Ian Roberts wrote:
>
>measures wrote:
>> The negative end of the capacitor stack is limited to a couple of volts
>> above gnd potential due to use of glitch diodes in the metering
>> circuitry. The logical place for a glitch resistor is in the positive > HV
>lead.
>
>Presumably there are two possible places to insert the resistor: in the
>HT a.c. lead right out of the transformer, thus protecting everything
>including the bridge rectifier and caps,
No - the problem we're trying to protect against is not a surge into the
caps (a step start protects against that) but a surge *out* of the caps,
triggered by the tube going almost short-circuit.
The main source of danger to the tube is the energy stored in the caps.
All this energy can be dumped into the tube unless there's something
else to absorb it. The basic information is in Eimac App Note #17 [*]
>or immediately before the anode
>of the tube, thus protecting only the tube (and maybe not the meters)?
>
Strip the DC circuit down to its barest essentials, and then think about
where the current flows (for example, see the first two diagrams in
http://www.ifwtech.com/g3sek/boards/triode/triode-3.htm). One or more
meters will always be in the path of the current surge, unless they are
protected.
The purpose of the glitch resistor is to limit the maximum possible
current surge, and absorb most of the energy coming out of the caps. As
well as protecting the tube, you're then in a position to design some
effective meter protection.
[*] Who do we write to in Eimac to persuade them to put up a library of
scanned Application Notes as PDFs on their web site - or to authorize
someone else to do it?
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|