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Post subject: Ugly distortion on Twin's clean channel
Posted: Wed Sep 14, 2016 12:56 pm
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Hey. I have an 80's red-knob The Twin. I hadn't used it in years and now notice a nasty distortion in both channels. I play through a 74 strat with factory single coils. Turning my guitar up and playing at a low volume distorts. I replaced the preamp tubes with no joy. Tried each speaker one at a time, a different guitar, and ran on various combinations of just two power tubes. All with no joy. I may get new power tubes anyway, but I don't think they'd break up like this. Maybe I need a cap job? Any ideas?


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Post subject: Re: Ugly distortion on Twin's clean channel
Posted: Wed Sep 14, 2016 3:55 pm
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Wahooyeeha wrote:
Maybe I need a cap job?


A distinct possibility.

Those electrolytics are now approaching forty years of age. I'd guess that they're hopelessly out of spec and leaking.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Ugly distortion on Twin's clean channel
Posted: Wed Sep 14, 2016 10:41 pm
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In my opinion the distortion may come from power supply voltage
Or phase inverter circuit / tube
Output tubes
It could be the Output transformer too

best is to see a good tech.


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Post subject: Re: Ugly distortion on Twin's clean channel
Posted: Fri Sep 16, 2016 11:20 am
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Sounds like one of your power tubes is not working properly or not working at all, try a new set of power tubes and make sure the bias is correct its also possible a screen resistor is open causing a power tube not to conduct which can cause some nasty distortion and loss of power.


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Post subject: Re: Ugly distortion on Twin's clean channel
Posted: Fri Sep 16, 2016 11:57 am
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These are all great (and valid) suggestions but IMO what the amp really needs is a full bench-check to identify, isolate, and address what's likely to be a number of geriatric-related issues. Electrolytics, tubes, screen resistors are all probable suspects but there may be others lurking within as well. A comprehensive overhaul will keep this amp healthy for another thirty years or more.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Ugly distortion on Twin's clean channel
Posted: Fri Sep 16, 2016 1:18 pm
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Retroverbial wrote:
These are all great (and valid) suggestions but IMO what the amp really needs is a full bench-check to identify, isolate, and address what's likely to be a number of geriatric-related issues. Electrolytics, tubes, screen resistors are all probable suspects but there may be others lurking within as well. A comprehensive overhaul will keep this amp healthy for another thirty years or more.
j

+ 1
Arjay


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Post subject: Re: Ugly distortion on Twin's clean channel
Posted: Sun Sep 18, 2016 4:01 pm
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Thanks, all. I suppose I'll take it in and get a firm diagnosis.


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Post subject: Re: Ugly distortion on Twin's clean channel
Posted: Sun Sep 18, 2016 9:48 pm
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The expenditure may represent serious money but that's a serious piece of gear you've got there and well worth the cost.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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