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@jeremy.mv.com]
> Sent: Monday, August 06, 2007 3:24 PM
> To: wc1m@msn.com; 'Robert Carroll'; amps@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@msn.com>
> To: "'Robert Carroll'" <w2wg@comcast.net>; <amps@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@comcast.net]
> >> Sent: Sunday, August 05, 2007 4:35 PM
> >> To: amps@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
> >>
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
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