From: patriot121@msn.com
To: jim.thom@telus.net
Subject: RE: [Amps] GS35B tuned input
Date: Tue, 23 Feb 2010 20:01:22 -0800
Iv decided to leave my input as-is .. New question .. how hot normally does the
Kp and P rings (heater - rated at 120Deg C = 248Deg F) get with 90cfm air?? Im
a little high on voltage .... sitting at 14Vac - need to add .3ohms or so ....
Just wondering, im sure im well with in limits.
KC7NOA
> From: Jim.thom@telus.net
> To:
> Date: Tue, 23 Feb 2010 06:19:20 -0800
> Subject: [Amps] GS35B tuned input
>
> Date: Mon, 22 Feb 2010 10:24:54 -0800
> From: "Bill, W6WRT" <snip
> Subject: Re: [Amps] GS-35B Input
> ORIGINAL MESSAGE:
>
> On Sun, 21 Feb 2010 16:42:36 -0500, "Gary Schafer"
> <garyschafer@comcast.net> wrote:
>
> >Leave the CLC (pi network) input circuit in there. A broadband input will
> >not provide the flywheel effect that you need. Neither will an LCL do the
> >job as there needs to be capacitance from cathode to ground that you only
> >get with the CLC type or a parallel tuned input circuit.
>
> REPLY:
>
> I agree and would take it a step further. The higher the Q of the
> input circuit, the less tendency toward VHF parasitics. Why? A very
> low Q input circuit will be very broadband and may allow the tube to
> have enough gain at VHF to oscillate. The higher the Q at HF, the
> lower the VHF gain.
>
> ### whoa, be real careful here. Big dif between a parallel resonant
> input.. and a PI net. I tried a Q of 5-6 on my 3CX-3000A7.. and it
> was bad news on the upper bands. The 3x3 tube is 50 ohms input.
> Out of interest, I put bird wattmeter's on BOTH sides of the tuned input
> PI net.. [ which is 2 x broadcast variables and a tapped 6 ga coil], then
> from bird to heath dummy load. With 200w in, I was only getting 160w
> out on the upper 20-17-15m bands. [200w on 160-30m] . The fix was
> to INCREASE the coil tap a tiny bit [1/4 turn].. and LESS C1 and C2. This
> LOWER'S the loaded Q .
>
> ## end result... power output on 2nd wattmeter shot up to 195 watts.
> With a Q of 5-6, I could actually get 6 ga coil warm with 200W cxr.
> That's 12 A of circulating current alone. Eimac's recommendation of
> Q=5 is way too high imo, and results in LESS drive/grid current.
>
> ## Now how many folks have measured the output of their tuned
> input circuits ?? IMO... a loaded Q of 3 is ample. In any case,
> measure the power out of it, and compare to input. I was burning
> up 40 watts, just from too high a loaded Q.
>
>
> I built my 8877 amp with a simple parallel resonant input circuit with
> a Q of five on all bands from 160-10 meters and it is perfectly stable
> without a VHF parasitic suppressor at all. Any time you can eliminate
> the VHF parasitic suppressor, you should, IMO. They are nothing but
> trouble.
>
> ### a Pi net IS a LP filter. Are you sure low Q promotes instability ??
>
> ## BTW, my buddy tried the T net tuned input on his single and also dual
> GS35B 6M amp. The T net is a dead loss. The PI net used 2 x small
> air trimmer caps and just one coil between em. Dead flat swr, and globs
> of power output. Again, don't run the Q too high. No suppressor's used
> either.
>
> ## If you use a suppressor on HF, use a real one.. with a globar. Deep 6
> the broadband tuned input, ala Henry 8 k... it's flawed, doesn't work, no
> flywheel action, and is a myth. The 3x3 tube is already 50 ohms, the
> broadband tuned input is doing nothing.
>
> later... Jim VE7RF
>
>
>
>
>
> 73, Bill W6WRT
>
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