[Drake] R-4C problem

[Garey Barrell]

Ed -

I've seen that cap as well, and wondered what the thinking was.....  it 
was added in the third version of the receiver, and is shown in both of 
the last two versions wired to the filament supply.

I never wondered enough to try and figure it out though!   A little 
thought would  say that it's a relatively small value cap, 20 uF, and 
connecting the negative lead to chassis wouldn't make much sense as 
there is already a 3000 uV cap to chassis at that point.  An additional 
20 uF to ground is insignificant.  I suspect it's to inject a little AC 
'out of phase' to the supply, limited by the voltage source and the 
reactance of the capacitor, so you'd want to stay close to 20 uF.

Maybe someone else knows the 'real' reason!  :-)

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>


djed1 at aol.com wrote:
>   I've been trying to track down a low level 60 Hz hum in the audio output.  I seem to have a fairly high level of 60Hz on the first filter capacitor in the 14V power supply.  I've replaced the filter cap before, but I noticed that the schematic has a 20 uF cap connected between this point and the filament supply.  Is this a typo on the schematic, or is this real, and if so, why would they do that?  It looks like the 20 uF cap is connected to ground, and not to the filament voltage, in my receiver.  Any other suggestions for what to look at?
> Ed  W2EMN
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