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Old 17th January 2012, 04:12 PM   #1
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Default Edison 12, can anyone help?

Hi, I recently resurrected my Edison 12 power amp which had been in storage for nigh on 15 years and had new matched valves before being put away. But it had always had a problem on switch off..a chirrup through one speaker.

I have found a friendly and valve experienced qualified engineer who has established that one channel, on switch off, goes unstable in the RF range...immediate switch on causes the amp to oscillate.

Not taking anything from him but to speed up diagnosis..any one got any ideas? I have supplied him the schematic copied from another Edison 12 thread so he has that but it is quite apparent that many of the values are different....

Anyway..any advice!?
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Old 17th January 2012, 04:16 PM   #2
DF96 is offline DF96  England
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Why not supply us with the circuit too?
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Old 17th January 2012, 04:53 PM   #3
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Schematic.

http://www.erikasson.se/schemor/edison12.gif
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Old 17th January 2012, 05:10 PM   #4
M Gregg is offline M Gregg  United Kingdom
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If the diagram in post 3# is correct,

And the fault is in one channel...

Check the bias voltage (output tubes) across the cathode resistors on the good and bad channel
Post the values that you get..

Its important that when you take these measurements (make sure a load or speaker is connected or you will damge the OP Tx)..(Also dont start swapping tubes about etc or the results are of no use)

Regards
M. Gregg
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Last edited by M Gregg; 17th January 2012 at 05:22 PM.
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Old 17th January 2012, 05:40 PM   #5
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I have a vague memory of a cheap multicap involved in some trouble in Edison 12.

The quality of the caps are probably not the best since it was designed as a fairly priced kit.

Is the amp factory buillt or a kit ?
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Old 17th January 2012, 05:40 PM   #6
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Hi,

Thanks Flatheadmurre (and M Gregg)...I was just logging on to post the circuit!

Any useful tips I will pass on to the engineer who has it..this is an area in which I have no qualification...

I posted on the off chance that someone may have had the same problem and solved it...so thank you all for any input!
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Old 17th January 2012, 05:44 PM   #7
M Gregg is offline M Gregg  United Kingdom
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OK,

First of all is the fault in both channels..IE is it a stereo amp or monoblock?
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Old 17th January 2012, 05:45 PM   #8
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..I don't have it here but as I recall it was "factory" built by a company in Brighton if the screen printing on the back panel is anything to go by! They have long gone...

It also has screened on the circuit board.."Edison 12 by Erik Anderson" or something similar...
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Old 17th January 2012, 05:47 PM   #9
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The link i posted is the sight of the engineer of edison.

Hes a nice man and will answer any questions we can not solve here.
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Old 17th January 2012, 05:48 PM   #10
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Its a stereo amp.
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