• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Layout

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

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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?
 

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tomchr

Member
Paid Member
2009-02-11 12:58 am
Calgary
www.neurochrome.com
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.

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

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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.
 

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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.
 
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.
 
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.

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Any and all input appreciated.
 

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