Hi, Al:
For what it's worth, I looked at the specification sheets
for both the U310 and the J310. They are virtually identical as I
thought. The only differences were a slightly higher output capacitance
(drain to gate in grounded gate configuration) and a slightly wider
Vgs-off (like the grid bias on a tube, i.e., how much voltage to "turn
off" the device). Also, surprisingly, the J310 has a lower noise figure
at 450-MHz but the same as the U310 at 100-MHz and I presume at 50-MHz.
The parameters should have very little if any effect on the TR-6 design.
I did click your link to the modification by WC9M. The RL Drake
design appears to be the cascode configuration, a common source stage
feeding a common gate stage. It is ostensibly a stable amplifier
configuration but depending upon lead lengths, either of the two
transistors could oscillate and at
a higher frequency than the 6M band. If moving a finger around the
stage causes "funny" noise or signals ("birdies") to sweep through the
passband, there's oscillation somewhere in the spectrum! A small value
(10-22 Ohms) in series with the drain, close the case, should kill the
oscillation. Also, keep the drain connection of the input transistor to
the source connection of the output transistor of the cascode stage as
short as possible. If you use the resistor de-Q-er, put it in series
with the drain lead from the output transistor of the cascode stage.
73 ES GL
Bob K9JU
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