Hi Paul, et al!
The fuse F3 is a 2 amp SB for the 77DX and a 3 amp SB
for the 77SX. Only the K2B contact is fused. The other
side of the line (K2A and R1) have no fuse. If K2B welds
closed, R1 will make a big mess in your box. If K2 never
closes at all, you will probably loose both step-start resistors. (R1 and R2.)
Very messy indeed! A lot of guys just keep changing F3 until the resistors
explode.
While one is in this area, it is good PM to check all of the
power resistors and wire-dress in the bleeder string and B- .
(((73)))
Phil, K5PC
Phil Clements
410 VZ CR 4903
Ben Wheeler, TX 75754
----- Original Message -----
From: "Paul Christensen" <paulc@mediaone.net>
To: "Phil Clements" <philk5pc@tyler.net>; "NOLL AMIDZICH" <NAMIDZICH@wi.rr.com>;
<amps@contesting.com>
Sent: Tuesday, June 12, 2001 9:19 AM
Subject: Re: [AMPS] SICK ALPHA 77DX
>
> This has always been a concern of mine and in fact an older Alpha PA-70V I
> restored suffered from this: At one point during the restoration process,
> the +28 VDC supply failed upon start-up. Since this inhibited the
> step-start process (K2 contact closure), both 10-ohm/25-watt step-start
> resistors quickly failed and left a Helluva mess afterwards. I had cuts all
> over my hands from the glass/vitreous enamel shrapnel during the clean-up
> effort.
>
> My current PA-70V was designed prior to the factory integration of the "F3"
> step-start fuse. I'm assuming that F3 is placed in series with one of the
> two 10-ohm @ 25-watt resistors? In factory units, is this fuse panel
> mounted or simply installed as a "pigtail" fuse holder on the step-start
> frame? Also, what is the fuse rating? I would think it's a slow-blow
> device? Thanks!
>
> -Paul, W9AC
>
> ----- Original Message -----
> From: "Phil Clements" <philk5pc@tyler.net>
> To: "NOLL AMIDZICH" <NAMIDZICH@wi.rr.com>; <amps@contesting.com>
> Sent: Tuesday, June 12, 2001 9:56 AM
> Subject: Re: [AMPS] SICK ALPHA 77DX
>
>
> >
> > This is a common problem in old Alphas.
> > F3 is a protection fuse in case the step-start
> > relay fails to close in its allotted time.
> >
> > Check K2 and R2 for failure/burning
> >
> > GL!
> > Phil, K5PC
> >
> >
> > Subject: [AMPS] SICK ALPHA 77DX
> >
> >
> > >
> > > Hello to all,
> > >
> > > I have an Alpha 77dx that had been working fine until yesterday.
> > >
> > > Now when I turn on the amp there is no high voltage. (There is about 230
> > > volts per the Alpha meter). The blower runs but the amp will not switch
> > > into the "standby mode". I checked the fuses and the 2 amp "F3" fuse
> had
> > > blown. I replaced this fuse with another 2 amp "slow blow" fuse.
> Powering up
> > > the amp again resulted in another blown fuse after about 3 seconds.
> > >
> > > Any advice would be appreciated.
> > >
> > > Thanks
> > >
> > > Noll W9RN
> > >
> > >
> > > --
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> > >
> > >
> >
> >
> >
> > --
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> >
>
>
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