[Amps] Electronic bias circuit shematic

[Carl]

>
> Subject: Re: [Amps] Electronic bias circuit shematic
> I don't like the idea of RF-operated EBS systems because it seems to me 
> very hard to avoid
> distortion at the beginning of a CW character or syllable when the system 
> first opens.
> What I have done in my last few projects is to drop the bias from cutoff 
> to operating
> level along with the t/r switching of the QSK/VOX system. Since there must 
> be a few ms
> delay built into this circuit before and after the start of RF, there is 
> plenty of time
> for the bias to change.
> I don't see how an RF operated system can have any advantage over this, 
> and it is much
> simpler -- it can be done with a couple of transistors or a reed relay.
>
> ##  His problem is his idle power is a whopping 800 watts on idle.  On the 
> russian
> 4CX-800s... its 225 ma per tube !   450ma for a pair..and an insane 675ma 
> for the
> 3 holer..and all at the same 2200-2500V.  You do the maths.
> Those tubes have lousy imd on ssb,  so to get the imd way down, the idle
> current is cranked way up.   A tri state bias works better than a bi state 
> bias scheme.
>
> ##  OK, on CW mode,  you don’t require EBS..whether you use VOX or QSK CW.
> On CW, you can increase the bias V..and decrease the idle current... like 
> crank the
> idle current WAY down.
>
> ##  On any GG triode, same deal, BUT you cant go much below 5-10 ma of 
> idle current
> on CW mode.   Biased to cutoff or beyond cutoff, the GG amp will generate 
> key clix.
>
> ##  On GG triodes that don’t require sky high idle power, on SSB, the 
> various ebs schemes
> don’t buy you anything when using VOX SSB.  None of em are fast enough to 
> cut off between
> syllables...or they will distort.   A little power is saved between 
> words..barely.
> The only real power savings is just  after the last spoken word..and when 
> the vox drops out.
> On PTT ssb, they do work.
>
> Jim  VE7RF


Ive been thinking about a variable bias for an AM linear. Something that 
would almost cut off the Ip when no speech. This would need some sort of 
audio activated carrier control that would not affect the Class C 
transmitter, just the amp.
Any ideas?

Carl