GS-31B 50mhz Amplifier Project..

VK3ZL Amplifiers
VK2OMD
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Re: GS-31B 50mhz Amplifier Project..

Post by VK2OMD » Sun Oct 06, 2013 11:21 am

VK3ZL wrote:Thanks for the link Owen..I will peruse it carefully...Bob..
I see Tom has written on the subject, I think after our discussion some years ago. See http://www.w8ji.com/tuned_input_circuit.htm .

It looks unfinished, and the page was last worked on a few months ago... so I suspect it is fairly new.

Owen

VK3ZL
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Re: GS-31B 50mhz Amplifier Project..

Post by VK3ZL » Sun Oct 06, 2013 4:21 pm

Sunday pm...Hi all...Well I have completed this project today...I will put some RF into it tomorrow and tune it up then run it for a few hoursto test reliability...

Pics show the finished amplifier..

Bob..VK3ZL..
Attachments
HPIM5848.JPG
Finished amplifier..
HPIM5853.JPG
On the work bench switched on into operate mode idling at 150ma...

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VK6OX
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Re: GS-31B 50mhz Amplifier Project..

Post by VK6OX » Sun Oct 06, 2013 6:27 pm

Looks like another superbly finished PA Bob...well done! 8)
I'm sure the on-air test will be just as designed!
73
Andy VK6OX

If you can't explain it simply, you don't understand it well enough. Albert Einstein

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VK2ZRH
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Re: GS-31B 50mhz Amplifier Project..

Post by VK2ZRH » Sun Oct 06, 2013 7:47 pm

Great stuff, Bob.

I want one :D

73, Roger Harrison VK2ZRH

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VK6OX
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Re: GS-31B 50mhz Amplifier Project..

Post by VK6OX » Sun Oct 06, 2013 9:14 pm

VK2ZRH wrote:Great stuff, Bob.

I want one :D

73, Roger Harrison VK2ZRH
Well you can't have mine Rog !!! :P :P :P
73
Andy VK6OX

If you can't explain it simply, you don't understand it well enough. Albert Einstein

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Re: GS-31B 50mhz Amplifier Project..

Post by VK3ZL » Mon Oct 07, 2013 10:03 am

Good morning all..Well I connected this amplifier up this morning to tune it up..I used an Oskerblok meter to monitor through and drive vswr..Under 1.2-1 ..On the output I am using a Bird watt meter with a 1kw slug into a Bird 500 watt dummy load..

First tuning I just had to adjust the T input capacitor to achieve 1-1 drive vswr...The rest tuned up perfectly..Using 25 watts of drive the Bird says around 550 watts output with the amplifier fully tuned...Drive vswr under 1.2-1..Amplifier efficiency is around 55% so that's pretty good for the GS-31B..I am not interested in driving the tube any harder as the new owner is just looking for a legal limit amplifier..I have no doubt the amplifier will run more than 1kw..This project is now complete...I only have to finish the cabinet sides with a final coat of paint and give the amplifier a good run test over the next couple of days to check reliability..

I checked the tube anode for heat after 5 minutes of carrier at 400 watts output with my infra red temperature gun...Tube anode core nut and cooler measures 74C so cooling is more than ample..

Thanks to all those with their encouraging posts and emails..I am now going to do a bit more work on a 70cm amplifier, complete but requires further work...Then my next project is another 2 meter amplifier..

Pics are the metering results this morning..

Bob..VK3ZL..
Attachments
HPIM5854.JPG
Oskerblok showing bypass vswr..
HPIM5855.JPG
Oskerblok showing amplifier drive vswr..
HPIM5856.JPG
Oskerblok and Bird watt meter readings...Drive vswr less than 1.2-1 and Bird meter showing around 550 watts output with 25 watts of drive..

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