Topband: Antenna matching question

Ray Benny rayn6vr at
Wed Mar 19 20:56:09 EDT 2014

I have burn up two output band switches on my Ameritron AL1200 while on
160m. The amp uses a single 3CX1200A7 tube. My swr may have been high, but
less that 3:1.

Could the discussion above be the same for the AL1200 amp? I'm tired of
replacing the band switch. I looked at replacing it with a larger switch,
but there is not enough room.

I am not an electronic tech, but I can understand most of the



On Wed, Mar 19, 2014 at 9:12 AM, Tom W8JI <w8ji at> wrote:

> Wrong reflector, but I disagree completely with this:
>  The HV build up was mitigated by the 10pf cap between the 40-20M
>> positions which also reduces arcing on the SB-220 which is a shorting
>> switch and a cap can be adapted to some 160-10M amps.  The right hand one
>> in that photo had the 80-40M contacts replaced and Id bet there was still a
>> carbon track that wasnt removed, you can easily see the deposits all around
>> that wafer; a good sign of a poor repair tech. Originally a sure sign of
>> high VSWR or open relay.
>> Same style wafers as in the SB-220, Clipperton L , AL-80 family and
>> others that lived on the edge that still arc today. The arcing is usually a
>> high VSWR, open circuit due to relay, way out of tolerance carbon parasitic
>> suppressor resistors, mistuning as was likely the cause on the left wafer
>> on 10M, and CB use since the NCL-2000 was one of their favorites in the
>> 70-80's. Another cause is not knowing how to read the manual tuning
>> instructions and tuning full bore key down in the SSB position. As built it
>> was a 1000W INPUT CW amp and 2000W INPUT PEP on SSB. That is about
>> 600/1200W output respectively as was common on many amps of the pre 1500W
>> output era. Funny how they all seemed to be OK before the rules changed and
>> switch configurations werent an easy way out to cast blame.....
> _________________
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