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BA23 Loud fans

leegleason

leegleason

Experienced Member
Joined
Jan 20, 2014
Messages
148
I've been using a couple of BA23 systems deskside lately. The fans are a bit louder than my liking. I was wondering if anyone has researched replacing them with modern quiet PC case fans.
 
A bit curious about this, as it's one reason I don't use my 11 more. The fans themselves don't generate too much mechanical noise on my unit, but the sheer volume of airflow is pretty noticeable; but I'd be leery of reducing that. If they put two heavy-duty fans on a box full of densely-packed MOS circuit boards, I s'pect there's probably a good reason for it.
 
The high CFM is required as mentioned above due to the hot-running electronics, plus any added loads from one or two disk drives and the power supply needing to be cooled. If you opt for quieter fans, you must either run a near-minimal configuration or match the CFM. Alternately, operate it in a sound-deadening enclosure, much like dot matrix printers used to be.
 
I remember sitting in an ex-bunker for long hours over a very long weekend with the fans of a MicroVAX II blowing right into one of my ears. I came down with an awful cold in the middle of a hot summer!
 
Part of the reason modern PC fans are quiet is because they run them at variable speed. When they run at full speed they are not that quiet.
However, in order to run at lower speeds you then need circuitry to monitor temperature so that you can run at just the speed you need.
No such circuitry exists in the BA23 (of course), so if you replace them with new fans, they will still be running at full speed, and the difference in noise won't be that much.

Now, if someone came up with some temperature monitoring and control to go with new fans, that could be an interesting thing. But then you'd need to figure out where to measure temperature as well. Not sure where the hottest places are myself.
 
bqt said:
Now, if someone came up with some temperature monitoring and control to go with new fans, that could be an interesting thing. But then you'd need to figure out where to measure temperature as well. Not sure where the hottest places are myself.
Click to expand...

Arctic has a line of thermocouple controlled fans, for example the F12 TC.

CW

PS Select 'TC' under features.
 
There are plenty of "PWM fan temperature control" modules with temperature probes very inexpensive on eBay. Most are rated for 12VDC, but there should be no reason that they can't be run at 10VDC.
 
I have researched this subject extensively before building my ultra-quiet MicroVAX II.

Bottom line is, DEC designed the BA23 to be cooled to spec at the extreme set-up possible, which is a fully-loaded QBUS cage (including a VCB board set at ~80 Watts?), a RD5x hard disk drive, and a RX50/TK50, all this running at the spec'd 40 degrees C ambient (104F) at an altitude of 2440m above sea level (8000 ft).

If you run a more or less minimal system, at approximately sea level altitude, at a convenient living room temperature of 23C, then the cooling requirements are much, much less demanding.

Installing a temperature-controlled fan is a possibility, however it is a good question where the temperature probe should be placed.

I think the BA23 fans can safely be replaced with quieter ones without any damaging effect. Unless you insist on high-altitude, high-temperature operation with many power-hungry QBUS boards installed.

My custom machine totals less than 80 Watts and runs non-stop since May 2020 with no hiccups, silently, with an airflow that's a fraction of an original BA23 fan.

-Alon.



leegleason said:
I've been using a couple of BA23 systems deskside lately. The fans are a bit louder than my liking. I was wondering if anyone has researched replacing them with modern quiet PC case fans.
Click to expand...
 
Be careful! If not you will end up with a fan controller that has more processing power then the PDP-11, Always saw that as the flaw in using a modern Windows system running a GUI as opposed to using a terminal was that the “virtual terminal” was more powerful a system then the PDP-11 but if you don’t have a old school terminal or drives imagine that’s the only way you can do it.
I always regarded the noise of the fans, drives and the like one of the best parts of running vintage systems, but that’s just me.
 
Qbus said:
Be careful! If not you will end up with a fan controller that has more processing power then the PDP-11, Always saw that as the flaw in using a modern Windows system running a GUI as opposed to using a terminal was that the “virtual terminal” was more powerful a system then the PDP-11 but if you don’t have a old school terminal or drives imagine that’s the only way you can do it.
I always regarded the noise of the fans, drives and the like one of the best parts of running vintage systems, but that’s just me.
Click to expand...

That pretty much already happens as soon as you put a DELQA in, since it has a 68000 processor on it. Faster and more capable than most Q-bus PDP-11s. And that's the way it has been since the 80s.
 
I don't know why you would want quiet. My old software partner still does support using SimH. He thinks I am mad to restore old PDP11s and MicroVAXes, but I say I love to hear the fans whirring! Mind you, the BA23 is in the clothes closet so that helps reduce the sound and the BA123 is behind the wooden entertainment centre in the living room. My wife says it is as good as a white noise generator to get you off to sleep!
 
The fan noise is nothing compared to the compressors in a bank of tape drives (CDC 657/659). It was white noise, but LOUD. Our department issued earplugs.
 
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