HW-16 QRP solutions

[Robert Wood]

Hello Ken,

I got a used 6GE5 from a friend late last night and put it into the rig this
morning.  She not puts out about 45+ watts after neutralizing it.  I will pick
up an RF choke at the next ham fest I visit and replace the one I fixed.  I
really appreciate all of your help and everyone else who provided me assistance
and tips.  Thanks again.

Thanks,

Robert Wood
K5MBA

-----Original Message-----
From: Kenneth G. Gordon [mailto:kgordon2006 at verizon.net]
Sent: Saturday, September 06, 2008 3:34 PM
To: Robert Wood
Cc: HEATH at LISTS.TEMPE.GOV
Subject: HW-16 QRP solutions

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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