[Amps] SWR & other things...

Jeff Carter amps at hidden-valley.com
Mon Mar 2 18:50:53 PST 2009


You know, I have always wondered about that, and I was hoping that
somebody would set me straight on it.

As I was building this SB-220, I was thinking how much the components
reminded me of the inside of an antenna tuner.  That led me to wonder
if that wasn't what I was actually doing, tuning the tube output
impedance to whatever the antenna system impedance was.

In that case, I wonder why people use tuners at all with these old
amplifiers.  Does it give you more range, or something?  Or is it
totally unnecessary?

Thanks,
Jeff/KD4RBG


---- Original message ----
>Date: Mon, 2 Mar 2009 21:29:13 -0500
>From: "Keith Schreiber" <schreiber at windstream.net>
>Subject: SWR & other things...
>To: <amps at hidden-valley.com>
>
>   Hey Jeff!
>
>   re: your query about the SWR range an SB-220 can
>   handle...
>
>   Not to worry OM.  You'll know soon enough if the amp
>   can't handle it - and if you do hear a little
>   spitting or arcing, just STOP.  Think of it this
>   way:  The pi-net output circuitry in a tube
>   amplifier (or transceiver) IS an antenna tuner !
>
>   I started in 1962, and back then, many hams didn't
>   even own an SWR bridge.  We tuned maximum antenna
>   current using an RF ammeter.  We just tuned for
>   maximum antenna current.  Very few hams realized
>   that the pi-net output circuitry in their amps were
>   really doing the impedance matching - just like an
>   antenna tuner would do.
>
>   Vy 73 de W8KTH
>   Keith


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