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  #11  
Old 20th April 2016, 11:01 AM
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pre65 pre65 is offline
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Default Re: gm-70 help

John Caswell (one of the forum moderators) might look at it for you if you take it to him, but not for free.

It would be about a 95 mile drive for you. I can't think of anyone nearer.
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  #12  
Old 20th April 2016, 01:08 PM
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Default Re: gm-70 help

Steve, do you have a multimeter, and if so are you happy to probe around inside the amp ?
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  #13  
Old 20th April 2016, 05:13 PM
bob orbell bob orbell is offline
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Default Re: gm-70 help

Philip, maybe you should point out to Steve that very high voltages will be inside this amp. and one momentary laps may kill . BOB
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  #14  
Old 20th April 2016, 05:25 PM
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Default Re: gm-70 help

Quote:
Originally Posted by bob orbell View Post
Philip, maybe you should point out to Steve that very high voltages will be inside this amp. and one momentary laps may kill . BOB
I hope he would already know that.

It's so difficult to diagnose valve amp problems without any accurate information and actual voltage measurements to go by.

If it were mine I'd want to find out what components had failed, and understand why, before doing any remedial work.
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  #15  
Old 20th April 2016, 05:45 PM
Tweeky Tweeky is offline
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Default Re: gm-70 help

Hi,
I do have a multimeter and am well aware of the potentially lethal voltages when powered up. I have no desire to fry myself but would like to repair it if possible. I used John many, many years ago and would happily do so again if necessary. Main problem is the fact that I can barely lift the amp with the additional transformers for the GM-70 heaters and the Tentlab supplies are mounted on the sides and susceptible to damage during transport.

Regards

Steve
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  #16  
Old 20th April 2016, 06:18 PM
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Default Re: gm-70 help

Can you see any evidence of "fried" components ?
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  #17  
Old 21st April 2016, 07:38 AM
Tweeky Tweeky is offline
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Default Re: gm-70 help

Philip,

There are no signs of fried components even in the area where I saw sparking/arcing before the channel went down.

Regards

Steve
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  #18  
Old 21st April 2016, 10:11 AM
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Default Re: gm-70 help

OK.

Are you prepared to "poke about" inside ?

If one channel is still OK you are looking to compare voltages between that and the failed channel to see where things are different.

Start with the anode and cathode volts on the driver.
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