开云体育

(continued) typo, C4399 is at the +15V rail.

Hi Tomas,

Since I was just curious what my 7704A would show I took off the upper side panels, attached probes and switched on the 7704A. A big very bright dot illuminated the center of the screen. At the same time smoke whirled up somewhere from the Hor Amp board! In hindsight I was glad that this happened with panels removed. A tantalum cap (C4399 at the +12V rail) was still hot. Replaced the cap and the scope was fine again.
I found no sign of 25 kHz ripple at TP41120 or in trace Intensity.
But I realized now that you monitored the TP via a plugin in your 7704A. What you see then is only the TP voltage when the sweep is running. You mis the voltage between sweeps (retrace etc.) since the CRT is blanked then. So you probably didn't notice that your plugin gets terribly overdriven by the TP signal. You discerned 2 mV ripple while the TP level varies a few volts between blanked and unblanked state! I think the ripple might be very well due to crosstalk with the plugin which is used to pickup the 25 kHz HV signal.
I started the same way but I new in advance that I should not increase the sensitivity that far. I repeated this with signal displayed at an other scope, only to be sure that both TP levels where in the dynamic input range of the external scope.
I must say that I had expected a larger 25 kHz signal from the 10X probe tip in the neighborhood of the HV box. Amplitude 50 mV or so at distance 1 cm from HV cable out location. But enough for stable triggering.

Albert

Hi all,

Hi Tom,
I tested for temperature this afternoon again, after I performed a full calibration on the scope.
So, the scope had been running for several hours when I did this measurement.
I used a 80-TK Fluke surface temperature probe, holding it flush with the small heatsink just next to the FET, that was the hottest spot I found.
At that point in time the scope was just running with both traces visible, where trace A was showing the "calibration" signal.

Hello Ed,
in the end I consider my modification of the PS minimal, I used a lower ON-resistance FET (better, but maybe a slightly higher "switch-on" current?), and I reduced the Gate series resistor, where Tek in some models removed it even completely. (maybe the faster current pulse is not filtered as it should be, so maybe some may be injected into the grid?)
In my humble opinion is adding a fan also in the category minimal, again, because Tek used several FAN configurations in basically the same Power Supply.

Hola Vincent,
I think even the 2-or 3-wire PC fans have electronics inside.
Usually these fans are brushless, so they need some form of rotating magnetic field, and this is generated by a cheap and simple oscillator and coil driving circuit.
Some information can be found here:

I added some pictures of the temperature taking in the album: /g/TekScopes/album?id=64919

Un saludo,

Leo

For as long as I have been a member of TekScopes there are two things I have
heard regularly from our members outside the US: It costs too much to ship
classic Tek scopes outside the US and they ae too expensive because there
aren't enough of them.



Someone recently asked me: "If I had access to an almost unlimited supply of
classic Tek scopes at no cost what would I do with them"? I answered
immediately: "I would find a way to send them around the world to TekScopes
members who care about these instruments".



What if there was a way to do this?. What I need from our entire membership
is to figure out a way to make this happen. I have an idea at my end for how
I can make this happen, but I don't have a very good idea what would work at
the other (overseas) end. Here is what I would do at my end:



To ship overseas at a reasonable cost the scopes and plugins must be sent at
the cheapest rates possible. This would be via ship in containers that could
hold at least a dozen or more scopes. The wooden shipping crates would have
to be all the same size to keep the costs to a minimum. My wild guess is it
will be somewhere between 3 and 6 cubic meters. Each crate will be filled
with a random assortment of classic scopes. There will be no choosing. This
is essential because the volunteer manpower to fill the crates must be kept
to a minimum.



Next thing to figure out is who in each country or region the crate(s) will
be sent to. We have members around the world but someone will have to
volunteer to either pick up the crate when it arrives or have it delivered
to their location. Once in their country they will have to have a way to
distribute the scopes to the other members in their country or region. I
don't have any idea how that will work. You will have to figure out this
part.



For each country or region if we have standard size containers the shipping
weight can be estimated in advance, the crating charges will be known, and
based on where it is going I can find out what the total charges will be. By
that point I will know how many scopes will be in a crate and the person
receiving the crate will have collected a proportional contribution from
each person getting a scope or scopes. At that point the person who stepped
forward to be the recipient in their country or region will send a payment
to the freight forwarder (or to me to pass along to the freight forwarder)
and the crate will be picked up by the freight forwarder and on its way. For
customs purposes the declared value will be $0.00 for each scope if that is
acceptable.



The members in each country will have to decide how they divide up the
scopes, how they each pay for their share of the costs, and how the scopes
will be delivered to them from whoever receives them on behalf of their
group. The scopes will be free but there will be no choice in what you get.
About all I know at this point is they will be mainly 1960 to 1970 era Tek
scopes. They will be in good physical condition and complete but I cannot
say if they will actually work when you receive them. Unfortunately I have
no resources to do more than put scopes in crates. They will be repairable
however as are any Tek scopes of that era.



THE MOST IMPORTANT PART:

I am swamped with running the TekScopes Forum as it is. I have a ton of
other things I am doing, I have a friend who is terminally ill. So please do
not contact me. PLEASE figure out how to make this work at your end. Do it
among yourselves and do it OFF LINE so this doesn't clog up the forum. I
suggest you contact the members you know are in your country or region and
assign one of you to be the focus as you try to work out details for your
region. When you have a plan that is workable and someone has stepped
forward to take charge for their countrymen and who will handle the shipping
charges and distribution of scopes then let me know and I will figure out
and I will work with that person to figure out the next steps from my end.



I DO NOT KNOW OF ANY ORGANIZATION WHO HAS TRIED SOMETHING LIKE THIS BUT IT
WILL BE AMAZING IF WE CAN DO IT!!



Dennis Tillman W7PF

Be careful when making changes to the operating characteristics of the switching parts of a SMPS. Faster tr and tf can improve efficiency, but can aggravate PS noise and cause EMC issues.

Ed

Hi Leo,
Could you give me the conditions under which you tested your Q9070 FET for the temperature, so I can get you an accurate temperature number to compare to a working 2215A here?
The recent discussion about adding fans to the lower 22xx models renewed my interest in this subject, so I collected some fan circuits they used in the various higher 22xx models and posted them to your photo album at:
/g/TekScopes/album?id=64919
(When? say 22xx, I mean just the smaller ones and not the larger models like the 2245, 2246, 2247, 2252 and their variations, which are a very different design)
This week I added that normal fan circuit to a 2215A using the traces on the mainboard and a 0.12 Amp 60mm fan. The voltage driving the fan was 8.13 VDC from the half wave supply using 1000 uF for C965, 3 Ohms for R965 and an ultra fast HER106 diode for CR965. The fan current was 54 mA in this configuration.
Then I added another identical diode between pin 22 of the transformer and the junction of CR 965 and R965 to see what kind of fan voltage improvement was available. The fan voltage was now 8.47 VDC and the fan noise was up slightly, but still quiet enough. I also thought about the folks who have the 2215 (and other) scopes or test gear which do not have the unused fan circuit traces on their mainboards, and wondered if they could simply add this same simple fan circuit. I posted a scan of the 2215's 8.6 volt supply schematic in your photo album that we could look at. It looks to me that it would be worth trying to add a fan directly to either the plus or minus filtered output to see if the theft of a small amount of fan current could be tolerated, using ground for the other fan connection. Also a small piece of perforated prototype board would hold the few components required to filter any other voltage you might steal off of any transformer secondaries to create a fan supply.
I saw that 'minimum fan voltage' was being discussed again this morning, my experience is that almost any fan you buy will start and run reliably at the 8 volts this half wave 2215A fan circuit provides.
tom jobe...

Here is the Type 60 / 2A60 Instrument Reference Book:

Hi Leo,

Thanks for your feedback / experiments :-)

About the fan, easiest is to use a simple fan without any electronics in it to begin with ;-)
A standard two wire fan, or a 3 wire fan where you just don't use the third wire. It's not required usually, just a tach output for an eventual external speed controller when the instrument has one, not here then.

As for minimum voltage required to get it going, it should all be indicated in the data sheet for this particular fan. A 12V fan should have no trouble starting at 9V, if I believe the experiments I ran on a few different 60mm 12V fans when I was searching for a replacement fan for my 2232. You will have to experiments of course, but from memory 9V was a sweet spot where the fan would be very quiet yet still manage to achieve useful airflow. Of course would depend on every particular fan, but it gives you an idea...



Regards,


Vincent Trouilliez

Hi all,

here is my follow up on the FET replacement in my 2215A, and the adding of an optional fan.

Using a P9NK70ZFP (the working one I started with) gave a FET housing temperature of 68 degree Celsius;
Now I received the 6R280E6, that brought the temperature (only) down to 63 degree Celsius?

Based on the 10x lower ON-resistance, dissipation should have been way lower, but it clearly did not work this way...
I still didn't like this, so I looked a bit further.

I had a look at the different PS schematics of a 2232 and a 2235 and learned that in the 2232 they lowered R908 from 3k to 2k2, but the serial resistance R909 was still 39 Ohm;
In the 2235 however the kept R908 at 3k, but the completely removed R909 ?!?!

A quick calculation with an input capacitance of 3nF and a series resistor of 39 Ohm learned, that the rise (and fall) -times would be around 200ns, so even with the better FET that could explain the dissipation.
So at first I lowered R909 from 39 Ohm to 18 Ohm, (a second 39 Ohm in parallel), that lowered the FET's temperature to 58 degree Celsius.

Since I don't like having no serial resistance to the gate of the FET (it might start to oscillate?), I replaced the original R909 of 39 Ohm with a carbon resistor of 4,7 Ohm, and kept R908 at 3k.

I have the scope running for a while now, and the FET temperature has settled at around 54 degree Celsius, this is still without fan.

Since I have the place for both the components and the fan, I will put one in a soon as it arrives.
I will use the half-bridge rectifier circuit using the one diode, capacitor and resistor, this will give a 9V DC for the fan.
If the electronics inside the fan allow for this low voltage I will keep it at that, if not, I will add the second diode to raise the voltage to 12V

To be continued when the FAN arrives,

Un saludo,

Leo

Timothy,
The AFG 3252, for square waves, is spec'd for a time equal or less than 2.5ns, which is good enough to calibrate a 25MHz scope (which has a risetime of 14ns).
But it wouldn't cut it for a 100MHz scope.
As a possible alternate to the leveled sine wave generator, in sine wave mode the AFG may be (arguably) good enough to perform a frequency response check (sweep) up to - say - 100MHz... but this usually doesn't help in the calibration... it only serves to check the response.

AFGs rarely have very good square waves, both from a rise time and flatness of the levels, because their outputs must be tailored to fit a multitude of analog waveforms, which requires a linear, low distortion and relatively high power output amplifier, which often can only be achieved with feedback.
While feedback is good to ensure low distortion, the very fast square wave will always be accompanied by an overshoot and the spec for this overshoot is usually as big, or bigger than the maximum aberrations that you want to calibrate the scope for...

Fast pulse generator output stages are usually not linear, and never have feedback, so they can be very good at producing fast and flat square waves and, as Harvey mentioned, need almost no calibration to achieve that level of signal integrity.

Rgrds,

Fabio

I'm mostly curious how you determined if the wound coil was good without installing it inside the scope.

Or support for board?

Den tors 9 aug. 2018 18:40Jeff Urban <JURB6006@...> skrev:

On Tue, Aug 7, 2018 at 07:47 PM, Jim Olson wrote:

it is a bushing for one of the control shafts

The focus control perhaps ??? Maybe that's where I saw one.

On Thu, Aug 9, 2018 at 06:50 AM, nielsentelecom@... wrote:

I use an external power switch for my equipment

Fine and good but watch what you plug in together. ALot of iron can be dangerous. At first glance you think OK, inductors in parallel so less kick but that is not so. That means the total current ramps up faster.

The spike induced in device A is applied to device B.

I remember some of the later Sony TVs didn't have a thermistor or big inrush resistor, instead the uProcessor was fed the incoming AC and with a zero crossing detector triggered the relay coil at just the right time to have no huge current peak.

Actually why they didn't use a TRIAC is beyond me, maybe it is too reliable. If they care about spikes on the AC there are always DIACs or MOVs.

The zero crossing thing may be a trend because it is cheap and efficient. Ihaven't seen it in Tek scopes but some people use those Tek scopes to work on other things, so it is possible to run across one. If so, if the signal to the zero crossing detector is missing it looks like a dead uProcessor.

Getting it to turn off at zero crossing of course does no good, only at turn on. I would put a cap across the whole switched output. Actually a cap across the switch can send the inductive kick upline and to everything else electrically closeby. i think such caps should be across the inductance itself, e.g. the primary of the iron. But engineers care about what they're designing, not everything else.

I've been loosely following this topic with some interest. From a simple wear perspective, I use an external power switch for my equipment because of the older equipment I own and the difficulty of finding a replacement after the effort to replace the often used measurement cursors selector switch on my older Hitachi scope hybrid analog/digital model VC-6025A.

NielsenTelecom

I have the parts to build a winding machine if necessary. What did the test jig look like?

Morris?Can you get the info on wire size and turns required to rewind transform from your friend that did them , was thinking of trying to rewind my 547 and 556 in case my 556 hv went down , thanks .
On Thu, Aug 9, 2018 at 1:57 AM, Morris Odell<vilgotch@...> wrote: From bitter experience I can confirm that both HV transformers in the 556 are prone to the thermal runway problem that has been discussed here ad nauseam with regard to the 547 and some other scopes. T1301 produces the PDA accelerating voltage for the CRT so if it's not working you won't see any trace. The only cure is a replacement or rewound transformer. It is possible that a failed transformer could cause the oscillator tube to fail and that could be what you are seeing. I? had both transformers in my 556 rewound by a friend - not an easy task and one requiring many iterations on a test jig before acceptable results were obtained. The mechanical arrangement of those two HV boxes? makes working on them quite a challenge.

Sorry to be the bearer of bad news :-(

Morris

Jeff, the meaning of a suffix after the model name and of the Options is given in the catalogs.
For instance, catalog 1987 says a 2465A CT is a 2465A with Option 9 (GPIB) and Option 10 (Counter/Timer/Trigger, Word Recognizer) factory installed. Also Option 22 (2 probes included).

Albert

From bitter experience I can confirm that both HV transformers in the 556 are prone to the thermal runway problem that has been discussed here ad nauseam with regard to the 547 and some other scopes. T1301 produces the PDA accelerating voltage for the CRT so if it's not working you won't see any trace. The only cure is a replacement or rewound transformer. It is possible that a failed transformer could cause the oscillator tube to fail and that could be what you are seeing. I had both transformers in my 556 rewound by a friend - not an easy task and one requiring many iterations on a test jig before acceptable results were obtained. The mechanical arrangement of those two HV boxes makes working on them quite a challenge.

Sorry to be the bearer of bad news :-(

Morris

On Wed, Aug 8, 2018 at 08:56 PM, Jeff Urban wrote:

OK specifics first.

561A - what is MOD 210E

2465 - what does the CT suffix mean ?

I also would like some info, maybe better opinions on the different phosphor
options. Someone could give me a link to what the books say and that would be
fine, but I would also like to hear from people who have experience with those
different phosphors.

Possibly counter timer?