critique my layout

[Randall]

here is the chassis layout for a one channel B-15 clone build. See anything amiss? Octals have .75" between them. This is my first blank chassis build, I don't want to start cutting holes if there is a potential issue with something being too close or in the wrong spot. Thank you.

B-15 clone.pdf

[loudthud]

Quite a small chassis. The biggest problem is the plate leads going to the output transformer being near or crossing the input wires and the tone control wires. Thankfully there is not a whole lot of gain in the B15. If possible the plate leads should be routed across the top of the chassis to near the output tubes. Another issue is where the HV wires from the PT enter the chassis. Keep them away from the tone controls. So you need to plan where the transformer wires will be routed and how much space the preamp and PI components will consume on the eyelet/turret/tag board. Having the speaker jacks next to the preamp tubes is not so good. Better if they were near the center. Grounding will be important.

If you moved one or both preamp tube(s) to the front of the chassis near the input jacks, that would help a little, you could shove the OT to the back of the chassis. That destroys the B15 cage look ... The Hammond big cage might be an option, do you plan on sort of a naked metal chassis or a wooden head box?

I would gravitate to having the filter cap near the rectifier or caps under the chassis.

[Randall]

Set back! Thanks for the insight loudthud. How about this?

B-15 clone rev1.pdf

Caps moved to right edge of eyelet board, speaker jacks in middle. PT secondary facing rectifier and close to caps. PT primary facing power/standby switches. OT primary aimed at plates and rectifier. OT secondary chasing the crease to the speaker jack.

I am going for a open chassis here, and I want it to be small. It is going to be the 25 watt cathode biased version, and I want it to look retro as well as sound retro. Think a fender with flats into a round tube amp pretending to be an upright. As a bass player Mr. thud, I know you get that! I want the tubes and trafos to stand out in their glory with no cage. I will have a wooden sewing machine type cover to clip to the base as the removable head cab.The trafos are not Ampeg style potted cans, and I do not need to follow the look of an original B-15, although I prefer to keep the tube backline intact if feasible.

Should I worry about the proximity or orientation of the two trafos?

[Randall]

Or, better yet?
B-15 clone rev 2.pdf

[loudthud]

I like rev 2 alot better! The only change I would make is moving the speaker jacks back to the original position so they won't be so close and overhang the 6L6 sockets. The only bad thing about the layout is what the turret/eyelet board will look like in the preamp. The preamp circuit has to kind of be folded back on itself with lots of connections on the side near the tubes. The PI will be nice because the driver tube is on the opposite side from the power tubes. The next step would be to establinh where the transformer wires will be routed and workout the component board.

[Randall]

The PI will be nice because the driver tube is on the opposite side from the power tubes.

This made me remember that the second 6SL7 is the PI, not a preamp. I'm not sure I would have put it there if I had realized. Why do you like it there loudthud? Also, do you see a problem with the transformers sitting so close and right on top of the board, or does the chassis shunt it all?

And does anyone know a good free layout application?

[Tom Phillips]

I think a true point-to-point wiring scheme using terminal strips could be a good approach with this layout if you are up for it.

[Randall]

Hmmm...

[JoeM]

I have a B15 sitting here. Would gut shots help?

[loudthud]

This made me remember that the second 6SL7 is the PI, not a preamp. I'm not sure I would have put it there if I had realized. Why do you like it there loudthud? Also, do you see a problem with the transformers sitting so close and right on top of the board, or does the chassis shunt it all?

In the typical Fender layout either the power tube grids or the PI plates have to be run to the other side of the board if the PI and Pwr tubes are on the same side.


In the improved layout those long wires are eliminated, that's usually a good thing.

Also, do you see a problem with the transformers sitting so close and right on top of the board, or does the chassis shunt it all?

The chassis makes a pretty good shield. Where the wires poke through the chassis is where you can have a problem. Try not to have the holes for the wires under the board. The plate wires are the worst because the voltage swing is so high.

[Randall]

Thanks again loudthud! That all makes sense. And thank you Tom, you convinced me to terminal wire it in the air sans board. Also, thanks for the kind offer JoeM, but I'm going to try to do without looking as an exercise. Here is the latest tweek:

B-15 clone.pdf

[Tom Phillips]

Randall,
Some thoughts.
If you are going for a really clean & simple finished product consider re-locating the power switch to the rear panel next to the line cord entry and deleting the standby switch entirely. You could also go with a single input jack.
Cheers,
Tom

[Randall]

Tom,

I adopted some of your suggestions. I went with one input, and moved the power switch to the back, and eliminated the standby. I am having the cab fabricated this week. Here is the latest drawing.

B-15 clone bare.pdf

[Tom Phillips]

Cool. I'll be interested in watching the progress. I think the simplifications will really be beneficial since the amp chassis is being kept small.
Tom