Chassis Layout

[defaced]

So, I'm working on a 11 tube behemoth. Single tube clean channel, three tube high gain channel, single tube FX loop, cathodyne PI and post PI cathode followers, and 4 x KT-88 output section.

I've prototyped the high gain channel before so I'm pretty comfortable with most of the layout, but I wouldn't mind some second opinions. Here are the things I'm not totally comfortable with or just simply don't know the "right" way to do it:

• Lamination orientation of the OT and Choke
• Distance between OT and V1 tubes
• Distance between choke and post PI CF
• Length of grid wires to power tubes (would shielding these save some heartache?)
• What about putting the choke on the inside of the chassis

[tbryanh]

Why the CFs? Are they AC coupled of DC coupled to the PA tubes?

[defaced]

The high gain channel, PI, and post PI CF are a copy of the VHT D120. Right now they are AC coupled, but because I have them wired based on a description and not a schem, I'm honestly not sure they're wired properly. I've got a fairly good image of the board from the amp but I haven't stopped to really decipher it yet - too busy doing chassis design.

[black_labb]

looks pretty good from my not that knowledgeable eye. maybe rotate the OT to keep it a bit further away from the inputs. you could probably move the PT closer to the cornerand fit the choke next to it.

[Steve Conner]

A tip: Keep the plate wires from the OT on the outside of the chassis, and don't let them in until they're near the power tubes. In a high-gain amp, you must keep those plate wires away from the input jacks and preamp circuit at all costs!

If you must run them inside, put them inside a grounded metal shield to stop capacitive coupling.

Similar guidelines apply to the grid wires from PI to power tubes, and the wires from OT to speaker (including the feedback wire to the PI) but they're about a factor of 10 less "dangerous".

You may also need a shield on the first tube of your gain channel, to stop its plates from "seeing" the power tube plates capacitively.

In a capacitor-input filter, the choke carries very little AC current, so I wouldn't worry about it coupling into the OT. Ditto for the PT as it's a toroid, so it should leak very little flux.

The magnetic fields from the transformers hardly affect tubes: it's the electric fields from the wires coming out of the transformers that cause trouble. The body of the transformer should give off no electric field, as it's grounded. (This may not be valid for a toroid, but the PT is far from your preamp tubes anyway.)

[defaced]

Excellent, thank you both for the consideration. I'm going to look at some dimensions and see if I can get a conduit of sorts into the chassis design. I've got a couple of ideas so we'll see what shakes out.