HW-12A Help Needed - A Different Approach

[Mark Johnson]

Doug...Its been a long time since I've had an HW-12 but I checked the manual 
and read the Circuit Description section and L2 is a driver coil and along 
with L3 which is a driver plate coil, they form a bandpass tuning circuit 
that covers the 75 meter range such that you don't need to tune the driver. 
I'm guessing from that, it means they are quite broad and it eliminates a 
"pre-selector" type tuning control set up.

If it were me, It hang my scope on the 12BY7 grid and with the main tuning 
dial at mid frequency range, say 3.85, with a dummy load connected,  go to 
tune and peak L2. I'd then move the scope to the inputs of the 6GE5 (grid) 
and then peak L3. its likely a broad peak as opposed to a sharp peak. If you 
don't have a scope, then it would be well worth getting one. If that is 
impossible, I'd leave the slugs alone. If you must play, you could put a 
watt meter on the output into a dummy load, and in tune position, see if you 
can peak RF power out by adjusting L2, then L3. Again, I suspect the "peak" 
will be broad. Just My opinion Doug.

Mark V. Johnson VE3DJU/VE3DDI


----- Original Message ----- 
From: "Davies, Doug A FOR:EX" <Doug.Davies at GOV.BC.CA>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Wednesday, January 17, 2007 11:39 AM
Subject: [HEATH-TEMPE] HW-12A Help Needed - A Different Approach


Since I didn't receive any replies to my first posting, I'll try a
different approach.  Would someone who is familiar with the HW-12A tell
me if there a way to determine the proper setting of coils L2 and L3 in
the HW-12A.  These coils, the 12BY7 driver grid and plate coils
respectively, were supposed to be pre-set at the factory and not require
readjustment.  However, on the rig I have, the tops of the covers have
been opened up and I'm sure someone has fiddled with them them.

There is nothing in the abbreviated manual I have that specifies the
value of grid or plate current for the 12BY7 driver tube.  With the
meter switch in the TUNE/OPERATE position, full scale meter reading is
300ma.  Can I use this to set these two coils?  This is all new ground
for me so any and all suggestions are appreciated.

Doug  VE7DRF

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