[Boatanchors] general PA question

[Brian Clarke]

Be careful Eugene,

The cathode idle current depends on the Class of operation. For Class C, key 
up, it should be zero; Class B will be higher and Class A will be even 
higher.

Unless the Class of operation is specified, all 'statements' of idle current 
are spurious.

Bias determines, in large measure, the Class. However, there are other 
possible problems - parasitic oscillations and incorrect neutralisation.

73 de Brian, VK2GCE.

Eugene asked:

> Hi there. I am working on a power amp.
>
> The unit runs 2 4cx1500B's in parallel driven by 2 8122's in parallel.
>
> When idle (no rf input, no key) the plate current is supposed to be 0 ma.
> However, I seem to get about 100ma.
>
> When keyed at 1KW output, I get a little 750-800ma plate current. The
 > unit is not supposed to exceed 750ma (800 absolute max).
>
> Does this sounds like a bias problem? Could an incorrect bias voltage
> cause about 100ma too much current overall?