[Milsurplus] R-388

Sat May 7 18:09:18 EDT 2011

Thanks DeWitt.. I did just that before buttoning it back up. Evidently, the
resistors just got tired as I could find nothing out of order to cause it.
Of course, these may be "famous last words" and a month from now I have the
same problem, HI HI

73,
Rick/K5IAR

-----Original Message-----
From: DeWitt Clay [mailto:n4qnx at yahoo.com] 
Sent: Saturday, May 07, 2011 9:48 AM
To: Rick
Cc: milsurplus
Subject: Re: [Milsurplus] R-388

Hi Rick, 
Suggest checkout the cause of the resisters overheating. If a filter cap was

added to the junction of the two resisters or if there is a filter cap (to 
ground) at the output resister side, check the cap(s)  for high leakage or
the 
new resisters won't last long before they overheat and go bad.
73, DeWitt

----- Original Message ----
From: Rick <rickb at tx.rr.com>
To: milsurplus at mailman.qth.net
Sent: Sat, May 7, 2011 9:59:00 AM
Subject: Re: [Milsurplus] R-388

Thanks Robert for the information. I found the change noted on the schematic
pasted to the inside of the top cover for R181 later on. When I get back in
the shack later today I'll see if I have the TM you referred to and contact
you as to whether I want the changes only or the entire manual. I replaced
the two resistors, R181 and R185. This corrected the problem and the
receiver works beautifully. 

Thanks again for your help...
Rick/K5IAR

________________________________________
From: WA5CAB at cs.com [mailto:WA5CAB at cs.com] 
Sent: Friday, May 06, 2011 10:28 AM
To: rickb at tx.rr.com; milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] R-388

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November 1963 (Change 3 was superceded by Change 4).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
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