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Post subject: standby blows fuse
Posted: Mon Jan 25, 2010 8:17 pm
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My Bandmaster powers up ok until I switch the standby up...then pops goes the fuse. Any answers?


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Posted: Mon Jan 25, 2010 8:34 pm
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Hey Teberwein, was the amp having problems before this happened? A short in a tube or filter cap usually causes this symptom. Art

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Last edited by aclempoppi on Mon Jan 25, 2010 11:00 pm, edited 1 time in total.

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Posted: Mon Jan 25, 2010 8:48 pm
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I just had it re-tubed & biased. It was sounding great. I plugged in a distortion box, that I've used on it before with no problems & it blew. Now the power light & tubes heat up with the power switch on, then blows flipping the standby.
Thanks Art


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Posted: Mon Jan 25, 2010 9:31 pm
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aclempoppi wrote:
Hey Teberwein, was the amp having problems before this happened? A short in a tube or filter cap usually causes this symtom. Art

+1 Tubes can fail any time. Some last hours some last for years. It could still be a shorted power tube. How old's the Bandmaster? I had one in 74.


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Posted: Mon Jan 25, 2010 9:48 pm
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It's an early 68 silverface with blackface circuit, silver drip edge on head & cab, 2 12" celstion greenbacks - no reverb..


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Posted: Mon Jan 25, 2010 9:49 pm
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Teber, I'm hoping it's just a preamp tube that failed. I would suggest you remove both preamp tubes on the right side of the amp, marking them as 1&2 (as viewed from the rear) and turn the amp on then switch the standby to play(nothing in the input jacks). If the amp stays on, you're in good shape. If you were using the normal channel with the distortion box when the fuse blew, then the tube furthest to the right would be the suspect(bad). The one to the left of it is for the vibrato channel and would be the suspect if you were using that channel. Determine the channel and put that tube aside.(before removing any tube draw a line on the glass and socket base for realigning the pins) Now reinstall the "good" tube in it's original position and power up the amp and switch to play. If all is well, you can try that"good" tube in the other socket and test. Of course, the amp is tuned off, unplugged, and allowed to cool down for the tube removal etc. You should only need to touch the glass and the wood cabinet. Art

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Posted: Mon Jan 25, 2010 10:08 pm
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A bad rectifier/rectifier tube would cause the fuse to blow too.

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Posted: Mon Jan 25, 2010 11:23 pm
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Yep, I agree, Chet. But Teber said the fuse was fine until the standby switch was turned to the "on" position. So I"m guessing the diodes and the two main filter caps are okay. Art

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Posted: Tue Jan 26, 2010 6:35 am
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From what I remember the Bandmaster has a solid state rectifier since about 1961 or so when the Blonde Bandmasters went to 40 watts.


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Posted: Tue Jan 26, 2010 6:49 am
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Thanks for the help guys. I've got it in the shop, I'll let you know what happens.
Thom


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Post subject: quick update
Posted: Wed Jan 27, 2010 7:07 pm
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Art, I hope you're right. The tech said it's a bad power tube. I dropped off another matched pair, hopefully I'll get it back tomorrow.
Thom


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Posted: Wed Jan 27, 2010 10:25 pm
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Actually Thom, Supro had it right about the power tube. I let that distortion box goof me up. With a blown fuse the right method is to start at the power cable and proceed towards the input jack, until you find the problem. Oh well, glad your tech has a handle on it. Art

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Post subject: it's back
Posted: Tue Feb 09, 2010 6:50 pm
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:D Well I got it back. Was a power tube less than 2 weeks old. At least it's back & sounds great. Thanks for all the input.


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Posted: Wed Feb 10, 2010 5:20 pm
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63supro wrote:
aclempoppi wrote:
Hey Teberwein, was the amp having problems before this happened? A short in a tube or filter cap usually causes this symtom. Art

+1 Tubes can fail any time. Some last hours some last for years. It could still be a shorted power tube. How old's the Bandmaster? I had one in 74.
Good call 63.............. 8) Mike

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Posted: Wed Feb 10, 2010 8:52 pm
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Current production tubes aren't built as well as the old tubes. Sometimes they can last for years, sometimes only hours or even minutes. Glad that's all it was. :D


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