HP 400D VTVM circa 1955 - diyAudio
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Old 15th October 2011, 02:30 AM   #1
diyAudio Member
Join Date: Oct 2011
Default HP 400D VTVM circa 1955

Cr1 & Cr2 (HP G111A) are bad. I can not obtain info on what to replace them with? They are not listed in the manual I have. Any help would be greatly appreceiated.
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Old 15th October 2011, 10:37 PM   #2
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Join Date: Jan 2007
Location: BC, Canada
On section 4-10 of the manual from here -> http://bama.edebris.com/manuals/hp/400d/ , it says they are silicon diodes. Try a 1N4007(standard recovery 1A 1kV) first, if frequency response is poor go with a UF4007 (ultrafst recovery 1A 1kV). Back in 1955, I don't think a fast silicon diode with high breakdown voltage exists so a 1N60 or 1N4148 might work.

How big are the original CR! and CR2 diode compared to a 1N4007?

If you are stuck, try this group ->hp_agilent_equipment : HP/Agilent Test Equipment
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Old 16th October 2011, 02:58 AM   #3
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Join Date: Jan 2007
Location: BC, Canada
I forgot to mention that you should match the forward drop of the diodes using a DVM (set to diode) test if you want to do it right.
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