[Test-Equipment] HP 8640B Final Amplifier Replacement??

[Steve Harrison]

What have folks been able to use as replacements for the final amplifier
module in HP 8640B signal generators? And do the original HP amps fail
often in the generators with the internal doubler??

>From my read of the manual, it seems that HP drives the amp to +19 dBm
output all the time, then attenuates it via the step attenuator. The
schematic of the version with the internal doubler shows the output of the
final amp connected directly to the common of a SPDT relay which either
directs output to the step attenuator or to the internal doubler then a
pair of 0.5 - 1.0 GHz amplifiers, which output to the 0.5-1.0 GHz LPF and
then step attenuator is selected by another SPDT relay.

I haven't read quite far enough to determine whether, when the range switch
is switched from the 256-512 MHz range, to the 512-1024 MHz range, the
input to that final amplifier is cut off until the range switch makes
contact again but if drive isn't removed, that means the final amplifier is
unloaded while the range switch is between bands, which would probably
reduce the life of the final amp (yes, it's also true that its input is
also open during at least part of that switch movement). The Final Amp
module is shown as having 16 dB gain, way more than the MAV-11 amplifier
chip that can be substituted for the preamp module. And I would venture the
guess that since the final amp's harmonic output is pretty good even when
putting out +19 dBm, it's 1 dB compression output power is probably more
like 1 watt.

So, what have folks replaced the final amp with????

Thanks,
Steve K0XP