[Amps] Alpha 86

[Vic Rosenthal]

R. Measures wrote:

> 
>>lou de beer wrote:
>>
>>
>>>Anyone own an Alpha 86...I have a question regarding the bandswitch.....
>>
>>I just replaced a bandswitch wafer on one.  ...
> 
> 
> ***  Vic --  I would like to buy the old bandswitch wafer from you if you 
> are willing to part with it.  I am also looking for kaput 3cx800A7s.   tnx
> -  If anyone else has some of these items, please name your price.  

I will be happy to send it to you at no charge, Rich.  I think the 
question "why did this burn out" is interesting, because I know the 
individual who was operating it when it happened, and he did not 
hot-switch it.  He was attempting to load an 80-meter coax-fed dipole on 
160 meters (it was late, in a contest, etc.).  The contacts which burned 
were used to switch padders in parallel with the loading capacitor of 
the Pi-L output circuit.

The question then is, "Why didn't the amplifier trip off from excessive 
SWR?"  My theory, which I will happily hear attacked or supported, is 
the following:

The amp doesn't exactly trip on SWR, it trips on reflected power.  My 
sleepy friend found a setting of the controls which was highly 
underloaded, producing a very high circulating current in the tank 
circuit, and very little power out (and hence very little reflected 
power).  The current was enough to burn the contacts.  He probably was 
not driving it very hard, or it would have tripped on grid current.

I'll send you the switch tomorrow, Rich.

Vic K2VCO