[AMPS] SB220 problem

[Rich Measures]

>
>Hi Ben,
>
>> I bought an SB220 amp that wasn't putting any power out on 10 meters, but
>> 1200 to 1300 on 20 and 15 mtrs.  It turned out to be a fried bandswitch on
>> 10 thru 20, but was hanging on with a hair on 15 and 20.  I replaced the
>> bandswitch and while I was at it, i installed Harbach mods. (parasitic
>> suppressor, soft key, soft start, and rectifier-metering board kits) I
>> also installed new resistors across HV caps from Rich Measures yesterday 
>> Now on 20 it will arc a bluish color on bandswitch when driving it up to
>> abt 300 watts out.  I tried it on another band(I think it was on 15) and
>> the exact same thing.  I noticed that the tune control on 20 mtr tuneup
>> was peaking out at the 10 mtr position(knobs are installed correctly). 
>> This tells me that there is too much inductance in the circuit.  
>
>You may have ruined the bandswitch from too little loading. Despite 
>what you hear, very few problems like yours (if any) are "parasitics".
>
>What happens is this.
>
>If the loading control is too far closed, or if you have a fault that 
>causes the load impedance presented to the tubes to go very high, 
>the peak tank voltage could easily become many times the normal 
>value. What happens is the tubes build up all that energy in the 
>tank, and it has nowhere to go.
>
€  Did the arcing occur when the loading cap was set near max. C and the 
load was disconnected?
........


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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