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

Tom Knox actast at hotmail.com
Wed Oct 16 15:44:07 EDT 2013


Thanks Rick; There is so much conflicting information I do not know what to believe anymore. George sounds like the person to talk to. It sounds like an aftermarket probe would be a great way for someone to make a few extra dollars. 
I like the Tomco option, it looks like a nice instrument. Thanks Again.
Thomas Knox



> Date: Wed, 16 Oct 2013 11:16:27 -0700
> From: richard at karlquist.com
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] HP 4193A 4815A probe compatibility?
> 
> 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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