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
>>
>
>
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