TT Re: [TenTec] Ten Tec amps and ALC

al_lorona at agilent.com al_lorona at agilent.com
Wed Aug 18 19:22:24 EDT 2004


Tommy,

Is this 500 W spike that "most radios" produce always there? If so, then what protects the grids of the tubes in the PA under normal operation?

Or maybe I don't understand exactly which radios have this spike problem. Are there modern radios in this category?

Al  W6LX

 

> -----Original Message-----
> From: tentec-bounces at contesting.com
> [mailto:tentec-bounces at contesting.com]On Behalf Of Tommy
> Sent: Wednesday, August 18, 2004 4:16 PM
> To: tentec at contesting.com
> Subject: Re: TT Re: [TenTec] Ten Tec amps and ALC
> 
> 
> A word of caution about ALC....do not EVER think ALC 
> completely protects the
> grids of your amps tubes. The 'little' problem that ALC has 
> is that it is
> slow. Most radios that use ALC for controlling output power 
> level,  produce
> a very short (microseconds), high level RF spike, until the 
> ALC circuit can
> grab hold of it and bring it back down to a 'regulated' 
> level. More that one
> pair of 3cx800a7's have mysteriously failed, and 
> investigation showed the
> HUGE RF spike (300-500 watts) present on the leading edge of 
> the RF waveform
> going to the amp, be it SSB, digital, or CW. If you want to 
> be sure, check
> your xmtr's RF output waveform with a scope, running at about 10
> microseconds per division. Otherwise just replace expensive 
> grid driven
> tubes, which seem to fail for no apparent reason. The Eimac suggested
> replacement, 3cpx800a7, is supposed to be more rugged in this
> respect....just in case one would need new  tubes.
> 
> Tom - W4BQF
> 
> ----- Original Message -----
> From: "Stuart Rohre" <rohre at arlut.utexas.edu>
> To: <tentec at contesting.com>
> Sent: Wednesday, August 18, 2004 6:37 PM
> Subject: TT Re: [TenTec] Ten Tec amps and ALC
> 
> 
> > An overdrive indicator on an amplifier seems an excellent 
> feature, to
> avoid
> > the possible non-compatibility of ALC circuits in light of 
> no universal
> ALC
> > standard.
> > -Stuart
> > K5KVH
> >
> >
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