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Author Topic: Linear amp for FT757GX  (Read 872 times)
GW4XXP
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Posts: 21




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« on: October 07, 2008, 05:23:31 AM »

Hi Folks,
 
I want to run a linear amplifier along side my 757GX and would be pleased to have your comments and suggestions as to what would be suitable.

What I have in mind is a linear with an output of 300 - 500 watts which is reasonably priced and will hook up without any problems. I have seen many amps for sale which could be suitable, but I haven't been able to get the information from the sellers that I am asking for here.

Your helpful suggestions will be appreciated.

GW4XXP Ray.
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N3JBH
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Posts: 2358




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« Reply #1 on: October 07, 2008, 05:44:03 AM »

Ameritron AL-811 (3 tube) I would say that amp would best fit your description, It is a 400 CW 600 watt pep amp. Requires a simple coax conection. 1 keying line. and a ALC line that is recomended but some folks leave off. Pretty simple really. Jeff N3JBH
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WW5AA
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Posts: 2086




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« Reply #2 on: October 07, 2008, 06:51:36 AM »

I second the AL-811...Run at 400 out it will last for ever.

73 de Lindy
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N6AJR
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Posts: 9930




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« Reply #3 on: October 07, 2008, 03:20:36 PM »

Or an IC-2KL if you have an Icom , or an ALS 600 auto tune manual band switch. or one of tha Al 811 or 811H amps would work too.

 if you get an amp that runs 600 to 800 watts and only run it at 400 or so, it wiill last for ever, and they can't hear the difference on the other end any how.

stay away form the sweep tube amps and some of the older ones like a clipperton l or such, and have fun
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WA3SKN
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Posts: 6526




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« Reply #4 on: October 08, 2008, 03:04:44 AM »

Keep your eye open for a used Yaesu FL7000.  That amp was designed to match the rig. (Unless you MUST have tubes, of course!)
73

-Mike.
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W5RKL
Member

Posts: 1032




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« Reply #5 on: October 08, 2008, 05:09:20 AM »

The FT-757GX's rear 8 pin molex connector contains pins that control an external linear amplifier's T/R relay. The maximum voltage and current rating of the switching pins is 50VDC at 300ma. The problem is finding the matching 8 pin molex connector.

The FRB-757 external relay control unit is no longer available and very difficult, if at all, to find used.

I simply duplicated the simple FRB-757 external control unit. The schematic is located in the FT-757GX/GXII's manual. The parts are readily available. The cost to duplicate the circuit, for me, was less than $10.

The relay is a cheap Radio Shack 12VDC relay, diodes are cheap 1N4007, transistor can be any PNP transistor; I used a 2N3906, connecting cables are cheap stereo interconnecting cables, and two 4.7K 1/2 watt metal film resistors.

The interface, when completed, should have 3 cables; 1 plugged into the 757's PTT, one plugged into the 757's 13.6VDC and one plugged into the AL-811's "RELAY" socket. You do not need the "PTT" socket (J01) shown on the FRB-757's schematic!

73
Mike
W5RKL
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