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
What I have done in my last few projects is to drop the bias from cutoff
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
4CX-800s... its 225 ma per tube ! 450ma for a pair..and an insane 675ma
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
## 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
idle current WAY down.
## On any GG triode, same deal, BUT you cant go much below 5-10 ma of
on CW mode. Biased to cutoff or beyond cutoff, the GG amp will generate
## 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
The only real power savings is just after the last spoken word..and when
the vox drops out.
On PTT ssb, they do work.