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Old 17th Nov 2017, 9:38 pm   #1
john777
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Default Testing a vintage Marconi signal generator

Hello
I have just acquired a Marconi signal generator (TF2015) which powers up OK.
What I want to do is test that it works properly. From researching on the web I understand you need a Oscilloscope to test it with.
I also have one of these, namely a Telequipment D83

So my question is can I use the oscilloscope to test the signal generator, and what type of wires do I need.
Also the oscilloscope does not have a power lead so is it possible to power this up - it has a strange 3 pin plug on the back.
Sorry if all this seems a bit basic but have only just started dabbling with this type of equipment
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Old 17th Nov 2017, 10:26 pm   #2
Station X
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Default Re: Testing a vintage Marconi signal generator

I have the service manual for this if you need it, It's 6 Meg and too big to post here, so send me a PM with your email address if you want it.

Personally, as a quick functional test I'd connect a couple of feet of wire to the output socket, set to say 98.5MHz, turn up the wick and see if you can pick up the signal on a FM broadcast radio.
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Old 17th Nov 2017, 10:58 pm   #3
MotorBikeLes
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Default Re: Testing a vintage Marconi signal generator

The mains lead for the D83 has been unobtanium for almost 30 years. What I do (did) was to use a blue TEK backplate with cord grip and wire in a fixed mains lead.
There was a modification listed requiring a little "plastic box) and screw kit to fit over the mains selector socket, since inquisitive fingers could get a mains shock. Worth knocking something up there at the same time.
Les.
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Old 17th Nov 2017, 11:12 pm   #4
WME_bill
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Default Re: Testing a vintage Marconi signal generator

Marconi TF2015 and Telequipment D83.
Graham StationX suggests how to check the Signal Generator.
If you really want to use the D83, you have a bit of engineering to do.
Telequipment used a quite unique mains input plug and socket, made by BellingLee. You will have to search for one, try ebay or try Electrojumble. But I believe I heard even he has not got one.
So what we usually do is to fit a standard IEC Eurosocket. If you pinch one off a disused computer power supply, you will save a trip to Maplin. But you will have to enlarge the hole, and that is a awful fiddle, as the new fixing holes just overlap the old ones.
Or else just run the mains cable direct from the connections inside. Which is what I have done.
But then remember that the D83 high frequency response is to 50Mhz, so response will fall off from about 20Mhz. So you will only be able to check the lowest range as it covers 10Mhz to 520Mhz. Both nice bits of kit and very useful. wme_bill
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Old 18th Nov 2017, 5:29 pm   #5
john777
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Default Re: Testing a vintage Marconi signal generator

Thanks for the interesting replies
I am thinking of wiring up the oscilloscope directly to the mains just so I can test both pieces of kit at the same time - if the oscilloscope is working then I will look to do something more permanent.
So this is what I am thinking
Wire up the oscilloscope and check it fires up
turn on the signal generator and set it to output below 20Mhz
If the oscilloscope is set to the same frequency it should then pick up the signal and I should be able to see it in the little window
Does that sound like a sane plan?
The only thing I will have to be careful of is not killing myself wiring this to the mains. I take it this is a plug with a wire and just wire up to the correct terminals in the box?
Thanks for all replies and patience on this
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Old 18th Nov 2017, 5:57 pm   #6
Al (astral highway)
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Default Re: Testing a vintage Marconi signal generator

Hello, you ideally need to check the ‘scope works independently of the signal generator , otherwise you have two unknown quantities. Do as Graham suggests first with your signal generator set to an FM radio frequency and a short wire which is gong to be an antenna - you’re going to ‘transmit’ a carrier wave to check the SG!

Then put a mains lead on the ‘scope. Attach a probe lead to channel 1. Move the time/div button to a lowish setting and move the horizontal and vertical position buttons until you have a trace in the middle of the screen . Hold the scope probe and touch your finger on it. The ‘scope will pick up the mains hum which is coupled from your body to the probe and you will See a 50Hz trace with the time/ div button in the correcttestvitv position .

After that you can test it in more advanced ways; this is just for starters!
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Old 19th Nov 2017, 12:54 am   #7
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Arrow Re: Testing a vintage Marconi signal generator

Generally, if testing involves checking the voltage output of a sig. gen. with a 'scope, don't forget to terminate the sig. gen's. O/P with 50 Ω. (That also assumes that you can rely on the calibration of the 'scope's vertical amplifier gain). Measure the p-p amplitude and divide that by 2.8 to get the RMS value. For high frequencies (say above 10 MHz), and using co-ax. from the generator with the 50 Ω at the end of that coax (which should be 50 Ω Zo), use a X10 probe to eliminate the effects of the cable. You need to be sure your probe is correctly compensated; that its attenuation is correct and that the bandwidth of the probe + 'scope is adequate for the freq. from the sig. gen.

Al.
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Old 20th Nov 2017, 3:45 pm   #8
dave cox
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Default Re: Testing a vintage Marconi signal generator

As Station X said, use an FM radio to test the generator!

I found the TF2015 controls rather quirky, but the other settings you need are :-
Carrier ON or +6db
Internal FM modulation
Deviation X10 and 10KHz (=100KHz)
Output -10 db on the switch
Output 7 on the dial

You should be able to tune your FM radio to hear the 1KHz tone !

dc
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Old 21st Nov 2017, 12:26 am   #9
john777
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Default Re: Testing a vintage Marconi signal generator

Hello
Found the lead to the scope, wired it up when I turned on the scope I got a brief red light and then it died - I am assuming that is bad.
I dont actually have a radio.
Can it be any radio that can pick up FM?
Where do i connect the wire to and what sort of wire should it be - just a piece of copper wire?
There isn't anything at the back marked output so which actual port does the wire go on?
Many thanks
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Old 21st Nov 2017, 2:58 pm   #10
Skywave
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Arrow Re: Testing a vintage Marconi signal generator

Presumably, that "brief light" was the LED just above the mains on / off switch. (If that is incorrect, ignore everything that follows.)

First: is there a switch at the back enabling this item to be run from 230-v. or 115-v. mains? If there is, make sure it's set to 230-v.

Second: check the fuse at the back of the unit. Is it the correct rating and type? Is it blown? If it is blown or the wrong type, replace it with the correct one and type and try again. If the fuse blows again - especially if it was originally the correct type - you have a fault to fix in that item.

Third: Arm yourself with the manual: read it. Use a suitable voltmeter and measure the voltages around the internal PSU. Compare readings to those stated in the manual.

Then, you may need to talk to us again.

Al.
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Old 22nd Nov 2017, 1:10 am   #11
john777
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Default Re: Testing a vintage Marconi signal generator

Hello
Thanks for the replies I will try to check the scope as advised above
My first priority though is to test the signal generator
Where do i put the wire that acts as an antenna to send the signal to the FM radio
I have been through the manual and can't work it out from there
There is a RF output socket on the front and an Int mod out socket on the back - is it one of those. Do you need the correct wire with the probe on or is it just a piece of any copper wire
Thanks for reading
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Old 22nd Nov 2017, 10:53 am   #12
dave cox
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Default Re: Testing a vintage Marconi signal generator

Just poke the end of a couple of feet of wire into the centre of the output socket on the front. When laid out straight it will act an as radiating antenna, turning the signal generator into a transmitter!

dc
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Old 23rd Nov 2017, 10:27 pm   #13
john777
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Default Re: Testing a vintage Marconi signal generator

Hello
Success, put the antenna wire in - set the dials as per instructions from Station X and Dave Cox and picked up a signal almost immediately on an FM radio. Hell of a signal as well, would have taken out my eardrums if I turned the radio right up
Now just have to try and sort the oscilloscope
Many thanks to all contributors
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Old 24th Nov 2017, 10:26 am   #14
dave cox
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Default Re: Testing a vintage Marconi signal generator

There are more tests needed, but it looks like you have a largely working generator

The attenuator can be tested further with just the FM radio. Just switch down the ranges 10, 20, 30 etc and see if you still get a signal. It WILL disappear eventually (normal) but you should still get something for the first few ranges.

The other frequency ranges need other test equipment (as they have seperate oscilators) but you could probably test at 50MHz where the FM radio might pick up the 2nd harmonic ...

dc

Last edited by dave cox; 24th Nov 2017 at 10:32 am.
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Old 24th Nov 2017, 1:25 pm   #15
Skywave
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Default Re: Testing a vintage Marconi signal generator

Quote:
Originally Posted by john777 View Post
I have just acquired a Marconi signal generator (TF2015) which powers up OK.
What I want to do is test that it works properly. From researching on the web I understand you need an oscilloscope to test it with.
I have one of these, namely a Telequipment D83
I have only just started dabbling with this type of equipment
I appreciate that you have only just started dabbling with this type of equipment (didn't we all start that way?) and I wish you every success with your subsequent endeavours. To "test if it works properly" actually involves quite a lot of detailed & knowledgeable work and requires a number of items of test equipment which you probably don't yet own - and some of them will be expensive! However, having said all that, at this point in your hobby that sig. gen. will be fine when at least used as a 'test oscillator' . As you gradually acquire more items of test kit, you will then be able to explore it capabilities - and functionality - more thoroughly.
I wish you all the best of fortunes in those future journeys.

Al.
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