Hammond X-66 - MJE340 Transistor Selection and Use

X66 Vibrato Driver Preamp Dec.2010
dan.vigin
Page 9
The overall new schematic diagram can be found on the next page.
This new schematic diagram is almost identical to the original one. Beside the
replacement of the old RCA transistor by MJE340, only the collector resistor has been
changed from 10K/5W into 12K/5W to slightly decrease the collector current and
reduce to a certain extend the power dissipation that is not negligeable due to high B+
voltage involved. Dale 12K / 5W – 1% resistors were installed.
Here is the new VDP board.
Transistors MJE340.
While not necessary by calculation, for reliability purpose, the transistors MJE340 were
mounted on heatsink. Silicon compound was used for better heat transfert.
It is strongly recommended to select h FE values (DC current gain) of those transistors.
h FE may vary from 30 up to 240 according to datasheet of the transistor supplier which
is indeed a very wide range.
The correct h FE value for each MJE340 transistor should remain in the range of min. 70
to max. 85. In my case, the three transistors had an h FE value of 83.
Datasheet of MJE340 are also provided in the next pages.
Simplified characteristics
RCA 39699 MJE340
NPN Technology Early generation Si Transistor
Planar Epitaxial Silicon transistor
VCB0 400 V 300 V
VCE0 300 V 300 V
VEB0 6 V 5 V
Collector Dissip. 8 W 20 W
h FE 40 ~ 80 30 ~ 240