[AMPS] Neutralising tetrode HF amplifiers

[km1h@juno.com]

On Sat, 10 Oct 1998 10:10:23 +0100 Chris W Tran <chris.tran@zetnet.co.uk>
writes:
>
>Saturday 10th October 1998
>
>Hello all
>
>I enjoyed a visit to Rich Measures AG6K web-site - thanks for
>the interesting info. Rich. (I also enjoy this reflector when
>you guys can't agree on something!)


There are often several paths to the same results. I just like to have
fun with those who have a fixed mind-set.



>Thinking about neutralising a tetrode for 1.8-30MHz use, I
>noted the method proposed by Rich (disconnect the tank cct.
>and terminate with non-inductive R equal to the load impedance,etc)
>- I was wondering if the simpler method (which I've only used
>once with a 2 x 4CX250B amp. for 144MHz) would give as accurate
>a setting ?  
>The method is to feed 2-3W of, say, 21MHz RF, INTO the 'RF output' 
>connector (with the HV and G2 supplies off, but filament and G1 bias 
>'on' and the T/R coax relays activated), then adjust the 
>'Neutralising' variable capacitor for minimum RF voltage developed 
>across the input (grid) tuned circuit ?
>(I'm not sure if the G1 bias should be 'off' or 'on')
>
>Any thoughts ?

Either way will get you in the ballpark but final touch-up will require
HV and is best done at the highest frequency used.
I prefer to get close with screen voltage removed, HV applied and
sufficient drive that does not exceed G1 ratings. 
A bit of caution is required but maximum neutralization is pretty much
certaim.

When running swamped grid input, neutralization should not be necessary.
What tube are you contemplating?

73  Carl   KM1H


>
>73    Chris GM3WOJ/GM8V
><chris.tran@zetnet.co.uk>
>
>
>
>--
>FAQ on WWW:               http://www.contesting.com/ampfaq.html
>Submissions:              amps@contesting.com
>Administrative requests:  amps-REQUEST@contesting.com
>Problems:                 owner-amps@contesting.com
>Search:                   http://www.contesting.com/km9p/search.htm
>
>

___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
or call Juno at (800) 654-JUNO [654-5866]

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm