[Drake] R4 Receiver

[Garey Barrell]

Doug -

Simple reason.  C90A was not used in the early R-4.   I don't have one I 
can get to at the moment, but if you look carefully at the underchassis 
photo in the manual you can see that there is no connection to the 
"blank" terminal of the electrolytic.   I had forgotten about it, but 
when you asked it triggered a synapse somewhere!  Maybe they got a good 
price on 4 section caps?

Then it looks like they forgot it was there, because when they added 
decoupling to the B+ for the product detector stage in the first version 
of the R-4A, they added an 8 uF @ 250V tubular cap as C156.  The 2nd 
version R-4A shows a three section electrolytic.  (Guess they ran out of 
the "bargain" caps and had to buy more??)  Then in the third version of 
the R-4A, when the PD and 1st AF were converted to solid state, they 
added yet another PAIR of caps, C172 and C173 to decouple the supply for 
these stages.  The version three photo shows a four section cap again, 
and with all four sections wired.  But C90A is STILL not shown on this 
schematic or on version four schematic.

Finally (!) in version one of the R-4B, C90A makes it's first appearance 
in place of C172, and is shown as 20 uF @ 250V.  Sections B, C and D are 
still shown as 100 uF @ 200V.  In version two of the R-4B C90A is 
changed to 20 uF @ 200V, and is the same in the third and final version 
of this series!

Your third cap is probably the cathode bypass on the audio output tube, 
Pin 1 of the 6EH5 to ground.  But there should be a third 100uF @ 200 at 
whichever (B, C or D) section is "missing"!

I KNEW there was a reason I didn't do a CD for the A Line!  :-)

73, Garey - K4OAH
Glen Allen, VA

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



ddswl wrote:
> I am told the first one did not go out, so this is the secend try, 
> sorry if it went twice!!!!!
>
>
> Ok, someone straighten me out!! I have received a Drake R4 receiver and
> looking under it, the filter cap has been replaced with a double cap ( 
> 2-150
> ufd 250V), however in looking at the schematic,  I find C90B, C, & D, 
> but I
> can not find C90A. A  third cap underneath has been added (12 uf) which I
> can not find on the schematic. The schematic sez all of C90's are 
> 100uf's at
> 200v. Can someone tell me what should be in the orginal radio???? If 
> you can
> help, please e-mail me direct.
> Many Tnx----Doug W7LNB  ddswl at centurytel.net
>
>
>