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[AMPS] construction of parasitics

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Subject: [AMPS] construction of parasitics
From: (2)
Date: Sat, 21 Jul 2001 06:48:37 -0700
Steve -
>Just bought an old dog sb-220 which has some Harbach mods including the
>parasitic kit---smooth as silk 80-10 including 12 and 17. Never owned a
>sb-220 before--guess it's going to be ok.

/\  To avoid the future possibility of a filament to grid short in a 
1.   the stock 1mH grid to ground chokes should have been replaced with 
1/4w or 1/2w,  24 - 39 ohm carbon film resistors.    Also, the grid choke 
bypass caps. should be padded with c. 1000 added pF to protect these grid 
{fusing} resistors from 10m RF. .
3.   there should be a 10 - 15 ohm, 10w vitreous-enamel (glass) coated 
resistor in series with the HV+.  A ceramic block type power resistor 
should not be used.  
>The Eimacs in it date 1971 and 72.

/\   One of the Amperex 8163/3-400Zs in my SB-220 was mfg. in 1967, and 
it still puts out normal PEP.  The reason is that unlike the TL-922, and 
four models of Henry Radio amplifiers, the SB-220 does not use excessive 
filament voltage.  An extra 12% in fil, V reduces emissive life to c.  
1/16  of normal.  

cheers, Steve

-  R. L. Measures, 805.386.3734,AG6K,  

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