[AMRadio] early parasitic suppression

John Lyles jtml at losalamos.com
Thu Apr 12 01:42:47 EDT 2007

Another source of early information on 'Stopper' networks in transmitters was the original 500 kW WLW report in Proc of IRE by Fyler of GE (1930s). They had large flames caused by parasitic oscillations and had to stop them to prevent distruction. 
John     K5PRO

> Message: 10
> Date: Wed, 11 Apr 2007 19:25:24 -0500
> From: "D. Chester" <k4kyv at charter.net>
> Subject: Re: [AMRadio] Parasitic Suppressors (or lack thereof) 
> To: <amradio at mailman.qth.net>
> Message-ID: <001901c77c99$10281010$a465a842 at D65Y8B21>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> 	reply-type=original
> > I've noticed most (if not all) if the PP-triode RF PAs of that period 
> > don't
> > show the use of any parasitic suppressors in the grid or plate leads. Also 
> > a
> > deck I have (exact vintage unknown) using PP triodes doesn't include them.
> >
> > How did they get away with this?
> >
> > I've never put power to the above-mentioned deck, but have another one 
> > where
> > I tried to follow the same practice (I just used copper strap for the 
> > plate
> > leads) and I appear to have an intermittent parasitic, so will be
> > incorporating some suppressors in the plate leads.
> >
> > -Larry/NE1S
> I think they just tolerated the parasitics, and used a lot of  trial and 
> error, not really knowing why their transmitters were so squirrely.  There 
> was no TV or VHF radio communication to interfere with at the time, and  few 
> hams had any capability of measuring the power output of their transmitter, 
> so if it ran at 30% efficiency with loads of parasitics they were none the 
> wiser.  I read a story about a Collins mid-30's transmitter, don't remember 
> the model, but I believe it was the one that used a 211 in the rf final.  It 
> was one of the very f irst commercial rigs that had the now familiar 
> parasitic chokes consisting of a resistor wrapped with wire.  It was reputed 
> to be exceptionally smooth and easy to tune up.  This  was considered a 
> major advance in transmitter design at  the time. Art Collins had figured 
> out the parasitic problem and how to cure it, and his transmitter was noted 
> for its exceptional performance.
> Don k4kyv

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