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OPT 003 (48-440 Hz compatible) fan (full size "Muffin" type fan) - replacement requirements?

 

Have a failing/failed cooling fan from a HP machine with OPT 003 (400 Hz), which appears to apply to the type of fan installed.

Are there any requirements (trying remember undergraduate EE class that described analysis of induction motors - does that describe a typical cooling fan of this sort? - but that is digging waaaaaaaaaaaaaaaaay back to the 70s... Should a generic 120 VAC 60 Hz fan of sufficient air flow be acceptable, or do I need search for a fan designed to support 400 Hz?)
 

Unless you plan to operate on 400 Hz AC current, you don’t need a 400 Hz fan. Depending on the instrument, you may be able to get by with a lower-power (quieter fan). HP typically spec’d their stuff to 50C; in a laboratory environment, the temperature should be considerably cooler.?

Jeremy?



On Wed, Mar 19, 2025 at 1:43?PM David Feldman via <wb0gaz=[email protected]> wrote:
Have a failing/failed cooling fan from a HP machine with OPT 003 (400 Hz), which appears to apply to the type of fan installed.

Are there any requirements (trying remember undergraduate EE class that described analysis of induction motors - does that describe a typical cooling fan of this sort? - but that is digging waaaaaaaaaaaaaaaaay back to the 70s... Should a generic 120 VAC 60 Hz fan of sufficient air flow be acceptable, or do I need search for a fan designed to support 400 Hz?)
 

What is the problem with it? I had a very noisy one of these fans and any 400Hz capable replacement was very expensive. In the end I simply took the old one apart and replaced the two bearings.
They were standard imperial sized units that were available from stock here in the UK, reassembled and all was well, took about an hour and even with top quality bearings (SKF) the cost <15 GBP.
 

The difference with the option 003 is that a DC fan is fitted rather than the mains (50/60 Hz) AC one in the standard unit. This give you more choice of replacment fan. Take the old one out and see what model it is. Any modern DC fan of the right size and voltage will work.
The OPT 003 fan can't be a 400Hz unit because it still has to run at 48Hz. There is no such thing as a 48Hz to 400Hz AC fan (unless it is really a DC fan with built in power supply).? I've actually used / installed HP and Tektronix kit on aircraft using the 400Hz supply.?
?
Robert G8RPI
 

Robert, Adrian - thank you both for adding to discussion - this information helps because I also have OPT 003 in old HP 8660 series synthesizer (also very heavy machine) so good to have these options.
 

If it is from a 8660, don't be tempted to go with a lower power fan, HP had some reliability problems with early 8660A & 8660B, this lead to them offering a free upgrade to a larger size fan in 1974 to improve the cooling;
?
David
 

Have both 8660B and 8660C; I was aware of the thermal issues with the 8660B (I believe it was in the pre-LSTTL era as I understand). It lives in a basement (lowest floor) workshop and fortunately is not on for long periods of time nor subject to ambient above about 70F.

The 8660B accepts regular 60 Hz fan and I ordered a couple of "high speed dual ball bearing 120x38mm 120VAC" fans so that when these things are next on the workbench I'll have spare ready.

As for the 8673D/003, I wasn't aware of the specifics of 400 Hz capable fan; most likely I'll see if I can add supply wires back to the switched 120VAC side of primary transformer (or however the 8673D normally gets power for it's upper assembly cooling fan, which should be revealed by the service manual (which is in competition for the heaviest service manual I've ever seen.)

Thanks again, much appreciate the comments!
 

Fans here, turns out on closer inspection the 8673D uses 92mm in the upper section, not 120mm - oops - so regrouping on that front (the 8660 series appear to be 120mm fans.)

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