[AMPS] Band Switch Heath SB-1000

[Rich Measures]

Warning:  This is a long reply.  Rich unfans are strongly advised to 
click Delete at this point.  
...snip...
>> Unless showered with spilt coffee, the AL-80 and the SB-1000 
>>bandswitches can withstand over 5500v.
>
>I believe you are wrong about the switch specs Rich....
 I did not say that these were the switch specs.  This is the measured 
withstanding voltage for a clean, dry switch. 
 When I receive your toasted AL-82 bandswitch, Carl, I will measure the 
voltage withstanding ability of the remaining good contacts, and post the 
result.  .  
....snip....
>In a mistuning test, the 
>>measured piv increased a bit under 30% maximum.  However, the settings 
>>to 
>>produce this condition were far, far removed from the settings that 
>>produced max. RF to the antenna, which is how most folks tune an 
>>amplifier.  
>
>That statement only holds true...with reservations....when you are
>dumping into a purely resistive load. Reactances as are typical with some
>ham antennas can transform that voltage to very high levels....if the
>load is not absorbing power the tank voltage can approach that calculated
>in the UNLOADED Q of the circuit...not the magic Q of 12. 
10 to 15 is close enough, IMO.  
> You were close
>the other day when you mentioned the Tesla Coil effect.  The actual
>voltage can vary between both extremes. 
Surely, but what percentage of amplifier operators tune up with the 
output coax disconnected?   When the antenna has a low SWR and the 
bandswitch mysteriously crispy-critters after the amp. has been tuned up, 
I know to check the value of the VHF suppressor R.  I got into the same 
argument with Mr. Rauch.  He presumes that bandswitches in Ameritron 
amplifiers only arc because of operator error (a euphemism for 
drooling-idiot), 'cheap coax' and 'bad antennas'.  However, I have spoken 
with a number of people who have had such bandswitches fail from arcing, 
and I am convinced that Mr. Rauch is using a Rauschian Fact-Filter.  (sic)
>>--.Carl:  Have you measured the VHF suppressor resistance in an 
>>amplifier 
>>that came in for repair with a crispy-crittered bandswitch? 
>
>No, the old suppressor usually gets trashed anyway and I use my own
>version for a replacement. 
If the VHF suppressor is being trashed, one snip, clip on an ohm meter, 
and you have a clue as to whether VHF oscillation was present.  It takes 
less than 15 seconds.  
>Time is money and my customers bitch when I do
>R&D on their nickle.  After 5,10,20 years any carbon comp resistor is
>going to change value when subjected to even its rated dissapation at DC.
> Severe changes in value I have found, and mentioned here months ago with
>nary a response, ...
I missed the post. 
>...are usually indicitave of high levels of RF above
>50MHz....parasitics, harmonics or whatever.  Those 2W carbons just do not
>like VHF heat  period.   
Agreed.  Knowing this as you do, why presume that a bandswitch was 
toasted by a drooling-idiot operator?  If you don't ohm, I don't see how 
you could have known.   
Rich---

R. L. Measures, 805-386-3734, AG6K   


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