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.....
The cure is often simple. Actually read and use the tuning instructions and
charts included in the NCL and several other manuals; its a starting
position. Then make up a chart for your own antennas and frequencies. Dont
underload as you are rather fond of stating elsewhere. Without a reduction
vernier the Load control was touchy on 10/15 as is the case in several amps
when the Jackson Brothers drives were rather unknown and Oren Elliott hadnt
cloned them yet.
Ive seen several AL-811/811H and AL-80 family switch failures also and Id
bet the designer would say it wasnt his fault.
OTOH the prototype NCL Ive had since 64 still has the original switch and
was run hard until 86 in contests and DXing including CW on the SSB position
at 1200W and is still going strong with some vintage SSB/AM gear. Another
one, absolutely mint, is paired with a HT-32B and SX-115; never a hint of
arcing.
Since the NCL-2000 doesnt cover 160 it shouldnt have even been mentioned by
you and Im not going to continue the thread here and get Tree upset. Youre
welcome to reply on QRZ.com where you appear daily.
Carl
KM1H
----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "Carl" <km1h@jeremy.mv.com>; "Bill Wichers" <billw@waveform.net>;
<topband@contesting.com>
Sent: Tuesday, March 18, 2014 9:55 PM
Subject: Re: Topband: Antenna matching question
If this is only 160-40 you probably won't have a series resonance issue
with unused turns, but if you cover a wide range you will want to
progressively short the large coil taps. This is why band switches that
do not short (like the old National amp) and why large roller inductors
mess up on higher bands.
If you mean the NCL-2000 I suggest looking at the schematic again. Or
did National make another ham amp that Ive missed??
Here you go, Carl
http://www.arizona-am.net/PHOENIX/W7CPA/W7CPA%20NCL-2000%20BS%20Before.jpg
That's the wrong way to do a bandswitch. It does not pick up and hold the
lower band contacts when switched to higher bands. This allows the taps to
build up high voltages on lower band taps when working higher bands.
Switches should be pick up and hold, or progressively shorting.
73 Tom
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