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NNTP-Posting-Date: Fri, 05 Apr 2024 15:38:46 +0000
Subject: Re: Favourite Test Equipment
Newsgroups: sci.electronics.design
References: <9k7j0jlnbhs8qfg5m17pium0835meean83@4ax.com> <uudm4h$23si2$1@solani.org> <uultes$iq0n$1@dont-email.me> <uum4h6$kmdl$1@dont-email.me> <uuoaea$61ca$1@solani.org> <1qrjb8o.u2ipkmlx8gzsN%liz@poppyrecords.invalid.invalid> <f8501j9o186i2os4ono0jcaq46gcip6h4o@4ax.com>
From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Message-ID: <d4c3761e-f966-acda-0ce0-1143e3b03db8@electrooptical.net>
Date: Fri, 5 Apr 2024 11:38:43 -0400
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On 2024-04-05 11:31, John Larkin wrote:
> On Fri, 5 Apr 2024 09:24:53 +0100, liz@poppyrecords.invalid.invalid
> (Liz Tuddenham) wrote:
> 
>> Jan Panteltje <alien@comet.invalid> wrote:
>>
>>> Giggle Hertz oscillations are not happening in LC circuits of specific
>>> kind where those can happen you can figure from the parts used, no giggle
>>> Hz in a BC109.
>>
>> Back in the 1970s I found that a BC109 could be used as a self-
>> oscillating transmitter output stage at 100 Mc/s on a 1.5v supply (it
>> was for small animal cardiography).  Most "R.F." transistors wouldn't
>> work under those circumstances.
> 
> I learned at an early age that emitter followers tend to oscillate. I
> did a powerup reset circuit with an RC feeeding a 2N2219 emitter
> follower feeding a TTL schmitt gate. The NPN oscillated at 100 MHz or
> so and never pulled up the gate. A series gate resistor fixed it.
> 
> My recent 50 MHz SAV541-based Colpitts oscillator couldn't be tamed
> with a gate resistor or with a bead, so I gave up on the phemt. I
> think the wire bonds are a basic hazard.
> 
> https://www.dropbox.com/scl/fi/bak4p5bty2os2wtrs0091/9.jpg?rlkey=91e37ctc70189hvka9g1ufar3&raw=1
> 
> 
> 

Try putting BLF03VK600 beads in source and drain. Besides being rated at 
3 GHz instead of 100 MHz, it has really nice low Q everywhere.

My cascoded lab amp proto is using three SAV-331+'s in parallel like 
that, running about 2.5 mA each, and shows no sign of trouble.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com