[Amps] AL-1500 pi-network capabilities

[Will Matney]

If the tank coil(s) are under-sized, this will in turn effect the Q due 
to the skin effect raising the resistance of the conductor, especially 
in the higher frequencies. You are exactly correct on this where the 
larger the conductor, the better. The recommended wire sizes for tank 
coils are in any ARRL handbook. The 10 meter band requires extremely 
large conductors to hold a Q of 10 to12 or so. A 1500 watt output will 
probably require something in the range of 3/16" to 1/4" diameter copper 
tubing. Silver plating the tubing or cleaning it and applying a 
polyurethane finish will help matters too. As the tubing tarnishes and 
forms a copper oxide on the surface, the Q that your trying to maintain 
is destroyed by raising the skins resistance. Another good coil can be 
made by using a wide copper strip about 5/8" wide and about 1/16" thick. 
Plating, etc. helps this too, and this can be a good substitute for 
using tubing. Tubing is easier to form around a mandrel though. 
Actually, if a piece of 1/4" tubing was split and flattened out, it 
would equal a strip 7/8" wide. 3/16" will equal a 9/16" wide strip.

Will Matney


You are far too kind, Vic!

IMO, the tank circuit in the SB-220 is as robust as the AL-1500, and
the 220 will not do near 2400 watts out.

I remember amp projects in the '60's and '70's that had larger coils
in the tuned input circuit!
Perhaps Ameritron has only one coil winding jig. All the models look
pretty much the same to me.

Miniaturization is nice, but not in a QRO type tank circuit. A good
test to see if you have under-engineered
a tank coil/bandswitch is to check their temperature just after a
80-160 meter RTTY contest weekend.

(((73)))
Phil, K5PC