[Amps] FW: GS35B tuned input

[MIKE DURKIN]

From: patriot121 at msn.com
To: jim.thom at 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 at 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 at 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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