[AMPS] Band Pass Filters for Solid State Amplifiers

[Steve]

Hi Jim, I went trough a similar exorcise with a home brew amp. I tried the
circuit in the ARRL hand book using the five pole filter design. I popped the
600 v mica caps at 800 watts. The middle caps of the filter run at app. double
the voltage of the input to the filter. I also noticed the SWR to the filters
are quite high when the frequency approaches the upper end of the band in use.
High voltage mica caps are available from Cornell Dulilier
http://www.cornell-dubilier.com/HCD10.HTM
They are expensive in small lot sizes but they will sell them through a dealer.
Commercial amp manufactures use several ceramic disc caps in parallel to
increase the current handling ability of the caps. I feel that the mica caps are
still the best for RF use. I settled on a 3 pole filter in a pi configuration
using two 600 v micas in series for 160m through 15m and a five pole filter for
10m. I checked with a friend close by and the harmonics were down at least 40db
which was good enough for me. I run a KW into the filters and they survive, the
caps don't get warm and I use 2" core for the inductors and air coils for 10m.
Obtaining high power or high voltage components is becoming harder all the time
and the price keeps escalating, and some people wonder why we don't home brew
amps and other items for the shack, they must be one of those hams that went to
hamfests for the last 40 years and has been hoarding all that good stuff that
was around 40 years ago because I sure don't see much I can use at the hamfest
these days. GL with the project and if there is any other info you need send me
an email.

73, Steve

w7ry wrote:

> I am searching for an alternative for the low power harmonic filters that
> are utilized for solid state amplifiers.
>
> RFElectonics has a kit for their amplifiers but are rated for 500 watts or
> if you are careful, 800 watts.
>
> I am looking for something that would handle 1500 watts RTTY.
>
> What about using "doorknob" caps instead of 1000 volt silver mica caps ?
>
> What about coax cable stubs ?
>
> Most solid state amps are run in push-pull so second harmonic is usually not
> a problem.  3rd harmonic and 5th harmonic are the killers.
>
> Thanks and 73!
> Jim W7RY
>
> Shop Safely Online Without a Credit Card
> http://www.rocketcash.com
>
> --
> FAQ on WWW:               http://www.contesting.com/FAQ/amps
> Submissions:              amps@contesting.com
> Administrative requests:  amps-REQUEST@contesting.com
> Problems:                 owner-amps@contesting.com


--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com