Hi guys,
I recently aquired a beautiful old Tektronix 2465. She's my first scope, and a bit of a fixer-upper. The first thing I had to fix was the main power switch, no biggie, and she works like a charm now.
I didn't know about the A/B sweep feature until after I'd bought it, but - WOW!
The problem I have is that the fan is unbearably loud. I did manage to reduce the squeeling by lubricating it, but now it just vibrates instead.
So, while there's a guy who's restoring these [http://www.antiqueradios.com/forums/viewtopic.php?uid=30281&f=8&t=235478&start=0], the process is pretty painstaking, expensive (he's offering to sell the bearings he had made at what's a very reasonable price for the effort - I'm not complaining) and somewhat risky, given that I'm pretty much all left-hand thumbs. I'm also not sure that I'd get another 3 decades out of a restored motor unless the fan axle is also refinished...
I had a hard look, and it turns out there just enough room for an 80x80x25 fan on the back of the scope's case behind the back cover. A fan that size will however pretty much block the case exhaust hole (~53mm diameter) with the fan hub, and also ends up blocking the right-hand (outside) exhaust vents.
So, I figure I can replace the original fan by a "standard" 12V 60x60x20mm case fan, which'll leave plenty of room for the exhaust path. To ballpark the fan sizing, I looked at the airflow figures for the 2465A scope's fan, which turns out to be on the order of 24cfm, and which is reasonably easily matched with a 60x60x20 fan - although it'll have to run faster and probably a bit louder.
So, I was thinking to give this a try using this fan:
http://www.digikey.ca/product-detail/en/PMD1206PKB1-A.(2).GN/259-1403-ND/1249276. I'm also going to copy the 2465A's fan control circuit. This is basically an LM317 with an NTC to drop the unregulated 15V to ~6-12V depending on ambient temperature.
Has anyone here done a mod like this? Is there anything I'm missing that would make this a stupid thing to attempt?
Now for a noob question (I'm a software engineer dabbling in electronics, bear with me

).
I have some LM317s in a TO-220 and I figure I'd better heatsink it a little. I think the dissipation will peak at ~220mA*8V (~19 on the unregulated rail, and ~12 out) or ~1.8W. The TO-200 is 80C/W to ambient, and I figure that'd put me in trouble without heatsinking, especially as the fan will be running full at when it's 65C ambient or thereabouts. Do you guys think something like this [http://www.digikey.ca/product-search/en?WT.z_header=search_go&lang=en&site=ca&keywords=HS365-ND&x=14&y=17&formaction=on] do the job?
On the face of it at 28C/W*2W+65 ~= 121C it's not outlandish, and I figure I'd be able to put it somewhere where there's a bit of airflow.
Apparently if you lose the fan on those old'uns, you'll shortly after lose U800 which is allegedly made of unobtanium, so I'd hate to build my fan controller in constant thermal shutdown

.
Siggi