Electronics > RF, Microwave, Ham Radio

Purchasing HP 432A (was: eBay HP 478A thermistors. Any good?)

<< < (8/8)


--- Quote from: Tony_G on March 31, 2024, 01:04:31 am ---Up front I have not tried what you are showing so my "guesses" may be way off - Before you go slamming V/I through the 478A I'd wait to get a consensus or commentary from someone who has done this.

--- End quote ---

Yep, I 100% agree with that

--- Quote ---The battery was chosen to achieve a 1mV meter resolution - From the manual:

--- Quote ---The value of this bucking voltage should be such that voltmeter resolution down to 0.001 volt is obtained.
--- End quote ---

--- End quote ---

Oops... typo. Yeah, 1 mV. Will edit my previous post

--- Quote ---#1 - No, if the mount zeros then it is pretty much working - TBH I've never seen one of these where it is working but 'almost failing', it seems that this is possible and may have been more common once given that the manual provides an explicit procedure to take to address but I think it is a pretty low chance case - YMMV as will others

#2 - +29V seems to be one of those numbers that are oddly specific - I would not be surprised to find out that the thermistors need to be seeing a certain amount of voltage/current so that the compensating thermistors react correctly to what would be expected from the thermistors exposed to the RF field. I would love it if someone had the real explanation for this and could share with us.

#3 - Most likely not given what the manual was saying earlier but you will still need to ensure that the V/I through the 478A is within spec - You could certainly math that from the manual but if the 478A was working then I lean towards this being a bit dodgy.

Sorry I couldn't provide more clarity - Interested in seeing what more experienced members say.

--- End quote ---

Yep, again I agree... If it doesn't look broken don't touch it. Still interested in knowing more about that, this knowledge could be useful some day to any people looking at 478A.


--- Quote from: TimYTTT on March 30, 2024, 03:40:49 pm ---G0HZU, could you please provide more info on how you use the 432A + 478A to check the 50MHz 1mW source using DC substitution. I do have similar needs and can probably benefit from your experiences.  :)

--- End quote ---

Sorry for any delay, sadly, I've been unwell recently but I'm a bit better now. I've had a go at putting the procedure into a word doc and it's probably best posted in the Metrology section. However, I've attached the first draft below.

It's been written in a hurry so it might not read that well....


--- Quote from: tatel on March 18, 2024, 11:39:18 pm ---Yeah, it seems to be for 431.

Well, it seems I found the limits of the forum. Of course, the probability of some guy being here, having both 431 and 432, is probably next to zero. I have never seen the slightest mention of cables for 431 and 432 being different. So, here it remains this piece of information. Hope it will useful for somebody in the future.

I already ordered another cable, this one no only has the notch, but also has golden pins |O

Best wishes

--- End quote ---

The difference in the cables might have something to do with the later 8478B thermistor mount (first seen in 1968 catalog), it requires an adaptor to use with the older 431A/B (thermistor is unbalanced), but can be used directly with the 431C & 432A.

There is even an adaptor for the 430C to allow use of the higher frequency waveguide mounts, thermistor is unbalanced and there is no temperature compensation.

Apparently I have a 431C in storage, I also have several 430C, several 432A and one 432B & 432C, these last two both use a digital panel meter, in place on the analog panel meter. I might have a TEA problem.  :-DD

The 432 series may contain two Sprague 109D capacitors (or equivalent) one at 33uF 10V/15V* & one at 220uF 8V, these are wet tantalum and can leak corrosive sulphuric acid electrolyte, picture below is from my 1969 432A.
*voltage seems to vary depending on the age of the meter.



[0] Message Index

[*] Previous page

There was an error while thanking
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod