[Amps] Source of Mica Caps?

[Jim Thomson]

Date: Sun, 2 Jun 2013 19:58:58 -0400
From: "Carl" <km1h at jeremy.mv.com>
To: "Jim W7RY" <w7ry at centurytel.net>, "Randall K Martin"
<rkmassoc at comcast.net>, <amps at contesting.com>
Subject: Re: [Amps] Source of Mica Caps?


I still dont understand the claim made by a few that increasing gain and 
power output increases stability when hard grounding the grids.

I would take various web sites with a grain of salt and try to separate the 
good from bad.

The 115pf caps were chosen by Heath at the end of the SB-220 run and a 
bulletin suggested changing them. The SB-221 and HL-2200 use the 115pf but 
Ive replaced with whatever 110 and 120pf I come across in bulk. Ive yet to 
have instability in a well built and updated SB-220, even on 6M, with the 
Heath design.

Carl
KM1H

##  TL-922 are rock solid  when oem suppressors used  and grids directly grounded, and chokes tossed. 
Ditto with drake L4B..and just about every other amp that floats the grids with caps... including SB-220. 

##  Sb-220  with grids  directly grounded to chassis works superb on 6m.   I have seen  KM1H  SB-220
6m conversions, where the grids  were grounded to chassis...after the fact by the owner..works  great. 

##  The 25 ohm DC resistance of the chokes used in the SB-220  isnt doing you nay good..just more 
unwanted V drop.    The DC resistance  of the chokes used in the  Drake L4B   is less than 1 ohm. 
I still tossed the chokes and caps  in all 4 of my L4B amps.    

Jim   VE7RF

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