[Heathkit] replacement caps for Heathkit

[Richard Knoppow]

----- Original Message ----- 
From: "Dick KF4NS" <kf4nsradio at verizon.net>
To: <heathkit at mailman.qth.net>
Sent: Saturday, January 07, 2012 11:42 AM
Subject: Re: [Heathkit] replacement caps for Heathkit


> Thanks guys for the info. I have the Sprague 160Ps and all 
> are the later ones. I am replacing them with
> polyester film from Mouser. Sure takes up alot less room. 
> I already had all the new caps I needed, just
> was curious about subbing a .22 or .33 for the .25, in 
> other words, up or down in value if the old values
> are not found.
>
> I like the orange drop but they are expensive. For this 
> purpose, polyester film or metal film or fine.
>
> Yes indeed, age does play a role in our absent mindedness. 
> I am constantly reminded.
>
> 73, Dick KF4NS
> St Petersburg, FL 33714 USA
> Keep The Glow!

    About the only places that precision capacitance value 
is necessary are timing circuits, including frequency 
control elements in oscillators, and filters. The difference 
between 0.25 and 0.22 is 12%, I suspect the original caps 
were no better than +/- 20%. Usually, using somewhat larger 
value caps does no harm. The original values may have been 
chosen partly on a cost basis. In certain circuits, such as 
multi-stage audio amplifiers with feedback the values of the 
coupling caps may be important in determining the phase 
shift or in controlling low frquency response. Here again, 
probably approximate values are OK, just not ten times or 
one-tenth the orginal.
    I don't know what the _original_ performance of the 
common wax or plastic shelled caps found in old equipment 
was but having measured a lot of them both dissipation 
factor and leakage of the "good" ones are significantly 
higher than modern caps.
    Of course, this is affected by age: I've found that most 
of the caps from, say, the mid-1960s or later are plastic 
types and are just fine.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com