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Ampeg SBT power amp

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Ampeg SBT power amp
Hangman Offline
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#21
12-19-2014, 10:05 PM
which capacitor blew?
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70spbase Offline
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#22
12-20-2014, 03:53 PM
(12-19-2014, 10:05 PM)Hangman Wrote: which capacitor blew?

I took a pic of which capacitor smoked. I am not getting a reading from the two caps in between the two large caps.


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Hangman Offline
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#23
12-21-2014, 01:05 AM
Is it the one near the 2n3767? I can't really see any signs of a smoking cap just by looking at the picture there.

Maybe circle the one that smoked?
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70spbase Offline
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#24
12-21-2014, 02:08 AM
(12-21-2014, 01:05 AM)Hangman Wrote: Is it the one near the 2n3767? I can't really see any signs of a smoking cap just by looking at the picture there.

Maybe circle the one that smoked?

Sorry , no it was one of the rectangular ones with the red writing to the right of the pic. So I'm going to get a new multimeter because mine may be inaccurate.
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Hangman Offline
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#25
12-21-2014, 10:22 AM
Oh, Those are not capacitors. Those are 5watt resistors.
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70spbase Offline
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#26
12-21-2014, 04:17 PM
(12-21-2014, 10:22 AM)Hangman Wrote: Oh, Those are not capacitors. Those are 5watt resistors.

Oh ok thanks. I found a website that still sells all of the resistors and transistors very inexpensively. So I think I will replace all of them and just to be safe.
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70spbase Offline
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#27
12-21-2014, 06:13 PM
(12-21-2014, 10:22 AM)Hangman Wrote: Oh, Those are not capacitors. Those are 5watt resistors.

I am finding that most of the original resistors are 10% tolerance and "modern" replacement resistors are 5%. Will that make a difference if I replace them all with 5%?
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Hangman Offline
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#28
12-21-2014, 07:08 PM
No. If there was. 1% tolerance resistor it would be a bad idea to put a 10% tolerance in its place. But going the other direction is all good
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70spbase Offline
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#29
12-22-2014, 02:02 AM
(12-21-2014, 07:08 PM)Hangman Wrote: No. If there was. 1% tolerance resistor it would be a bad idea to put a 10% tolerance in its place. But going the other direction is all good

Thank you! I'll let you know what I find out. Thanks for all your help so far in this mess.
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#30
05-21-2015, 12:45 AM
Hello I finally can tell you that the amp is repaired! It turns out that there were 17 blown(bad) transistors and resistors. Including the four main transistors on the back. It is back to operation and will be put in the cabinet tmrw. Oh and I finally found an SBT preamp head all original so I will be running it as a whole unit. I am also in the process of building a second cab and using a vintage ampeg A-120 slave power amp. I am going to use two 16 ohm speakers in parallel to accomplish the 8 ohm minimum load.
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