I have some suggestions, see below..... -WB2WIK/6
> -----Original Message-----
> From: Jeffrey Madore [SMTP:K1LE@ARRL.NET]
> Sent: Tuesday, March 04, 2003 9:58 PM
> To: AMPS@contesting.com
> Subject: [Amps] New question
>
> I'm working in a 2 meter solid state 100 Watt PA using a pair of 2SC2694's
> in parallel, with a Pi network output. The Pi network components are fixed
> except for a trimmer cap in the load position. With the correct values of
> chip caps installed, the output power peaks with the load trimmer plates
> fully un-meshed. I'd like to see this adjustment peak within range of the
> trimmer for obvious reasons.
>
> So, I assume the best thing to do is lower the value of the fixed cap in
> parallel with the trimmer in the "load" position?
>
> Since transmitting chip type caps are expensive and difficult to find
> (most are rated 100 volts or less), is there any reason why I couldn't
> replace it with an appropriate value dipped silver mica cap rated for 500
> volts, while keeping the leads very short.
>
>
> //You could also make a mica chip capacitor out of the dipped mica by
> breaking the insulation away, cutting the leads off entirely and soldering
> the end caps of the plate stack directly to the PCB foil. I've done this
> many times, it increases the srf (self-resonant frequency) of nearly any
> dipped mica substantially. It also damages the cap, at least the first
> few times you try it (unless you're very careful, or very lucky, or both),
> so it pays to have some spares.
>
>
> I also have some ceramic disk capacitors of roughly the value needed, that
> came from RF parts.
> Is there any advantage of ceramic vs. silver mica in this application?
> However, I have no idea of the voltage rating on these caps. They are
> listed as NPO in the catalog. I probably should know what that means but I
> don't.
>
>
> //NPO = zero temperature coefficient (reasonable change in temperature
> produces no change in capacitance). The dielectrics used to make these
> are usually also very voltage stable and have a lower voltage coefficient
> than other ceramics, so they are the #1 choice for use in power circuits.
>
>
> Once upon a time I was smart, made the big bux, etc. Then, while bending
> over a machine, I had a 100# steel cover fall from 3 ft, hit me on the
> back of the head, driving my forehead into the solid steel of the machine
> I was bending over. I awoke a changed man. I could write a book about the
> things I used to know, if only I could remember what they were.
>
>
> //What did you say? I forgot.....
>
> 73 and thanks for any help,
>
> Jeff - K1LE ><>
>
>
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