[Amps] Re: Amps Digest, Vol 15, Issue 10

[R.Measures]

•  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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