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[AMPS] SB-1000 mods?

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Subject: [AMPS] SB-1000 mods?
From: (2)
Date: Tue, 11 Sep 2001 09:25:17 -0700
>Wouldn't the 4CX5000 tend to have a larger filter capacitor, and thus
>a bit more energy to dump, or is peak current the real concern? 

//  The "Plywood Box" amplifier has  >1000-joules of stored energy in the 
filter C .  A SB-220 amplifier has c. 80-joules.   Initially, the PB had 
an intermittent parasite problem c.68MHz.  Until I came up with a 
lower-Rp parasitic suppressor, the 
"big-bang" from a parasite was louder than the muzzle blast of a 12-gauge 
shotgun.  Judging by the schrapnel I saw, part of the noise probably came 
from the disintegration of the glitch resistor.  My guess is that a PCN80 
surge resistor would have survived a major glitch in the PB.  

>With Rich's example of the 10 ohm glitch R in the SB-220, and assuming some 
>stray R in caps and chokes, you are still talking about a peak current
>pulse on the order of 180 amps!! Seems like an awful lot of current. What 
>can the average plate choke withstand??

//  Apparently it's quite a bit,  The total ESR in an unmodified SB-220 
anode supply is probably c. 6-ohms,  At 2800v, that's  c.400a-peak.   
However, the current pulse is brief, so a 220's HV choke is seldom 
brought to grief.   
- The main reason for adding a glitch resistor is to reduce the 
peak-energy available (during an intermittent parasite) to bend the hot 
filament helix, and cause a filament to grid short,  
cheers, Mike

>----- Original Message ----- 
>From: "Tom Rauch" <>
>To: <>; "Ian White, G3SEK" <>
>Sent: Monday, September 10, 2001 10:16 AM
>Subject: Re: [AMPS] SB-1000 mods?
>> > In any case, the glitch resistor is one of those components that needs
>> > to be located in a cooling air stream.
>> > 
>> > Any idea how to get hold of these resistors in small quantities  at
>> > reasonable prices? Now it's Monday, is somebody gonna call 
>> RCD?
>> I'd suggest people check manufacturers. I'm sure many have stock 
>> components that will do.
>> For example, Ameritron has a variety of globar resistors and also a 
>> 400 joule 13 watt dissipation 1500 volt 10 ohm resistor as a 
>> standard component. A series combination of 10 ohm resistors 
>> would be a fairly inexpensive solution.
>> The resistance actually needs to be selected by the ruggedness of 
>> other components, not just by voltage. For example, a 4CX5000 
>> can take a big current whack compared to frail small tube like a 
>> 4CX800. With the 4CX5000, your biggest worry is other 
>> components like RF chokes and screen regulation systems.
>> I don't think X ohms per volt is a good rule, although I suppose it is 
>> better than nothing.
>> 73, Tom W8JI
>> --
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-  R. L. Measures, 805.386.3734, AG6K,  

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