[Hallicrafters] Tech Tip - Modifications

[Duane Fischer, W8DBF]

Mods For The SX-117 -

Duane, as requested

************************************************************

          Making the Hallicrafters Twins Transceive

In the HT-44 transmitter the carrier oscillator (V1A) must be
set to the
exact frequenct following the manual for transceive
operation.  However,
since capacitor C1 is a mica compression type, the oscillator
is not stable
with regard to temperature or time.  When set on Monday, it
will be off
frequency by Friday.

T o correct this problem:

1    Remove C1, 7-100 pf mica trimmer.

2    Install a fixed DSM or NPO capacitor in place of C1.  A
value of 47 pf
is a good value to use.  This might need to be changed later.

3    Remove C2, 330 pf DSM.

4    Install a small air variable through the chassis hole
used to access
C1.  The rotor of the new air variable will be grounded by
the mounting.  A
tuning range of 5-35 pf or 10-100 pf or anything close can be
used.
(Surplus Sales of Nebraska PN:  (CAV)193-10: 2-35 pf)

5    Connect the stator of the new variable to pin 3 of V1A.

6    Connect a DSM or NPO cap in parallel with the air
variable (pin 3 to
ground).  Use a value that will allow the combination to
center tune accross
330 pf.    IE:  If you used a 10-100 pf variable, then a
fixed value of 270
pf will allow tuning from 280 - 370 pf.  If 2-35 pf, then use
315 pf
combination.

7    Now follow the manual and set the carrier oscillator for
transceive and
it will stay put week after week.

8    If you can not reach the exact frequency, you can vary
the value of the
new 47 pf up or down as needed to compensate for crystal
aging.


DSM  = dipped silver mica
NPO  = zero drift ceramic
**********************

73

John


Duane Fischer, W8DBF - WPE8CXO
E-Mail: dfischer at usol.com
Hallicrafters web site: www.w9wze.net
HHRP web site: hhrp.w9wze.net