Reg, Tarmo,

sorry for the delay, because I have been sick for a few days..

I am using some 3000 volts and some 300 volts screen-grid supply.
That should lead to some 5400 volts p-p

And yes, for the moment I am using L and c values comparable
to those mentioned by Tarmo. (designed for a loaded Q of around
12 as recomended by the ARRL handbook) However the inductor is
becoming quite hot, so I was wondering what could be done to
improve efficiency, without neglecting harmonic suppression.

I used Reg's program to recalculate things a couple of times
and to get a Q of around 12. However I could only realize this
by entering a phase-shift of about 90 degrees, which in turn
gave me the 'strange' C and L values...
However somehow (and do I feel stupid !) I do not succeed in
getting 'normal' values when using Reg's program....

Maybe his Q value is another value than mentioned by the ARRL ?

Arie.

Arie,

The only two ways I can think of to reduce coil heating/losses is to lower
the loaded Q and increase the unloaded Q. I don't remember if you told us
what frequency this amp was for, but I have seen coils wound from 1/4 inch
copper tubing, or flat straps.For lower frequencies you could consider using
powdered iron toroids, perhaps several epoxied together, and wind them with
#16 or #14 wire. I don't know how large your coil is, but for 80 meters,
dimensions like 2 inch diameter and 5 inches long air core also come to
mind. Have you looked at construction articles in the ARRL, RSGB, or other
handbook?

Tam/WB2TT
"arie" wrote in message
om...
Reg, Tarmo,

sorry for the delay, because I have been sick for a few days..

I am using some 3000 volts and some 300 volts screen-grid supply.
That should lead to some 5400 volts p-p

And yes, for the moment I am using L and c values comparable
to those mentioned by Tarmo. (designed for a loaded Q of around
12 as recomended by the ARRL handbook) However the inductor is
becoming quite hot, so I was wondering what could be done to
improve efficiency, without neglecting harmonic suppression.

I used Reg's program to recalculate things a couple of times
and to get a Q of around 12. However I could only realize this
by entering a phase-shift of about 90 degrees, which in turn
gave me the 'strange' C and L values...
However somehow (and do I feel stupid !) I do not succeed in
getting 'normal' values when using Reg's program....

Maybe his Q value is another value than mentioned by the ARRL ?

Arie.

Arie,

I took a look at some handbooks to see exactly how the coils for their high
power amplifiers were made. (Personally, I chickened out at about 600V).
Anyhow, for a bandswitching transmitter:

A) All of them separated the coil into 2 or 3 segments.

B) Averaging about 6 designs, the 10 - 20 meter coil was wound with 3/16 or
1/4 inch copper tubing. In one case silver plated.

C) the remaining coil was most often wound with #10 copper wire; in one case
on 3 toroids glued together.

I had once calculated the Qs for inductors to use in antenna traps, and
unless I messed up, the coils described above would have unloaded Qs of at
least 400.

Tam/WB2TT