>
>
>> -----Original Message-----
>> From: Richard [mailto:2@mail.vcnet.com]
>> Sent: 25 April 2002 04:01
>> To: g0ruz@btinternet.com; AMPS
>> Subject: Re: [Amps] homebrew glitch resistors
>>
>>
>>
>>
>> >Is there any mileage in making a homebrew glitch resistor for
>> use in series
>> >with the B+ using Nicrome wire on a 1 inch diameter ceramic
>> former. It seems
>> >to me that it should be fairly easy to make one with the necessary
>> >resistance,current and voltage breakdown characteristics.
>> >
>> >Has anyone done it? The commercial equivalents are really
>> expensive here in
>> >the UK and we seem to see very few surplus nowadays.
>> >
>> ? I would build one out of groved Delrin or ABS tubing and Ni-Cr
>> resistance wire. 12' of #22 Ni-Cr should be about right.
>> However, we buy glass-coated wire-wound resistors for glitch service and
>> the price per 250 is just over $1US each. One 10-0hm, 10W unit will
>> safely discharge c. 30uF @ c. 2900v. For higher V, we put more in
>> series. For tetrode-with-handles glitch resistors, which need to be able
>> to carry 4 to 6 amperes and discharge c. 2kJ of filter C, a real
>> pulse-rated R would be better, despite the added cost.
>> >
>> cheers, Conrad
>>
>
>Hi Rich yes we have resistors like that here in the UK. They are 12watt
>devices rated at 750 volts each
The 750V rating is max case to chassis V - provided the resistor is
touching the chassis. Glitch resistors should not be mounted against the
chassis/gnd. Glitch resistors need to be glass-coated/glazed ceramic in
order to be able to withstand the end-to-end peak-V without breaking down
between turns.
>and are made by Welwyn, its the low voltage
>handling that worries me, the supply is 4.5kV with 25uf of smoothing,
I would put 2, 12-ohm, 12Wers in series for RTTY duty at 1A ccs. For
SSB. a bit more R could be used. Two, 10 - 12 W glitch resistors in
series are better than one 20 - 25 W glitch R since they share the peak
potential during a fault.
>I suppose 6 x 4R7 in series would fit the bill. They just look a little small
>to me :-)
>
The acid-test for a glitch R is to short HV+ to the chassis. If the
circuit breakers open and the glitch R has zero damage, it's a winner.
cheers, Conrad
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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