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[AMPS] SB-1000 bandswitch damage

To: <>
Subject: [AMPS] SB-1000 bandswitch damage
From: (km1h @
Date: Thu, 12 Mar 1998 09:20:49 EST
On Wed, 11 Mar 98 16:45:49 -0800 Rich Measures <> writes:

>>>vhf regeneration. at roughly 155MHz.  .......
>>VHF Parasitics...highly unlikely.  ...
>Carl:  Please explain how  the 100 ohm resistor in the vhf suppressor 
>becomes damaged by 80m RF during episodes of intermittent bandswitch 

I cannot since I have yet to see resistor damage caused by 80M arcing.
The more likely scenario is that the resistor has already been overheated
during excessive tune-up time on 10-12M . That 2W carbon is very marginal
in that amp anyway, going to 2 of them or even better still a  5W metal
oxide is advised.
I have replaced AL-80A and SB-1000 bandswitches that have arced on all
bands; 160-10M. There is no particular pattern and roughly 90% of the
time there is no resistor damage. 
The PI-L that is used on 80 and 160M only in those amps can cause all
sorts of problems when mistuned, loaded into the wrong or high VSWR
antennas, and also when using an ATU.

Note that the Amp Supply LK-450 is a single 3-500Z amp but exhibits none
of the switch problems of the above pair. The LK-450 also uses a
different tank circuit design. 

Note also that the SB-1000 and early AL-80's require a plate choke change
for 17/12M operation.

73  Carl  KM1H

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