HW-16 QRP solutions

[Kenneth G. Gordon]

After cogitating on this problem for another few hours, I 
keep coming back to the fact that you removed a good 
portion of the grid RF choke's windings.

One result of not having the correct value of choke in the 
grid circuit is that all of your RF drive power from the driver 
stage could be being shorted to ground, or getting lost in 
the power supply.

After all, the purpose of the RF choke is to keep that RF 
drive power from going any other place than into the grid of 
the final amp, and at the same time to allow the DC voltage 
to get TO the grid.

Now, Heathkit engineers, in 99.9% of cases, used 
particular values of components for completely valid 
reasons, some of which, at first glance, don't appear to 
make sense (the 200 pfd grid bypass caps in the SB-200 
being a case in point), but after more careful analysis, one 
learns that their value is critical for proper operation (in the 
case of the SB-200, that value, 200 pfd, acts as part of a 
tuned circuit which includes the inherent inductance of the 
grid and actually couples the grid MORE securely to ground 
than if a different, larger, value were used.)

Therefore, in YOUR case, although to my way of thinking 
that 0.5 mH choke is too small, Heathkit engineers may 
have chosen it for a reason I don't know or haven't thought 
of.

In ANY case, the present value of your repaired choke is 
MUCH too small, and should be replaced by one of at least 
identical value.

For testing purposes, in order to discover whether or not 
the repaired choke IS the reason your HW-16 is now a 
QRP rig, ANY larger value choke can be used.

As I said previously, I would substitute a 1 mH or a 2.5 mH 
choke, then thoroughly test the rig on all three bands. If 
nothing appears out of whack, then leave it in.

If you don't have such a choke, you can temporarily make 
an adequate one by taking a small dowel, say 1/4", and 
scramble-winding a "large" amount of small-diameter 
enameled wire on it. You can get such wire in large 
quantities from the flyback transformer of an old TV set.

But, after being sure that all the voltages (plate, screen, 
grid, cathode) are within range, I would replace that choke 
FIRST and re-test, BEFORE I suspected the 6GE5.

Ken Gordon W7EKB

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