[time-nuts] HP 4193A 4815A probe compatibility?

SAIDJACK at aol.com SAIDJACK at aol.com
Wed Oct 16 19:22:13 UTC 2013


Hi Rick, Tom,
 
one little bit of knowledge I learned: I like the HP 54701A FET probes for  
frequency-domain stuff.
 
Available for $300 on Ebay sometimes. I built a small power supply for  one 
of mine, and use it as a probe for my Spectrum analyzer and scopes. Almost  
indestructable.
 
It works really well up to about 3GHz and beyond, especially for relative  
measurements.
 
The only disadvantage is that it has 100K resistance to ground which may  
affect sensitive capacitive circuits, and that it has 20dB attenuation.
 
Otherwise it works really well for Spectrum analyzer and Network analyzer  
applications.
 
bye,
Said
 
 
In a message dated 10/16/2013 11:33:11 Pacific Daylight Time,  
richard at karlquist.com writes:

The  4815A used P channel FETs which were available 50 years ago
and are now  unobtainium.

The 4193A used N channel FETs which were available 10 to  30 years
ago and may even be currently available.

They are  DEFINITELY NOT INTERCHANGEABLE.

This is according to ex-HP'er George  Standford, who used to
support vector impedance meters with HP's  blessing.  He held
the worlds remaining supply of P channel FETs for  fixing probes.
He was in New Jersey, but my contact info for him is no  longer
valid.

I don't know how to identify them, but in principle an  ohmmeter might
be able to identify the polarity of the FETs.

While  we are on the topic, it turns out that the market is such
that a 4193A with  probe might sell for $5000, but if you break
up the set, the probe is worth  $4999 and the instrument is worth
$1.  Well, maybe I exaggerated that  a little, but not much :-)
I actually know someone who paid $5000 for just  a 4193 probe.
He made the mistake of purchasing an instrument without a  probe,
and paid way too much.

It is also worth noting that now you  can buy a very nice vector
impedance meter from Tomco in Austrailia for  only $3000 new.
I A/B'ed one of these with an HP one, and I will have to  admit
that the Tomco is the real deal, not a cheap knockoff.

Rick  Karlquist N6RK


On 2013-10-16 09:15, Tom Knox wrote:
> I hope  this is not to far off topic. Does any one know if the 4193A
> and 4815A  probe are physically interchangeable and electronically
> compatible? If  not does anyone know the differences and how to
> identify which is  which? If you feel this is to far off topic please
> contact me  directly. Thanks very much.
> 
> Thomas Knox
> 
>  
>                    
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