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 Post subject: Newcomb E-75 schematic
PostPosted: Sep Thu 15, 2011 1:49 am 
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Joined: Dec Sat 04, 2010 4:24 am
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Location: WV
Looking for a schematic for a Newcomb E-75 amplifier. I found one some time back on the web and cannot locate it again. This amp has a pair of 6550's in it that replaced the original 7027's. One of them is getting excessively hot. If anyone knows where a schematic can be located or could spare a copy of one or has some ideas about it, it would be appreciated.


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 Post subject: Re: Newcomb E-75 schematic
PostPosted: Sep Fri 16, 2011 12:25 am 
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Location: Rochester NY USA
E25, E50, E504 are in Sams, but E75 isn't. But looks like grid leakage on output tube or leaky coupling capacitor.

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 Post subject: Re: Newcomb E-75 schematic
PostPosted: Sep Fri 16, 2011 2:43 am 
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Thanks Tom, I'll give that a try. The really irritating thing is that I had a schematic and misplaced it somewhere.


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 Post subject: Re: Newcomb E-75 schematic
PostPosted: Sep Fri 16, 2011 7:42 am 
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Location: Lakewood, California
I may be stating the obvious here, but is there a schematic on the inside of the bottom cover? Every Newcomb amp I’ve run across had one there.

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 Post subject: Re: Newcomb E-75 schematic
PostPosted: Sep Sat 17, 2011 12:42 am 
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If you swap the positions of the tubes and the same tube still gets hot then that tube likely has grid leakage. If the other tube gets hot then the problem is with the bias circuit. A bad coupling cap or resistor could be the problem. The slightest leakage in the grid coupling caps will upset the bias voltage.


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 Post subject: Re: Newcomb E-75 schematic
PostPosted: Sep Sat 17, 2011 2:42 am 
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Joined: Dec Sat 04, 2010 4:24 am
Posts: 15
Location: WV
Looks like there was one on the bottom cover at one time, but not any more.
Believe there is a problem in the bias circuit, swapping tubes didn't make any difference, different tube in same socket still overheated.
Will have to check the coupling caps anr resistors and see what turns up. Appreciate all the suggestions.


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 Post subject: Re: Newcomb E-75 schematic
PostPosted: Dec Sat 15, 2018 9:55 pm 
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Joined: Dec Sat 15, 2018 9:51 pm
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Not sure if you are still interested in this but I have a copy. It uses 7027 tubes.


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