W8ZR and "gudguyham"
THANKS
Conclude with:
Alpha 89 Schematic is in error on 2A fuse location
The fuse probably would protect R10 on failure of relay by opening and perhaps
protect equipment downstream from low voltage.
although my guess is amp won't enter OP mode before fuse blows and nothing
occurs (assuming relay is failed).
Agree with Jim on this one and I'll word it as The 2A fuse adds extra equipment
and labor to wire in that isn't worth it....
Robert W5AJ
Midland, Texas
http://pages.suddenlink.net/w5aj/
-----Original Message-----
From: MU 4CX250B [mailto:4cx250b@miamioh.edu]
Sent: Sunday, April 04, 2021 7:50 PM
To: gudguyham <gudguyham@aol.com>
Cc: Robert W5AJ <woodr90@gmail.com>; amps@contesting.com
Subject: Re: [Amps] 89 Alpha schematic
Clearly there’s an error in the schematic. So far as I can tell, the fuse
should be in series with R10, the surge-limiting resistor. It’s purpose is not
to protect R10, but to protect the amplifier in case the soft-start relay (or
associated timing circuit) malfunctions and doesn’t close. In that (unlikely)
event, the amplifier will try to run with R10 in line. The operator may not
notice anything awry until the amplifier starts to draw plate current.
Eventually R10 will burn out, but in the interim the filament voltage and bias
voltage will be too low, and the plate voltage will sag. The fuse, if properly
placed, will blow and shut the amplifier down before any damage could can
occur. We can debate the wisdom of including the fuse in the amplifier, but I’m
inclined to leave it out. It reminds me of the fuse designers used to place in
the cathode lead of grounded grid amplifiers. Again, it’s best left out.
73,
Jim w8zr
Sent from my iPhone
> On Apr 4, 2021, at 12:22 PM, gudguyham via Amps <amps@contesting.com> wrote:
>
> If the relay fails the fuse should blow before the resistor burns out.
>
> Sent from the all new AOL app for iOS
>
>
> On Sunday, April 4, 2021, 2:20 PM, Robert W5AJ <woodr90@gmail.com> wrote:
>
> This probably same for Alpha 86..
>
> photo of schematic showing incoming line and soft start at this link
> http://pages.suddenlink.net/w5aj/89Fuse2A.jpg
>
> Traced single wire from the 2A fuse to R10 - no other connections with
> that wire Indicates to me that the 2A fuse is in line with the
> resistor, should be shown in line above where it is shown.
>
> now to the question:
> decades ago, some designer for Alpha must have thought that fuse would
> serve a purpose.
> I can think of a few pointless purposes but nothing that justifies
> adding in the fuse.
> ANY Thoughts ?
>
> PS: Can't find other published designs that fuse the limiting
> resistor
>
> 73 W5AJ
>
>
> Robert
> Midland, Texas
> http://pages.suddenlink.net/w5aj/
>
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