MARSHALL JTM 100 SUPER PA A PLEXI AND IN RED

COSMETICALLY REASONABLE FOR THE AGE APART FROM THE UNDERSIDE WHICH HAS LOADS OF SCRAPES AND SCUFFS

SOMEONE HAD PREVIOUSLY ADDED AN INDICATOR STRAIGHT THROUGH THE MIDDLE OF THE JTM LOGO

BUT OVER THE YEARS ALL SORTS OF THINGS GET DONE TO OLD AMPLIFIERS THIS AMP IS ABOUT 46 YEARS OLD

THEY HAD ALSO ADDED ANOTHER INDICATOR AT THE REAR TO SHOW MAINS AVAILABLE this has been REMOVED

THE ORIGINAL 6.3 VOLT SQUARE INDICATOR NONE WORKING WAS REPLACED

WITH ONE THAT I HAVE HAD FOR A LONG TIME AT LEAST I CAN USE IT NOW

WITH REFERENCE TO THE HISTORY OF MARSHALL BOOK BY MIKE DOYLE EXTREMELY USEFULL AND VERY HELPFULL

THIS AMP IS MOST CERTAINLY A PIECE OF MARSHALL HISTORY

THE SERIAL NUMBER STARTS WITH THE NUMBER 2 FOR 2ND YEAR OF MANUFACTURE 1965 OR 1966

THIS IS MY LATEST RESTORATION PROJECT

I DONT GET A LOT OF TIME NOWADAYS AS DAY JOB AND WRITING SONGS FOR THE MADDERTHANN BAND

BUT I AM DETERMINED TO SEE THIS ONE THROUGH AS A RESTORATION PROJECT

PLEASE DON'T ATTEMPT THIS TYPE OF RESTORATION UNLESS YOU ARE SUITABILY QUALIFIED OR EXPERIENCED

SOME OF THE VOLTAGES ARE HAZARDOUS EVEN LETHAL IE 480 VOLTS DC AND THAT CAN SERIOUSLY HURT

SOMEONE HAD DRILLED A HOLE IN THE FRONT PANEL TO ADJUST THE TREBLE SOMETIME IN THE PAST

I REMOVED THIS MODIFICATION AND FITTED A POT TO ADJUST THE OUTPUT TUBE BIAS

THIS AMP IS ONLY USABLE BY SOMEONE WHO IS AN AMPTECH / ENGINEER

OR HAS AN AMP TECH ON HAND AS MISSUSE OF THE BIAS CONTROL

COULD CAUSE DAMAGE TO THE OUTPUT STAGE

THIS CERTAINLY CAN ALTER THE RESPONSE OF THE AMP

I AM THINKING ABOUT ADDING A POT IN PLACE OF ONE OF THE FOUR VOLUME POTS TO ADJUST THE PHASE

ANGLE OF THE PHASE SPLITTER WHICH CURRENTLY HAS AN 82K AND 100K RESISTOR ON THE ANODES

OF THE PHASE SPLITTER

ALSO I AM THINKING OF MODIFYING TWO OF THE INPUTS INTO A HIGH GAIN STAGE

WHICH COULD BE USED TO AD GAIN VIA PATCH LEAD TO THE REMAINING INPUTS

OR USE FOR OTHER STUDIO APPLICATIONS TIME WILL TELL ON THIS STILL WANT ORIGINAL STYLE MAINS AND

STANDBY SWITCHES

I THINK THAT THE DECOUPLING CAPS FROM PHASE SPITTER TO OUTPUT GRIDS ALSO REQUIRE REPLACEMENT WITH HIGH SPEC POLEPROP 100nF 1KV CAPS

Most of the Electrolytics on the capacitor board short circuit

Bridge rectifier shorted as previous owner had fitted 13 amp fuse

in the HT fuseholder what should have been 1.5 amps

Luckily the mains fuse was still the blown 2 amp fuse

Or the mains transformer would have been burnt out.

Note that some of my picturers are composite picturers

THE CATHODE BIASING CAPACITORS ON THE ECC83 TUBES ALSO REQUIRED REPLACING

NOTE THE 3 INCH LAY DOWN MAINS TRANSFORMER

TO START WITH I CONNECTED A 60 WATT LIGHT BULB IN SERIES WITH THE MAINS TO CHECK THAT ALL WAS WELL IE IF THE BULB GOES BRIGHT SOMETHING IS WRONG

AFTER THAT THE BIG POWERUP AND SOUNDED A1 BUT STILL NEED TO CONSIDER MABEY HOW TO PROTECT THE OUTPUT AND CAPACITOR BOARD AGAINST

FAILURE WRONG FUSES ETC ALTHOUGH THIS IS NOT VERY EASY AS WHO IS GOING TO DO WHATTEVER TO THIS AMP

IF I EVER DO DECIDE TO SELL THIS ON QUALIFIED AMP TECHS/ENGINEERS ONLY OR SOMEONE WHO HAS A 24/7 AMP TECH/ENGINEER

UNSUITABLE FOR GENERAL PUBLIC USAGE, AS I FOUND WITH THE 13 AMP FUSE IN THE HT 1.5 AMP FUSE SOCKET

NOT FOR SALE

WHERE ELSE WILL YOU FIND AN LALMOST ORIGINAL RED JTM100?

I HAVE ADDED AN NTC THERMISTOR IN SERIES WITH EACH OF THE TWO AC WINDINGS TO THE AC INPUTS OF THE BRIDGE RECTIFIERS

tO REDUCE STRAIN ON THE OLD MAINS TRANSFORMER INITIAL ON POWER UP WHEN

ALSO THINKING OF ADDING A 1 OHM SERIES RESISTOR IN SERIES WITH THE CATHODES AND CHASSIS OF EACH EL34 OUTPUT VALVE / TUBE

SO THAT IF AN OUTPUT VALVE STARTS SHORTING OUT THE RESISTOR CAN HOPEFULLY BLOW BEFORE THE HT FUSE BLOWS.

THE 100 OHM AND THERMISTOR MOD CAN EASILY BE REMOVED

I HAVE STILL KEPT THE BLOWN SHORT CIRCUIT 32U 450v ELECTROLYTIC CAPS

JUST NEED SOME ORIGINAL SPST MAINS AND STANDBY SWITCHES.

THIS OLD AMP WAS MADE LONG BEFORE ELECTRICAL STANDARDS STARTED WITH THE CE MARKING IN THE 1990'S AND SOME OTHER STANDARDS

IN THE EARLY 1970'S

THERE IS JUST NO COMPARISON BETWEEN THIS OLD VALVE AMP AND A MODERN AMP

AT FULL VOLUME INTO TWO 4X12 CABS THIS AMP CUTS INTO YOUR EARS LIKE A KNIFE THROUGH WARM BUTTER

AN AMAZING SOUND

WHO WANTS A TRANSISTOR /SEMICONDUCTOR AMP THAT COMPRESSES THE SOUND

SO VALVEAMPS ALWAYS RULE