Cohu 355 DC Voltage Standard

[Solodolo47]

Hello, does anybody happen to own a Cohu 355 DC Voltage Standard? I have just purchased one and I need a manual for the calibration. I could only find half of the manual online that basically just has the circuit description. Any help would be appreciated. Thanks.

[trobbins]

In your travels if you find any cal/circuit/service details on the 303B then I'd appreciate a PM as I haven't attempted to restore that unit yet.  Kintel is the other relevant search term to Cohu.

[Solodolo47]

There is actually a manual for the 303B on ebay for 20 dollars. It t should have service info in there. The seller also has other Cohu manuals but unfortunately not for the 355. I'm tempted to buy the manual to see if I can use its calibration info for my 355. The controls are the same but laid out in a different configuration. I assume the circuitry would be somewhat similar .

[bnz]

I had a COHU 355 and manual but sold it. I still have a scan of the manual (no original print just an old copy) which I just uploaded to KO4BB. It is available there at recent uploads:
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=07_Recent_Uploads

[Solodolo47]

Thank you very much bnz!! I really appreciate uploading the manual 

[trobbins]

I was able to confirm the Cohu 303B electronics were significantly different to the 324, and the 355 models (from their service manuals), so if anyone has a scan of the 303B schematic I'd appreciate a PM to assist some careful rejuvenation of the e-caps and confirming the all-valve electronic sections are operating as intended.

This 303B has an ovenised reference 7817039-001, and uses a Stevens-Arnold CH-801 DC-AC chopper.  The 7-decade feedback resistor network has the 12 largest resistors using their own CONELCO 0370L-2 trimpot. The 1400V raw HVdc uses a large oil-can cap, rather than the latter models that went for a series string of 450V e-caps.

It's interesting that the 303B, from circa 1964, was bested at that time by the 304 model.