[time-nuts] HP and other equipment failure

Mark C. Stephens marks at non-stop.com.au
Fri Jun 14 14:26:50 UTC 2013


Talking of Cooling HP 5370's, I have a 12V fan Gorilla taped to mine fed from a wallwart.

Not elegant, but it has reduced the heat sink temperature dramatically.

Is anyone else concerned about the heat sink temperature on the 5370?
Has anyone done a fan modification they would care to share?

Also, my 8566A RF section pass transistor heat sink gets awfully warm too, does anyone have a sensible solution?


-marki


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of David Kirkby
Sent: Friday, 14 June 2013 7:14 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP and other equipment failure

On 14 June 2013 05:48, Perry Sandeen <sandeenpa at yahoo.com> wrote:

> There are two long standing truths about electronic equipment.  One 
> you can't have too much filter capacitance.  Two, you can't cool too 
> much.  (Please spare me the  liquid nitrogen or submarine battery
> comments.)
>
> Regards,
>
> Perrier

Well, I have to disagree with both comments.

More filter capacitance in a standard linear power supply means the diodes take more current for a longer period of time. For any given diode, that puts more strain on it. At very high levels of capacitance, the amount of stored energy is huge, and can be dangerous. In the event of a fault, higher stored energy has the potential to do more damage than lower stored energy. Once you have sufficient capacitance, which includes calculating the effects of reduced supply voltage, minimum capacitance of device with tolerances, and some safety factor, I don't see what more capacitance does other than increase costs, weight, and the potential for more damage in the event of a fault.

Whilst it is well known that increasing temperature gives rise to shorter component lifetimes, more cooling also requires more noise, and so a compromise has to be met. I have here an Air Control Industries VBL9 blower, which I want to sell in fact. That will move about 1000 cfm at 6" of water pressure. It happens to take 2.8 kW from the mains, the startup current is too large to not blow a normal mains fuse in a plug here in the UK, and the noise is enough to get neighbours wondering what the hell it is, despite I live in a detached house, some 50 m from the nearest property. So while a HP 5370B needs far more cooling than provided, I think the VBL9 would certainly provide too much cooling air.

Engineering is always a compromise. HP usually got that balance about right, although in some instances, like the 5370B, that is not true. I know mine got pretty damm hot, and I'm quite near sea level. I would imagine for someone at a high altitude, it would be even worst.

I have to agree with you about the serviceability of older HP equipment though. It is much more serviceable than modern equipment.
However, you would have to go back a long way before finding equipment which one could guarantee one could keep going, as most things I'd contemplate buying will have a ASIC and/or some other specialist component which if it failed would be impossible to get except by taking one from a similar piece of equipment.

Dave
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