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Old 6th Nov 2018, 7:40 am   #1
Chris55000
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Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 534
Default Home Made Wobbulator Design?

Hi!

My apologies for asking this again but now that more mags are on American Radio History and archived elsewhere, I'm hoping someone may recognise it!

A good few years ago I bought two Gould Oscilloscopes off eBay from the same seller, and included was a home–made AM Wobbulator covering about 400kHz to about 12MHz in three switched ranges.

As well as the input from a 'scope TB/X–amplifier, this unit could also be swept at mains rate, and incorporated two small "Eagle" manufactured 9–0–9V centre–tapped transformers, one for the sweep–voltage with resistors of about 10k going to two strips on the Veroboard circuitry, (see next paragraph) the second transformer feeding a conventional 12V 7812–regulated power supply.

The design used an FET based oscillator based around three blue Denco 'Transistor' coils, with a two–gang variable tuning capacitor of about 365pF, the oscillator was built in an old Pye Connectors junction box from a Clansman – I think!! – and a sweep/control arrangement built on a small and very densely packed piece of Vero containing a 741, 555, quite a few transistors and a round Mullard Ceramic trimmer cap. soldered to the back, this plugged into a 0.1" edge connector screwed to the case bottom.

Unfortunately I gave this tackle to a colleague at one of my former jobs for safe keeping and I've lost touch with him so I no longer have access to the bits! Even when I did have it, trying to reverse–engineer the circuit defeated me as that piece of Vero was too much!

The overall circuit of this, particularly on the piece of Vero it had, looked far too complex to be totally home–brew without some input from a Magazine Article somewhere, so I'm wondering if any Member knew anything about this?

It most definitely was NOT Practical Wireless by the way! "Rad–Com", '73' or 'Ham Radio Today' design perhaps?

If any Member can find this design out and can supply coils and another 365pF two gang, please PM me!

This is my "Homebrew" challenge for 2019!

Chris Williams
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It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

Last edited by Chris55000; 6th Nov 2018 at 7:54 am.
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Old 6th Nov 2018, 9:20 am   #2
Terry_VK5TM
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Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 594
Default Re: Home Made Wobbulator Design?

Can you pinpoint the year you bought the scopes?

Would give a starting point to work back from.
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Old 6th Nov 2018, 11:33 am   #3
Chris55000
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Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 534
Default Re: Home Made Wobbulator Design?

Hi!

I bought the scopes from a seller in the Wigan area, Hindley I think it was, uring 2011/2012, and I remember him saying the Wobbulator had been built by his late Father, and the case had "G4MEG" pencilled on it, but unfortunately the seller of the scopes couldn't locate any paperwork relating to them or the Wobbulator – I paid "cash on collection" so saw the seller peesonally, but I got a manual for the scopes (OS3500s) at a later date from Cooke before they closed!

Chris Willuams
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It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

Last edited by Chris55000; 6th Nov 2018 at 11:40 am.
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