[Amps] add on MUFFIN FAN

[Robert W5AJ]

The 89 amp that I'm working on has a PAPST 4850 X muffin fan installed on back

This fan is of questionable value as I see it
the fan curve passes 45 CFM at 0.04 Inches of Water pressure 
It's unknown who installed this fan or when this fan was installed

IF you're going to install a muffin fan to help cool for RTTY or contesting or LONG rag chews
Get a good one!
A Comair muffin fan curve (graph) model MX2B3 / MX3A3, MX3B3 passes through 50CFM at 0.2 inches of water
A significant improvement from the 4850X muffin! 
http://pages.suddenlink.net/w5aj/dentron/dentron8.jpg


73
Robert W5AJ
Midland, Texas
http://pages.suddenlink.net/w5aj/

-----Original Message-----
From: Robert W5AJ [mailto:woodr90 at gmail.com] 
Sent: Sunday, April 04, 2021 9:31 PM
To: 'MU 4CX250B' <4cx250b at miamioh.edu>; 'gudguyham' <gudguyham at aol.com>; 'Amps at contesting.com' <Amps at contesting.com>
Subject: RE: [Amps] 89 Alpha schematic

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 at miamioh.edu]
Sent: Sunday, April 04, 2021 7:50 PM
To: gudguyham <gudguyham at aol.com>
Cc: Robert W5AJ <woodr90 at gmail.com>; amps at 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 at 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 at 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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