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Author Topic: help tuning a uhf tpl mobile amp  (Read 1699 times)
KC2BAZ
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Posts: 4




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« on: January 10, 2011, 03:57:15 PM »

i bought a tpl uhf amp model pa6-1fe its tuned for 468.25 can someone please tell me how to get it on the ham bands thanks 73s ...
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AD4U
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Posts: 2151




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« Reply #1 on: January 11, 2011, 07:40:43 AM »

Are there any adjustable components inside?  If there are mica compression caps you may be able to adjust the amp.  If there are no adjustable components inside, the first thing I would do it try it like it is.  Most UHF amps have a rather wide useful range.  Have you tried it "as is" with low drive into a dummy load with a wattmeter to see how it works?

You can use this test to calculate the efficiency of the amp in the HAM band.  Power output as measured on the wattmeter divided by power input to the amp (voltage to the amp X the current drawn by the amp).  Since I don't know what class this amp runs (probably class C), I suggest that if the amp's efficiency is over 60% just run it as is.

Dick  AD4U
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KK5J
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Posts: 76




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« Reply #2 on: January 11, 2011, 12:40:15 PM »

There is a service manual in pdf format on the internet, locatable by a Google search.  This amplifier is similar to a Motorola design for UHF amps and has adjustible input to tune the amp.  It does require two separate wattmeters at UHF (Bird) to minimize SWR while maximizing amp output.  You will need a power supply, two Bird meters or equivalent, coax jumpers, proper adjustment tools (non-inductive type tuning tools) to adjust the capacitors (they also recommend a spectrum analyzer but you could probably get around that), and of course you need the service manual in order to locate the two caps. Hope this gives you a general idea, and yes it is tunable across the ham bands with output near 100 watts according to TPL literature.
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