[Amps] Low Input SWR Amps Networks

[Roger (K8RI)]

On 11/3/2010 12:59 PM, w3hvq wrote:
>      I'm currently comparing various linear amplifier input networks with intent of changing the one int my HB 4-1000A Amplifier.  This amplifier was used for fifteen years with a tube type transceiver using 6146B tubes in the final and there was never a problem.  The input network in the amplifier used six simple LC tuned resonant circuits, with a bandswitch selecting one tuned for desired HF band.   Fixed mica capacitors and 3/8" diameter coils wound on wooden-dowels were used with good success.
>      I now have only a solid-state transceiver that's allergic to any RF power reflections from my trusty amplifier (an SWR that was acceptable before).
Many of today's solid state rigs can handle an SWR of up to 2:1 or even 
3:1. It's not that many of them can't handle an SWR of 2:1 or 3:1, they 
*can't* handle is a *dynamic* load impedance which causes an input SWR 
to vary *rapidly* over a relatively wide range. Range in this case being 
a relative term. My old Icom 756Pro can easily handle up to some where 
between that 2:1 and 3:1 SWR into an antenna, but drive a GG or even 
some grid driven amps with passive input (which should be static when no 
grid current is drawn) and the auto matching network will go nuts.  Just 
turn the auto function off and it works quite nicely.

73

Roger (K8RI)