-----Original Message-----
From: Jeffrey Madore <K1LE@arrl.net>
To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: 03 September 2002 19:09
Subject: [Amps] cap ratings in tank ckt
>Gentlemen,
>
>I'm repairing the pa board (100w) in an Icom 275H and need to replace all 3
>of the monolithic chip capacitors in the output circuit, as they are burned
>open. I also need to replace the ceramic DC blocking capacitor between the
>tank coil and the antenna.
>
>My questions are:
>
>Where is a good place to purchase these caps? Icom has all but one of
them,
>but they want $6 to $8 each for a chip cap. I haven't bought these types of
>devices but that seems like a lot. In addition, Icom tech support says that
>they can't supply a replacement component for the one that is no longer
>available...I would have paid their price if they could have just given me
>what I needed.
>
>Secondly, the Icom service manual shows only capacitance values. What would
>be a conservative voltage rating for caps in a 12 volt 100w pa tank
circuit?
>
>Chip capacitors are really new to me. Is there any one type that would be
>preferable in an RF power application? What % tolerance is acceptable?
Without seeing the schematic I'm guessing, but they could be 'Hi-Q' ceramic
chips, often referred to as 'ATC', although ATC is but one manufacturer
(Dielectric Labs, Johanson and Murata are some of the others). Mostly they
come in 250 or 500V DC rating but in a low voltage PA, it's probably the
high current handling that's needed. Usually they are 0.1" cube. I'd be
surprised if you needed better than 10% tolerance, whether they are in the
amp section or the filters. Trade price for most brands in the UK is around
$1.50 each, 3-5x that for ATC brand (and I've yet to find them better
despite the ads). What are the values?
Steve
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