Heath SB102 on 40 meters

[Kenneth G. Gordon]

On 1 Oct 2006 at 21:55, Bernie Murphy wrote:

> I am at a loss to figure out why my SB102 has about 5 db loss on
> receive and won't transmit at full power on 40 meters.

In my experience with the restoration of several SB/HW transceivers, 
this is a common problem if the alignment procedure is not followed 
exactly.

The coils associated with the driver/preselector tuned circuits are 
connected in a series-parallel arrangement: i.e., the 80 meter coil 
stands alone, then the coils for all other bands are connected in series, 
then that series string is connected in parallel with the 80 meter coil.

The adjustments of all those coils interact.

First of all, for a correct alignment, the 80 meter coil is adjusted first, 
then 10, then 15, then 20, and lastly 40, in that order.

Secondly, the driver/preselector tuning must be set carefully to those 
positions shown in the manual in the alignment procedure, WITH THE 
EXCEPTION that on 40 meters, especially, the tuning of those 
capacitors must be centered, and the VFO set for the exact center of 
the band.

Due to the design of the driver/preselector tuned circuits, there is ample 
range, extending beyond the band edges, for every band, EXCEPT 40 
meters. On 40 meters, there is BARELY enough range of the 
driver/preselector control to cover the entire band.

In fact, in some instances, I have favored one end of 40 over the other 
if the operator uses one end more often than the other.

Thirdly, I always align the driver/preselector coils in TRANSMIT, not 
receive, as specified in the manual. I use a wattmeter, or, sometimes, 
and oscilloscope connected to the antenna output jack with the rig 
feeding a dummy load, then adjust the MIC/CW Level control for SOME 
output, usually no more than 30 watts or so, final resonated, and adjust 
the coils for maximum output.

After having done the entire procedure once, I go back and do it, if 
necessary, several more times to make sure everything is correct.

Oh! I probably should have mentioned this first: the FIRST thing I do is 
to neutralize the final on 80 meters, as specified in the manual, not on 
10 as is usual. However, I remove plate and screen voltages from the 
final amp, use an oscilloscope on the antenna output jack, and adjust 
the neutralizition as accurately as possible.

I also set the carrier null using an oscilloscope.

Lastly, I adjust the "neutralizing wire" for the driver as closely as I can 
before starting the alignment procedure.

You might also make certain that your heterodyne oscillator coils are 
tuned to the right peak. If any of those are on the wrong peak, it can 
badly effect output on a particular band.

If the alignment is all correct, you should get 110 watts output on 80, 
100 watts output on all the rest, except 10, which should be at least 80 
watts, and can be as much as 90.

Good luck.

Ken Gordon W7EKB

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