>
>
>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
HV is not used with the method I use.
>and is best done at the highest frequency used.
agreed
>I prefer to get close with screen voltage removed, HV applied and
>sufficient drive that does not exceed G1 ratings.
In Class AB1 there is Zero grid current.
>A bit of caution is required but maximum neutralization is pretty much
certaim.
>
>When running swamped grid input, neutralization should not be necessary.
For large tetrodes, which require 200 ohm (8166, 8169, 5cx1500) and 450
ohm (8170, 8171, 8281) grid termination, I found that neutralization is
necessary to avoid oscillation. Eimac recommends neutralization for grid
driven service.
- cheers, Carl
Rich. Measures. Web site: www.vcnet.com/measures
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