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mashaffer 25th October 2010 11:35 PM

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Thinking of using this layout for a SE KT88 amp for my mini-console project.

Normally one wouldn't want the PT and OPTs lined up like that but in alternating the PT, Choke and OPTs I end up that way. Do you think they are far enough apart that it would be OK, or should I allow the chokes to line up with either the PT or OPTs so that the PT and OPT don't line up? Some other option (45 degrees) better?

tomchr 25th October 2010 11:49 PM

Are the chokes used for power supply filtering? If so, they'll have 50/60 Hz and harmonics in them just like the power transformer. In that case, you could align the the chokes and PT and place the OPT at 90 degrees to that.

If the chokes are used as plate loads, I'd place them at 90 degrees to the PT.

Your KT88's are mighty close to each other. I hope you aren't planning on dissipating maximum anode power in those...

One option for figuring out the layout would be to assemble one channel and play with the orientation. Watch the output with an oscilloscope or AC voltmeter and turn the magnetics for minimum hum.


Miles Prower 25th October 2010 11:51 PM

Being clear across the chassis, I don't think it'll be a problem. I'd worry more about cross talk between OPTs, however. For that, I'd definitely want those to not be in line like that.

mashaffer 26th October 2010 12:16 AM

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The chokes are B+ filter chokes. Tom, I was wondering about the KT88 being so close. PA section will be something close to this...

Right now the rectifier is directly behind the PT. I suppose I could exchange the right hand KT88 and the recto which would give more room but put the KT88 pretty close to PT and also make the B+ wiring a bit convoluted (PT across to recto - forward to chokes - back and left to KTs - to the right past recto to preamp etc.). I had hoped to avoid re-drilling for the tube sockets since everything needed was already there. Maybe that is not possible.

Maybe I could figure out a way to move the preamp tubes toward the front (close to the controls) and spread the power tubes out some.

The chassis was designed for 6L6 class tubes in guitar amp use so spacing is a bit tight. I was planning on drilling a ring of cooling holes around the power tube sockets but this will be in a small console type enclosure so I suppose that one should give the tubes every opportunity to breath.

hidnplayr 26th October 2010 08:34 AM

How about placing it like this:

Power TX
choke choke
opt opt
KT88 KT88
input tubes

mashaffer 27th October 2010 12:10 AM

Hidnplayr, I am not exactly sure what you are proposing.

One possibility I just thought of is that I could extend the cutout for the left power tube about an inch to the left. The screws on the socket would hold it in place just fine and the original hole would just provide some air circulation.

One of the things I don't like with these guitar chassis is that the tubes are lined up on the back with the controls on the front so that the signal wiring has to go all the way front to back.

Another possibility might be to hang the chokes off the back and move one power tube toward the front where the chokes are now.

hidnplayr 27th October 2010 08:20 AM

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Originally Posted by mashaffer (
Hidnplayr, I am not exactly sure what you are proposing.

I didnt realise your chassis already had holes in it on the top..
(You dont have a buddy who can weld? :p)
Here is what I meant:

mashaffer 28th October 2010 02:28 AM

Well my buddy "JB Weld" can. ;) I had rather hoped to keep that to a minimum but I do kind of like your layout as it would make routing of signals and controls easier.

I am thinking about placing a smoked plexiglass front on the unit so that when lit the chassis becomes visible. If I do that then the artistic aspect would become important. In that case would probably want iron across the back with the writing facing forward and the tubes in front.

mashaffer 29th January 2011 10:52 PM

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After many missteps including letting the magic smoke out of my hand drill I finally have a beta version of the power amp section drilled. It will need to be tidied up and painted but I thought I would run it by you guys and see if you think it is workable. It will be enclosed in a small console so won't really be seen. KT-88s are about 1 1/8" apart at the widest part of the envelop.

Any and all input appreciated.

2wo 30th January 2011 09:26 PM

that is thinking outside of the box. I am just a little concerned of the placement of the PS chokes. I would not let them touch. Even better looks like you have room to put one inside, using the same mounting holes...John

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