>
>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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