[Amps] Dual 3CX1500A7 144 MHz Linear Motorola Conversion

[craxd <craxd1@ezwv.com>]

Chris,

Charles Byers who makes the chassis kits may be able to help you on 
this. Explain to him what you need, and direct him to that website with 
the drawings for the parts. His e-mail is below. He's doing some work 
for me right now but is going in for knee surgery (on both knees) later 
this month. You would need to get up with him before this.

His Email:   k3iwk@flash.net

Will Matney



Hi,

In June there was a post to the group from someone looking for information on the conversion of a Motorola Quarter Kilowatt high band VHF PA which uses two small conduction cooled tubes that are replaced with two 8877/3CX1500A7 triodes.

You can find pictures of the first PA converted at this URL: http://webhome.idirect.com/~ve3kh/amplifiers.html - I have since built a second unit which is much nicer, but has not been tested yet. After testing is completed I intend on drawing it up on autocad and providing pictures of the new version early next year. The differences fromt he first to the second PA are as follows:

Two fil transformers, one for each tube instead of a single shared xfmr.

Two separate B- bias circuits for each tube instead of one.

Filament feed throughs moved from rear of unit to left and right side of chassis, re-using the four original ceramic chassis feeds throughs (moving two of them to the right side).

Two large holes cut into the top of the PA (with chrome fan guards to keep it safe) to let air out instead of a large small diameter hole pattern drilled into the top of the unit.

A single large dual "squirrel cage" fan attached directly to the underside of the PA instead of using a hose coupling from an external blower.

Metering jacks moved to left and right side of PA for left and right tubes instead of one grouping of connectors on one side.

Two large handles attached to the front of the PA to make it easier to carry and mount the PA to a 19 inch rack.

Input tuning control knob moved to the front of the PA instead of being located on the rear side of chassis.

At the time I built this I had intended on using G3SEK's triode board for this PA, but at the time he didn't have one to run two 8877's off of one board so I just duplicated the W6PO bias and control design twice. 

I hope this post doesn't show up twice because I tried sending it late last night right after joining, but believe it was probably rejected because I either did something wrong, or sent it too soon after submitting my request to join.

I have a few pictures of the 2nd PA if anyone wants to see them email me and I will email the pictures, but they are high resolution and will require several meg of download.

73 Chris KL7FB Palmer, Alaska.


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