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 Post subject: Interesting sweep-marker generator
PostPosted: Sep Mon 20, 2021 2:40 am 
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I found this at Kutztown and was intrigued by it. The price was right so I bought it.

I was surprised to see how it is built! Very impressive! Someone really put alot of work in this thing!
Each marker is a crystal controlled oscillator (I think unless the sweep just rings each one as it passes) including 10.7 MHz.

The attenuator is impressive too!

Very few electrolytics, so I'm tempted to replace them and see how it works! :D

-Steve


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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Mon 20, 2021 5:06 am 
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Wow, do you think that is a one of a kind, or a production generator?

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Mon 20, 2021 5:29 am 
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I would guess one of a kind. Perhaps a prototype.


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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Mon 20, 2021 1:25 pm 
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Looks to be a very laborious design to be production.
However everything appears to be professionally made. Holes appear to be punched rather than drilled.
The lettering on the front are all dry transfer with a clearcoat over them. They are not perfectly straight.
Clearly completely handmade I guess either prototype or very limited manufacture.... If it is a one-off, its one heck of a good homebrew! I really don't know!

No name anywhere inside or out!

-Steve

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Mon 20, 2021 1:52 pm 
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The sound IF frequency in intercarrier TV sets made for the US (NTSC) market was 41.25 MHz and the picture IF was 45.75 MHz. Both are visible as marker frequencies on the panel, along with some above and below that which presumably were the beat frequencies that needed to be trapped or filtered out.

My guess is this is a custom one-off instrument built by a company that made TV sets or broadcast equipment, or perhaps by one of the "big three" TV networks. It no doubt lost its place in the lab or factory when DTV came in. I do not think it was an amateur or home project because whoever built it had a budget and access to specialized components--not to mention a well equipped metal shop--above and beyond what is normal for home constructors.

You probably don't need to replace the electrolytics. They are not terribly old, and if they are as high quality as the rest of the unit they are likely to be better than anything you'd be replacing them with. Just disconnect them from the circuit and bring them up gradually to full voltage using a variable power supply. If the leakage current settles down to a low value, discharge them and then measure the capacitance. I am pretty sure you will find that they are fine and ready to reconnect back into the circuit.

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Mon 20, 2021 2:11 pm 
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I'd be tempted as well to just plug it in and see what happens. Just monitor the electrolytic cans for any increase in temperature above some "normal" rise. I bet it works fine.

Incredible job of construction if it is indeed a one-off, which I'd say appears likely.

I could not help but notice that in one of the photos there is clearly shown, a bicycle tire in the middle of the instrument; no doubt, it's designed to run off AC wall voltage, or pedal power in an emergency. :mrgreen:

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Mon 20, 2021 3:28 pm 
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From the components I would date it from the late 60s to early 70s. If home built from surplus parts it could be later.
I noticed a marker for 10.7, FM broadcast radio, so it wasn't just for TV. That would suggest a home built, not something built for a TV company for internal use.

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Mon 20, 2021 5:22 pm 
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Yup , I also noted a 3.9MHz switch. Substitution for the color burst oscillator in a TV for testing purposes? Not sure I ever needed that one but handy I suppose if you suspect a crystal...

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Tue 21, 2021 2:21 am 
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:lol: Yep my bicycle got caught in the photos :D

Whatever the origin, its one solidly built piece of equipment.

I just wish whoever did build it would have left some indication of identification a ham call or name.
As nice as it is, wouldn't they be proud of their work?

-Steve

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Tue 21, 2021 2:44 am 
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Whoever build this did a fantastic job, very neat and professional work: I can't stop watching the pics.

I wouldn't be surprised it will still work at 1st power up.


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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Tue 21, 2021 4:51 am 
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What an interesting piece, Steve!

I can hardly wait to see the schematic when you get it traced out. :mrgreen:

Well, maybe at least one typical circuit.

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Tue 21, 2021 7:04 am 
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The last picture looks reminiscent of a '60s era TEK scope. I realize the the terminal strips are not ceramic and silver, but still . . .

John


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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Tue 21, 2021 4:19 pm 
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It struck me that someone had access to parts at work. Whether it was made at work, or at home is a secondary question. The parts are all the same, no scrounging. Those terminal strips weren't common, so why use them unless they were available.

I knew someone who worked for RCA. And through him I got various bits of ",junk". They were not products, but they were built and used parts like they were high end production items. If someone else is paying for parts, why not use them. This looks like that.


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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Tue 21, 2021 4:28 pm 
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It's a great work of art. I'd love to meet the builder.

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Tue 21, 2021 7:41 pm 
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Since the switches have no functional labels (e.g. power for the on/off switch, attenuation for the step attenuator switches) and don't have units (e.g., MHZ for the frequency switches, db for the step attenuator switches, I am assuming that this is a very well constructed home brew unit and was never used in a production environment.


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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Tue 21, 2021 8:29 pm 
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This goes a bit beyond the typical hammy-joe home rolled project. I had a friend years back who was an engineering technologist at Gould Center outside of Chicago. He would have been one of the guys who worked with design engineers to put together prototypes of new products. This is reminiscent of the electronic gear he would build for his own hobby use- As in components that stuck to his fingers from work and metalwork done with professional tooling. Some careers had their advantages in the day!

-Mark-

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Tue 21, 2021 9:44 pm 
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There was a story in QST some years back. It was about someone who'd worked at Collins, so an employee discount. And he built a whole receiver, either in the 75A line or the 51J line, all built from parts bought by employee discount. So it was thereal thing, but built at home.

Heathkit sold parts, intended as replacements. But there were lots of projects where people bought tge cases, and built matching equipment in them. The first issue of CQ I saw, Sept 1972, the author bought an LMO, or parts to build it, so they couid have an external VFO to go with their SB or HW line transceiver.

Of course, building a whole Heathkit from individual parts was more expensive than buying the kit


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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Wed 22, 2021 6:01 pm 
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Quote:
Since the switches have no functional labels (e.g. power for the on/off switch, attenuation for the step attenuator switches) and don't have units (e.g., MHZ for the frequency switches, db for the step attenuator switches, I am assuming that this is a very well constructed home brew unit and was never used in a production environment.


It all appears to be hand-done "Lettraset" dry transfer lettering which is extraordinarily time consuming and tedious. I doubt any home constructor would go to that much trouble, and it also explains why they didn't bother to label certain things which are obvious, like the on/off switch. Somebody spent days putting the markings on that panel, and they certainly deserved to get paid for it.

Normally test equipment used in a production environment is set up by the factory technical staff when they tool up a production run, and then it sits unchanged until it is due for calibration or repair. Production line workers do not touch the equipment and often don't even know much about it. They are only told what to look for on an oscilloscope screen (which often has a template pasted on it) or a meter reading, so the equipment did not need to have every last detail marked for the person or team people who were familiar with it. Of course the same would be true in a lab setting or for a very patient home builder.

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Wed 22, 2021 8:55 pm 
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Thanks everybody! Yes I would like to trace out the schematic which will take some time.

I did power it up gradually with a variac and turns out the unregulated power is a + and - 25 volts DC, then these are regulated to a + and - 15 volts.
I've yet to check any further.

I'm quite familiar with dry transfer lettering. The capacitor tester I built back in the early 1990s uses the sheets Radio Shack used to sell.
I applied them all as you see. Though this isn't in the same league as the sweep generator :lol:

-Steve

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 Post subject: Re: Interesting sweep-marker generator
PostPosted: Sep Wed 22, 2021 10:29 pm 
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The chassis with the crystals should be easy to trace, probably the same circuitry for each crystal.

The other chassis, the attenuator takes up space, and the power supply shouod be straightforward.

I'd say it's obvious that the frequencies are in MHz and that there's a stepped attenuator, and an unmarked on/off switch. It's only oblique to those who wouldn't be using it.


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