Madison, your idea got me thinking (always dangerous). I'd like to do the same thing, pots close to the tubes. The only trouble I can see would be the heater wires. If I twist 'em right, would there still be more likely hood of picking up hum where they go past the other wiring?
Yup, those heater wires are a concern.
I'll very soon find out.
I've spent more time planning my current build than I've probably spent building all the other amps I've ever built, combined.
So here's what I'm doing:
Similar to Darryl's phase inverter in the pictures above, I'm arranging the preamp tube sockets in a row, then putting a single strip of turrets on either side (in parallel with each other). Components get mounted (generally) by spanning from one turret strip to the other, and arranged above the tube sockets. Wiring to connect the components to the socket travels a very short distance down from the turret to the socket pin.
Because of this, the heater wiring will be run first, twisted, and dressed flat against the chassis.
Matching the original Standel style, the preamp tubes wind up being mounted horizontally; as a result, I've looked at the tubes themselves to identify the major axis of the tube, meaning the axis that the grid support rods are on. When inserted in the socket, the tubes will be naturally rotated so that the axis of the grid support rods is perfectly vertical.
The key with heater wiring is to keep the wiring away from high impedance circuits, and keep the "loop area" small. "Loop area" means the area enclosed by the heater wiring. If I ran the wiring to a given socket, then added a second wire from that heater pin to start the run to the next socket, and
wrapped that wire around the socket, I might stay perpendicular to the socket pins but I've also made the "loop area" bigger.
Fortunately, the particular rotation of the sockets I arrived at allows me to run the heater wiring from a given pin (say, pin 9 of a 12A_7) right over the socket to continue on to the next tube. If you look hard at it, the heater wire still stays perpendicular to the other pins (as much as it can), while having the smallest possible loop area. And since the sockets are down on the chassis, but the components are elevated by the turret strips, they're nearly an inch away from the heater wiring, and run perpendicular to it. I'm pretty confident there will be no hum due to heater wiring.
And my preamp chassis is only going to be 4" wide, from front panel, controls, to components/sockets, to rear panel controls and rear panel. It could have been only 3" across that span, but I chose to use bigger-bodied PEC pots, and have some indivudal turret terminals to mount a ground buss seperately from the components. Filter caps and dropping resistors are at one end of the chassis, where power supply voltages enter (I'm using seperate preamp and power amp chasses).
All this is to say, sure you can do it. It would be nice if you were doing it because it provided a technically-better layout (mine has a LOT of happy accidents that make it technically-good). But you're probably familiar with this stuff to figure what is an obviously-bad idea. Just don't stick with cool-looking if it causes you to build something you knew was bad, which you'll have to fix later. Regardless, I think you also know that you can often break rules without consequences.
Topic: Chassis layout, tubes up front? (Read 5570 times)