[Drake] R-4C

[Eric M Tichansky]

>
> I have a couple of R-4Cs here, one of which has the K4ZS audio 
> (LM380), product detector (SA602AN), and power supply (7812) mods.  
> The other has been retrofitted with homebrew mods based off of the 
> K4ZS mods, and in all practicality are identical to such; so both 
> units are electrically similar and should behave similarly.  Now, I am 
> noticing different operating characteristics that bring about concern.
>  
> The K4ZS mod R-4C (# 26xxx) pops on power up (normal according to 
> various sources, also I understand the Sherwood P.S. mod does also.) 
> and white noise when left in the STBY position remains at the same 
> level immediately after the 'pop'.  There is no hum or buzz present 
> and it is very very quiet when muted.   I consider this rig to be the 
> standard I am trying to achieve with the other R-4C.
>  
> The homebrew mod R-4C (#28xxx) does not pop, but rather powers up with 
> typical white noise for a second, then noise all but disappears, and 
> then slowly builds back up to the level observed immediately after 
> power up.  There is also very noticeable hum/buzz present.  I had 
> replaced all the filter caps, but noticed no improvement at all, so I 
> returned the filter caps to the stock cans.  The buzz/hum is being 
> noted when the receiver is muted (STBY) of course. 
>  
> What is the source of the power-up popping? (transformer saturation?)  
> What would cause the pop not to occur, and the reason for the 
> "warm-up" noise level? Finally, where could hum be leaking from the 
> power supply? (note that it is observed in mute condition, so RF/IF 
> chain should not be part of the cause I assume) 
>  
> Eric NI3S