[AMPS] Re: Clipperton L parasitic choke circuit

km1h @ juno.com km1h@juno.com
Mon, 13 Oct 1997 11:17:11 EDT

On Sun, 12 Oct 1997 14:46:25 -0700 "Michael S. Mitchell, W6RW"
<w6rw@earthlink.net> writes:
>Hi there Carl.....in a AMPS reflector posting that you made to
>Rich Measures on October 10 concerning B+ glitch resisors you
>briefly mentioned the Clipperton L problem that I have been
>experiencing....mainly that the parasitic choke resistors start
>to smoke when I tune up on 10 meters. The circuit consists of
>a 100 ohm 2 watt carbon resistor with a coil formed around the 
>(or in parallel with it) consisting of 5 turns of wire. There is
>one of these on each of the four 572B tubes. I have tried reducing
>the number of turns on the coil to 4, but the resistors still 
>smoke on 10 meters but at a higher power output level than before.

Dentron issued a Svc Bulletin early on for that amp. DO NOT place the
Load control BELOW 5 on 10M or 3 on 15M otherwise the amp will go into

If you cannot get a KW out then the tubes are probably soft. 

Another thing to check is the condition of the buss wires from the plate
blocking capacitor to the coil and the 10M switch position. If they are a
dark color they have become overheated and annealed. I usually replace
with #12 or #14 stranded silver plated Teflon insulated wire. ( I dont
think you can find stranded that is not Teflon covered) Solid silver
plated or silvered strap is OK too. 

The L is definitely a compromise amp but not too bad with a bit of work. 

If you run out of 2W Carbon resistors, Mouser now carries a nice 5W Metal
Oxide that  works real good....cheap too. You can't wrap the coil right
on the resistor so you might have to experiment with a bit of air gap
spacing or wind the coil externally. 

I also sell suppressors with two 5W resistors and a strap  inductor that
is pretty near bullet proof. 

>I am thinking about using a 68 ohm 2 watt carbon resistor and
>reduce the turns on the coil to 3 turns.

Not recommended unless you have lots of resistors and patience. Plus
fully understand the relationship between R and L in the suppressor along
with the parasitic frequency in the amp. Almost Black Magic.......

>I wonder if you have had any experience with this problem with
>the Clipperton L and if so what you did to fix it.

I developed my own suppressor design for 572B's so they would work on 6M
as well as they do on 40M.  After that 10M was a snap!

>I am sending a CC of this to the AMPS reflector to see if
>anybody else out there has figured this one out.

I'm sure Rich will have the usual canned reply........Maybe Tom will
share his suppressor design in the new Ameritron version with four

73    Carl    KM1H

>Thank you for your help es 73 de Mike/W6RW

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