HW-101 power update

[Ed Lambert" "K1ZOK]

The HW-101 uses a series/parallel string for the filaments.  This is so
that the filaments can be run from 12 volts, even though they are six
volt filament tubes.  However, the current that is drawn by each is
specifically balanced so that there is an equal amount drawn from the 12
volt source as well as the second half which is run in series.

If there is an unbalance in the tube string....  possibly by the
substitution of another type in place of an original, it might unbalance
the load significantly.

I would first suggest measuring the filament voltage with a meter.
Measure each side of the filament on each tube with respect to ground and
see what you get.  I would expect a significant difference to get the
symptoms you describe.  This is possibly why changing the tubes had no
effect on the problem.

You might also have a shorted filament bypass capacitor.  If you look at
the other tubes, you might also find some that are different in filament
brightness.

If you look at the connectivity shown on the schematic, you will see some
tube filaments are run directly from the supply voltage (12 V and
ground).  Others, like V3 and V4 are series connected to ground.  And
others are connected from the supply voltage to a mid point which happens
to be one of the 6146 filaments.  I can't tell from the schematic (it's
all I have) which of the 6146s is toward the front of the set, V8 or V9,
but V9 is the one that is connected from the mid point to ground.

Ed
K1ZOK
On Fri, 15 Dec 2000 16:23:43 -0500 Greg Hockenjos <nunu726 at LYCOS.COM>
writes:
> Hello. After checking all resistors and changing 5 badly out of
> tolerance ones I checked the power supply voltage and it stays
> steady under load and no load. One strange thing happens now, I
> might not of noticed it before, The 6146 closest to the rear of the
> radio glows very bright, twice as bright as any tube in the radio.
> The 6146 near the front of the radio barely glows at all, you have
> to turn off the lights in the room and put your face 2 inches from
> it to see a very faint, dim filament glow. I chaned both tubes with
> others and the same result. Now when you tune the radio from cold it
> starts at about 60 watts on 10 meters, before it was 40, well
> getting there slowly. That final thing can't be right, the one tube
> is almost white, thats how bright it gets. 73 Greg.
>
>

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