[Hallicrafters] voltage ratings on HT37 C79A/B - another viewpoint

[Kenneth G. Gordon]

> > > Is this an absolute rating or can modern 450v
> > electrolytic caps do the job 
> > > safely??
> > 
> > Huh?  475VDC is 475VDC is 475VDC, ratings do not
> > change with new 
> > manufacturing processes..... 
> 
> Right!
> 
> KABOOM!!!

I think what the original question concerned was whether or not the 450 
VDC rating on his substitute caps was a WORKING VOLTAGE or the 
ABSOLUTE MAXIMUM voltage.  Most modern electrolytics have a 
working voltage that is lower than their absolute-maximum "holding" 
voltage. In fact, I have heard that some manufacturers test their 450 
VDC working-voltage caps at 500 VDC.

However, I also understood from a discussion we had on this topic a 
few years ago on another list, that electrolytics which are rated for 
much more than about 450 VDC actually, in many cases, contain two 
identical caps in series.  The ones under discussion at that time being 
rated at 600 WVDC (working volts DC), and upon being disassembled 
were found to contain two identical series connected capacitors rated at 
450 WVDC.

The theoretical maximum voltage that any SINGLE electrolytic cap can 
be EASILY and CHEAPLY manufactured for is 500 VDC.  The process 
that forms an electrolytic cap limits the maximum voltage to that.  This is 
one reason why electrolytics rated for more than 450 WVDC cost a lot 
more.

Now, after saying all that, although, IMHO, the person who asked the 
original question could probably safely use 450 WVDC rated caps to 
replace his 475 WVDC caps, doing so would probably shorten their 
normal life span, especially considering that our modern line-voltage is 
higher than the line-voltage was at the time his receiver was made.

So, I too would do what was suggested recently by another member of 
the list: install capacitors rated for at least 600 WVDC, (or two 450 
WVDC caps in series, with equalizing resistors), for each of the 475 
WVDC caps, mount them under the chassis on terminal strips after 
disconnecting the original dual-475 WVDC cap, leaving it in place, but 
unused.

Ken Gordon W7EKB