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In my 30 plus years in the elevator craft, I have never seen or heard of any standard of L1 and L2, and I have worked on many DC motor starter/reverser panels. Different manufacturers used whatever designation they wanted to, every print I ever saw made it clear which input terminal was to be positive and which was negative. Polarity is very important, large contactors have "blowout" coils or magnets, improper polarity can prevent the arc formed when a contact opens from being snuffed. A flashover between contacts is a sensory experience you will not forget! It is great to hear someone discussing old control gear, learning about it is vital for proficiency with newer controls, and there is a surprising amount of that gear still in use today.

Bruce Gentry, KA2IVY International Union of Elevator Constructors, Local 62, Retired

I ran into the same issue. So I replaced the pull out cable with an insulated BNC female, chassis mount connector:

Shaun M.

Need not be working, project units are more interesting,

I have some units that are available if interested in the 222 series.
Contact me off list if intrested in more details at electronixtoolbox@....

Craig

On the schematics pertaining to DC shunt/series motor starters, is there any naming convention relating to L1 and L2 being positive/negative?? I ask because I'm used to DC systems specifying polarity, and the only "polarity" mentioned on the schematic I have is the name "D.C. Automatic Starter".
I'm cross posting on Tekscopes2, where any discussion should take place, and adding more info there.
-Dave

I am looking for Tektronix hand held scopes with CRTs, such as the 222, 224, 211, 213, 214 and others of those series. Need not be working, project units are more interesting, completeness is more important than anything else. Carrying bags, manuals, parts for these are also of interest. Thanks,

Bruce, KA2IVY

Chuck ,Sorry to disagree with you, have you even taken the time to look at the schematic, In principle yesI agree with you but this supply is different than what you? described.? It uses a multitap transformer to minimize dissapation and a comparator thand maze of switching transistors that is where I suspest the problem lies or the feedback circuit.
Why does everyone state the obvious repeatedly and think I haven't checked it???
I think I metioned several times that I checked everything and cannot find any faults.I know when I turn the voltage up all the way I'm getting? about 15 volts and it should be 31 and the relay is oscillating on and off? about 2cycles a second , What is that, where to look. The problem lies in the op amp area . This is only the main side.what about the slave side which has little to know voltage.
Chuck , I know you know your stuff, and I do very much Thank you fot your input,but I could use one person to walk me through the regulator,comparator error amp ,feedback and such to the output of the series pass transistors.
There are dual fullwave bridges and filters ,bleeders? per side one low current feeding the references the other high current feeding the series pass transistor.
Why isnt anyone talking about that! Im not an idiot!
Many thanks!
Dave

Hi, all,

My favourite scope, a TDS 694C, has developed a nasty screeching sound when the display comes on. It's quiet during boot-up, but when the screen comes on the sound is very loud and unpleasant. Any wisdom?

Thanks

Phil Hobbs

Hi Colin,
Those 7CT1N captive leads are problematic. I've fixed several 7CT1Ns and they almost all had bad cables. By now most of insulation on the cables has gotten brittle and is cracking. The plug on the end gets banged around and twisted and/or bent which stresses the strands inside until they start breaking. I don't think the design engineers realized they would have a 50+ year useful life.

Somewhere along the way I realized I was going to need those cables. I think I bought a bunch from Deane Kidd but it was so long ago that I can't recall where they came from for sure.

Esmond's replacement cable is on the way to him.

Dennis Tillman W7PF

If I had that need abd that concern, I’d mill some wooden blocks to temporarity replace the feet and store the original feet away.

DaveD

Sent from a small flat thingy

Hi All!
I've got a bare 7704 frame that's in the way, and I'd like to reposition it from the vertical, to the horizonal, to store it.... "upending" it, so to speak. I'm a little leary of doing it... because I think those plastic feet, and rubber pads, on the back, might not hold out, in the long run.
Best regards and wishes.
Roy

, here is a good informative video on capacitors if anyone is interested

Thank you Chuck for the reply, I am trying to avoid electrolytic capacitors when possible.

I just took apart the HV XFMR from my 561. The core is a ferrite or powdered iron E-E type. After removing the wrap around the core, the two E's separated easily at room temperature.

Still hoping someone has the winding data for a 120-225 or a 120-275 transformer. That data might confirm my reverse engineering of my 120-225.

There appears to be two variants of this captive lead. The picture in my manual shows an in-line white plastic "plug", as does Tekwiki. It is given as p/n 195-0095-00 "Lead, test: BNC" and the manual also lists p/n 348-0301-00 "grommet: plastic, 0.312 ID x 0.43 inch OD" associated with the lead. However, my 7CT1N has a black lead with a double-ended connector forming a tee with the lead. One end mates with a BNC male, the other with a BNC female, but still only one connection, no shield. I might add that I purchased the 7CT1N from Dennis Tillman about a year ago.

Colin.

Thanks Miguel,

That's what I was looking for - the info is now saved in my 576 notes.

I like that little HV transformer in the picture. It's a fine example of a common method of attaining good HV performance by stacking the sections of winding. If one could be found in the right size range, and with a primary that can be readily modified, it may be the ideal solution for a drop-in replacement.

This same sort of HV structure is used in transformers for LCD CCFL running, and in laser printer toner charging, etc. None that I've seen look quite "right" for a single-piece replacement, though. The next closest thing would be a two-transformer combo - a low voltage one for making the raw HF power and +225 V, and a small HV type that can tap the HF power and scale it up to the proper 4 kV range. With lots of winding flexibility in the first transformer, it should be doable, and attain the proper ratios and voltage regulation. I estimate that the +225 V and 4 kV each need about half of the total output power available - about 3W each.

Ed

576 Transformer
Inductance Resistance AWG mm Turns AL=L/N^2
Pin 2-3 305,0E-6 22,0E+0 25 0,45 26 451,2E-9
Pin 7-8 918,0E-3 85,0E+3 40 0,08 1400 468,4E-9

Transformer core size
50mm
13mm
31mm

Inductance 1khz 1mA

2-3 305uH 22R
7-8 918mH 85K

Rubber potted

/g/TekScopes/album?id=94656

I have the idea to use a pre made transformer and rewind it, reusing the HV coil. Something like this:




But I think that’s is a little bit smaller.

Regards

Miguel





-----Mensaje original-----
De: [email protected] [mailto:[email protected]] En nombre de Ed Breya via Groups.Io Enviado el: miércoles, 28 de agosto de 2019 3:40
Para: [email protected]
Asunto: Re: [TekScopes] Tek 576 Curve Tracer HV Transformer winding

Has anyone measured the low frequency (like 1 kHz) primary inductance of a normal, OK 576 HV transformer? I looked at the data sheets (at tekwiki) on the part, and none appear to show any inductance value. I've been pondering possible alternate solutions to the "bad epoxy" transformer problem. The first is a drop-in two-transformer (one to provide the HF power and +225V, the other to make the HV) scheme, to sub for only the original transformer. The other is a replacement for the HV supply section, basically an independent SMPS that can run from the +100V supply, like the original.

My 576s are good, with the newer "black" transformers, but all the recent talk got me interested, and revisiting ideas I've been thinking about over the years.

In case anything major should happen to the HV transformer or HV guts, I'd like to be ready to fix it, without resorting to rewinding the HV transformer. In either scenario, the plan is to use a "modern," off-shelf type small HF-HV transformer to provide the 4 kV. I'm picturing the little kind commonly used in Royer converters for LCD CCFL backlighting. I have many dozens of all sorts of these things. I'm sure that some types are just right for this particular setup, but would need a lot of experimenting to figure out.

Anyway, if anyone has more info on the original transformer, please let me know.

This is a low priority project, but I like to think about it. If I ever get around to actually making it, I'll put up the how-to info.

Ed

/g/TekScopes/photo/86536/0?p=Created,,,20,2,0,0

I included a picture from the service manual of the floating power supply that involve these capacitors

I'm troubleshooting a noisey step generator, when I turn the step generator off I don't get any flickering noise artifacts on the display. I figure as the first step is replace any old electrolytic capacitors and tantalum capacitors as I don't own a ESR meter to check them.

Upon further study I found C391 C393 come off a floating power supply in the the step generator circuit

The only reasons I use an oven over the water
technique (aka teacup method) for a couple of
simple reasons:

1) it seems less likely to burn me. Water soaks
through my leather gloves, and it gets hot quickly.

2) Businesses have strict rules about what they can
dump down the sink. Since they would have to prove
that the water carried nothing dangerous, I prefer
to avoid the issue... and use air.

-Chuck Harris

Miguel Work wrote:

Thanks Chuck!

I put transformers in boiling water some minutes, with the same results

Regards

Miguel


-----Mensaje original-----
De: [email protected] [mailto:[email protected]] En nombre de Chuck Harris
Enviado el: miércoles, 28 de agosto de 2019 18:36
Para: [email protected]
Asunto: Re: [TekScopes] Tek 576 Curve Tracer HV Transformer winding

Having done hundreds, I find removing the core to be very simple.

1) remove any tape, clips, clamps, etc that are holding
the core halves together.
2) heat the core to 130C in an oven. There should be no
smell to speak of.
3) using gloves, grab the top core with one hand, and the
bottom core with the other, and twist so that the faces
of the core shear their glue.
4) use a knife to scrape the excess glue off of the core
faces, and anywhere else it annoys you. Keep the core
hot for this operation.

And you are done.

I have never had to put any great effort into this process.
It happens very easily, and non destructively... .The coil and its terminals come free, and could be put back together if you wished.

-Chuck Harris

ulf_r_k via Groups.Io wrote:

Yes, if you can make them fit.

Are the electrolytics bad? If not, I would leave them
alone.

-Chuck Harris

DW wrote: