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Old 17th July 2008, 04:01 PM   #1
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Default Smallish chassis feasible? Multiple pics

I have aquired a couple of nice Edcor OPTs for my 6EM7 project but they have exposed lugs for connection rather than insulated leads so it seems that they are best used in a completely enclosed case. This has caused me to again consider using an old equalizer chassis to house the PA and crossover.

Realizing that things will be a little bit tight I wanted to post some pictures of a possible layout and get your opinions.

There is an octal socket for rectifier and two more for the 6EM7s. The rectifier socket is the one toward the back of the case. There are four 9pin sockets for crossover and meter driver/mic preamp for SPL meter (possibly 3 9pin and one 7pin if I use a different tube for meter driver).
Two of the 9pin sockets are for a woofer BP filter and one is for a subwoofer LP filter.

First pic shows the meat of the layout. The metal plate on which the sockets will be mounted will be raised up on stand offs with a large screened ventilation hole in the top and bottom of the chassis. I will have to move the input jacks further to the right as the OPTs are right up against their current location.

I would run heater wires underneath and at the front of the chassis and keep shielded signal wires above the plate as much as possible and orthogonal to the heater wires. Heaters will be raised above ground potential by voltage divider on the power tube cathodes.

The question is whether this chassis is just too small for effective cooling and noise avoidance? If not any suggestions on improving the layout?
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File Type: jpg chassisinteriorsm.jpg (64.7 KB, 528 views)
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Old 17th July 2008, 04:02 PM   #2
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Showing how input jacks would be relocated.
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File Type: jpg chassisfrontanglesm.jpg (89.1 KB, 431 views)
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Old 17th July 2008, 04:05 PM   #3
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For your entertainment a shot of the front panel. I will leave the cutouts for the eq sliders open and remove the dust felt behind them. The included dB meters is what gave me the idea of including a SPL meter for adjusting the crossovers. I suppose they could be used for power meters when not being used for setup.
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File Type: jpg chassisfaceplatesm.jpg (47.7 KB, 406 views)
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Old 17th July 2008, 04:06 PM   #4
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And the back panel. The round hole happens to have screw holes in exactly the right place for power cord socket.
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File Type: jpg chassisbacksm.jpg (47.5 KB, 364 views)
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Old 17th July 2008, 04:11 PM   #5
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and lastly the hole in the bottom of the chassis. The plate I am planning to use for mounting the sockets was orriginally used as a access plate over this hole giving access to the PCB. Will cut similar hole in the top and cover both with screen.
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File Type: jpg chassisholesm.jpg (62.3 KB, 386 views)
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Old 17th July 2008, 04:17 PM   #6
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Looks pretty tight to me. I've made the mistake more than once of trying to cram everything into a small space - I succeeded but generally come to regret it later..

No space for things like upgraded coupling caps because they are too large..

Cut fingers on chassis edges because I have used every sq inch of available space and getting to parts has me brushing up against the lips..

Magnetic coupling into transformers, particularly annoying with SE amplifiers and transformer coupled line stages.

Finding out that the thing runs way too hot..

AND:

Some day you might want a choke...

Where are you going to put the power supply caps?

What if someone hands you a lovely GZ32 or GZ37 to replace that lowly GZ34 and it won't fit due to height restrictions?

What if you decide to try EL34 instead of say 6V6..

What happens if some part fails a few years from now - are you going to be able to get at it without totally tearing this thing apart? (Believe me I know - been there, done that.. )

It looks like it will all fit, but you definitely have a job ahead of you to do it.. First thing I would do is move the opts further away from that power transformer...
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Old 17th July 2008, 04:49 PM   #7
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This is what I feared. I suppose I could use the guitar amp chassis and put a cage on it. Maybe some nice wood side panels to connect the cage to. Down side is that the tube sockets are on the back so all you see is iron.

Another possibility is separate caged chassis for the PA and put only preamp crossover in the eq case.
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File Type: jpg runningsm.jpg (95.1 KB, 387 views)
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Old 19th July 2008, 03:08 AM   #8
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Doesn't look all that tight for a smallish amp. If you wanna see tight, check out my "Shrine" thread. I used a switching power supply and packed all the goodies int a 6" cube with tubes poking up on top. I plan a somewhat larger version, as the bitty Edcor output transformer I used limited the bass somewhat.
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Old 19th July 2008, 06:16 PM   #9
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What are the dimensions of the chassis?
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Old 19th July 2008, 07:04 PM   #10
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About 16x4.5" That PT is 3x4". Height I am not sure of but is plenty tall for tubes to fit with clearance.
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