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Old 6th November 2006, 02:26 AM   #1
imix500 is offline imix500  United States
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Default Hp 204c

Hey all, I got this HP 204C for free the other day. I've learned my lesson on powering up old test equip so I'm not going to even try before replacing all the 'lytics. While I'm doing that are there any other parts I should consider replacing?
The parts list mentions "Al Elec" caps and "Ta Elec" caps, what is the differance?
Also, should I go ahead and replace the ceramics, and these odd Titanium Dioxide capacitors in here? Thanks!
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Old 6th November 2006, 05:55 AM   #2
clem_o is offline clem_o  Philippines
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Al - aluminum electrolytic - general purpose run of the mill stuff.

Ta - tantalum electrolytic - smaller, higher density, less leakage, teardrop shaped.

No need to replace the other types of capacitors...

Good luck!

Cheers
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Old 6th November 2006, 11:09 AM   #3
imix500 is offline imix500  United States
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Hi clem_o, that's what I figured. Should I just replace the Tantalums (they are axial "Tantalex" types) with modern equivilents or are there better options available now? Thanks!
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Old 6th November 2006, 12:06 PM   #4
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When Tantalums "go", they go catastrophically.

With respect to the non-electrolytic caps -- you would only replace these at your peril -- HP, Fluke, Krohn-Hite, Boonton used very high quality film (polystyrene, polycarbonate) caps from TRW and GE.

It would be cheaper to get a variac and power it up slowly -- although powering a Hewlett Packard 204C isn't like powering up a prewar Hallicrafters SX-28.
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Old 6th November 2006, 12:51 PM   #5
imix500 is offline imix500  United States
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Hi jackinnj, I may just do the aluminum elecs, there are only a half dozen in there, and wait and see about the tantalums. All the electrolytics are sprague.
The output capacitor is a 300uF 10v electrolytic. Could this be something better?
Now, my biggest concern. This one has the Option 02, rechargable ni-cads. These appear to make a voltage divider and do some free filtering for the bipolar supply maybe? Are they needed for operation? The only reason I ask is the standard version uses a discrete regulator for -/+, this version does not.
Thanks!
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Old 6th November 2006, 01:01 PM   #6
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the 300uF on the output is fine --

The first thing you do with any old equipment is get rid of the nicads.

you can get a CD-ROM of the manual from many vendors on EBay or through www.w7fg.com
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Old 6th November 2006, 02:21 PM   #7
paulb is offline paulb  Canada
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AudioXpress magazine had an article about restoring an HP403B, I believe in the June 2006 issue. The author replaced the NiCads with zeners and more filtering.
I don't think you'll find the article on the web but you can buy back issues.
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Old 6th November 2006, 03:30 PM   #8
imix500 is offline imix500  United States
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Yeah, all the ni-cads are all toast. Could I use a 7812 and 7912 here? Or should I build a little board for the hp regulator circuit?
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Old 6th November 2006, 03:59 PM   #9
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There's not center tap on the HP204C power transformer so you will need to create an articificial ground. The author did this by connecting a 1K resistor from each of the the trafo secondaries to ground. Not elegant, but it will work -- he also used 12V Zeners, 4,700 uF filter caps etc.
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Old 6th November 2006, 09:55 PM   #10
imix500 is offline imix500  United States
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That issue isn't on their website yet, maybe I can find one at the NY flea market in a couple weeks.
4700uF filter caps? Isn't that a big much for a ~40mW output?
Thanks!
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