Hi all....I have just completed a new single band 160 meter GS-35B
amplifier...After troubleshooting a minor bias problem I put some RF
into it this morning....Sadly I seem to have a problem which I have been
unable to resolve as yet....The HT supply is 3300volts using a new
AL-80B Power transformer....All this is operating normally....
Variable bias controlled from the front panel gives me a range from
nearly zero to 250ma.....This is also operating normally and for testing
purposes I have set idling current at 90ma......
Applying 20 watts of drive the amplifier tunes and loads properly grid
current loading down to around 60ma anode current to around 200ma...If I
increase the drive beyond 20 watts the anode current immediately shoots
to 800ma and the grid current off the scale tripping the protection
circuit....Power also drops to zero prior to the fault condition..
I have thoroughly checked all the components in the pi network and all
appears fine.....
I am wondering if I have a bad tube or is something else breaking down
in the output network somewhere...Maybe someone may have some ideas....
Happy Easter all........Bob VK3ZL....
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