>
>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" <w8ji@akorn.net>
>To: <amps@contesting.com>; "Ian White, G3SEK" <g3sek@ifwtech.com>
>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
>> W8JI@contesting.com
>>
>> --
>> FAQ on WWW: http://www.contesting.com/FAQ/amps
>> Submissions: amps@contesting.com
>> Administrative requests: amps-REQUEST@contesting.com
>> Problems: owner-amps@contesting.com
>>
>
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/amps
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>
>
- R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.
end
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|