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

[mikea]

On Mon, Feb 26, 2007 at 04:12:06AM +0000, Steve Harrison wrote:
> 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????

I hadn't run far enough through the manual and schematic to see that
the final runs full tilt boogie all the time, but that makes a great
deal of sense -- until you need to replace it. I did see this question
come up in another forum -- don't remember which one -- with no really
good answer. As I run an 8640B with the internal doubler (option
what?), this is of concern to me, too.

I hope there's something that will do the job, but I'm by no means 
confident of it, and the original semiconductor is Unobtainium now.

-- 
Mike Andrews, W5EGO
mikea at mikea.ath.cx
Tired old sysadmin