[Elecraft] K1 toroid turns spacing fiddling

[Wallace, Andy]

I was concerned that I couldn't tweak any more than 
2W out on 15m with my dad's 2-band (KFL1-2) K1 filter
board. After emailing Gary at Elecraft, he reminded me
that the output does depend on power supply voltage. In
my case, I am using a 12.0V supply, which yields only 
11.6V after the protection diode, as shown on the K1 
readout...

Well anyway, he also said that in some cases, people have
coaxed more power out by compressing or expanding the 
turns on their filter board input and output toroids.

Hope he doesn't mind me quoting him:

====
From Gary Surrency:

I've seen the best results by expanding the turns on either L9 or L11 (the
input to the LPF), and  then compressing the turns on either L12 or L10,
depending on which band is set up for 15m.

The optimizes the match between the PA and the load, for maximum power
transfer. Be sure to do it at maximum power, as the power level is a factor
in the PA to load impedance match.

Compressing the turns increases the toroid inductance, and vice-versa.

====
Back to Andy...

In the case of my dad's rig, it made a difference. Instead
of 5W on 20 and 2W on 15, I now get 4W on each band, with
the 12V supply. However, I can't say that expanding L9 and
compressing L10 did it -- I believe I expanded both of them
slightly. Obviously depending on how symmetrically you wind
these things, the direction may change.

My own 4-band K1 got 5W on 40, and then dropped off from there
for 30/20/15, so I thought tweaking my toroids would help
also. 

Gary says to do this with OUT=5W and with a 50 Ohm dummy load
on the antenna jack. 

With the 4-band board, you have two groups of three toroids in
the in/out sections. What I did was transmit into the dummy load
at 5W and watch the wattmeter needle as I gently squeezed or
expanded the turns of the toroids. Touching them makes a difference,
so you have to let go to see whether it helped or not. (Or use the
plastic trimmer tool to push on the turns.) It didn't take a huge
amount of compression or expansion, but I was able to see an 
improvement. Be sure to swap back and forth between bands in the 
same filter path to make sure you're not improving one at the cost 
of the other.

I then went back and repeaked the trimmer caps at
2W, and now my output with a 12V supply is 5+W on 40/30 and 4W on 
20/15, which is an improvement. Receiver seems a little more sensitive
now, too. Power output is very even across each band. I did not
check to see if power resolution (steps between powers below 5W)
was affected. Since my antenna is just a 35' randomwire I generally
run at 5W!

This was achieved without substituting values for R11, for more
drive, etc. 

Do this at your own risk -- at worst you'll have to readjust the 
toroids for even spacing and repeak the trimmers or coils as appropriate.
My guess is that other K1s (and maybe K2s) could benefit from a little
toroid nudging. The design inductance may or may not be critical, but
the tightness of the windings and the spacing between turns could make
enough of a difference that the rig is not quite "all it can be."

Good luck!
-Andy