Got a 1725a here that needs the vertical IC. It's designation is A5U2 and I THINK the part number is 5061-0024. The manual is a ****ty scan, but any other numbers I can get out of it are too off the wall, at least that number googles back to SOMETHING.

The Thing about this is that it is missing. Is it a high failure rate part ? Another question I have is if it fits any better scopes. I assume of course they would be HP, but why would someone take it out unless either it was bad, or they wanted it to use in another unit. If they used it in another unit, what would that be that would warrant effectively scrapping this one ? A higher end scope using the same part ?

OK, I could see in a business setting where it owuld not be feasible to replace the thing even with the same model because of anal regulations, but is that a reasonable assumption ? Also, if they fail that much, maybe I should be leary of a used one. I assume there are no new ones.

According to the print, this thing only has four transistors and a half dozen resitors in it. Think there is a possibility of some sort of retrofit ? Like building the equaivalent out of discrete parts ? Might not be absolutely perfect but the thing is useless now.

Either that or part it out. Are the other parts worth much ?

wrote in message
...
Got a 1725a here that needs the vertical IC. It's designation is A5U2 and I
THINK the part number is 5061-0024. The manual is a ****ty scan, but any
other numbers I can get out of it are too off the wall, at least that number
googles back to SOMETHING.

The Thing about this is that it is missing. Is it a high failure rate part ?
Another question I have is if it fits any better scopes. I assume of course
they would be HP, but why would someone take it out unless either it was
bad, or they wanted it to use in another unit. If they used it in another
unit, what would that be that would warrant effectively scrapping this one ?
A higher end scope using the same part ?

OK, I could see in a business setting where it owuld not be feasible to
replace the thing even with the same model because of anal regulations, but
is that a reasonable assumption ? Also, if they fail that much, maybe I
should be leary of a used one. I assume there are no new ones.

According to the print, this thing only has four transistors and a half
dozen resitors in it. Think there is a possibility of some sort of retrofit
? Like building the equaivalent out of discrete parts ? Might not be
absolutely perfect but the thing is useless now.

Either that or part it out. Are the other parts worth much ?

++++++++++++++++++++++++++++++++++++++++++++=


HP part number 5081-3024

Used also in the 1710B and the 1722B.

El 26/02/2014 7:05, escribió:
Got a 1725a here that needs the vertical IC. It's designation is A5U2
and I THINK the part number is 5061-0024. The manual is a ****ty
scan, but any other numbers I can get out of it are too off the wall,
at least that number googles back to SOMETHING.

The Thing about this is that it is missing. Is it a high failure rate
part ? Another question I have is if it fits any better scopes. I
assume of course they would be HP, but why would someone take it out
unless either it was bad, or they wanted it to use in another unit.
If they used it in another unit, what would that be that would
warrant effectively scrapping this one ? A higher end scope using the
same part ?

OK, I could see in a business setting where it owuld not be feasible
to replace the thing even with the same model because of anal
regulations, but is that a reasonable assumption ? Also, if they fail
that much, maybe I should be leary of a used one. I assume there are
no new ones.

According to the print, this thing only has four transistors and a
half dozen resitors in it. Think there is a possibility of some sort
of retrofit ? Like building the equaivalent out of discrete parts ?
Might not be absolutely perfect but the thing is useless now.

Either that or part it out. Are the other parts worth much ?


Here you have a retrofit; it makes me remember the "Back to the future
part III" time machine repair with 1955 components.

Schematic:

http://elektrotanya.com/files/forum/...eplacement.jpg

Forum (in hungarian):

http://elektrotanya.com/?q=hu/conten...szkop-javitasa

--
Saludos
Miguel Giménez

"HP part number 5081-3024

Used also in the 1710B and the 1722B. "

Thanks. Having the right part number helps no matter what. I notice both of those numbers are lower than 1725, should I assume then that the 1725 is the best of the "family" ? If that's the case, the mystery remains of why this one got the axe. Of course the thing might have just went bad, it does happen.

"Schematic:

http://elektrotanya.com/files/forum/...eplacement.jpg "

WOW ! Now that might just save the day. Thanks. I notice a dot RO in the picture there, does that mean Romania ? I've been told by some from across the pond that alot of parts are very hard to get, it's not like the US. They have had to become more resourceful as a result.

So it pretty much boils down to do this unless I can scare up a jubnker with the IC. This looks highly doable. the only thing now is the selection of the MOSFETs. Voltage, current and frequency response are obvious, the only question is gain.

It's obvious that the 1K resistors set the gain to some extent, but the highest gain possible is not always best in tis type of application. Or is it ? a thousand ohms isn't much, maybe the highest gain within reason would be best. If you want to make a suggestion I am highly suggestable. The main thing I know is to get devices that will work in the linear region. That will probably mean looking at some datasheets because most linear applications I've seen are either audio or video amps and neither of them are going to have the frequaency response for this. At least not necessarily. Also, surely the devices exist, it's just that I haven't seen them in the stuff I've worked on.

I actually thought of a retrofit myself, but I was going to stick more to the original, using bipolar. Of course that was not thiknking outside the box in a way - we only need this to do a certain thing, if FETs work, use them and make it easier. I would guess devices like that were not available when they built that unit, but they are now !

:-)

On 2/26/2014 9:34 AM, wrote:
"Schematic:

http://elektrotanya.com/files/forum/...eplacement.jpg "

WOW ! Now that might just save the day. Thanks. I notice a dot RO in the picture there, does that mean Romania ? I've been told by some from across the pond that alot of parts are very hard to get, it's not like the US. They have had to become more resourceful as a result.

So it pretty much boils down to do this unless I can scare up a jubnker with the IC. This looks highly doable. the only thing now is the selection of the MOSFETs. Voltage, current and frequency response are obvious, the only question is gain.

It's obvious that the 1K resistors set the gain to some extent, but the highest gain possible is not always best in tis type of application. Or is it ? a thousand ohms isn't much, maybe the highest gain within reason would be best. If you want to make a suggestion I am highly suggestable. The main thing I know is to get devices that will work in the linear region. That will probably mean looking at some datasheets because most linear applications I've seen are either audio or video amps and neither of them are going to have the frequaency response for this. At least not necessarily. Also, surely the devices exist, it's just that I haven't seen them in the stuff I've worked on.

I actually thought of a retrofit myself, but I was going to stick more to the original, using bipolar. Of course that was not thinking outside the box in a way - we only need this to do a certain thing, if FETs work, use them and make it easier. I would guess devices like that were not available when they built that unit, but they are now !

:-)

Have you ask for a quote from the 100+ companies that won't give you
a price online.
I found a couple of others looking to replace the same ic in the same
scope. You might be better off building it yourself, for reliability.
Mikek

" Have you ask for a quote from the 100+ companies that won't give you
a price online. "

You mean the ones you send your email address to and if they ever come up with one you have to buy 100,000 of them ? No, I didn't bother doing that.

" I found a couple of others looking to replace the same ic in the same
scope. You might be better off building it yourself, for reliability. "

Not a bad idea really. Any one I get now would be used. The problem now is finding the right MOSFETs. I bet recalibrating it will be loads of fun. Actually it might not be all that bad. The HF response will probably be better if anything. I might have to remove some of the peaking caps or something if they won't adjust down enough. Then if the gain is really up there of course then I might need to change some resistors. They got the internal 50 ohm changeed to a 47, but that won't mean **** to differential mode. I hope the static plate voltages come close enough ! Then comes getting the thing straight.

OK, at this point I am wondering just what kind of FETs to use for this thing. I'm sure y'all are alot more familiar with what kind of MOSFETS are out there than I am. Some of youse iz real injunears, I am just a half decent hack. As such I am not all that familiar with what is available.

Max limits are pretty obvious and not taxing. Just with some quick mental math I see Pd as being easy, maybe 3 W if that. Max Id is not even an ampere and Vds about 100 V. The problem is getting the frequency response. Even the gain should not be all that critical because there is a 1 K resistor from gate to drain. The problem is that offhand I just don't know of an otherwise suitable MOSFET for use up to 275 Mhz. Even a video output in a high end CRT monitor would not handle it I think.

Because of the massive level of feedback, maybe I could get away with a 100 or 150 Mhz device no ? I doubt it would be a good idea to go below 150 Mhz here, in fact I would like to have 300 Mhz.

So what will amplify that high linearly ? I think a TO 220 case would be nice, in fact a plastic TO 220 would be alot better as I won't have to insulate the tabs and there would be less radiation. Altogether much more desirable I would say.

I haven't had much luck at Digikey. I select my parameters and mostly the thing comes back with no matches. I really want TO 220 plastic but when I dropped that from the parameters I got some in a funky RF type cass, round but with a football kinda shaped clamp like portion. I would really rather not use that case style, especially if the drain is internally tied to the case. It just looks like a PITA and/or it might make a bit too good of an antenna. Probably intended for grounded drain operation or perhaps to run in a metal box. I dunno, I just prefer a plastic TO 220 type, unless someone around here has a better idea.

Another thing I haven't done in a very long time, and don't even know if you can anymore, is to call a manufacturer and talk to one of their reps about it and maybe even get them to send me a couple of free samples. Do they even do that anymore ?

Of course I have no qualms about paying for them, but then again I don't need 5 KW transmitter finals either here. It's a nice scope but not that nice..

Any suggestions ? I am in a quite suggestable mood here.

Thank you.

On 3/4/2014 9:15 AM, wrote:
OK, at this point I am wondering just what kind of FETs to use for this thing. I'm sure y'all are alot more familiar with what kind of MOSFETS are out there than I am. Some of youse iz real injunears, I am just a half decent hack. As such I am not all that familiar with what is available.

Max limits are pretty obvious and not taxing. Just with some quick mental math I see Pd as being easy, maybe 3 W if that. Max Id is not even an ampere and Vds about 100 V. The problem is getting the frequency response. Even the gain should not be all that critical because there is a 1 K resistor from gate to drain. The problem is that offhand I just don't know of an otherwise suitable MOSFET for use up to 275 Mhz. Even a video output in a high end CRT monitor would not handle it I think.

Because of the massive level of feedback, maybe I could get away with a 100 or 150 Mhz device no ? I doubt it would be a good idea to go below 150 Mhz here, in fact I would like to have 300 Mhz.

So what will amplify that high linearly ? I think a TO 220 case would be nice, in fact a plastic TO 220 would be alot better as I won't have to insulate the tabs and there would be less radiation. Altogether much more desirable I would say.

I haven't had much luck at Digikey. I select my parameters and mostly the thing comes back with no matches. I really want TO 220 plastic but when I dropped that from the parameters I got some in a funky RF type cass, round but with a football kinda shaped clamp like portion. I would really rather not use that case style, especially if the drain is internally tied to the case. It just looks like a PITA and/or it might make a bit too good of an antenna. Probably intended for grounded drain operation or perhaps to run in a metal box. I dunno, I just prefer a plastic TO 220 type, unless someone around here has a better idea.

Another thing I haven't done in a very long time, and don't even know if you can anymore, is to call a manufacturer and talk to one of their reps about it and maybe even get them to send me a couple of free samples. Do they even do that anymore ?

Of course I have no qualms about paying for them, but then again I don't need 5 KW transmitter finals either here. It's a nice scope but not that nice.

Any suggestions ? I am in a quite suggestable mood here.

Thank you.




I can't seem to get a post to the newsgroup this morning.


I think posting is working now, here goes!



Check this,


https://groups.yahoo.com/neo/groups/...s/topics/24109

2pcs MOS-FETs(D16NE) and 3pcs resistors
which I soldered on a FR4 small board.

You might send him a letter, he is asking about his frequency response.

About 8 pictures down is schematic drawing, (shows internal IC parts),
note: a possible bad resistor.

http://www.amplifier.cd/Test_Equipme...her/1725A.html

This guy did a lot of work on his.

I suspect you have the schematic, but here it is,
http://elektrotanya.com/files/forum/2013/07/Y_amp.pdf




Mikek

Yahoo Groups own't load on this thing. I also have a certain measure of disdain for Yahoo anything.

On 3/4/2014 11:17 PM, wrote:
Yahoo Groups own't load on this thing. I also have a certain measure of disdain for Yahoo anything.


Well there is enough info there to get the scope working, without
looking at Yahoo.
The suggested D16NE FET is obsolete. Mouser suggests a
512-HUF75307D3ST, which they then say it is obsolete.
These are high current devices, Are deflection plates
low impedance? I thought they would be high impedance high
voltage devices.
If you can't get or don't like these two devices, try looking at other
scopes and see if you can find a drive the uses discretes and try their
FET/transistor.
What is the bandwidth of the scope?
Mikek

"The suggested D16NE FET is obsolete. Mouser suggests a
512-HUF75307D3ST, which they then say it is obsolet"

Thanks, at least I have somewhere to start. I can just look for the spec sheets on those. I finally did start getting some results on Digikey's selector guide. I guess on soem things it's better to just aplly one filter at a time.

"These are high current devices, Are deflection plates
low impedance? I thought they would be high impedance high
voltage devices. "

As far as I know deflection plates are very high impedance like a control grid, though they migh pick up a chargee due to their placement in the envelope. They do have capacitance though, so at 275 Mhz (the rated -3Db point of this scope) they could concievably impose some load. As far as DC is concerned, the load resistors are IIRC like 160 ohms coing out of 53 volts which is only about 34 mA. I believe the engineers probably chose tthe 160 ohm value becaause it would make the interelectrode capacitance negligible at the highest operating frequency. This makes the compensation less of a PITA. there is no other reason to use such a low resistance.

I also notice that on this unit, the current from the load rresistors is passed through two terminals for the deflection plates. In fact it shows it actually going through the plates, lke it is not just two pins, it is the two ends of each plate. Not sure exactly what they're getting out of doing that but it doesn't bother me. Of course it must make some difference at 275 Mhz.

This is probably one of the faster non storage CROs out there. In digital they can just digitize the waveform and display it at a rate a cheaper deflection system and amps can handle. Not in this baby, what you see is really what you got. Really, once you get through all the hurdles to get flat bandwidth up to that point, I think some RAM and a processor would be cheaper, but of course not when that thing was built.

Thanks. Later today I am off to look at a few datasheets.

Hmmm, the std16ne10 says something about 2100 pF. Seems a bit high.

On 3/5/2014 12:17 PM, wrote:
Hmmm, the std16ne10 says something about 2100 pF. Seems a bit high.


This all a little confusing to me. The suggested mod uses high current
FETs (12 or 15 amp). Just doesn't seem correct.
Looking at the schematic it shows 165 ohms in series with each plate,
with a B+ of 53V, the current would be limited to 320ma.

Here's a schematic I found that makes more sense regarding high voltage
low current..
http://michaelgellis.tripod.com/scope/vert.html

Mikek

"The suggested mod uses high current
FETs (12 or 15 amp). Just doesn't seem correct.
Looking at the schematic it shows 165 ohms in series with each plate,
with a B+ of 53V, the current would be limited to 320ma. "

Correct. Actually there is nothing really "in series" with the plates. They operate electrostatically, the only load they impose is capacitive. the way they have it congigured is apparently they have electrodes at each end of the plates, for whatever reason. I do not see much advantage in it. the plates are not all that large, and 270 Mhz's wavelength is about 1 meter.

The schematic to which you linked is not what this thing uses. It already has pushpull drive coming in. The transistors that drive it have their bases directly connected and the emitters are fed. Maybe, MAYBE the chip only puts out a single ended signal, but I really doubt it. Even looking back to the delay line, which is literally a roll of coax, it isa actually to rolls of coax. That would seem to indicate the signal is already fully diffeential at that point.

However people there and at places like tektronix are anal like that. Of course they have their reasons, some of them have to do with rejecting interference, and some of them have to do with avoiding the generation of interference.

I just thought 2100 pF was a bit much, but then across a 1K resistor and feeding a 160 or so ohm resistor, it is not all that bad.

Incidentally, that schematic in your link makes a mistake that is one of my pet peeves. the fact is that it is incorrect to call a phase inersion 180 degrees out of phase. A phase shift is when you delay something. If you delay a 1 Khz wave by ½ a mS, that is 180 out of phase. If you send it through an inverting amplifier it is inverted, not SHIFTED in phase. Delayed by 180 degrees and inverted are only the same on waveforms that are bidirectionally symmetrical, such as a sinbe wave, or a 50/50 duty cycly square wave or ene a pefect triangle wave. Only things like that which only contain odd order harmonics, it does not apply to any waveforms that are non-symmetrical BOTH WAYS.

But I didn't come to rant about that. The point is that in most scopes, the phase splitter doe not work like that, which is like ones in old tube audio amps, but not even all of them. Some of them actually used a tube that was high gain and configured about like an inverting OPAMP. Two equal resistors, the junction of which is at the grid of the invertor stage resulting in unity gain. Most scope amps don't even do that, they just make either the emitters or bases of a pair of transitors common and feed one of the elemant while bypassing the other. this causes it to invert, and after a coule of stages of the the CMR is high enough. (common mode reduction, not rejection ratio)

If you have good enough transistors, one stage does it well enough, but in these instruments, after the first phase splitter, ALL stages are differential and they ALL have some CMRR. It all adds up, and you get a perfectly balanced signal.

Interestingly, they think this has been reinvented with the way the signal gets to the display on some TVs now, called LVDS. The same scheme is used in the USB, HDMI, firewire and other signal transmission methods.

It is about the same as the old twinlead anrenna wire back in the old days, just refined. It doesn't radiate alot and it rejects noise. by keeping the signal perfectly balanced and at a low lever, capacitive effects of the transmission line are also minimized allowing for greater bandwidth.

But it is still a rehash of the **** that came out befor eI was born, and that was 1960. Circuit boards and IC were still forthcoming back then.

So they haven't really invented much, they have just refined it some. boils down to, for one, you are right, the current needed is not that high, but then if it happens to have the good rating then it does. I guess it will not blow as easily. I found that in Digikey's selector guide. They are talking 12 and 16 amps, I don't need anything like that even if there is a friggin capacitor across those plates. thing is I was looking at TO220 type cases because I believe they will make it alot easier to build the thing. there is only so much room for mounting and I don't want to leave them hanging by their leads which might only be .040" in diameter, and then maybe use silicone to keep things from shorting out.

Anyway, back to the drawing board on finding a MOSFET. One thing I do have to do is ggo to Electronic ****house (ESI in Mentor). REALLY, I mean no disrespect calling them that, my Uncle came up with the name. He used to go there every Saturday for quite some time. That is a long story. His kids (my cousins) built their own stereos.

Anyway, I tried to go to their site and it was down at the time. I will try again and see. Since the scope is old enough for a military pension, maybe the parts shouls be older as well. However the MOSFETS will not be as opld beecause they did not exist then.

You know how I know that ? Because HP would have used them ! lol. Those engineers have no clue of costing, they are trained that way. If the thing costs ten grand, so what ?

OK, enough chit chat for now. I am offf to do something. No idear what but........

"hanging by their leads which might only be .040" in diameter, "

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

LOL

wrote in message
...
"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.

2) The circuit is not driving the deflection plates directly. They are
driving a delay line with taps that connect to the deflection plates. This
is so the deflection signal follows, in time, the electron beam as it moves
through the deflection plate assembly.

3) HP really spent a lot of time in getting the whole system to work
correctly. Making changes that try to second guess what was done may lead
you down a rabbit hole.


Good luck with getting it to work. They really are a nice scope when right.


Regards
tm

On 3/5/2014 5:42 PM, wrote:
"The suggested mod uses high current
FETs (12 or 15 amp). Just doesn't seem correct.
Looking at the schematic it shows 165 ohms in series with each plate,
with a B+ of 53V, the current would be limited to 320ma. "

Correct. Actually there is nothing really "in series" with the plates.

Are you sure?

I have HP1725A schematics from two different sites and both have a 165
ohm resistors in series with each plate. Then I find another 50 ohms in
series with the transistor emitters (the ones in your defective IC)



They operate electrostatically, the only load they impose is capacitive.

The way they have it configured is apparently they have electrodes at
each end of the plates, for whatever reason.

One electrode goes to the transistor that pulls it low, the other
electrode goes to the 165ohm resistor that is tied to +53V.
Yes it is push/pull.

Post a schematic or something to convince me the schematic I have is
not correct.

btw, the 165 ohm resistors seem to reside on their own board (A5A1)
all by them selves.


Mikek

PS. I have seen some owners raving about their HP1725A scopes.

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

wrote in message
...
"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

"amdx" wrote in message
...
On 3/5/2014 6:26 PM, Tom Miller wrote:

wrote in message
...
"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



No, the delay line for the deflection plates is inside the tube, parallel to
the segmented plates. Its purpose is to align the instantaneous deflection
voltage with the moving electron beam. Just for the learning experience why
don't you calculate the speed of the beam as it passes from the beginning to
the end of the vertical deflection plates. remember it is in a vacuum i.e.
ideal.

The delay line you speak of is usually a coil of coax and does exactly what
you said. It lets you see the beginning of an event after the trigger.

The schematic is correct.

tm

On 3/5/2014 10:38 PM, Tom Miller wrote:

"amdx" wrote in message
...
On 3/5/2014 6:26 PM, Tom Miller wrote:

wrote in message
...
"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



No, the delay line for the deflection plates is inside the tube,
parallel to the segmented plates. Its purpose is to align the
instantaneous deflection voltage with the moving electron beam. Just for
the learning experience why don't you calculate the speed of the beam as
it passes from the beginning to the end of the vertical deflection
plates. remember it is in a vacuum i.e. ideal.

The delay line you speak of is usually a coil of coax and does exactly
what you said. It lets you see the beginning of an event after the trigger.

The schematic is correct.

tm

He has not said that he sees the 165ohm resistors-- yet. Once he does,
then I'll feel more confident that I have the schematic of his circuit.
I'll also remind him to check for the open resistor (R26) to the -15
volt line, I saw someone had that defect.
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 **** 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.

On 3/6/2014 3:58 AM, 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 **** 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.

On 3/7/2014 9:39 AM, amdx wrote:
On 3/6/2014 3:58 AM, wrote:

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

http://www.amplifier.cd/Test_Equipme...her/1725A.html

Mikek

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.

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

"Michael Black" wrote in message
xample.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).