[Milsurplus] R-388

[WA5CAB at cs.com]

Rick,

First, the 0A2 supplies regulated B+ to the 6BA6 HFO and Buffer, not to 
V113, the 6AQ5 audio output.  Assuming that the manual you are referring to is 
TM 11-854 dated 25 April, 1952, there were four changes issued up to 25 
November 1963 (Change 3 was superceded by Change 4).  Resistor R181 was changed 
at twice, first to 3100 ohms and then to 1400 ohms plus R185 of 1800 ohms.  
In the latter case, C239, 8 ufd, is added from the junction of the two 
resistors to terminal 1 of C217A,B.  R185 is installed in place of the vertical 
line on the schematic from the junction of L122 and L123 to the junction with 
the horizontal line above. So V113 draws its B+ through R185.

There are several other changes that will or may affect your receiver.  It 
depends upon what order number your receiver was bought under, and in some 
cases what the serial number is.

I sell a reprint of the TM, with changes, for $22.50 plus shipping.  Or if 
you have an original basic TM, the Changes alone are $7.50 plus postage.

In a message dated 5/6/2011 9:16:16 AM Central Daylight Time, 
rickb at tx.rr.com writes: 
> This is my first venture into the circuitry of the R-388 and I have found 
> a
> confusing circuit hopefully someone can clear up for me. In regards the 
> OA2
> regulator (V116) the plate of the tube is connected per the  schematic to
> R181, a 4000 ohm (probably 20 watt ) wire wound resistor. However, in
> reality, it is connected to two 2000 ohm (or they were 2K ohm before they
> over heated severely) in series. Of course, this is still in essence a 
> 4000
> ohm resistor. One of these series resistors is R181 and is listed in the
> parts section of the manual and on the schematic. The second 2000 ohm 
> series
> resistor is labeled on the chassis as R185 and is NOT on the schematic or
> listed in the parts section of the manual. There is a wire also not to be
> found on the schematic soldered between the two series resistors. I do not
> know where this wire leads yet. These are current limiting resistors and 
> the
> output supplies the 6AQ5 (V113) audio output tube with its B+. My question
> is, has there been an update to the schematic issued describing these
> changes? This is not a hack someone has put in the receiver as the chassis
> reflects the new part numbers just as it does the original part numbers 
> with
> the exception the new numbers are a little larger type. I obviously have 
> an
> excessive current drain in that line as one of the resistors heated to the
> point of melting the solder on the connections. I have audio, but not 
> signal
> whatsoever. Any help locating the addendum will be greatly appreciated.
> Please, excuse my long winded description.
> Rick/K5IAR

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480