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Tube Flame Out


ROBERTLATHAM1
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hello guys!

well im back i have a harmony h535/silvertone 1484 as they are almost identical to one another. i knock it over while looking at the wiring and busted one of the 6L6GC. not knowing the tube glass had been jared loose from the base i turned the amp on. guess what? FLAME_OUT! the damn tube poped and flashed very bright flames out. it was a sylvania i went and bought a new duet (mesa boogie)and replaced the old tubes but now all tubes glow and you can hear the normal power hiss or hum throught the speakers but no signal comming out from the guitar. i have checked all the obviouse (loose wires burnt looking components ect.) everything looks good but no sound HELP! HELP !

p.s. i have a sheamatic if this might help in diagnostics.

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Did it work correctly before the tube was broken?

yes it worked fine. i checked all resistors last night and found 1-200ohm 7watt that was reading open and it just so happens to be comming off of pin#8 of the tube that flamed (6L6GC tube) and the other side goes to chasis ground no other paths tapped off of this leg.

pin# 8----- resistor------grnd

so im going to replace it and see what happens.

do you think there might be other damage as well?

thanx for the help

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the one i saw LK was Cathode biased. unless it was a mod done later.

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bingo in fact that is the very same schematic i have but as ansil said it has had some mods done to it. i have but 5 preamp tubes they are all 12ax7a the reverb and tremlo section does not have the tube shown in this drawing (silvertone 1484) my amp is a harmony 535 but looks identical just harmony in place of silvertone name.

yes its fixed bias. i took pin 8 straight to ground lost the resistor it worked but the 6L6's(sylvania=original..mesa=replacements) got very very hot! much hotter than the 12ax7a's which the cathode also go to ground via a 200 ohm resistor. i assume this is the biasing and the resistor value here controls how much positive voltage or current that will be bled off the tube, if you will parden my laymens terms.

after i fix this problem i would like to ad a gain stage and presence to this amp but first things first :D

is this amp a copy of major brand design. i was told that the silvertone/harmony/truetone did alot of design coping back in those days?

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It sounds like your amp is cathode-biased, since there is a resistor from the cathode to ground, in whixh case it is definitely not the same amp as the 1484, which is fixed bias. We'll need the correct schematic to do any serious diagnostic work. Paul has had remarkable luck finding schematics for Harmony amps in the past - maybe he can dig this one up, too!

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if you seen the photos of the 2 amps togather you would swear the only difference is the name but as far as architecture goes i have no idea, but yes i would love to have a good schematic. if anyone could help that would be great.

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still tring to find schematic. i think this amp might have really been made by valco rather than harmony! its pots all have the matching serial numbers which are used in early fenders that were made by valco #1376647

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it was in one of those links that are pinned at the top of the fourm actualy i think it was a link inside of one of those ! anyways thats what they said, "that valco made many amps for many different manufacture brand names in the early days" now if this is to be true or not i have no idea, as i do not claim to be a technition, but the section on dating an amps production date is where i got the pot#'s from and mine matched what they say where early valco made fender amp pots. dont know! you know much more about this topic than i. i would however would like to know who really did manufacture the harmony 535!

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sorry lovekraft i searched and could not find it again i should have booked marked it! anyways it was all about dateing vintage gear you might do a search under valco harmony amplifiers and see what comes up. i believe it might have been on another page i was surfing quite a bit that day.

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