stratkiller51

hey, new to this marshall forum and im having tough times with my jcm dsl 100.yesterday i was playing along and asll of a sudden a small pop and no sound! i went to check it out and all tubes were lite but nothing! these tubes have @10hrs on them and they are jj kt'77's well after checking them out i noticed one's writing was changed from red lettering to gray so i though bad tubw and its under warranty (tube depot) so i called they said send it in and they would replace it but in the meantime i should pull the power tubes out and put back in the stock el34's,that being done i checked the ht fuse and it was blown so off to radio shack and the guy gave me what was what he said quik blow 1 amp fuses, i replace the fuse fired it up and waited for the stock el 34's to heat up and rebias them well all lit up fine but when i went to set the bias 1 side was 134 and the other 164 and the same tube that cooked was now red plating very hot!!! so i tried to set down the bias and the i brought down the right to @90 and the other side went up to 183 wow and i had no more ajustment to lower the bias down so i turned it off!what is happening? i was afraid that tube was going to explode! so my marshal tech wasnt in but i snatched his cell number as he was out of shop for the weekend he said a burnt tube wasnt causing it to get hot but might be a resistor any clues or any one had this problem?

timstoel

It could be a bad resistor in the output section, a power supply putting out an abnormally high voltage, or possibly a shorted output transformer winding. It's hard to make a specific diagnosis based on what you're describing. Have you checked the voltages on the power supply? If you heard an audible "pop", I would inspect around the tube sockets to see if any arcing took place, maybe there was a short to the chassis somewhere?

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stratkiller51

thanks for the reply i changed the tubes the nite before and yesterday i went to recheck it (after it looked like melt down from before)and now its biasable i rebiased @ 90per side and wailed on it for a couple hrs and sounded killer, but i went to recheck the bias again after @6 hrs and the bias was off again so i re biased and this time even though it didnt heat up it sounded very stale and not as sharp and the clean channel was flat sounding, ihope its a resiter or socket and stay clear of transformers, but i'll take it and have it scoped with another fresh set of kt'77's monday and keeping my finger crossed,my marshall tech is very honest!

stratkiller51

also i did notice a few little ticks like cord noise nothing consistent, but with it stale sounding and flat in the clean channel and some volume loss it just doesnt seem to be hitting on all cylinders, i left the back off and place a tiny slow 3" fan blowing diagnal about 2 feet away just to diapate some heat and it stays cold never heats up to hot at all, the dsl 100 is a 2006 but my tech hated warranty work, last time he replaced a resister in another head and bias was $65, its a shame these dsl will flat outslice and dice when they are running right!so its onward to shop

Chris

Junk. Find a better vender. check out eurotubes.com

stratkiller51

yea! i have had it with them and really the jj's! im trying sed winged c's next!

timstoel

I don't think your problem is because of "defective" tubes. I would recommend the Svetlana Winged "C"s for this particular amp too. JJ tubes aren't junk, they just aren't for every amp.

Tim

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