[Hallicrafters] s-38D

[W4AWM at aol.com]

<<  Lights up, rf is good, makes audio, but the bandswitch is 'snap, crackle, 
pop'!
Tap the metal case and the audio rumbles.
restoration 101: >>

Hi,

The S-38 series are relatively easy and fun to work on, however there is one 
BIG CAUTION right from the top: Use an isolation transformer when working with 
these AC/DC sets and if you can spare it, when you are using it, too. The 
reason for this is that one side of the line cord is connected to the chassis. If 
you insert the plug wrong, the chassis is hot even when the receiver is off. 
If you insert it the other way, the chassis is hot when the receiver is on.

The very first thing you should so is replace the line cord with a properly 
connected polarized plug set. Also, check the cap that goes to ground from the 
line side of the power cord.  If, for any reason, you remove the cabinet, be 
sure to replace the rubber isolation insulators between the chassis and the 
cabinet.  If age has gotten to them, replace them.

Now, on to your other problems.  Rumbling when tapping the cabinet can be 
caused by a number of things from loose connections, dirty tuning capacitor 
contacts or insulation to tubes. Tubes are the first suspect and you should check 
them all as a first stem in any restoration. Then there is, what I call the 
Hallicrafters boinggggg.  This happens when the BFO is in use and is usually not 
fixable, but then one does not normally tap the cabinet while copying CW.

The bandswitch problem can usually be eliminated by a good contact cleaning 
with De Ox It or similar product. Do not spray it on the wafers since some have 
been known to swell up after application and become permanently damaged.  
Instead, use a Q-tip or toothpick to carefully apply the solution to the 
contacts. Tape head cleaners are available which have a chamois like material at the 
end and do not tend to snag like a cotton swab.  While you are there, check for 
loose contacts, wipers and bad solder joints. 

Check for loose ground connections at terminal strips and tube sockets.  Many 
times loosening and retightening screws that have associated lugs they are 
holding will cure the problem. Other times it could be necessary to drill out 
rivets holding tube sockets and terminal strips and replace them with a screw, 
toothed washer and nut.

Check the tuning cap as stated above. If it is dirty, clean it first with 
compressed air if available and then with contact cleaner. compressed air should 
be used before cleaning the band switch so that it does not become 
recontaminated after cleaning.

You will probably want to replace the multi section filter cap and any paper 
caps that appear to be deteriorating. My practice is to replace all the paper 
caps from the top, but you will find controversy over this procedure. If you 
have any problems, don't overlook the fact that carbon resistors in these older 
sets have a nasty habit of changing values and may need replacement also. 
Finally, you may have to align the set but I would see how it performs and then 
make that decision.

Hopefully, one or more of these suggestions will cure the problem and leave 
you with a fun little receiver that will give you many hours of enjoyment.