MARCH 2009 NOTE: WE HAVE DONE SOME MORE WORK ON THIS RADIO ....... DETAILS BELOW......STILL A "WORK IN PROGRESS"
LET'S START on a restoration of the best of the S-38s we had in the pile. Serial number 161218 We decided to restore the chassis, and decide what to do with the cabinet AT A LATER DATE. If it cleans up well, we will use this as an original restoration. If not, we will repaint the cabinet.
This will be a "step by step" look at this restoration
HERE IS A SHOT OF THE TOP CHASSIS AND UNDERNEATH
1) ... REMOVE FILTER CAPACITOR. WE CUT THE WIRES AT THE CAPACITOR AND DRILLED OUT THE RIVOT WITH A 9/64 DRILL
2)... REPAIRED FRAYED AUDIO TRANSFORMER WIRE. (YOU CAN'T SEE IT IN THE PICTURE). THE INSULATION ON THE SECONDARY OF THE TRANSFORMER HAD FRAYED, LEAVING EXPOSED COPPER WIRE. I CUT THE WIRE AT THE TRANSFORMER AND ADDED A NEW LEAD.
3)...R-9 , A 470 OHM RESISTOR WAS BROKEN FROM THE AM/CW SLIDE SWITCH TO GROUND AND WAS REPLACED
4)...REPLACED C-36 , A .25 MFD CAPACITOR (USED A .22)
5)...DRILLED OUT POWER CORD HOLE TO 3/8 " TO ALLOW FOR GROMMET. REPLACED POWER CORD.
6)...REPLACED C-34 .02 PLATE BYPASS CAP TO THE 35Z5 TUBE
7)...FOUND FRAYED WIRE TO TO THE PILOT LIGHT, USED HEAT SHRINK TO SEAL THE WIRE.
8)...MOUNTED NEW FILTER CAPACITORS (C-29, 31, 32, 33) TO TERMINAL STRIP. (SEE BELOW)
9)...DRILLED 9/16 HOLD TO MOUNT TERMINAL BOARD, AND WIRED THE 4 CAPACITORS. THE THREE LARGE CAPS ARE THE POWER SUPPLY CAPS, WHILE THE SMALLEST IS THE CATHODE CAP FOR THE AUDIO OUTPUT TUBE (35L6)
10)... NOW IS A GOOD TIME TO CHECK THE PILOT LAMP. (#47) DO NOT RUN THIS RADIO WITH A BURNED OUT PILOT LAMP
11)... IT IS ALSO TIME TO CHECK ALL THE TUBES. YOU HAVE A CHOICE TO CHECK JUST THE FILAMENTS OR ALL THE FUNCTIONS OF THE TUBES, I USUALLY CHECK JUST THE FILAMENTS. (ONE BAD FILAMENT MEANS NONE OF THE TUBES WILL WORK) TUBES DON'T GO BAD THAT OFTEN. I LIKE TO MAKE SURE WE GET ALL THE TUBES TO LIGHT UP, THEN TROUBLESHOOT BY DIRECT SUBSTITUTION. IT IS ALSO A GOOD IDEA TO CHECK THE TUBE LOCATIONS !!! I HAVE OFTEN FOUND TUBES IN THE WRONG SOCKETS !!.. CONSULT YOUR DIAGRAM !! OF THE 5 S-38'S THAT I HAVE ON THE BENCH FOR THIS PROJECT, ONLY ONE HAD ALL THE TUBES IN THE CORRECT SOCKETS !!!!
11a)..THE BEST TUBE CHECKER IN THE WORLD...... ANOTHER WORKING RADIO !!! I KEEP ONE S-38 CHASSIS ON THE BENCH WITH WORKING TUBES THAT I CAN SUBSTITUTE AT A MOMENTS NOTICE... I FIRE IT UP AND TAKE THE TUBES (ONE AT A TIME) OUT OF THE RADIO I AM WORKING ON AND CHECK THEM IN A WORKING CHASSIS. ANY THAT ARE BAD ARE "PLAINLY MARKED !!" THE DEAD TUBES WILL BE USED IN THE TUBE SOCKETS ON CHASSIS THAT I WILL BE SAND BLASTING LATER. THIS AVOIDS DAMAGE TO THE TUBE SOCKETS..
12)...NOW IT IS TIME TO MAKE SOME DECISIONS. SOME SAY YOU SHOULD NOT POWER UP THE RADIO UNTIL ALL THE CAPS HAVE BEEN REPLACED. ONCE I REPLACE THE POWER SUPPLY CAPS, I USUALLY POWER IT UP. (SLOWLY!!). LOOK FOR ANY RESISTORS THAT MAY HAVE OVER-HEATED OR ANY OTHER SUSPECTED DAMAGE, AND REPAIR IT FIRST. IF NOTHING ELSE IS FOUND, I LIKE TO POWER IT UP. (SEE THE PAGE ON ISOLATION TRANSFORMERS!!!. BRING THE POWER UP TO ABOUT 50 VOLTS AC, AND LOOK FOR ANY OVERHEATING. IF ALL IS WELL, I TURN THE VARIAC UP TO 110 VOLTS. YOU SHOULD HEAR SOMETHING FROM THE SPEAKER.
(ADDED NOTE) I AM SERIOUSLY RE-THINKING THE ABOVE (12) A NUMBER OF THESE CAPS ARE USED FOR BY-PASS AND YOU ARE TAKING A CHANCE OF DAMAGING A NON-REPLACEABLE PART BY POWER UP TOO SOON......SO LETS NOT GET IN A BIG RUSH...CHANGE ALL THE CAPS FIRST, THEN POWER IT UP......
13)...IN OUR CASE, THE UNIT POWERED UP JUST FINE. I WAS ABLE TO HEAR THE 5 KW LOCAL STATIONS (900 & 1370) AS WELL AS NOISE, STATIC AND SOME SIGNALS ON THE OTHER 3 BANDS..... THE AUDIO WAS A BIT DISTORTED AND NOISY, BUT GOOD ENOUGH TO CONTINUE WITH THE RESTORATION. NOW WE CAN CONTINUE WITH THE CAPACITOR REPLACEMENTS.
14).ITS BEEN AWHILE SINCE WE WORKED ON THIS PROJECT AS WORK, PLAY AND OTHER MATTERS HAVE GOTTEN IN THE WAY.WE FINALLY GOT AROUND TO REPLACEING THE OTHER CAPACITORS.
IN THE SCEMATICS WE POSTED FOR THE S-38 WE FIND TWO DIFFERENT WAYS OF NUMBERING THE CAPACITORS. IN ONE SCHEMATIC THEY USED JUST A NUMBER WHILE ON ANOTHER THEY USED DIFFERENT NUMBERS WITH A "C" IN FRONT. HERE ARE THE CAPS AND HOW THEY ARE DESIGNATED
| C-36 | 8 | .25 | LINE ISOLATOR |
| C-30 | 10 | .02 | 35L6 PLATE BYPASS |
| C-35 | 18 | .05 | RF BYPASS POWERSUPPLY |
| C-4 | 9 | .02 | LINE BYPASS |
| C-28 | 11 | .01 | AUDIO COUPLING |
| C-24 | 12 | .005 | AUDIO COUPLING |
| C-37 | 13 | .01 | BFO PLATE BY-PASS |
| C-20 | 14 | .05 | IF CATHODE BYPASS |
| C-17 | 15 | .25 | SCREEEN BYPASS |
| C-16 | 16 | .02 | AVC FILTER |
| C-1 | 17 | .01 | ANT. COUPLING |
| C-39 | 25 | 510* | RECT. RF BYPASS |
| C-29/31/32/33 | 7 | 40/30/30/20 | POWER SUPPLY AND AUDIO |
* ALSO LISTED AS 470 MMF. ALTHO A MICA, I STILL REPLACE THIS CAP.
CAP REPLACEMENT WENT SMOOTHLY. I DID FIND THAT THE END OF C-37 THAT CONNECTS TO THE B.F.O.COIL WAS HARD TO GET TO.....SINCE THAT END IS NOT SEEN, I WENT AHEAD AND BROKE THE "DO NOT" HOOK ENDS OF NEW CAPS TO THE OLD LEAD RULE..
RADIO WAS FIRED UP AND I FOUND STATIONS ON ALL BANDS. RADIO SEEMS TO BE HAULING THEM IN AS I WAS ABLE TO HEAR WSM/ WLW AND A LONG LIST A CLEAR CHANNELS FROM MY CENTRAL FLORIDA LOCATION. IN FACT A QUICK SHORT WAVE SEARCH FOUND RADIO CHINA IN LIKE A LOCAL.
15) THE AUDIO WAS A BIT FUZZY AND DISTORTED SO A QUICK SPEAKER CHANGE WAS NEEDED. AUDIO NOW MUCH BETTER.
16) FURTHER CHECKS FIND THAT THE B.F.O. DOES NOT SEEM TO BE OSCILLATING. I UNDERSTAND THAT IS ABOUT NORMAL FOR THESE RIGS AND I EVEN REMEMBER SEEING A MODIFACATION TO THE CIRCUIT TO HELP THIS PROBLEM. I JUST CANT RECALL WHERE I SAW IT....TIME FOR GOOGLE. I ALSO NEED TO LOOK AT THE MAIN TUNING CAP. IT SEEMS TO BE "SHORTING" WHEN CLOSED... TRIED SOME CLEANER BUT THAT DIDNT SEEM TO HELP.
2007 NO COPYRIGHT.. USE WHATEVER YOU WANT, I WONT SEND AL GORE AFTER YOU....JUST LEAVE A LINK BACK TO THIS SITE, O.K. ?? E MAIL US !!!!
02/25/2009