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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Fri 13, 2020 6:04 am 
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As has been mentioned, any demod probe should work. Here is what is inside the B&K PR-151 and PR-152. The PR-151 was sold for use with the 415 and has an Amphenol MIC connector. The PR-152 has a UHF connector. Based on the color bands, Red-Gray-Orange, it seems they used a 1N283 Germanium diode but 1N34 or 1N60 will work fine if you want to roll your own.


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Sun 15, 2020 3:20 pm 
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Posts: 88
Location: Magnolia Texas
Tim wrote:
As has been mentioned, any demod probe should work. Here is what is inside the B&K PR-151 and PR-152. The PR-151 was sold for use with the 415 and has an Amphenol MIC connector. The PR-152 has a UHF connector. Based on the color bands, Red-Gray-Orange, it seems they used a 1N283 Germanium diode but 1N34 or 1N60 will work fine if you want to roll your own.



That's interesting because when I took mine apart when I first got mine it was packed with a fine black powder which I thought was odd but put it right back together. Was yours empty like the pictures show when you originally took it apart?


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Tue 17, 2020 10:09 am 
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Empty, no black powder.

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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Tue 24, 2020 2:01 am 
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Location: St. Louis, MO
Hey, thank you very much, Tim! I got one built from odds and ends I had on hand. I'll fart around with it with this upcoming 4 day weekend. I searched all over for the correct schematic and you came through with one when I didn't ask and wasn't even expecting it. Thanks again!

Any idea what "47N750" stands for? 47 nanofarads? Because the one in the picture looks a little small for that in a ceramic disc cap.


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Tue 24, 2020 2:06 am 
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ZombieElvis wrote:

Any idea what "47N750" stands for? 47 nanofarads? Because the one in the picture looks a little small for that in a ceramic disc cap.

47 pF and N750 is the temp coefficient.


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Tue 24, 2020 3:58 am 
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Location: St. Louis, MO
Scott wrote:
ZombieElvis wrote:

Any idea what "47N750" stands for? 47 nanofarads? Because the one in the picture looks a little small for that in a ceramic disc cap.

47 pF and N750 is the temp coefficient.


That'd explain some things then! My prototype was only a thousand times over and its output didn't make sense... Thank you!


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Fri 27, 2020 5:27 pm 
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Location: Phoenix, Arizona
Is the demod diode in the probe or back in the 415

I always like to connect the sweep output to the probe input so I can see the sweep actually working on my scope.

I have managed to use all kinds of scopes from digital to old cheap analog. You need a decent DC input on the vertical and should be able to trigger to the horizontal which as I recall is 60 Hz line.

I didn't keep a 415 as they won't sweep down to the 25 MHz range needed for early TV's.

Jim


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Fri 27, 2020 7:01 pm 
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jimmc wrote:

I have managed to use all kinds of scopes from digital to old cheap analog. You need a decent DC input on the vertical and should be able to trigger to the horizontal which as I recall is 60 Hz line.

Jim

Actually I think you want to use the 415 Scope Horizontal output as the scope Horizontal sweep, not trigger on it. It is a 60 Hz sawtooth.

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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Fri 27, 2020 7:11 pm 
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Location: Long Island NY
If the OP uses his Eico scope, that’s exactly how to do it. But if he uses his digital scope he may have no choice but to trigger off the X output of the B&K. Many of the newer scopes no longer have an X input available. Triggering works but the display usually ends up a little distorted.

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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Nov Mon 30, 2020 6:41 am 
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Location: St. Louis, MO
Chris108 wrote:
If the OP uses his Eico scope, that’s exactly how to do it. But if he uses his digital scope he may have no choice but to trigger off the X output of the B&K. Many of the newer scopes no longer have an X input available. Triggering works but the display usually ends up a little distorted.


I use the Eico scope. It gives me an excuse to pull it off the shelf. Granted, it's a 7" scope, so it's a very deep shelf...


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Fri 04, 2020 12:56 am 
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Location: St. Louis, MO
OK, I've hit a wall and would appreciate any help. I'm on section 12.4.1 in the book by the way, on the last paragraph in the left column. I've built my own PR-151 probe, only with BNC on the plug end. Well, SMA to BNC via and adapter then a normal BNC-BNC cable, but you get the idea. I made it out of strip board and components I had lying around. I used a 1N34A diode as a substitute. I've double and triple checked my work. This board is correct, but I can't seem to get any output from the thing.

Now I've got markers for each marker switch on my Eico 470 so I'm good on the part of 12.4.1 before that, but the next part of 12.4.1 is confusing me. I don't have a VTVM with a microphone input (or BNC) like the book suggests, so I plugged it into my Fluke 87V with a BNC double banana jack adapter. No matter the settings on the B&K 415, it reads zero volts DC, even on the mV setting. I haven't even touched the coil adjustments for the markers yet. Is that what I need to do?

I'm suspecting that it's the probe I built. I can't seem to get any of the expected results off of Youtube videos I've seen of people's oscilloscopes when combined with a signal generator and the probe plugged into the scope. Nothing makes sense and I'm not sure where I went wrong. I'd really appreciate any help.

Also, as is it is now, would I just need a BNC to 1/4" phono adapter to plug that probe into my Heathkit VTVM?


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Fri 04, 2020 1:07 am 
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I don't know what you have but if it's a probe with a 1N34 it must be a detector probe. If so, its output should be a signal that depends on its input. That is, radio frequency, perhaps modulated, will give dc and perhaps modulation envelope.

Post the diagram of what you built. A detector probe is a simple affair, a diode and a capacitor and a resistor, usually. With a 1N34 one must be careful not to burn out the diode; check it with a VOM. It does require enough signal amplitude to make the diode conduct, maybe a few hundred millivolts, which most signal generators can supply.


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Fri 04, 2020 2:24 am 
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Location: St. Louis, MO
I basically built the B&K PR-151 at the top of this page. It's supposed to be a demodulator probe. The only difference is that I used a 2200pF cap at the tip instead of a .002 one since that's a weird value. Here's some pictures. The red lines are where I cut the traces, nice and wide.

I tested the 1N34A with my DMM and it passes a diode test.


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probe top.jpg
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probe bottom.jpg
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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Fri 04, 2020 4:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1795
Location: Phoenix, Arizona
I was playing with sweep / marker generators to sweep my late 1940's TV's.

I tried most of what was available usually cheap on ebay.

I ended up using an Sencore SM152 unit which has the sweep / marker / Adder all in one neat little box. It has the markers for color sets but I use an RCA marker generator and the Sencore has an External marker input.

To get started, I set the frequency range and sweep width on the sencore with the sweep output probe connected directly to the input probe diode input and I look at a pedestal on my scope.

I turn on the morker generator and move the marker frequency up and down the pedestal so I know which way it is going and can see what I am getting from my test equipment.

Then I insert the TV set. This is usually feed the sweep output to a tube shield partially over the mixer tube in the tuner and connecting the probe to a designated (by Sams) in the IF path.

I tell this little story because in trying various sweep setups to work, The RCA didn't put out enough level to do the above. It was in three seperate box's although my home made probe worked fine. I sold the sweep generator on ebay, I can't give away the adder box, and I am using the marker generator with the Sencore.

The B&K 415 doesn't have an external marker input and doesn't sweep down to 21 MHz for early B&W sets.

I use an HP digital scope that I can recall the complete setup, easy peasy. Note: Digital scopes are a "PITA", but once you figure out the trigger and the rest and save it, you never have to do it again.

Since I sweep about one TV set every two years I don't always have things ready to go.

I also have a split of the Marker genertator feeding a frequency counter so I know exactly what the pip is one turned intpo a marker.

Jim

I will send the RCA Marker Adder to anyone who wants to pay the shipping, otherwise I amd going to scrap it.

On that same topic I will give free. an RCA Television Sideband adaptor (early 60's), all tube, heavy, (working) used to sweep out an analog broadcast transmitter.

Jim


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Fri 04, 2020 6:34 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 3490
Location: Dallas, TX
ZombieElvis wrote:


I'm suspecting that it's the probe I built. I can't seem to get any of the expected results off of Youtube videos I've seen of people's oscilloscopes when combined with a signal generator and the probe plugged into the scope. Nothing makes sense and I'm not sure where I went wrong. I'd really appreciate any help.

Also, as is it is now, would I just need a BNC to 1/4" phono adapter to plug that probe into my Heathkit VTVM?

No point in adjusting anything if your test set up doesn't work.
If you should be able to see 100mV DC on your meter or scope then you need a RF signal to attach to the probe that is about that large. Some Rf sources won't put out that much signal because they are intended to used to input a signal into something that will amplify the signal. The input impedance of the meter or scope also needs to be high enough that it doesn't load down the RF probe output, 10Megohm would be fine. Make sure the scope is set on DC input and the sweep is auto triggered or free run.
Did you ohm out the probe and cable to make sure there are no shorts? Those diodes are easy to damage with soldering heat.

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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Fri 04, 2020 8:31 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 989
Location: St. Louis, MO
I'm still fairly new to this scope stuff, so bear with me. I can't remember if DC on a scope is Vpp or Rms. I think it's Rms? I got my SG dialed into a 100mV RMS signal right now according to my scope. Scope is on DC coupling, trigger on auto. How should I apply that impedance? Croc clips on the scope and SG with a 10 Mohm resistor in the middle?

Probe ohmed out OK. I pulled the diode out and it still passes a diode test.

What about my adapter idea for my VTVM? Would something like this work? https://www.amazon.com/dp/B06Y1HDSCS/re ... UTF8&psc=1

You know what? I'm going to take this probe compeletely apart then put it back together, verifying every part as I add them with my DMM.


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Fri 04, 2020 8:58 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3775
Location: Seattle WA US
Verify that you don't have a short to center conductor at the end of the coax shield.
-Chuck


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Fri 04, 2020 9:06 pm 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 2806
A scope doesn't display rms or average, etc. It displays instantaneous voltage. The average and rms and peak to peak are computed from the display; they don't exist in real time.

To measure a signal generator output you need a probe on the 'scope. For frequencies in the audio range, a 1:1 or direct connection is usually fine. Anything else probably should use a 10:1 probe.


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Fri 04, 2020 10:10 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 989
Location: St. Louis, MO
I took this thing completely apart and rebuilt it, verifying every connection. I am much more confident in its construction now.

K7MCG wrote:
Verify that you don't have a short to center conductor at the end of the coax shield.
-Chuck


My probe doesn't have coax on the end. I'm using an SMA connector on the probe along with a BNC adapter. That way I can just use a plain BNC cable. It's reading 12 Mohms center to shield at the SMA connector.

bob91343 wrote:
A scope doesn't display rms or average, etc. It displays instantaneous voltage. The average and rms and peak to peak are computed from the display; they don't exist in real time.

To measure a signal generator output you need a probe on the 'scope. For frequencies in the audio range, a 1:1 or direct connection is usually fine. Anything else probably should use a 10:1 probe.


I got BNC on my SG, so it's plugged straight in to my Rigol scope with a BNC cable via a tee and 50 ohm terminator. I got that input set on 1X.


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 Post subject: Re: B&K 415 Sweep/Marker Generator
PostPosted: Dec Sat 05, 2020 12:01 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3775
Location: Seattle WA US
Looking closely at the photo of the bottom side of your probe breadboard, it looks like the center conductor of the coax connector is not soldered..... suggest you check with a good magnifier.
-Chuck


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