HP IC, Unobtanium ?

[amdx]

On 3/5/2014 6:26 PM, Tom Miller wrote:

jurb6006@gmail.com> wrote in message
news:7b3a4d23-cddc-4a28-8a24-1537af30e67d@googlegroups.com...
"hanging by their leads which might only be .040" in diameter, "

HAHA.. what a mistake. Really, forty thousandths ? Try more like
fourteen...

LOL

Just a few comments:

1) The original circuit used bipolar NPN transistors in the hybrid. You
might consider using some high voltage video driver transistors for your
design.

That works for me.

2) The circuit is not driving the deflection plates directly. They are
driving a delay line with taps that connect to the deflection plates.

Only going by what I see on the schematic*, but the delay line are
back two stages before the plates.

This is so the deflection signal follows, in time, the electron beam as
it moves through the deflection plate assembly.

My thinking is the delay allows you to see the triggering event,
but it is a wag on my part.



*The OP has intimated that my schematic is not correct, but I want
him to
reinforce that, as of now I'm going with, it is correct.
Mikek

 

I can't believe this.

the terminsals for the deflection plates are dual. The deflection plates run on voltage, not current. The 165 ohm resistors are simply pulling the output up to the +53 volt supply. The fact that HP decided to put the 165 ohm resistors on the other connections to the deflection plates is irrelevant as far as I can see, the only reasons are quite esoteric and beyond the scope of this discussion obviously.

If you are trying to claim thet this CRT uses some form of electromagnetic deflection rsather than electrosstatic, state your case. I can't say it is not true for sure. I said I do not know why they used the two connections per deflection plate, because as a rule they do operate electrostatically. If this CRT works on a different principle, say so.

I believe this arraingement with the plates its mainly to reduce and/or reject EMI. Either that or to eliminate or use standing waves in the plates themselves, which I find unlikely because they are too small.

I could be wrong, but I understand how this shit works, until I don't. Claim it works other than electrostatically or don't. If I am wrong, fine, but until themn it is a voltage amplifier only. It only has to overcome the capacitance of the load, which is the deflection plates. The low resistance 165 ohms iss to provide a low output impedance to this effect.

If I am wrong, explain. tell me the differnce between tis and most other eletrostaically dflected CRTs.

 

[amdx]

On 3/6/2014 3:58 AM, jurb6006@gmail.com wrote:

I can't believe this.

the terminals for the deflection plates are dual. The deflection plates run on voltage, not current.

The 165 ohm resistors are simply pulling the output up to the +53 volt supply.

We are now on the same page.

The fact that HP decided to

put the 165 ohm resistors on the other connections to the deflection plates is irrelevant as far as I can see,

the only reasons are quite esoteric and beyond the scope of this discussion obviously.

It is what it is.

If you are trying to claim that this CRT uses some form of electromagnetic deflection rather than electrostatic,

state your case.

I don't have a case, I'm just looking at the schematic. I don't think
it is electromagnetic, I don't think that would be fast enough. Hmm, can
you do an inductance test? A resistance test will be near zero ohms
whether it is a plate or a coil.
It is still all confusing because of the mod that we know, it uses
high current devices. But that seems wrong when you see the 165 ohms in
series with the deflection (plate).

I can't say it is not true for sure. I said I do not know why they used
the two connections per

>deflection plate, because as a rule they do operate electrostatically. If this CRT works on a different principle, say so.

I'm as confused as you. The label says Plate, the drawing is a coil.
And, why is the voltage labeled +53.3VF?

I believe this arrangement with the plates its mainly to reduce and/or reject EMI. Either that or to eliminate or use

standing waves in the plates themselves, which I find unlikely because they are too small.

I could be wrong, but I understand how this shit works, until I don't. Claim it works other than electrostatically or don't.

If I am wrong, fine, but until then it is a voltage amplifier only. It only has to overcome the capacitance of the load,

which is the deflection plates. The low resistance 165 ohms is to provide a low output impedance to this effect.

If I am wrong, explain. tell me the difference between this and most other eletrostatically deflected CRTs.

I don't know.

A question for you, assume for a moment it is electrostatic, I would
think only one plate is energized at a time. There is no negative drive
for the other plate, to drive the beam the plates would need to have
opposite polarity OR only one plate is driven at a time. (I think only
one plate is driven at a time)
If it was electromagnetic, then the leads could reversed on one coil
to develop the opposite drive.
Do you have another dual trace scope to look at the drive to the
defective IC? Pin 7 and Pin 5. I don't know, you might need to open the
circuit to the defective IC. Also have you checked that R26 (31.6 ohm)
resistor? I see at least one person had that problem.
Mikek
PS. see if you can find waveforms on a schematic, might save you from
checking it with your scope.

 

[amdx]

On 3/7/2014 9:39 AM, amdx wrote:
> On 3/6/2014 3:58 AM, jurb6006@gmail.com wrote:

Here's the page with the defective resistor, page down to find it.

> http://www.amplifier.cd/Test_Equipment/Hewlett_Packard/HP_other/1725A.html

Mikek

 

[William Sommerwerck]

One way to determine whether the 'scope uses magnetic or electrostatic
deflection is to look at the specs. They'll probably indicate the deflection
type.

If not, look at the bandwidth. It's unlikely a magnetically deflected 'scope
would have a bandwidth much greater than 100kHz.

 

[Michael Black]

On Fri, 7 Mar 2014, William Sommerwerck wrote:

One way to determine whether the 'scope uses magnetic or electrostatic
deflection is to look at the specs. They'll probably indicate the deflection
type.

If not, look at the bandwidth. It's unlikely a magnetically deflected 'scope
would have a bandwidth much greater than 100kHz.

You mean like those plans in the back of the magazine to convert a tv set
to an oscilliscope?

Yes, that's definitely going to put a limit on bandwidth.

The concept did work if you wanted some large screens to display lisajous
patterns or something more deliberate in the way of visual organs, but
fairly useless as test equipment.

Or, there was that project in Ham Radio circa 1973 or so, where someone
turned a tv set into an oscilliscope, and then used it to show various ham
bands visually. In essence a pandaptor that displayed five bands at the
same time.

Michael

 

[William Sommerwerck]

"Michael Black" wrote in message
news:alpine.LNX.2.02.1403071341450.1151@darkstar.example.org...
On Fri, 7 Mar 2014, William Sommerwerck wrote:

One way to determine whether the 'scope uses magnetic or electrostatic
deflection is to look at the specs. They'll probably indicate the
deflection type.

If not, look at the bandwidth. It's unlikely a magnetically deflected
'scope would have a bandwidth much greater than 100kHz.

You mean like those plans in the back of the magazine to convert a TV set to
an oscilliscope?

No. I remember commercial magnetically deflected oscilloscopes. I think HP
made one. But don't hold me to that. I think their purpose was (as you
suggest) to get a large display not possible with electrostatic deflection
(which would have required extremely high deflection voltages).