Marshall JCM 2000 cooked connector
- Thread starter CJ
- Start date
Help Support GroupDIY Audio Forum:
CJ
Well-known member
four EL34 tubes draw big heater current upon start up, figure maybe 10 times, so 1.5 amps x 4 = 6 x 10 = 60 amps!
don't know for sure if it is that high, maybe a experiment is in order but it does go high.
loose connector with some low ohms will create heat, pc board does not like heat,
don't know for sure if it is that high, maybe a experiment is in order but it does go high.
loose connector with some low ohms will create heat, pc board does not like heat,
Attachments
CJ
Well-known member
CJ
Well-known member
tube sockets need to be hand soldered, but accountants must meet the bottom line, so they get waved soldered.
solder tank heat set so it will not warp pc board, results: big parts that take more heat get marginal flow,
so we always reflow some 44 into the voids,
before touch up>
solder tank heat set so it will not warp pc board, results: big parts that take more heat get marginal flow,
so we always reflow some 44 into the voids,
before touch up>
Attachments
Yeah I know that era of Marshall only too well ,never saw that fault before .
What I do notice about them is a bit of a growl from the transformer the moment the power switch is engadged ,must be the high inrush current at turn on with cold heaters. They do seem to be reliable enough ,straight clean tone channel doesnt come near JMP's ,or JCM 8/900 series though .
What I do notice about them is a bit of a growl from the transformer the moment the power switch is engadged ,must be the high inrush current at turn on with cold heaters. They do seem to be reliable enough ,straight clean tone channel doesnt come near JMP's ,or JCM 8/900 series though .
CJ
Well-known member
yes that transformer does growl and shake the chassis upon startup,
there is a Classic Tone OPT that someone stuck in there, the amp blew a 4 amp slo blo at full power, wtf?
red and wht wires were swapped, amp should have hi-freq oscillated but did not,
switch the wires and no more fuse problems, customer wanted to know why he was going through power tubes so fast, now he knows,
took some readings off the OPT, leakage inductance changes depending on which speaker tap you short out, 16 ohm tap shorted = lowest leakage, often wondered why using the 16 ohm tap sounds slightly better, more hi end due to less leakage, 4 and 8 ohm taps means unused chunks of copper sitting there, >
there is a Classic Tone OPT that someone stuck in there, the amp blew a 4 amp slo blo at full power, wtf?
red and wht wires were swapped, amp should have hi-freq oscillated but did not,
switch the wires and no more fuse problems, customer wanted to know why he was going through power tubes so fast, now he knows,
took some readings off the OPT, leakage inductance changes depending on which speaker tap you short out, 16 ohm tap shorted = lowest leakage, often wondered why using the 16 ohm tap sounds slightly better, more hi end due to less leakage, 4 and 8 ohm taps means unused chunks of copper sitting there, >
