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Blackstar HT Stage 100 with blown power tube
Blackstar HT Stage 100 with blown power tube
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Old 18th August 2019, 11:28 PM   #1
PhantomBox is offline PhantomBox  Venezuela
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Default Blackstar HT Stage 100 with blown power tube

Hi guys.
So someone brought me a Blackstar HT Stage 100W amp head for repair.
He said that he was playing it when suddenly it made a pop-pop sound, and then he immediately turned it off.
After first checking, I found that one of the EL34 power tubes quit its job (thought it doesn't show any signs of fog inside) ... I also changed a 12AX7 tube that tested "not sooo good" on my tube tester.
Other than that, I have not taken out any of the PCBs.
Is there anything I should pay special attention to as for why the EL34 stopped working in the first place?
Does anyone have a service manual or at least the schematics for this amp? I cannot find them anywhere online.
Is it possible to run this amp on just 2 EL34s, instead of 4 tubes? If so, which ones can I take out? How is the bias setting for running on 2 tubes?
By the way: Since is says "Designed and Engineered ..." on the back of the amp but not "Manufactured" or "Assembled", and based on my observations of its PCBs, I assume it was made in China. Am I correct?
A 1000 thanks for your help.
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Old 19th August 2019, 03:09 PM   #3
Enzo is offline Enzo  United States
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Tubes can fail at any time, I don't necessarily expect some external cause for it.
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Old 22nd August 2019, 04:16 AM   #4
PhantomBox is offline PhantomBox  Venezuela
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I got it working again. Seems that actually nothing was wrong with this amp.
I put in an EL34 that I borrowed from a Buguera amp and hooked it up to a 212 cabinet. Calibrated the bias as close to 100 mV as I can get, almost on the spot (it fluctuates little, maybe its power lines in my house...), and it sounds great.
Now I have to wait until the owner gets a new set of quad-matched EL34s and return my EL34 to its rightful amp.
Thanks for your help...
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Old 23rd August 2019, 06:03 PM   #5
PRR is offline PRR  United States
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> I have to wait until the owner gets a new set of quad-matched EL34s and return my EL34 to its rightful amp.

No, return my EL34 to its rightful amp NOW, *then* wait until the owner gets a new set.
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Old 23rd August 2019, 06:26 PM   #6
PhantomBox is offline PhantomBox  Venezuela
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"Potatoes - potatos".
That's what I meant.
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