Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bakerlite on June 16, 2011, 07:11:16 pm
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I am almost embarrassed to type this - i was probing the amp taking voltage readings and my elbow slipped on the counter top :BangHead:
result is i for a split second shorted w7 (HT) and w5 (OT centre tap)
http://www.lydian.ca/Marshall_DSL_files/jcm2-60-02-iss5_TubeBoard100w.pdf (http://www.lydian.ca/Marshall_DSL_files/jcm2-60-02-iss5_TubeBoard100w.pdf)
there was a spark and for another split second i heard a hum appearing but i was so quick turning the amp off i didnt get a chance to hear it escalate but i have a feeling the bias was skyrocketing.
Does anyone have a clue component wise what the consequences of such clumsiness would be?
sorry to be buggng you guys about this amp again - all the others have gone so well for me but this fella has my heart broke and i am getting rather depressed about it -
not only have i not figured out why it ate a transformer, now i have messed it up more....
its one of those days that feels like the mountain of knowledge to climb seems unassailable :help:
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Look and make sure nothing is burned or damaged. Make sure you have the correct PT secondary voltage. Look at the tube sockets and make sure you dont have a carbon burn arch across any of the tube sockets. Pull your power tubes and and flip the amp on. Check the plate voltage on the power tubes. Check all power supply resistors and caps for obvious damage. Put tubes back in and play
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You basically shorted D4, and that will really stress the other bridge diodes. Check D3, D4, D5, and D6 before powering up.
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I have calmed down from the shock now - i was still hyper ventilating making the first post!
It seems i infact shorted w5 (OT centre tap) and the positive node of the 330uf filter cap c39.
sorry i was a bit up in a heap and rushed my cry for help!
secondaries are still spot on voltages
plates read 504vlts
no scorching except right on the +node trace of the capacitor i shorted.
this node now reads -55v?
before it used to be intersection +- 244v and the final + is 490v
now the intersection seems to read zero and the final + reads -54v
i refer to the two main filter caps c38 and c39
thank you guys so much for listning!
i guess the diodes are still suspect - is there any way of testing in circuit?
Also
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It seems i infact shorted w5 (OT centre tap) and the positive node of the 330uf filter cap c39.
Ugh, that's the same point and would not have caused any sparking or other problems. What did you really short?
Best to lift one end of each diode to test. Better check C39 and C38 too.
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Don't feel bad. I think everyone blows something up sooner or later. I managed to fry the filament section of a PT, in a similar incident (among other things which I won't admit to). Amps are surprisingly resilient. More importantly, no one got hurt!
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Hey, I pulled a chassis out and had it setting on top of the amp cab and fired it up. Cabooom!!!! The metal ends of the carry handle had some really nice blast holes in them - BOTH of them.... :BangHead: :BangHead: :BangHead: :BangHead:
Don't feel like the Lone Ranger!
Jim
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Hi guys,I found that the black dot on two res cap lugs for a SS build were - not + and lined the inside of the head cab with GOOOO.
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More importantly, no one got hurt!
Yes, you didn't get hurt. More important than a 100,000 amps.
Brad