Heyo. I've built a bunch of amps inside pre-used chassis, and it can become logistically daunting. Which I can see you aware of by how you've placed the rec tube and power filtering - interesting! Although you might want to give that 5watter a little more room to breathe because it will stay cooler that way.
One of the first things I realized - well, it took me a while actually - was to stop using those on/off switches on the volume knobs. Having the AC so close to the signal is always a recipe for hum. I recommend using a dedicated power switch and a separate vol pot, and keep them as far apart on the face-plate as possible.
Next, I encourage you to run the heater wiring as far from any signal wiring as possible, including the vol pot. In the pic, it runs right by it, so...more hum/noise. I'd also encourage you to move your tone pot in between the vol pot and input jack, so that you have shorter signal wire runs. Actually, I'd put the vol pot next to the input jack, probably, and the tone pot where the vol pot is. Keep all signal paths as far from power sections as possible.
In that same light, I'd move the OT closer to the rear of the chassis, and I'd move the 6V6 socket to the rear also, perhaps using one of the big, pre-drilled holes if possible. I'd also move the nine-pin socket to the front of the chassis, nearer the input. i.e. almost as if swapping the nine pin for the octal and vice-versa.
That mini-switch is probably to switch speaker impedance, and it could go on the back panel, or somewhere a little further away from the power filtering is possible. It might also be okay where it is, but my rule of thumb is to separate all stages in terms of distance where ever possible, and it should be easy to relocate.
Possibly annoying advice, I know, and I realize that I'm recommending a redesign of much of the chassis, but I'm not trying to undermine the progress and work that you've already put in. I built a bunch of amps similar to this and then wondered why they hummed and oscillated out of control half the time. Then I came to understand that there are electro-magnetic fields emanating from most of the AC and high voltage paths, and they will overwhelm the signal paths every time. So amp layout became a top priority if I wanted success of any sort.
The other big lesson I learned was to lift all the grounding points off the chassis and create a star-ground system, or at least take charge of the grounding system effectively. So first, the preamp section is grounded to a single point off the chassis using a terminal strip (although some people use the input jack sleeve for this, I don't), which then connects to the power tube ground point - again, using a terminal strip - which then connects to the main ground point somewhere near the power transformer end actually on the chassis using a sturdy lug. So the grounding all flows downhill, as it were. Otherwise, you'll run into ground loops and hum etc. When learning about amp design, I looked inside old amps from the 50s and they seemed to be grounded all over the place, so I thought I could too. Ha!
Of course, feel free to ignore this advise :). Just trying to help. Good luck with the build.
Topic: Custom 5F1 Build (Read 5900 times)