Also I would add that if the tube is a tetrode or pentode, you must have a screen current
trip circuit as well. Otherwise, if the fuse blows for any reason you will destroy the screen.
On 10/25/2013 1:51 AM, John G3UUT wrote:
In a microwave, I believe that these fuses are before the rectifier in the AC
part of the
circuit. I'm sure everybody knows this but I'll mention it again. As AC drops
to zero
volts during a cycle, the chance of getting long lasting destructive arcs
(plasma arcs) is
much lower, therefore using them on DC in an amplifier is potentially
problematic.
Having said this I've used a microwave fuse in an amp, putting it before the
glitch
resistor on about 2.4 kV and it seemed to blow ok. They are very inexpensive
and
certainly attractive for use in amps and so a bit of research on their
usability would be
very useful. The fuse I used was in a white plastic insulating enclosure so
that if it
blew up removing the bits of glass wouldn't be difficult and I had a glitch
resistor to
limit the potential arc current. I suspect the voltage and the value of the
glitch
resistor are going to be the biggest factors determining whether there will be
an arc.
Take care doing the experiments.
73 John G3UUT
On 25/10/2013 07:49, Fuqua, Bill L wrote:
I would wait until New Years or July 4th to give one a try.
Hi Hi
73
Bill wa4lav
________________________________________
From: MU 4CX250B [4cx250b@miamioh.edu]
Sent: Friday, October 25, 2013 1:48 AM
To: Fuqua, Bill L
Cc: Amps@contesting.com
Subject: Re: [Amps] HV fuses
It didn't sound right to me either, Bill. The seller provided no data
sheets other then claiming a 900 mA/5kV rating for the fuses. I think
they were intended for microwave ovens, but am not sure. As I said, I
bought them out of curiosity because they were so cheap.
Sent from my iPad
On Oct 24, 2013, at 23:38, "Fuqua, Bill L" <wlfuqu00@uky.edu> wrote:
This does not sound right. I assume you are saying that they are glass fuses.
I suspect if you blow one in a HV powe rsupply it will shatter or explode into
pieces if
you have a reasonable value of filter capacitor. Do you have a data sheet on
these
fuses?
73
Bill wa4lav
________________________________________
From: Amps [amps-bounces@contesting.com] on behalf of Jim Garland
[4cx250b@miamioh.edu]
Sent: Thursday, October 24, 2013 7:58 PM
To: Amps@contesting.com
Subject: [Amps] HV fuses
Out of curiousity, I bought several 900 mA/5 KV fuses from an eBay Chinese
supplier. They arrived today. They fit fine into 3AG fuse clips, but are
about 50% longer. Internally they have a spring connected to the fuse link
which pulls the connection apart when the fuse opens. If they work, they're
pretty cool. and VERY inexpenisve. I'm wondering why one couldn't parallel
two or three of them to multiply the current rating? Assuming they're
reasonably well matched, so that the current divides equally among the
fuses, it would be a very compact and inexpensive HV protection circuit. I
would mount fuse clips on a piece of G10 circuit board and mount the
assembly on ceramic standoffs. When one fuse opened up, all would open up,
but replacing three fuses would cost only a dollar or so. I'll test some of
the fuses ( I bought twenty) to see how accurate their current rating is. I
have no convenient way to test their HV rating, but I'd use them only at
2500V in my dhomebrew amplifier.
73,
Jim W8ZR
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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