Jim,
SSB VOX for N7CXI is a definite no-go. ;-)
I'll probably eke an EBS circuit out myself just for fun, but I like to
study what other people have done first. Call it plagiarism or whatever,
but every once in a while I find a design laying around gets my
attention and proves to me once again that there smart people out there
if you look hard enough. Sometimes bits of two or three things I find
laying around end up working better than the single thing I came up with
myself. Sometimes not.
Just for fun and to horrify everyone, I may put together something that
gives an inverse log bias voltage curve from a divided down, rectified
and smoothed directional coupler output. Now wouldn't an amp with that
drive the ARRL lab nuts? Heat-efficient and "dirtier" at low output,
with better and better IMD as output increases, not just one two or
three levels. The two adjustments required would be the desired "hard
bias" bias voltage and the range. Cutoff would be assumed and associated
with range, but then maybe not... I'll have to think about it.
Just daydreaming out loud here. ;-)
73,
Jim N7CXI
On 4/3/2012 8:46 AM, Jim Thomson wrote:
> Date: Mon, 02 Apr 2012 12:59:10 -0700
> From: Jim Barber<audioguy@q.com>
> Subject: Re: [Amps] amp cooling / triodes vs tetrodes
> Leigh,
>
> Not to drive everyone up a tree with this topic, but do you know of any
> non-proprietary designs that might serve at least as a basis for a
> properly-done EBS implementation?
>
> I'm not thinking so much of modifying my (newest) commercial amp, but I
> do have a YC156 project that seems to be in eternal overhaul, as well as
> a Henry 3KA that could benefit from such a beast.
>
> Along that line I also (still) have one Alpha 77 left with their EBS,
> but I'm not sure I'd qualify that one as more than a good start at
> "properly done", at least by today's standards. (It's from before they
> added the control pot, early design)
>
> Thanks,
> Jim N7CXI
>
> ### You can buy the entire TRI-state EBS from the Ameriton catalog.
> They have 1-2 versions of it. Complete, ready to go.
> It might need some tweaking to obtain higher V levels for a YC-156.
>
> ## I dunno why you would want to mess with EBS....if you use VOX on SSB.
> You don’t need to suck 350 ma of idle current on a YC-156. 150-200ma is
> plenty.
> 150 ma idle on a 3CX-3000A7 triode is plenty for superb imd .
> 150-200 ma idle on a 3CX-6000A7 is ample for good imd.
>
> ## On CW mode, there is NO reason at all to suck
> 150-350 ma of idle current !!!! On CW, just crank up the bias V..until the
> idle current is down to 10-20ma. Use a string of series 1N5408 or 6A10
> diodes
> for this job.. and or... a single wire wound resistor. On CW..with any
> GG triode
> you can not run the idle current at zero ma...or you will get key clix.
> With 10-20ma
> you wont get any at all. Tank eff will be improved a whole bunch too. Your
> idle power
> will be so low, it’s a non issue.
>
> ## EBS, even tri-state is a fubar way to go on CW..and also FM.
>
> ## EBS, if using PTT SSB is ok..and saves heat. If using VOX on ssb,
> the ebs will
> not buy you much for heat savings at all. The only time it kills heat is
> between when you
> stop talking..and when the VOX drops out. The EBS is NOT gonna be fast
> enough to toggle
> between syllables !
>
> ## If you want to see something really stupid, check out the 3 x hole
> tetrodes from QRO, etc.
> They idle at a whopping 750ma ! The 2 x holer idles at 450 ma (225 ma
> per tube)
> Using the 3 holer with the same plate xfmr as the 2 holer is even more silly.
> If any
> sb-220 etc, sucked 750ma, it would burst into flames.
>
> ## sure the small tetrodes can be driven with 10-20 watts. Who cares. The
> typ xcvr puts out
> 100-250w these days. You run a 200w xcvr at just 20 watts out..and the eff
> goes straight to hell,
> and ditto with the TX imd. You really require a good 3-9db pad to run
> those low power tetrodes
> properly..when driven from your typ xcvr.
>
> Later........ Jim VE7RF
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