[Test-Equipment] Interest in Replacement Amps for HP8640B?

[Steve Harrison]

At 12:34 PM 4/23/2007 -0500, Larry Phipps wrote:
>I don't know what you're planning on using, but the Gali-84 or GVA-84 
>from Mini-Circuits is flat as a pancake from DC-1 GHz, has an  output of 
> > +20 dBm, requires only three parts (two blocking caps and a 
>resistor), has >25 dB input and output RL and is unconditionally stable 
>and easy to use. I have used the Gali series MMICs on a number of 
>projects and they are great (and cheap... around $2). They are 50 ohm 
>devices, so I don't know if that works on the input side with the 
>HP8640B... but the input would probably need to be padded anyway (25 dB 
>gain), so a matching pad would be OK.

Those sound good, although the devices I was looking at, which Miles, K2CBY
pointed out to me, are WJ's ECG-003B and ECG008B. Those are a bit more
costly at $5.72/each and have less gain. But their 1 dB compression point
is a bit higher, too. What would be really nice would be the ability to
plant at least 3 dB attenuation after the amp to help "shield" it from open
switch contacts while stepping the 8640's output attenuator. It's been
rumored that is suspected as the cause of some original 8640 final amps'
demise. I strongly suspect that originally, the AGC circuit on the output
of the original amplifier took care of high RF output voltage when that
attenuator went open-circuit. Perhaps the AGC has drifted just enough over
the years that it could no longer react quickly enough to protect the final
amp when the switch was shifted. 3 dB attenuation after the amp should
provide sufficient protection, I'm certain.

Then again, using those WJ parts would get one right back into the trap of
using a very specialized part for which there would be no replacement, and
which availability through the future could be considered uncertain. I'd
have no such worries about the MCL amplifiers; and one could even tape a
small container of spares right there in the AGC/Amplifier module for a
future repairman  8-))))))))

Steve, K0XP