Quote:
Originally Posted by G0HZU_JMR
Here's an image of my old Maplin YN48C DIP meter and the schematic diagram taken from the manual. It isn't a very good dip meter but it is a bit different because it uses a BJT in the oscillator section.
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I'm not sure to what extent the use of BJT was too unusual during the sort of era when I think your GDO was made. I don't have any numbers to quote, simply the recollection that there were various models using BJT. Perhaps I should try make contact with the American guy who has a collection of 64 models and see if he has studied their 'evolution'?
Re the 3819's, I used one for my very first GDO, felt it ran out of steam at VHF and then went to a...2N5457 (I think) which seemed better. Given that the 3819 was a very early device, I wonder if some of the even the slightly later options look better when modelled? There's no denying that many well-respected GDO designs do use FETs. I've now sidelined the tunnel diode design (Heathkit) I considered and my "Homage" version of the Model 59 is a work-in-progress.
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