HV fuses are still produced:
https://kentec.net/pdf/eska/eska46.pdf
https://www.eskafuses.com
73
Peter
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Carl
Sent: Freitag, 20. September 2019 23:50
To: Paul Christensen; 'amps'; Mike McCarthy, W1NR
Subject: Re: [Amps] HV Fuse
Time to make your own from an open one or start from scratch..
Carl
----- Original Message -----
From: "Mike McCarthy, W1NR" <lists@w1nr.net>
To: "Paul Christensen" <w9ac@arrl.net>; "'amps'" <amps@contesting.com>
Sent: Friday, September 20, 2019 3:38 PM
Subject: Re: [Amps] HV Fuse
>I have an old Henry that has a Bussman HVB fuse. The larger HVJ is rated
> for 5KV. They are sand filled cardboard, not ceramic. Available from
> Mouser but are quite expensive. I'd look around for better pricing. I've
> never seen "small" high voltage fuses that were not cardboard.
>
> W1NR
>
> On 9/20/2019 3:04 PM, Paul Christensen wrote:
>> Yesterday, I lost all four HV bridge rectifier modules in my Alpha PA-70V
>> vapor-cooled amp. After replacement, HV returned but whatever caused
>> the
>> fault event also took out a 2N3053 switching transistor that controls a
>> 8.2V
>> Zener bias diode from the EBS circuit. I used the opportunity to change
>> it
>> to a more robust transistor in a TO-220 package that effectively doubles
>> Ic
>> and Vceo. The transistor is already configured as a "discrete
>> Darlington"
>> with a 2N4401 ahead of it so the shock didn't get very far on the EBS PC
>> board.
>>
>> Going back through the list archives, I see mention of using a HV fuse
>> just
>> ahead of an amp's glitch resistor. VE7RF recommended a second HV fuse
>> placed between one leg of the HV transformer secondary at the C-input
>> filter
>> cap. Sounds like a nice way to potentially save the HV bridge diodes.
>>
>> I have sized the glitch fuse adequately and will use a HV microwave oven
>> type as discussed in the archives. However, because of some unknown
>> variables, it's a bit tricky to calculate the HV transformer's secondary
>> fuse. I can use PSUD II software but primary and secondary HV
>> transformer
>> ESR are unknown variables.
>>
>> I'm also a bit skeptical that a fuse on the HV secondary will work as
>> intended due to the extreme initial C charging current (35 uF/5KV filter
>> cap), even though step-start will limit the initial inrush and that too
>> factors into the equation. I could just keep stacking 900 mA HV fuses in
>> parallel until they don't blow but that isn't an intelligent approach to
>> a
>> solution. Any guidance here?
>>
>> I don't see sand-filled ceramic HV fuses in this category and I dread the
>> thought of cleaning up glass shrapnel in an amplifier. I'm thinking that
>> Teflon heat-shrink tubing placed only over the glass portion should keep
>> the
>> shattering damage under control.
>>
>> Paul, W9AC
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
---
This email has been checked for viruses by AVG.
https://www.avg.com
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|