[time-nuts] 8657B HET Switch

[J. L. Trantham]

I have an 8657B signal generator that does fine at and above 1030MHz but
below that, the level is uneven and down about 10 to 15 dBm.  I have traced
the (or at least a) problem to a defective HET switch, part number
08657-67102, which switches the outputs to the mixer or to the doubler,
depending on the frequency chosen.  There is about -3.5 VDC on the connector
on the HET switch that comes from J303 on the A6 board that supplies the 0.1
- 129.999999 MHz output when that frequency is selected.  This knowledge
cost me an 8482A power sensor.  I think there is a shorted semiconductor
inside the unit.  There are two control inputs that are either +12V and -12V
or just the reverse, depending on the frequency chosen.

I have tracked down a replacement part and it is on the way.  However, does
anyone have any idea of what is inside the switch?  I have been told there
are two GASFET switches inside and the GASFET's are obsolete.   

Assuming that the replacement part solves the problem, I was wondering if it
would be possible to disassemble the unit and replace the defective part
(assuming I can find NOS parts) or design a new circuit that will fit in the
enclosure and serve as a replacement.

Does any one have any specific information on the HET switch or a suggestion
do deal with the next occurrence of this problem?

Thanks in advance.

Joe