Author Topic: HP 400D Tantalum Capacitors?  (Read 713 times)

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Offline KK7DTETopic starter

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HP 400D Tantalum Capacitors?
« on: October 21, 2024, 10:31:50 pm »
I'm not finding tantalum capacitors listed in the HP 400D VTVM service manual, but I have two in mine and I have seen two others online with the same capacitors. How do I find their values? They are heavily corroded. Maybe there are other schematics or parts lists I'm not seeing? This unit's serial number is 28830. Picture below:
 

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Re: HP 400D Tantalum Capacitors?
« Reply #1 on: October 22, 2024, 01:03:05 pm »
And what is it connected too? I can't tell from the picture.

David
 

Offline HalFoster

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Re: HP 400D Tantalum Capacitors?
« Reply #2 on: October 22, 2024, 05:59:54 pm »
Looks more like a diode to me...
--- If it isn't broken... Fix it until it is ---
 

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Re: HP 400D Tantalum Capacitors?
« Reply #3 on: October 22, 2024, 08:51:07 pm »
Guessing it's these unlabelled parts on the layout drawing?

They seem to be C20 & C31 in the earlier book here; https://www.kennethkuhn.com/hpmuseum/scans/hp400d_h.pdf

C20 is 8uF 30V part #18-17 (aka 0180-0010 tantalum)
https://www.parttarget.com/5910-00-644-3743_5910006443743_PP8B30A1.html

C31 is 4uF 60V part #18-15 (aka 0180-0008)
https://www.parttarget.com/5910-00-643-6892_5910006436892_PP4B60A1.html/

David
« Last Edit: October 22, 2024, 09:09:28 pm by factory »
 
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Online factory

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Re: HP 400D Tantalum Capacitors?
« Reply #4 on: October 22, 2024, 09:17:30 pm »
Looks more like a diode to me...

Apparently they are an early form of tantalum capacitor made by Fansteel, attached is an advert from 1956.



David
« Last Edit: October 22, 2024, 09:19:35 pm by factory »
 
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Offline KK7DTETopic starter

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Re: HP 400D Tantalum Capacitors?
« Reply #5 on: October 22, 2024, 10:10:21 pm »
Thats them! Thanks!!

I can find the 8uF 30V easy enough, but the 4uF 60V is proving more challenging. I know with test instruments it is best to stick with the values assigned by the factory, but is there any flexibility here? Would and Aluminum Electrolytic be too different? I can get 8uF 50v much cheaper.

Edit: I found the 4uF 60V at TTI. Now is $75 for both caps the best I can do? Are there cheaper alternatives to these wet tantalum caps?
« Last Edit: October 22, 2024, 11:43:54 pm by KK7DTE »
 

Offline Hexley

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Re: HP 400D Tantalum Capacitors?
« Reply #6 on: October 23, 2024, 02:15:33 am »
Now is $75 for both caps the best I can do? Are there cheaper alternatives to these wet tantalum caps?
These $2.50 modern film capacitors will have less leakage than those wet tantalums and should work well for you. Use a single piece for the 4 uF cap, and two more in parallel for the 8 uF cap. https://www.newark.com/illinois-capacitor/405phc400k/capacitor-polypropylene-pp-film/dp/30K6733
 
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Online factory

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Re: HP 400D Tantalum Capacitors?
« Reply #7 on: October 23, 2024, 12:58:44 pm »
They are both in parallel to low value resistors, leakage isn't going to matter, I would go with some  modern electrolytics at 4.7uF 100V and 10uF 50V.

David
 

Offline Dave Wise

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Re: HP 400D Tantalum Capacitors?
« Reply #8 on: October 24, 2024, 02:19:16 am »
If you use aluminum electrolytics, I'd like to know how flat it is at high frequency.  If I did it, I'd try either low-ESR parts, or parts with small series resistors and the combo paralleled with a moderate-size (say 10nF or 100nF) film or ceramic part.  Like HP did in late production.
 


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