is, that every dent has a crease where
the blow struck, and away from the crease is the
point where the sheet metal bent from flat to
allow the crease. That is what I call the rim
of the dent. When you tap on the rim, your light
blow is transmitted to the crease, and shrinks the
metal that was stretched to make the crease.

As you tap around, and around the rim, the rim will
move in towards the crease, keep following it in
until it gets to the crease.

This takes time, and a lot of tiny taps.

After a bit, try moving the case again..

Wash, rinse, repeat...

When you get the case off, find the crease that is
hanging things up, and tap it from the inside of the
case with a small flat hammer. You can put the
case flat on a hard surface, but do not hit the
crease into the hard surface... ever... or you will
again stretch the metal... you want to shrink the
metal at the crease, not stretch it.

-Chuck Harris

Jeet D wrote:

Hi all!
I bought a 492 SA (used & non-functional, ofcourse 😅) but due to some dents on the outer case, I'm unable to slide it out completely. Seems like those dents are catching something somewhere. It slides out about half way but then gets stuck. I've tried a few times to slide it out with increasing force but have given up after about 3-4 tries. Any suggestions on how to get past this first obstacle and remove the case completely would be much appreciated and thanks.
-Jeet


Re: Stuck outer case of 429

Albert Otten
 

Jeet,

It might help if you can tell approximately where those dents are located. When I look at pictures I took from my 492P I can more or less judge the left and right hand sides of the frame. The only obvious obstacles seem to be at the rhs, upper side. All over the rhs there are shields for the pcbs and packed units. All of these have the same distance to the case. But at about 1/3 length from the rear there is a separate bracket, parallel to the case, which has (near the screws) slightly less space to the case. Also at the rear end a thick blue cable loom and a rigid cable require some more space (could be 492P specific).
There are also a few overview pictures at Google images.

Albert

On Fri, Jun 28, 2019 at 08:04 AM, Jeet D wrote:


Hi all!
I bought a 492 SA (used & non-functional, ofcourse 😅) but due to some dents
on the outer case, I'm unable to slide it out completely. Seems like those
dents are catching something somewhere. It slides out about half way but then
gets stuck. I've tried a few times to slide it out with increasing force but
have given up after about 3-4 tries. Any suggestions on how to get past this
first obstacle and remove the case completely would be much appreciated and
thanks.
-Jeet


Stuck outer case of 429

Jeet D
 

Hi all!
I bought a 492 SA (used & non-functional, ofcourse 😅) but due to some dents on the outer case, I'm unable to slide it out completely. Seems like those dents are catching something somewhere. It slides out about half way but then gets stuck. I've tried a few times to slide it out with increasing force but have given up after about 3-4 tries. Any suggestions on how to get past this first obstacle and remove the case completely would be much appreciated and thanks.
-Jeet


Re: CSA803A: screen copy and trace sample data download

gjm45janssen
 

Leo,

Yes, that may be interesting. I did not try to download data while the scope is set to color grading. Also the graded information could be determined from the downloaded data when the scope is set to persistence.

Regards,
Gerard


Re: TDS520B - the screen gradually expands and then darkens in about 20 mins

unclebanjoman
 

Hi nonIonizing EMF,

Thanks for your comment.
Yes I know that I could make a DIY HV probe, but I think it's better, as soon as I get the chance, to buy an old but still useful used P6015 probe....

Max


Re: TDS520B - the screen gradually expands and then darkens in about 20 mins

unclebanjoman
 

Hi Stephen,

at this point obviously I prefer to get the complete board, not just the transformer!
I wrote you an email about eight hours ago.
I request a quote for 2 complete and functioning boards (I would like to have one as a spare).

Thanks,

Max


Re: TDS520B - the screen gradually expands and then darkens in about 20 mins

unclebanjoman
 

On Wed, Jun 26, 2019 at 04:39 AM, greenboxmaven wrote:
Do you
have good focus and a reasonably bright image when you first turn the
scope on?
Yes, when the scope is first turned on, brightness and focus are both perfect.
After approx. 10 mins, the screen starts blooming, first fractions of a millimeter, then gradually more accentuated but the display is still well focused and bright.
After 20 minutes the blooming dramatically accelerates and screen darkens to totally black.

I turn off and let it cool for at least 10 minutes. Then turn on the scope and the scene repeats itself.

Max


Re: 7854 with strange intensity/focus problem (to me)

Albert Otten
 

On Wed, Jun 26, 2019 at 03:29 PM, unclebanjoman wrote:


Can be something's wrong with the focus grid.
Hi Max,

I don't think so, but I got even more confused after other measurements in my 7704A. I measured the cathode current by means of the voltage drop across the 100 ohm resistor between supply and cathode. When I suddenly turn intensity to maximum then the voltage jumps to a "high" value (somewhere 1.0 - 1.5 mV) and within seconds drops to a lower value (say 0.8 mV or even less). I tested this also with very defocused trace; the maxima seem higher with trace at the screen than with trace off-screen. The multiplier current sense works different in the 7704A but current got never limited by this sense line.
I'm afraid I can't help you any further.

Albert


Re: 7854 with strange intensity/focus problem (to me)

Chuck Harris <cfharris@...>
 

In the 2465 family CRT's, I have noticed that tek did
most of the internal element connection welds quite well,
but others, like the control grid, were universally weak.
No real deformation of the steel by the heat of the weld,
and the pressure of the welder's electrodes.

As a result, I have seen a couple of 2465 CRT's that had
open circuit control grids. The weak, barely there, weld
snapped, and the thin ribbon of material used to make the
connection sprung away from the electrode it was "welded"
to. You can see these failures through the glass neck of
the tube.

The effect of this failure is obvious in operation, the
intensity slowly grows brighter and brighter until it is
too bright, and you feel compelled to shut the scope down.

Of course, the intensity pot does nothing.

Our scopes almost all have been shipped, or banged about,
by the time we get them, and weak CRT welds will sometimes
break, ruining an otherwise beautiful looking the CRT.

-Chuck Harris

unclebanjoman wrote:

Hi Albert,

Can be something's wrong with the focus grid.

One month ago I've repaired a 475. It did not regulate the intensity.
After a careful check of all the components of the HV section and after many hours of useless work, I solved it simply by changing the CRT (luckily I had a spare one).
Changed the CRT, everything has started to work properly.
Probably something wrong with the G1. Mystery....

Max




Re: Tek 577 for sale and a note about the display

Oliver Viitamaki
 

I have some interest. Please contact me at 8850hp at gmail dot com

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