[R-390] c609 replacement

[Roy Morgan]

At 08:51 PM 8/14/03 -0500, wb5tcd@sbcglobal.net wrote:
>     I need to replace this capacitor.   Should it be the same tantalum type?


Not necessarily.  It serves as the cathode bypass cap in the audio preamp 
stage.  Modern electrolytic caps will be both smaller and longer 
lasting.  The actual voltage on the cap is far below the rating of the 
original cap, being the self-bias voltage developed by the cathode current 
in the cathode resistor..Something on the order of a few volts (do check 
the tube voltage charts/diagrams to see what the normal voltage is.)

I recommend you find whatever small cap you can that fits physically and 
has a capacitance value greater than the original and any DC rating above 5 
volts. The bass response of the receiver may be extended to a lower 
frequency.. I doubt that you will mind that

>Why is  this type used for this circuit is there something critical about
>it?

The only thing critical about it is that it be small enough to not get 
mashed when you put the module back in the radio.. You can mount the 
replacement UNDER the circuit board if you have only a cap which is 
physically too large.  Go to rat shack with two bucks and solve your problem.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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