? If it was possible to neutralize a grounded-grid amplifier, why did
Eimac fail to mention this in *Care and Feeding*? In a grounded-cathode,
AB1 tetrode amplifier, neutralization is possible with a Bruene
neutralization bridge:
http://www.somis.org/D.a.05.GIF
- However, such neutralization occurs only at the operating frequency,
as I learned the hard way with an 8170. Neutralization had no effect at
the place where VHF parasites spawn -- i.e., the VHF resonant circuit
between the anode and the Tune-C. (In the 8170 amplifier, this was
68MHz) The result was stentorian parasitic arcing until I reduced the Rp
(parallel-equivalent R) of the 68MHz circuit by using a lower-Q VHF
parasitic suppressor. .
cheers
>Ed, look at the neutralizing capacitor at the base of the tube. It sounds as
>you may have unintentially moved that little piece metal near the chimney
>base, mounted on the hole cover. If you move that, it will cause parasitic
>oscillations which will take out the plate choke, tube, or that little
>diode on the
>P/S near the edge of the board. I can not sit here and tell you how to
>adjust
>it. It one of those things you have to know! Call Mike Ennis at Ameritrons
>Service Dept. and talk to him about it. Check the cap at the base of the
>plate
>choke to make sure that did not get wiped out also. The flash-over is
>going to be
>in the RF deck, most likely. One time I did have a short from the metal
>supports for the capacitor board to ground, ( those metal supports are at
>chassis
>ground) and I had to adjust them. Some of the wires to that board that go
>between the diode board and the capacitor board, are close to those
>support post's.
>Without looking at it, that is as far as I can trouble shoot on the
>internet!! Willy K3VW
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>
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