It didnt faze Alpha Rob. There is room for a socket on the tube box and
thats all they did for the PA/CA. The rest remains the same except for the
transformer and top cover. Some also had holes on the rear panel for a
transformer muffin fan as the PA EI version got rather hot at 1800-2000W
out.....when tubes were cheap.
Once the extra hole is punched and detailed for air flow its just as easy to
go with a pair of 3CX800's and get a real transformer to take full advantage
of the tubes, especially the 3CPX version. You can even just relocate the
one 8874 socket.
Carl
KM1H
----- Original Message -----
From: "Rob Atkinson" <ranchorobbo@gmail.com>
To: "Charles Hedrick" <cchedrick@gmail.com>
Cc: <amps@contesting.com>
Sent: Monday, January 30, 2012 1:01 PM
Subject: Re: [Amps] 3CX400/3CX800 Socket
Adding a 3rd tube is an interesting issue.
First I am speaking in general terms. I am not familiar with the 76.
I have pondered this as a paper exercise and came away thinking there
is a lot more to it than just adding a socket and connections for a
third tube with the chassis space. It seems to me that in general an
additional tube:
changes the anode Z so the output network may need a redesign or adjustment
may cause stress to the bandswitch, inductors and load caps
may draw too much current on the plate choke
Assuming cooling and h.v. supply are not issues, you have to work out
the new filament supply and maybe a change in the input Z
If the plate blocking caps were barely okay before they may have to be
replaced.
Anyway I found it an interesting thing to contemplate.
73
Rob
K5UJ
On Mon, Jan 30, 2012 at 9:16 AM, Charles Hedrick <cchedrick@gmail.com>
wrote:
> Good morning all,
> I have and would like to add a third 8874 to my Alpha 76 but need a socket
> and plate cap. If anyone has these to part with, please let me know.
> Thanks,
> Cam
> WA4JKW
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