[Amps] tetrode push-pull amp schematics

[Roger (K8RI)]

Isn't class A idle current max (tube dissipation) with max signal giving 
minimum dissipation? (The tube is never driven "into" cut off)  Class B 
is at cutoff while class C is deep into cutoff?.

73

Roger (K8RI)

On 6/18/2015 7:13 AM, KA4INM wrote:
>
>   I disagree, it allows you to sit at a very low idling current with 
> little or no signal.  Every 100 Watt Japanese HAM transceiver that I 
> have looked at except for the latest units with LDMOS final amplifiers 
> (the ones with a Class "A" button) use a push pull class "B" stage.
> You do not need to change the bias or the amount of high Voltage to 
> suit different modes of use.  (modulation)  That includes AM.
>   You also get the power of two devices.
>   Someone hear-a-bouts said the devices need to idle at about 30% 
> current, but the transistors in my FT-990 idle at 100 mA with a peak 
> current of 10 Amperes.
>   Second harmonic cancellation gets the transceiver manufacturers a 
> low pass filter that is much smaller on each band and a fuller 
> utilization of the output devices power capability.
> If you use grid driven tetrodes your gain is so high that grid 
> swamping is normally or frequently used, even then low driving power 
> is used.
> At higher frequencies cross neutralization is easy for extreme 
> stability.  If you don't need as much drive power the intermodulation 
> products from your exciter is reduced.
>   The only rub is the balanced output tank circuit.
>   For your effort you get something, if it doesn't suit you don't do it.
>
>   Why anyone is happy with a pair of 3-500Z's operating class "A" 
> plate current beats me.


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