[Amps] amp cooling / triodes vs tetrodes

[Jim Thomson]

Date: Mon, 02 Apr 2012 12:59:10 -0700
From: Jim Barber <audioguy at 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