[QuadList] Colortec board 12 capacitor corrosion

[L.E. Odham]

Hi Don & Park, 



Yeah I wondered a little bit about why/how such a big mess was made, too. This particular colortec may have been exposed to extreme temperature changes over a period of time in an uncontrolled storage situation. 

I'm thinking it was one of the spare pieces that came from out back of the Winston-Salem cat house guy.  The fellow's name escapes me, but I do remember all those cats running around all inside the building.    There were a couple t ractor t railers full of equipment & various parts-pieces  parked out back and this colortec came from one of those vans I'm pretty sure. 

Maybe  the 15-20 degree freezing temperatures made them pop, or the 120 degrees inside heat in the summer. 



The last batch of those exact OEM type caps  I purchased was at Sky Craft in Florida last Feb. after the Orlando  hamfest. $4. dollars each for 270 uf. 



I shoulda bought more! haha. 



At this late date, I really want to stay as true to original as possible. Those oem's have lasted for 40+- yrs, a tall order for any electrolytic. Many years ago attending the engineering program at NE State Tech, I was taught  that electrolytics have a shelf life; i e., they will go bad new sitting on the shelf after enough time passes and the electrolyte dries out enough. The sealed 'wet' caps were an attempt at stabiliz ing and extending the useable life by keeping the electrolyte stable(from drying out). 



Seems that idea worked pretty good! 



Larry Odham 



Quad Tape Transfer 

www.QUADTAPEXFER.com 





----- Original Message -----





Hi Larry: 

I've seen a few failures like this, but not this bad!!! 
  
Most of the tantalums that Ampex used in the quad era were mil-spec, hermetically sealed units, and they almost never go bad.  However, these particular ones are wet tantalums which are not hermetically sealed.  Since these are simply filters across the power supply busses, you could replace them with modern-day electrolytics which are small enough these days to fit in the space available.  However, if you insist on the "original" parts, they are still available from suppliers like Avnet or Arrow, but you'll pay $40 to $50 EACH for them.  I did spot a few on eBay for $15/ea....a real deal!!! 
  
I have seen some instances where a board was "shotgunned" and all of the expensive hermetically sealed caps (the ones that almost never fail!!!) were exchanged for cheap electrolytics.  I've never believed in doing that, because I've experienced more failures with the new electrolytics than with the old mil-spec caps.  But in the case of actually needing to replace one of the expensive caps, if we don't have the original part, I'll go with an electrolytic unless the customer requests otherwise. 
  
Don Norwood 
Digitrak Communications, Inc. 
www.digitrakcom.com 



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