[Amps] Tuned Input

[Peter Chadwick]

G3SEK said:
<the Collins authors show a driver with an output pi-tank, the magic length 
of line and a pi-tank input on the amplifier.>
I believe that there was a 'magic length' that covered all the ham bands....
Of course, the GG doesn't necessarily have to have a pi network, as long as there is a low impedance to ground from the cathode at the harmonic frequencies. A parallel tuned circuit works quite well, provides it is designed for high C, and the coupling to it is arranged such that the Q is low - I use that with a 4-400 on 10metres. It's a bit more trouble for multi band use. Passive grid with tetrodes having some NFB gets around that problem.
And before anyone asks, passive grid does NOT mean the G2DAF circuit
>and after that, it'll be "GM3SEK" for good<
Good?? HF proagation is noticeably worse that far north................
73 Peter SM/G3RZP This week - W6 next week!)







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Message Received: Jan 23 2006, 11:37 AM
From: "Ian White, GM3SEK" 
To: g3rzp at g3rzp.wanadoo.co.uk
Cc: Amps at contesting.com
Subject: Re: [Amps] Tuned Input

Peter Chadwick wrote:
>> From memory, didn't some of the Collins amplifiers specify a
>> certain length of coax to go between exciter and amplifier to get
>> the total phase shift right on all bands? i.e. to reflect an
>> impedance such that as far as the GG amp was concerned, it was fed
>> from low impedance voltage source.


Yes, they did, but that recommendation didn't rule out the use of a 
pi-tank. In the first edition of 'SSB Principles and Circuits', the 
Collins authors show a driver with an output pi-tank, the magic length 
of line and a pi-tank input on the amplifier. They didn't say how you're 
supposed to switch bands, though.



> 73 Peter SM/G3RZP This week - W6 next week!)


and after that, it'll be "GM3SEK" for good!