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Old 28th March 2005, 06:10 PM   #1
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Question mj headphone amp

i am building a morgan jones head phone amp ams would like to know if two inch spacing between tubes is ok
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Old 28th March 2005, 09:08 PM   #2
PRR is offline PRR  United States
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You can mount them so close you can't get a finger between. No problem.

But that's from the bad old days when we stuffed too many tubes on too-small chassis, and suffered the heat. I remember TV sets where it was tough to grab a tube: there was actually a special tool for this.

Two inch spacing on a 3-tube amp seems much more sane to me.
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Old 29th March 2005, 01:50 AM   #3
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> if two inch spacing between tubes is ok

This is how IBM used to jam tubes together:
Click the image to open in full size.
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Old 29th March 2005, 05:17 AM   #4
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Default spacing

Quote:
i am building a morgan jones head phone amp ams would like to know if two inch spacing between tubes is ok
Hi,
don't forget that you have to wire those tubes up, and then you'll appreciate a little more space.
Exactly right now I'm building an MJ also, and my tubes are spaced apart by about 2 inches......only the EZ81 rectifier that I'm using is a little further away from the trio....

rgds,
Oliver
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Old 29th March 2005, 02:15 PM   #5
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thanks all i was worried about heat
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Old 30th March 2005, 07:01 PM   #6
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Gentlemen, are you building the MJ or the CJ?
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Old 31st March 2005, 05:29 AM   #7
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Alex,

I'm building the MJ with a slightly different psu. Once it's finished I will post on headwize....

Oliver

PS I've seen all your schematics.....
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Old 31st March 2005, 05:43 AM   #8
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while we are at it.....

this is the schematic how I'm building the MJ...

Click the image to open in full size.
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Old 31st March 2005, 08:58 AM   #9
EC8010 is offline EC8010  United Kingdom
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Rather than using a full silicon bridge rectiifier plus EZ81, why not use the EZ81 as part of the bridge and a pair of silicon diodes as the other part? This will give much cleaner switching and prevent the mains transformer from ringing as well as being cheaper and simpler.

Also, do have a look at the various modifications to the original circuit - the addition of variable feedback and optimisation of the anode resistor on the upper valve makes a significant difference.
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Old 31st March 2005, 02:13 PM   #10
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EC8010,

thanks for the input....I've seen both ways of building this "graetz bridge" sort of thing, but didn't know which is better, so I'll happily get silicon diodes (the bridge I have lying about) and do as you suggested.
I'm well aware of the other version of this schematic, but since I'm going to use high Z headphones (Senn HD600) I might be better off with no NFB.......so I have learned.

But it will be easy to try the optimizations also.....

Oliver
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