[Amps] Alpha 89 Fuse Blowing

[jeremy-ca]

I dont know the impedence of the Alpha PS but that sounds like too low a 
resistance to do much good. The 89 is blowing fuses before the high priced 
fault protection takes effect.
Since Alpha never bothered with any surge resistor until recently it doesnt 
speak much for "design excellence". Maybe they copied it from the Titan or 
by reading this reflector since its inception. I know that Tom, myself and 
others always stessed its importance.

As Ive mentioned before the NCL-2000 had surge limiting since the design 
started in 1962.

Carl
KM1H

----- Original Message ----- 
From: "Dick Green WC1M" <wc1m at msn.com>
To: "'jeremy-ca'" <km1h at jeremy.mv.com>; "'Robert Carroll'" 
<w2wg at comcast.net>; <amps at contesting.com>
Sent: Monday, August 06, 2007 3:43 PM
Subject: RE: [Amps] Alpha 89 Fuse Blowing


> An HV surge resistor is shown on the 87A schematic: 25W 10-ohm. Haven't
> pulled the cover of mine, but I'd bet it's an enamel wire wound. Wouldn't
> expect anything less from a top-of-the-line amp designed by Dick Ehrhorn.
>
> 73, Dick WC1M
>
>> -----Original Message-----
>> From: jeremy-ca [mailto:km1h at jeremy.mv.com]
>> Sent: Monday, August 06, 2007 3:24 PM
>> To: wc1m at msn.com; 'Robert Carroll'; amps at contesting.com
>> Subject: Re: [Amps] Alpha 89 Fuse Blowing
>>
>> If those amps dont have a HV surge resistor then install one. Something
>> in
>> the area of 20-25 Ohms 20-50W will do. Be sure it is a true wire wound
>> "Vitreous Enamel" style and not cement. The purpose of the resistor is
>> to
>> limit fault (gas arc) current and survive.
>>
>> Carl
>> KM1H
>>
>>
>> ----- Original Message -----
>> From: "Dick Green WC1M" <wc1m at msn.com>
>> To: "'Robert Carroll'" <w2wg at comcast.net>; <amps at contesting.com>
>> Sent: Monday, August 06, 2007 3:17 PM
>> Subject: Re: [Amps] Alpha 89 Fuse Blowing
>>
>>
>> > Sounds like a gassy tube. I had a similar problem with my 87A. I
>> replaced
>> > one of the original tubes because the amp was periodically failing
>> with a
>> > filament current fault. Then the amp started getting random faults,
>> mostly
>> > related to power supply voltages. Eventually the faults became more
>> > frequent, and one of the 20A fuses kept blowing. Even the 1A fuse in
>> the
>> > step-start faulted once.
>> >
>> > After tearing the amp apart and thoroughly testing the power supplies
>> and
>> > other components, I realized it had to be a tube arc and replaced the
>> new
>> > tube with the old one. Sure enough, that fixed the problem. The
>> filament
>> > current problem went away, too. I'm pretty sure that fault was the
>> result
>> > of
>> > poor pin/socket contact that occurred when I removed and reinstalled
>> the
>> > old
>> > tube to troubleshoot another problem. Eimac replaced the bad tube
>> under
>> > warranty. So, my amp is still operating with the original set of
>> tubes
>> > installed at the factory in 1995.
>> >
>> > Evidently, if the arc is big enough it can blow the fuse before the
>> fault
>> > detection circuits in the 87A have time to react. I suspect the same
>> is
>> > true
>> > of the 89. I don't think it's a good idea to rely on the "fuses are
>> > cheaper
>> > than tubes" credo. If the arc can cause the fuse to blow, it may
>> cause
>> > other
>> > damage. If I were you, I'd see if I could borrow a spare 3CX800 tube
>> and
>> > use
>> > it to confirm that the problem is being caused by a bad tube, and if
>> so,
>> > which one. Then I'd replace the bad tube.
>> >
>> > 73, Dick WC1M
>> >
>> >> -----Original Message-----
>> >> From: Robert Carroll [mailto:w2wg at comcast.net]
>> >> Sent: Sunday, August 05, 2007 4:35 PM
>> >> To: amps at contesting.com
>> >> Subject: [Amps] Alpha 89 Fuse Blowing
>> >>
>> >> Seeing there have been several recent discussions of amps blowing
>> >> fuses, I'd
>> >> like to ask for opinions on my Alpha 89.  For about two years now
>> the
>> >> amp
>> >> will be trouble free for a couple of months and then while sitting
>> idle
>> >> in
>> >> standby, blow what has been every time but once the upper of the 20A
>> >> fuses.
>> >> I replace the fuse and all is well for a month up to a few months
>> and
>> >> it
>> >> blows another fuse.  Most of these have blown when I am out of the
>> >> shack,
>> >> but occasionally I will be watching while it occurs-no pop no snap,
>> but
>> >> the
>> >> amp suddenly is off-no sign of the red fault light.  The last time
>> this
>> >> happened, I had keyed the amp with very little drive and when I did
>> so
>> >> I saw
>> >> the red fault light turn red as everything coasted to a halt.  This
>> was
>> >> the
>> >> first time it had failed during transmit, and again a fuse
>> replacement
>> >> revived it. The tubes in this amp probably have 300 hours or so on
>> them
>> >> and
>> >> deliver 2KW without complaint.  It is easy to suspect a tube
>> flashover,
>> >> but
>> >> replacing a fuse every few months is a lot cheaper than replacing
>> the
>> >> tubes,
>> >> especially given their relatively low hours. I have snooped around
>> >> looking
>> >> for spit marks and have found none.  I have vacuumed the amp with no
>> >> change.
>> >> This amp has been a little squirrelly from the day it arrived from
>> the
>> >> factory, in contrast to an Alpha 86 which has not missed a beat
>> other
>> >> than
>> >> having the fan changed-still on the original tubes.  I suppose I
>> could
>> >> swap
>> >> tubes at some point to see if the trouble follows the tubes, but I
>> like
>> >> to
>> >> keep the mitts off something which is working.  If any of you have
>> >> suggestions as to possible causes or methods of tracking down such
>> an
>> >> infrequent problem I would appreciate hearing them.
>> >>
>> >>
>> >>
>> >> 73
>> >>
>> >> Bob W2WG
>> >>
>> >
>> >
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>> >
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