[Hallicrafters] SR-2000, SR-400/A, SR-150, and SX-117 tube experiment

[Jim Liles]

I made a typo regarding the 6GH8A.  I use only 6GH8A's not the 6GH8.  It is 
a significantly improved tube over the 6GH8.  The following is the corrected 
note:

Good morning:
Here is an experiment that will peak your interest:
The SR-150, SX-117, SR-400/A, and SR-2000 use 6U8, 6EA8, 7059 tubes.  The
7059 is a 6U8 with a 13.5 volt filament.  The 7059 and 6U8 have a
transconductance of tetrode 5200 and triode 8500;  the 6EA8 tetrode 6400
triode 8500; and the 6GH8A tetrode 7500 triode 8500.  All have the same pin
out's.  We have used the 6GH8A in the SR-2000 V3 and V7 positions, rewiring
the filaments in series with great results.  The innate low transmit drive
problem is fixed so normal standard tune up procedures can be followed and
receiver gain produces an MDS below -140 Dbm with 10Db s+n/n at less than
.15 uv.  The SR-150 change that is worth while is to replace the 6EA8's V3
and V17 with 6GH8A's.  In both cases you will be quite happy.  The next tube
with even more gain is the 6HL8 but beware it's transconductance figure is
10,000.  If you try this tube you will have to modify the circuit to
stabilize it and it can be a bit noisier than the 6GH8A.  The 6U8, 6EA8,
6GH8A, and 7059 have the same pin outs.  The SX-117 can also be made to be
significantly more sensitive with tube change out.

Final note:
Any radio using the 6U8 can and will be a better performer when using the
6EA8 or 6GH8A and any using the 6EA8 will improve with the 6GH8A.  Also, we 
do
not change out mixers only amplifiers.   Hope this peaks you interest ---
Kindest regards Jim K9AXN