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

Tom Knox actast at hotmail.com
Wed Oct 16 20:42:09 UTC 2013


I agree the 54701A is really a great product. Great point on attenuation, I always forget the 10x attn value changes when not being used on a O-Scope as a voltage probe.
Thanks;
Thomas Knox



> From: SAIDJACK at aol.com
> Date: Wed, 16 Oct 2013 15:22:13 -0400
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] HP 4193A 4815A probe compatibility?
> 
> 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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