Subject: [Amps] 10 meter amp coil
Hello all,
I'm building a 10 meter mono band amp for my m/m contest station here in
VA.
What is the group consensus on what diameter the conductor for the plate
tank circuit?? I tried looking in the archives, but it's not the best
for searching (it's monthly).
I'm thinking 3/8 inch should be fine.? Half inch is starting to get
'stupid big', IMO.
Will be an 8877 @ 4kv.? Class of operation: not sure of yet.? 12 volt
bias is probably fine.? I ONLY run CW.
And, looking for a filament transformer for the 8877.? Anyone have one
that is not in use?
73 de Steve NR4M
Use at least 3/8" copper tubing. That, or 5/8" to 3/4" wide copper
strap, wound into a coil, called a strap coil.
Since it's a 8877, no parasitic suppressor is required.
Ok, now you can insert a small, fractional uh coil, between the plate
block cap...and the C1 tune cap. The tube's anode to grid C (+ any
stray's) and the extra 'pre-coil', will form a step down L network. This
will transform the plate load Z down to a lower value, low enough that a
practical PI network, with a lower tank Q can be used.
The pre-coil and main coil can be one coil, with the C1 cap connected to
the junction point. OR you can use 2 x separate coils. Each of the 2 x
coils can be made from tubing or strap, in any combo u want. IE:
coil-coil. Strap-coil, coil-strap, strap-strap.
I design those networks in software all the time. You need a LCR meter to
tweak the coils / taps though. Lemme know if u need help on this. I need
to know aprx loaded B+ and also loaded plate current.
This is no place for 1/4" tubing, too small a diam, and coil will run hot
on 10m.
The way I deal with heat is...... don't generate it in the 1st place...or
at least minimize it.
Since it's only used for CW, you can reduce the idle current by a huge
amount, just more bias with a simple string of diodes. You can't reduce
the idle down to zero, or you will get key clicks. Increase bias V, till
idle current is reduced to aprx 20-40 ma. No clicks, tank eff is improved,
and minimal idle power. I can work that out for 4 kv if u like.
Jim VE7RF
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