[AMPS] Re: Alpha 76A

km1h@juno.com km1h@juno.com
Thu, 13 Mar 1997 21:21:01 EST

Hi Dick, I'm glad to see that you made it to this reflector.

With regard to the 2 holers, wouldn't it be advisable to use only one
3CX800? My reasoning is that the one tube can easily crank out 1300-1400W
and would closely match the output tank parameters. The other concern is
all of the extra heat thru that plenum with 2 tubes and the drag on the
power supply. We all know that most hams do not read the manual and tune
for max. Since the Ten-Tec Titan, Commander 2500 and other dual 3CX800
amps can easily do 2500W out at 100W of drive, what is to stop them from
attempting the same in a converted 76? Can it be done SAFELY?  In either
case it looks like you got your work cut out.....how to protect one tube
from 100W of drive and/or keep the whole shooting match from melting

On another subject you mentioned earlier:

I just completed a MLA-2500 conversion to 6M with a single 3CX800; I
think we talked about that on the telephone a month or so ago.  With some
deliberate input swamping, 50W of drive will give 1300W out.  Removing
all the HF parts made adding some air steering baffles fairly easy and it
exhausts mostly thru the top. The original muffin fan is more than
adequate when the normal speed is stepped up by changing the series fan
resistor. In fact, the high speed only comes on after extended
The old Amp Supply used two 3CX 800's in their LK-780 and 3 in the
LK-800; both with muffin fans. I have run the LK-780 for 8 years in
contest service with no problems; just periodic cleaning of the tube

73...Carl   KM1H

On Wed, 12 Mar 1997 18:08:47 -0500 (EST) Richard Byrd
<n4uq@mindspring.com> writes:

>Each one of the 8874's is good for about 500 watts output.
>I have not decided how to handle the two-tube 76 in regards to the 
>upgrade.  The two 8874's are mounted nearest the front.  There is no 
>for the rear tube so that presents a bit of a hurdle since the forward 
>the rear sockets are utilized in the upgrade.  The 374A is the same
>story...two tubes mounted near the front.

FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Sponsored by:             Akorn Access, Inc. & N4VJ / K4AAA