I like this description...thanks !

And that is why Class F (with parallel L/C traps tuned to 3f at the cathode and plate) gives the 90% efficiency it is famed for.

Is the 6cl6 operating straight through (80M in/80M out) ?

If yes, it may need to be
neutralized too with a few turns near L5 going to a few turns near L4 (you'll have to
experiment with the number of turns). The loops should be connected with one 180 degree twist in
the wires connecting them, or with one wire between them and the loops oriented in the opposite
sense, i.e., on the L4 loop ground the turn nearest L4 but on the L5 loop ground the turn farthest
from L5 and connect the loops with a single wire.

Also, it wouldn't hurt (I think) to put a parasitic suppressor on the 6cl6 plate.

Peter

why not put a variac on the power supply to correct the voltages, verify the article's design, and then experiment with higher voltages and a variable bias supply...don't forget that you shouldn't exceed the
maximum plate dissipation at rest.

if you have a 500 or 1000 pF feed-thru capacitor use it instead of grounding that 150 pF (or its
replacement) under the chassis and then running a wire through the chassis. The neutralizing
cap can be soldered directly to the top side of the feed-thru capacitor and, if properly placed,
the bottom side of the feed-thru can be soldered directly to C1 or S2 (whichever is closer).

Good job OM !


if your PA is not neutralized then you should be getting lots of grid current variation as you turn the plate tune capacitor (with a dummy load on and no plate/screen volts). So another way to neutralize is to tune the neutralization capacitor so that the grid current stays constant as you turn the plate cap through its range.

Blue neutralization wire (under the chassis) too long. Can you move the neutralization capacitor to
the other side of the 6146 ?

thanks for the discussion.

Here's two versions of the original schematic in handbooks of the early '70s:

http://postimage.org/image/9gxmodkyf/

http://postimage.org/image/k2oumdxi9/

why did they drop the connection of the grid to cathode through the 150 pF shown in the
original post ?

Peter

interesting ! I saw the evolution of the posted circuit in the 1975 arrl hb (pg. 172) and there's a 1500 pF in place of the 150 pF and is going to ground instead of going to the cathode of the 6146 (as shown in the 3rd image posted above)...

Could you discuss a bit the relative merits of these two ways ?

73 de Peter

'KEP,

if the metering checks out but the issues remain then try the following:

that 150 pF going from the grid tank to the junction of the 1000 pF bypass and the
6146 cathode pin 1...disconnect it from that junction and ground it. If no change then
try 500-1500 pF for that 150 pF and ground it.
The way it is now, it returns the grid bypass to the cathode instead of to the ground...it
looks funky to me...

you need a choke and cap to take the DC off the secondary...here's how it can be done with cheap toroid power xfmrs: http://amfone.net/Amforum/index.php/topic,13307.0/

Peter

Google is your friend.

http://en.wikipedia.org/wiki/Plasma_antenna

look here http://www.amwindow.org/tech/htm/wb9eckseriesmod.htm
and here http://www.amwindow.org/tech/htm/pw.htm

Also, you may want to sign up at http://amfone.net/Amforum/index.php

Peter

obviously the 807 class C stage in the original post is a KEYED class C stage. It's not being
used to amplify cw.

Peter