[Heathkit] 6N2 PLATE CURRENT

[mrapps at grandrapids-mn.com]

Waitaminute

The 75 pf cap from link to ground is not a loading cap as in the case of
a PI circuit.  It is used to tune the link to series resonance.  All the
way out is not maximum loading.  If anything, all the way in would be
max loading and somewhere in between should be appropriate.

Good luck and have fun

KoDCF / Tony

In God we trust



The 2 meter amplifier "tank" section is a pair of
parallel lines connected directly to the plates of the
6146 tubes.  A coil for 6 meters is connected across
the end of the lines which is shorted out on 2 meters.
 The link coupling is as simple as possible consisting
of a 1 turn variable link with a 75 pf variable from
one side to ground and the other side connects
directly to the antenna connector.

The only difference between 6 meters (which works
fine) and 2 meters is the fact that the coil is
shorted on 2 meters.  The circuit checks out fine
using a Millen grid dip oscillator (resonance is right
in the middle of the tuning range of the butterfly
capacitor that tunes the lines) and the output
frequency is fine checked using the Millen GDO as a
wavemeter and on one of my service monitors.  The grid
circuit checks fine on both frequency "dip" and again
using the GDO as a wavementer.

I am loading the transmitter into a Bird 6154
"Termaline" wattmeter which consists of a 50 ohm dummy
load and wattmeter combined.  The output on 2 meters
is too lightly loaded to allow the final to draw full
current.  Unfortunately, the loading capacitor (the 75
pf variable) is already at minimum capacitance which
represents maximum loading.  The transmitter loads
fine on 6 meters, it is just that it isn't "happy" on
2 meters.

If it were parasitic oscillations then the tendency
should be towards drawing too much plate current and
not enough!  The specifications are for 230 mA of
plate current maximum and I can only get around 60 mA
on 2 meters.  On 6 meters I can draw over 300 mA if I
want to.  Of course this is too much for the 6146
tubes to draw for very long.

Glen, K9STH