Hsu wrote:
>Hi,
> Many years past.but why not use semiconductor device to protect your tube?
>many modern flash light in camera with muliti-times flash funtion,
> I think we can use similar schematic in our HV power supply.But the
> HV device(more than 5000V even higher ,thyristor or SCR) is very hard to
>get,manybe we have to put many
> SCRs in series.It'll very fast to cut the HV power supply.
That is "the next level" of protection, beyond the simple glitch
resistor and fuse/breaker. There are some classic papers by RCA
involving thyratron or ignitron tubes, and also a modern thyristor
design by OE5JFL:
http://www.qsl.net/oe5jfl/flashover.htm
OE5JFL uses 1000V thyristors in series, triggered by opto-couplers. The
thyristor stack "crowbars" the smoothing capacitor through an inductor
and a resistor, while at the same time a solid state relay shuts off the
mains supply. Almost no destructive energy gets through to the tube or
the RF components.
Many European moonbouncers are using this circuit to protect expensive
UHF TV transmitting tubes (which are now obsolete and maybe could not be
replaced at any price). Siemens data sheets for these tubes specify that
if the B+ supply is short-circuited by piece of 3A fuse wire, the supply
must shut down WITHOUT blowing the fuse! The OE5JFL circuit will do
that.
Data for older tubes specify that the B+ can be shorted onto a piece of
cigarette foil without burning a hole in it... but nobody tries that any
more because cigarette foil is dangerous to handle :-)
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
>----- Original Message -----
>From: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
>To: <amps@contesting.com>
>Sent: Tuesday, February 03, 2009 2:14 AM
>Subject: Re: [Amps] Glitch Resistor
>
>
>> Bob Maser wrote:
>>>I'm having a hard time finding a 50 ohm 50W resistor for a glitch
>>>resistor for my 4CX1500B amp. Seems I remember that I could also use
>>>some AWG 30 for
>>>a glitch.
>>
>> If they mean to use it as a fuse instead of a resistor, then NO.
>>
>> A fuse provides no current limiting until *after* it has blown. In the
>> time it takes for a fuse to blow (which depends on the size of the
>> current surge) an arc from B+ can do a lot of damage.
>>
>> That is why Eimac recommends a resistor, to provide truly instantaneous
>> current limiting. The resistor is there to buy time so that some other,
>> slower device like a fuse or breaker can shut the HV supply down safely.
>> The resistor also guarantees an absolute maximum level of surge current,
>> that the rest of the circuit can be designed to tolerate.
>>
>> See the copy of Eimac Application Bulletin 17:
>> http://www.ifwtech.co.uk/g3sek/misc/bull17.pdf
>>
>>
>>
>>
>> --
>>
>> 73 from Ian GM3SEK
>> http://www.ifwtech.co.uk/g3sek
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
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