Jimmie D wrote:
I am trying to modify a 1 tube amp for 6 meters using a 6146. I think the
amp was origionally used for CB though it does tune up on 10 meters. It
worked OK before I removed the input circuit and put in one for 6M. The
problem is I cant neutralize the damn thing. It makes a great osc.I was
thinking of scraping the tuned input and replacing it with a 200 ohm
resistor and a 4:1UNUN. I figure this low of an impedance on the grid would
swamp out any feedback that might me causing it to osc. I have about 5 watts
PEP of drive.

Jimmie


Transmitter in the 1967 ARRL HB used a 6146 in gk on 6m.
The input circuit was 9 turns of #20 spacewound 5/8" dia.
It was center tapped, with the center tap connected to a 7uh
rf choke, other end of the choke was grounded to bias supply
(or 22k 1w resistor for grid leak bias, class C). One end of the
coil goes to the grid of the 6146. The other end of the coil is
connected to ground via a 30pf tuning cap, and also to a probe wire
that serves as one 'plate' of the neutralizing capacitor (the plate
of the tube is the other capacitor plate). This probe wire is simply
moved near the tube till adjustment of the plate tuning capacitor does
not vary the grid current, this indicates the tube is neutralized.

The three cathode connections of the tube are connected together at the
socket by a "Y" shaped piece of copper, this is then grounded at a
single point.