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Keller's CRT publications - Re: [TekScopes] Tektronix 2465A noise on readout

toby@...
 

On 2020-10-15 3:56 p.m., Tom Lee wrote:
Those who are interested in learning more about the amazing technology
of scope CRTs might want to read Pete Keller's terrific book on the
subject. See http://w140.com/tekwiki/wiki/Peter_Keller
Thanks for the link! But looks like parts 1, 2, 3 and 5 are missing?

Tektronix also published "Storage Cathode-Ray Tubes and Circuits" and
"Cathode-Ray Tubes" (Chuck DeVere and Bob Orwiler) in their Circuit
Concepts series. Both are online.

--Toby



And Hans Springer's article on the 7104 discusses the microchannel-plate
CRT used in that scope. The physics of that bottle is mindblowingly
impressive.

-- Tom


Re: Air filters for big 500 series scopes

Roy Thistle
 

On Thu, Oct 15, 2020 at 12:37 PM, DaveH52 wrote:


type of filter that is used in a range hood
Yes... at least here in the colonies...Al range hood filter material is the samesimilar Al material that was used in the 500 filters (I think it has been mentioned earlier... or in another thread.)
Don't know if the range hood filters are coated? But if not, there's an opportunity there to market a reasonably expensive application specific Pam type spray, for them.
Back in the day... were you guys frying bacon in the test lab? Just wondering.


Re: Tektronix 2465A noise on readout

Tom Lee
 

Those who are interested in learning more about the amazing technology of scope CRTs might want to read Pete Keller's terrific book on the subject. See http://w140.com/tekwiki/wiki/Peter_Keller

And Hans Springer's article on the 7104 discusses the microchannel-plate CRT used in that scope. The physics of that bottle is mindblowingly impressive.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/15/2020 12:41, Siggi wrote:
Hey Chuck,

Why am I not surprised that you went and measured this :).
I agree that the capacitance of the lenses is pretty insignificant (by 3
orders of magnitude) compared to the bypass cap. It's interesting though
that there's a 10Ohm resistor between the cap and the CRT element - I
wonder what that's for.
Now, I've never really taken a close look at the structure of these CRTs,
and I can't say that I really did now. Looking at the images on VintageTek (
https://vintagetek.org/crt-time-capsule/ - search for T2440) OMG the
structure of the neck is intricate. Some more pictures here (
https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg419298/#msg419298
).
Sadly the images are fairly low resolution.

Reading through the schematic depiction you have:
- The filament.
- The cathode (-1900V).
- The grid.
- First anode (+87V)?
- The focus lens (-200V to -100V).
- The astigmatism lens.
- The vertical deflection plates (0 through +42V).
- The edge focus lens.
- The Y-alignment coil (I assume this is wound on the outside of the neck?).
- The horizontal deflection plates (0 to 87V?)..
- The/a geometry anode (+15 to 87V).
- The final anode (-900V)??.

Am I even naming things correctly here?

And then I guess you get into the ceramic funnel with the:
- Trace rotation coil, and
- The PDA anode.

Such an amazing physics hack :).

Siggi

On Thu, Oct 15, 2020 at 1:18 PM Chuck Harris <cfharris@erols.com> wrote:

Hi Siggi,

If you measure QP1 across its elements (12,5), you get 33.7pf.
If you measure QP2 across its elements, (13.6) you get 25.6pf.

Compared to the 0.022uf filter, that is pretty insignificant.

I don't know where the recommendation to use high temperature
low ESR for this film cap came from, but obviously it is
in a league of its own as far as that goes.

-Chuck Harris

Siggi wrote:
On Tue, Oct 13, 2020 at 11:38 AM Chuck Harris <cfharris@erols.com>
wrote:
I doubt that the capacitor was damaged by the circuit in any
way. There really is little voltage and almost no power there.
Yeah, I wondered about this. It looks like the collector of Q1852 will go
between approximately -100V to -200V depending on the focus pot setting,
but unless you're moving the focus pot, the output is DC. The only "load"
the circuit sees would be capacitive coupling of the VQ signal through
the
CRTs focus lens. VQ is depicted as a fairly sharp square wave with a ~50V
swing on a 3us period (in my 2465 service manual), but I don't have a
feel
for the capacitance of a focus lens. Can't be much, though?










Re: Tektronix 2465A noise on readout

Siggi
 

Hey Chuck,

Why am I not surprised that you went and measured this :).
I agree that the capacitance of the lenses is pretty insignificant (by 3
orders of magnitude) compared to the bypass cap. It's interesting though
that there's a 10Ohm resistor between the cap and the CRT element - I
wonder what that's for.
Now, I've never really taken a close look at the structure of these CRTs,
and I can't say that I really did now. Looking at the images on VintageTek (
https://vintagetek.org/crt-time-capsule/ - search for T2440) OMG the
structure of the neck is intricate. Some more pictures here (
https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg419298/#msg419298
).
Sadly the images are fairly low resolution.

Reading through the schematic depiction you have:
- The filament.
- The cathode (-1900V).
- The grid.
- First anode (+87V)?
- The focus lens (-200V to -100V).
- The astigmatism lens.
- The vertical deflection plates (0 through +42V).
- The edge focus lens.
- The Y-alignment coil (I assume this is wound on the outside of the neck?).
- The horizontal deflection plates (0 to 87V?)..
- The/a geometry anode (+15 to 87V).
- The final anode (-900V)??.

Am I even naming things correctly here?

And then I guess you get into the ceramic funnel with the:
- Trace rotation coil, and
- The PDA anode.

Such an amazing physics hack :).

Siggi

On Thu, Oct 15, 2020 at 1:18 PM Chuck Harris <cfharris@erols.com> wrote:

Hi Siggi,

If you measure QP1 across its elements (12,5), you get 33.7pf.
If you measure QP2 across its elements, (13.6) you get 25.6pf.

Compared to the 0.022uf filter, that is pretty insignificant.

I don't know where the recommendation to use high temperature
low ESR for this film cap came from, but obviously it is
in a league of its own as far as that goes.

-Chuck Harris

Siggi wrote:
On Tue, Oct 13, 2020 at 11:38 AM Chuck Harris <cfharris@erols.com>
wrote:

I doubt that the capacitor was damaged by the circuit in any
way. There really is little voltage and almost no power there.
Yeah, I wondered about this. It looks like the collector of Q1852 will go
between approximately -100V to -200V depending on the focus pot setting,
but unless you're moving the focus pot, the output is DC. The only "load"
the circuit sees would be capacitive coupling of the VQ signal through
the
CRTs focus lens. VQ is depicted as a fairly sharp square wave with a ~50V
swing on a 3us period (in my 2465 service manual), but I don't have a
feel
for the capacitance of a focus lens. Can't be much, though?










Re: Air filters for big 500 series scopes

DaveH52
 

We had an electrostatic air cleaner on our HVAC system that used expanded aluminum filters. Or how about the same type of filter that is used in a range hood?


Re: Air filters for big 500 series scopes

Roy Thistle
 

On Thu, Oct 15, 2020 at 06:43 AM, Grayson Evans wrote:


I had not thought about coating the filter
I've cleaned the oldest dirtiest (I mean dirty!) original (or as they came with) series 500 Al mesh filters.
I never, when I can get them, throw the filters away... I just simply clean them.
I don't coat them with anything (no oil, or wax, or decene homopolymers!). My thinking (if you want to accuse of that)... my thinking is that the coating will migrate into the scope... eventually... helping to preserve the filth that only a circa 1960s vacuum tube device seems to be a magnet for.
For whatever good it does, I run the filters on clean 500s bareback... and simply, keep the scopes in as clean an environment as can be. If need be, I'll vacuum out the dust, or blow it out (where applicable) with clean, dry, oil-free air.
By the way... WD40 will only leave a small amount of a powdery white non-sticky substance that is probably the wax component. That white stuff will probably just migrate into the scope, as it doesn't really stick to the Al.


Re: How to clean Helitrim potentiometers?

Alexandre Souza
 

Helitrim pots cheap? Do you have a source? Thanks!

Enviado do meu Tele-Movel

Em qui, 15 de out de 2020 13:40, Stephen Hanselman <kc4sw.io@kc4sw.com>
escreveu:

Replace them, they are fairly cheap, easy to change, and not noisy.
Besides you could change a 10 turn into a 25 turn and make the adjustments
way less twitchy.

We have seen a significant improvement in unit stability by replacing pots
in the Valhalla electronic resistors we work on.

Regards,

Stephen Hanselman
Datagate Systems, LLC
On Oct 15, 2020, at 08:47, Alexandre Souza <alexandre.tabajara@gmail.com>
wrote:

Greetz All!

My FG503 got dirty pots. I need to clean it, but they seem to be sealed.
Is there any technique to clean these pots?

Thanks
Alexandre


--
---8<---Corte Aqui---8<---
https://www.tabalabs.com.br
https://tabajara-labs.blogspot.com









Tek 468, X-Y mode not working, spot hard left, requires beamfinder

John
 

I have a problem with X-Y mode not working on my 468 scope. The spot it hard left and beamfinder is required to show it. Other running traces are absolutely fine. I had another discussion open for the storage side of the scope which has not got rather long so it seemed sensible to open a separate discussion for this issue. I hope that is allowed?

While a trace is running there is a sweep ramp on both plates as might be expected. In X-Y mode there is 100VDC on one plate, zero volts on the other.

With U564 (4x transistor DIL package, horizontal amp section) removed, the spot is centered.

With pin 2 of U564 grounded the spot is centered.

With Q760 and Q772 removed and U564 in place, approximately 0.64V is present on U564-p2/Q760-c/Q772c. The spot is now hard right instead of left and beamfinder is required to locate it.

With Q760, Q772 and U564 present U564-p2 is at around 180mV. According to the diagram it should be 0V. I am not finding any faulty component so am not sure why the voltage is above 0V. At Q760 E there is 45mV but at Q772 there is 160mV. Swapping Q760 and Q772 around makes no difference. Same for Q781 and Q782. U690 and U789 have both been substitued to rule them out. Made no difference.

Clearly there is an imbalance somewhere but only affecting X-Y mode it seems. I have stared at the diagrams for a very long time today and have to admit that I am rather stumped at this point.

Any ideas would be appreciated.


Re: Tektronix 2465A noise on readout

Chuck Harris
 

Hi Siggi,

If you measure QP1 across its elements (12,5), you get 33.7pf.
If you measure QP2 across its elements, (13.6) you get 25.6pf.

Compared to the 0.022uf filter, that is pretty insignificant.

I don't know where the recommendation to use high temperature
low ESR for this film cap came from, but obviously it is
in a league of its own as far as that goes.

-Chuck Harris

Siggi wrote:

On Tue, Oct 13, 2020 at 11:38 AM Chuck Harris <cfharris@erols.com> wrote:

I doubt that the capacitor was damaged by the circuit in any
way. There really is little voltage and almost no power there.
Yeah, I wondered about this. It looks like the collector of Q1852 will go
between approximately -100V to -200V depending on the focus pot setting,
but unless you're moving the focus pot, the output is DC. The only "load"
the circuit sees would be capacitive coupling of the VQ signal through the
CRTs focus lens. VQ is depicted as a fairly sharp square wave with a ~50V
swing on a 3us period (in my 2465 service manual), but I don't have a feel
for the capacitance of a focus lens. Can't be much, though?






Re: How to clean Helitrim potentiometers?

Stephen Hanselman
 

Ooops sorry I read pots to mean trim pots. Still if you can replace them they will never be as stable after cleaning as new.

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Oct 15, 2020, at 09:40, Stephen Hanselman <kc4sw.io@kc4sw.com> wrote:

Replace them, they are fairly cheap, easy to change, and not noisy. Besides you could change a 10 turn into a 25 turn and make the adjustments way less twitchy.

We have seen a significant improvement in unit stability by replacing pots in the Valhalla electronic resistors we work on.

Regards,

Stephen Hanselman
Datagate Systems, LLC
On Oct 15, 2020, at 08:47, Alexandre Souza <alexandre.tabajara@gmail.com> wrote:

Greetz All!

My FG503 got dirty pots. I need to clean it, but they seem to be sealed. Is there any technique to clean these pots?

Thanks
Alexandre


--
---8<---Corte Aqui---8<---
https://www.tabalabs.com.br
https://tabajara-labs.blogspot.com








Re: How to clean Helitrim potentiometers?

Stephen Hanselman
 

Replace them, they are fairly cheap, easy to change, and not noisy. Besides you could change a 10 turn into a 25 turn and make the adjustments way less twitchy.

We have seen a significant improvement in unit stability by replacing pots in the Valhalla electronic resistors we work on.

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Oct 15, 2020, at 08:47, Alexandre Souza <alexandre.tabajara@gmail.com> wrote:

Greetz All!

My FG503 got dirty pots. I need to clean it, but they seem to be sealed. Is there any technique to clean these pots?

Thanks
Alexandre


--
---8<---Corte Aqui---8<---
https://www.tabalabs.com.br
https://tabajara-labs.blogspot.com





Re: How to clean Helitrim potentiometers?

Colin Herbert
 

Hi Alexandre,
You could try squirting some Deoxit or Servisol into the pots via gaps near the connectors. You might get lucky and enough goes in to do the job. You need to turn the pot from end to end when you do this, of course. If that doesn't solve the problem, it is worth trying a couple of times, providing that you can see that the cleaner _might_ get inside. Otherwise, I think someone has managed to remove the four "rivets" that hold the metal cover on the back to gain access to the insides. If that is possible, then I suspect that getting some cleaner in there will be easier, but the problem of how to re-seal the pots has to be solved. Good Luck.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Alexandre Souza
Sent: 15 October 2020 16:47
To: TekScopes@groups.io
Subject: [TekScopes] How to clean Helitrim potentiometers?

Greetz All!

My FG503 got dirty pots. I need to clean it, but they seem to be sealed.
Is there any technique to clean these pots?

Thanks
Alexandre


--
---8<---Corte Aqui---8<---
https://www.tabalabs.com.br
https://tabajara-labs.blogspot.com


Re: How to clean Helitrim potentiometers?

Stephen
 

Hi,

What personally do, and it works fine for me, is I remove the knobs, and let isopropyl alcohol drip inside the pot from the front, between the shaft and the casing. And I keep turning and turning.
This method works great for me on all sealed pots.

Hope this helps.


How to clean Helitrim potentiometers?

Alexandre Souza
 

Greetz All!

My FG503 got dirty pots. I need to clean it, but they seem to be sealed. Is there any technique to clean these pots?

Thanks
Alexandre


--
---8<---Corte Aqui---8<---
https://www.tabalabs.com.br
https://tabajara-labs.blogspot.com


Re: Tektronix 2465A noise on readout

Lawrance A. Schneider
 

On Wed, Oct 14, 2020 at 11:06 AM, Gregor wrote:


Hi larry,

That's a good idea!
Thank you!

larry


Re: Air filters for big 500 series scopes

Grayson Evans
 

Since I posted, I've done more searching, and yes, there are several companies that sell the aluminum filters, mostly for cooking exhaust fans. I had not thought about coating the filter with anything. I have another 547 with the original filter. It doesn't seem to be coated with anything, but it's very old.
Never considered PAM. I was thinking a light spray of WD40, but probably will try it dry and see how well it works.
Thanks for the tips!


Re: Tek 4654M; No Trace, No +5V, No +95V; Help

Simon
 

Check this capacitor C582, but since you have disconnected the HT from the secondary of T550, I would concentrate on the primary circuit and find out whether the oscillator constituted by Q552 and Q556 is working. Ideally you need a scope for this.
Simon


Re: 516 Triggering not working

Tom Lee
 

Hi Mark,

Of the things that tend to be overlooked when debugging VT circuits, the level-shifting neon bulb surely ranks high (here, that's B167). If the bulb no longer fires, the loop breaks and the sweep stops sweeping. It's easy to check, so be sure to include that among the things to look at, if you haven't already. And while you're in that neighborhood, check R167. If it's a carbon comp (and I think it is), it could have drifted upward in value to the point where it's a near open. That would have the same effect as a bad B167.

--Cheers,
Tom


--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/14/2020 14:34, Mark Vincent wrote:
I have been working on the circuit for a week after the 27mmfd to the Sweep
Gating Multivibrator and Hold-Off Circuit with no success. All I get now is
a spot, no horiz. line. The part before the 27mmfd condenser, C44, works
and was adjusted so signals will trigger on the plate side. Lifting the
"hot" side or a signal into the Ext. Trig. post will not start the
sweeping. There is zero output unless R114, R184 and R185 are unsoldered.
Using the cal. voltage output of another scope up to 100V made no
difference. Output was zero with the resistors soldered in. This is with
the scope on or off. Touching any of these resistors to its respective
point with them unsoldered will make the signal go to zero. The bias of
V135A and V185A is deep enough to cut these sections off. The valves are in
very good to like new condition and the resistors are 1% types. The power
supply voltages are right. The unit has been overhauled. This problem
suddenly came up. The diode across the 4700 ohm resistor is good and
another one did not make any difference. The hold-off caps are Orange
Drops. The timing cap is the original type. I did a resistance A-B with my
working 317. The resistances were the same. Reference was to the chassis.
Putting a signal in a vertical or horizontal input causes the spot to be
two spots with a thin dim trace in between them. I cannot figure out what
happened to cause the loss of triggering. I know this circuit is used in
other 300 and 500 series. Thanks.

Mark




Re: 516 Triggering not working

John Williams
 

Mark the first thing I always suspect is causing the problem is a tube. Rightly or wrongly. But is the easiest check to make. I turn out the lights (keep flashlight in hand) and look for a tube that is dark. Take each tube out of its socket and spray contact cleaner in the socket. I even clean the tube pins gently with a piece of sandpaper. I spent a week on a 541A that had the same symptoms as your scope. I finally resorted to wiggling each tube in the trigger circuit and I’ll be darned the thing stated to work. I also try cleaning the pots and switches. I know you no doubt have thought of a lot of this. It just takes time and patience. More of the old scopes have been scrapped for sweep problems than anything else, so please don’t give up.


Re: Tektronix 2465A noise on readout

Mark Vincent
 

Gregor,

I read somewhere online about R1853, R1854, R1871, R1872 and R1880 are prone to opening or going high causing focus problems. The originals are 1/4W. The suggested replacements should be 1W 1% types. Make sure these are the standard size, not the smaller size. Mouser has these. C1972 can also be a problem. The replacement should be a high temp, low ESR type. A heatsink on Q1981 likely should be added. I did these things and replaced other resistors and all the other condensers with higher capacitance. I added a ,047mfd condenser across the two ,022mfd in the half-wave doubler for the 300V supply for better filtering. A heatsink on U800 with good quality compound is recommended. The heatsinks are available online. I made one for mine. It is not pretty. It works well. The mounting tabs on the IC are NOT at ground.

Mark

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