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Old 16th January 2012, 06:40 PM   #1
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Default Amplifier Troubleshooting

Hi i have a tube amplifier that's playing up making my speakers cut in and out i want to just try and identify the problem by going in with a multimeter and testing the values across the components (look for a possible capacitor discharging).

Would i be able to remove all the the tubes and turn it on? Obviously with the speakers still connected.. (I'm not that stupid)

Also... Any ideas as to what could be causing the amp to cut out every 3 seconds? ... it does it on both channels but at different intervals. It doesn't do it straight away when you turn amp on, but a minute later and the pads of speakers move in and out strangely.
The amp is a Unisis from TubeTechnology. It has the Prophet Pre-Amp aswell.

Anyway..
Thanks guys <3 ,
Cogline
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Old 16th January 2012, 06:51 PM   #2
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Default You got a schematic?.....

Tube or solid state rectification?

Can you post a schematic?
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Old 16th January 2012, 06:53 PM   #3
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Frequently in & out signal is a bad solder joint.
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Old 16th January 2012, 07:02 PM   #4
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Thank you so much for quick replies, can't find any schematics about! very frustrating...

All i can show you is
http://www.tubetechnology.co.uk/ds/ds_uni_power.pdf
I'll look for some bad solder joints still need to know if i can operate my tube amp without any tubes inserted.

Cogline
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Old 16th January 2012, 07:23 PM   #5
DF96 is offline DF96  England
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Does it do it with the preamp disconnected?

Your tube amp won't do much with tubes missing, so the fault won't occur either.
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Old 16th January 2012, 07:29 PM   #6
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Bad contact of some sort such as Indiana Joes' bad solder joint would be high on my hunch list.

If both speakers are cutting out and in together then it would seem the fault must be in a component common to both channels. The trick in fault finding is to narrow down its whereabouts using careful analysis. Intermittent faults are much harder to track down than a constant fault.
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Last edited by Soonerorlater; 16th January 2012 at 07:51 PM. Reason: Should have read OP's full post
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Old 16th January 2012, 07:30 PM   #7
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Oh okay, well i haven't tried disconnecting it from the pre amp yet, shall i give that a bash first then?
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Old 16th January 2012, 07:40 PM   #8
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Glad your all keen to help me!

okay so I'll give you the process which occurs.

So i turn on my pre-amp, leave it for a min then turn on my amplifier. the problem does not occur straight away but instead kicks in about a minute or sometimes longer later. When i turn the amplifier back on after being on not long ago (so it's still a bit hot) the problem occurs STRAIGHT away.
The speakers will cut in and out from channel to channel every 2-3 secs. they do not cut out in sync but one after another so there is always sound coming out of one of the speakers. while this is happening the pad on the speakers are continuously moving in and out as if producing a low frequency sound. This however does happen at the same time.

The amp is about 15 years old. I obtained it from the previous owner who said something had "blown in it" on the last use. sure enough one of the front power tubes was smashed.

So it works PERFECT for a few mins. So surely no massive damage has been done?

Thank you,
Please ask if further info needed.
Cogline
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Old 16th January 2012, 08:34 PM   #9
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Quote:
The amp is about 15 years old. I obtained it from the previous owner who said something had "blown in it" on the last use. sure enough one of the front power tubes was smashed.
Smashed tube suggests mechanical damage rather than blown up. After replacing the tube did it ever work properly?
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Old 16th January 2012, 08:45 PM   #10
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I should have specified that I'm not entirely sure that the power tube is the thing that blew... it could have been damaged in the shipping, but i did replace all of the tubes once i got the amp.
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