Topband: Antenna matching question

[Carl]

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 at w8ji.com>
To: "Carl" <km1h at jeremy.mv.com>; "Bill Wichers" <billw at waveform.net>; 
<topband at 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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