[Amps] TUNER

[Jim Thomson]

Date: Wed, 13 Oct 2010 07:18:21 -0700
From: "Jim W7RY" <w7ry at inbox.com>
Subject: Re: [Amps] TUNER

EXCEPT when you get to the higher bands. (10 and 15. And sometimes 20). You 
need a way to cancel out the reactance. At least you do on a pair of 4CX800 
Russian tetrodes.

73
Jim W7RY

### agreed.  Alpha achieves that by switching in  a tiny bit of uh   in parallel  with the  grid to chassis resistor.
## On these 8170/8171 tetrodes,  they use a small roller inductor in parallel with the 450 ohm resistor.   That
cancels out the XC  from the  C between  control grid  and cathode. 
If you don't do this,,, you will have SWR on the input, between xcvr and input of amp. 

Jim  VE7RF 


--------------------------------------------------
From: "Jim Thomson" <jim.thom at telus.net>
Sent: Tuesday, October 12, 2010 11:19 PM
To: <amps at contesting.com>
Subject: [Amps] TUNER

> Date: Tue, 12 Oct 2010 18:04:53 -0400
> From: "Roger (K8RI)" <sub1 at rogerhalstead.com>
> Subject: Re: [Amps] TUNER
>
>
>  I wonder how one of these tuners, or input boards would work with a
> passive grid input on a Tetrode.
>
> 73
>
> Roger (K8RI)
>
> ##  what for ?   The xcvr 'see's  flat swr anyway.  You either have a 50 
> ohm passive grid R
> or a  200 ohm resistor.....and a 4:1  un-un.  On the big boy tubes 
> [handles]  they use a 450 ohm
> resistor and a 9:1 un-un.    In all cases the xcvr is happy, and no tuner 
> required.
>
> Jim   VE7RF
>