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Author Topic: Alpha 78 3CX800A7 Conversion  (Read 3067 times)
W0VT
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Posts: 1




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« on: July 19, 2006, 05:17:43 PM »

Has anyone made the conversion to 3CX800A7 tubes in this amp on this reflector?  (I have another amp that uses 3CX800A7 tubes and am getting a pair to place within this amp which is a Harris.  That is another story).  I am thinking of making a conversion in my Alpha 78 to also use these tubes as the present 3CX400A7 tubes are weak and not up to PAR.  Getting my Harris amp up and running with these tubes has got me thinking of making the change to these tubes in my Alpha.  It might be a fun project to perform.  I'd be interested in hearing from anyone who has made this change to their Alpha model 78. (Going from three 3CX400A7 tubes to two 3CX800A7 tubes).  I see there is a web page out there showing a few of the neccessary changes but I'd like to hear from any others who have made this mod.
Lee
w0vt
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N0UA
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Posts: 22




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« Reply #1 on: August 08, 2006, 09:51:56 AM »

I am also considering the conversion. Here is some information that I have found.

AI4BB has a 76A for sale on QTH.com with the conversion.

Also, note that Peter Dahyl (http://www.pwdahl.com/) has  two replacement power transformers with the correct filament voltage for the 800s:
ALPHA 76A-1 POWER XFMR
FILAMENT WINDING FOR 3CX800A7'S
CORE) A-0393/ C-CORE        STYLE #) 10  HIPERSIL C-CORE
PR) 120/240 VAC 60 HZ 1 PH
S1) 0-1100-1750 VAC @ 0.5A CCS
S2) 40 VCT @ 0.5A CCS
S3) 25 VAC @ 1A CCS
S4) 13.5 VAC @ 3.0A CCS
================================================================
ALPHA 76A-2 POWER XFMR
SPECIAL HEAVY DUTY 3CX800A7'S VERSION
CORE) B-0393/ C-CORE        STYLE #) 10  HIPERSIL C-CORE
PR) 120/240 VAC 60 HZ 1 PH
S1) 0-1200-1950 VAC @ 0.5A CCS
S2) 40 VCT @ 0.5A CCS
S3) 25 VAC @ 1A CCS
S4) 13.5 VAC @ 3.0A CCS

Glenn of Alpha recently told me that Alpha "might" have the chassis work available for a conversion this fall (this in addition to the work by n4uq)!!! I am considering the hi-power version of the xformer with the correct filament voltage rather than the boost xformer.
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