HP6633A DC PSU heatsink power dissipation + quiet fan choice

[Pat Pending]

I recently acquired a HP6633A PSU (50V 2A) that was also missing its fan.

It been talked about here on the forum that an nice upgrade would be a quieter fan
but I don't see that being  a good option for low voltage high amp loads.
If for example, I draw 1V@2A or 2W then by reason more than 98W is dissipated in the heat sink.

I don't see a quiet fan upgrade being possible/safe with these HP PSUs. Am I wrong?

[starphot]

  Just as long as the quieter fan has or exceeds the CFM rating of the original. Today, the fans are quieter and push more air than the original when the unit was introduced. 12v fan according to the manual. Unit has a thermal shutdown feature anyway. Just keep it safe.

Joe

[pigrew]

I just bought this model (6633A rev 3004A, from 1990 or so), and finally found where it listed its fan as 25 CFM. The OEM fan is "Fan-Tubeaxial 12-VDC 6100-RPM 23.5-CFM 35dB(A) 60X60X25.4mm Plastic", made by Papst in West Germany. The modern replacement (according to the Keysight site) is the Mineba (NMB) 2410ML-04W-B60.

After cleaning my unit's fan, it is much quieter, but I think I'll still order a new fan. I might also order a thermal controller, though I'm not sure about the easiest way to mount the thermometer to the heat sink.

ADDENDUM: I'm thinking about a cheap fan controller, like https://www.amazon.com/Qianson-Automatic-Temperature-Controller-Governor/dp/B01KH2U2XK/ref=sr_1_3?ie=UTF8&qid=1471622356&sr=8-3&keywords=automatic+cpu+fan+controller+12v+case. My only worry is that it would introduce too much noise on the 12V rail, but the fan is on its own regualator, so it'd probably be OK.

-Nathan

[edpalmer42]

I'm not familiar with the 6633A, but most decent linear power supplies use a transformer with multiple voltage taps.  They select the tap that will allow them to provide the required output voltage while minimizing the wasted power.  Does the main transformer look like it has a ridiculous number of connections?  If so, it probably uses that kind of switching.

If you can measure AC current, you can also compare the input and output power levels to see how much power is being dissipated internally.

Ed