-=> On 03-28-98  20:29, Bruce Legrande said to All,<=-
-=>"About Filter Cap values in R-4...,"<=-
 
 BL> Hello All!
 
Hi, Bruce;
 
 BL> I have a Drake R-4 that has a VERY bad hum in it
 BL> that doesn't seem to change with the AF level control.
 BL> Not SURE about the source, but I figure the AC filter
 BL> caps probably need replacement anyway, as the OEMs have
 BL> probably dried out quite a bit.
 
As you suspect, that is probably the filter capacitor.  I am not
familiar with that model, but if it has tubes, there could be a
heater-cathode short in one.
 
 BL> The schematic calls for a multi-section 100uf 200v can,
 BL> and I've found a single radial unit (three would be used)
 BL> that have ratings other than what the schem' calls for,
 BL> 250 (300v surge), 350 vdc (400 surge), and 450v (500 surge),
 BL> that are available in several capacities in addition to
 BL> 100uf, and I'm wondering for this application - what would
 BL> be my range of acceptable values ?
 
The voltage is unimportant as long as it is at least as high as the
origional.  Likewise, the capacity needs to be at least the origional
value.  Higher values for both will not hurt anything.
 
 BL> Would it be worth it to
 BL> go with the larger VDC ratings (above 250), and I've heard
 BL> that a cap as low as 47uf might be OK - but what about going
 BL> the other way higher than 100 (ie 220uf) ?
 
Don't go below the origional!
 
 BL> Will either modification provide better performance ?
 
If you had a trace of hum origionally, higher capacity values SHOULD
correct it.  One question: Is there hum on your transmitted signal,
(any mode)?
 
 BL> I plan on making a PCB mounting board for the radial caps,
 BL> connecting the outer leads to chassis gnd and having PCB
 BL> pads for the anode (+) connections (inner circle), and
 BL> mounting that in the same place as the OEM can.
 BL> The physical size of the new components (18x32mm) [DxL]
 BL> doesn't seem to present any problems.
 
As long as there's room.  If not, and you can manage to put them into
a solid "box" which you may be able to mount on the back of the rig,
making sure that nobody can possibly come in contact with the wires.
 
KB6LWN DE KB9QPM
   Ivy
 
 
 
... Are flames supposed to shoot out of it like that?   8-O
 
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