[Amps] Source of Mica Caps?

[Louis Parascondola]

Carl, your beloved LK-500 has hard grounded grids.  Did you change that design and float them?  If not what might be the difference in that design that makes it OK?  Always wondered about that.


 Ive yet to 
have instability in a well built and updated SB-220, even on 6M, with the 
Heath design.





-----Original Message-----
From: Carl <km1h at jeremy.mv.com>
To: Jim W7RY <w7ry at centurytel.net>; Randall K Martin <rkmassoc at comcast.net>; amps <amps at contesting.com>
Sent: Sun, Jun 2, 2013 8:03 pm
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 seperate 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


----- Original Message ----- 
From: "Jim W7RY" <w7ry at centurytel.net>
To: "Randall K Martin" <rkmassoc at comcast.net>; <amps at contesting.com>
Sent: Sunday, June 02, 2013 4:38 PM
Subject: Re: [Amps] Source of Mica Caps?


> Ground the grids directly and remove the caps and chokes. BUT install a 
> glitch resistor in series with the B+ and a diode from chassis ground to 
> B- (anode to ground, cathode to B-).  W8Ji's web site has lots of 
> information on this.
>
>
> 73
> Jim W7RY
>
>
> -----Original Message----- 
> From: Randall K Martin
> Sent: Saturday, June 01, 2013 5:39 PM
> To: amps at contesting.com
> Subject: [Amps] Source of Mica Caps?
>
> Does anybody know where I can buy a replacement for one of the mica grid
> bypass capacitors used in the Heathkit SB220? I believe they are 115 pf.
> Can't find anything close in the mouser catalog.
>
> 73
> Randy K0EU
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