Order of operations when building amp?

[MarkF786]

I recently ordered an Allen Chihuahua kit (Allen Amplification - Chihuahua). It's based on a blackface Champ but with Treble, Mid/Raw, and Bass controls, a AB763 reverb, improved transformer and power supply (with an additional filtering stage), and extra gain stage, a master volume, a second input jack, and it uses a 6L6 instead of a 6V6.

I have an Allen Sweet Spot, built by David Allen, and LOVE them amp; I've had it for years now and I haven't felt the need to get any other amps. But the hobbyist in me decided to step up from building guitar pedals to building an amp. I've read a few books on tube amplifier theory, I've been tinkering with electronics for 25 years, know how to read a schematic, am good at soldering, have all the tools, etc. so I feel I'm up to the task.

The one downside of the Chihuahua kit is that it doesn't include instructions; only a schematic, layout, and pictures are included (though the layout is supposed to be pretty detailed, including the lengths of the fly leads). So I'm looking for some basic advice on the order of operations when assembly the amp. So far, this is what I've gathered, but please correct me if I'm wrong or offer any additional advice:

1. Mount the face plates, pots and jacks to the chassis.
2. Mount all the other hardware to the chassis (transformers, etc).
3. Populate the circuit board (he uses eyelets).
4. Add the fly leads to the board.
5. Mount the board and attach all fly leads to controls, jacks, tubes, etc.
6. Connect heater wires to tubes.

Does that sound about right? I'm going to take it slow and try to be very meticulous, but I want to make sure I'm doing things in the right order so I don't paint myself into a corner.

Thanks,

Mark

[Chuck H]

Swap five and six and your list looks fine.

[MarkF786]

So the heater wires won't get in the way when soldering to leads to the tubes? I guess it could go either way; the leads to the tubes get in the way when soldering the heater wires ;-)

[Chuck H]

I suppose they could. But a standard alteration in the stock circuit is to wire the filaments as a twisted pair. In this case you would want them lying flat on the chassis. That would be harder to do if all the other leads are in place first.

[MarkF786]

Yeah, they're supposed to be a twisted pair, but Allen specifies having them hover an inch above the tubes (Fender style?) versus lying them flat at the back of the chassis (Marshall style?). Obviously either would work.

[Chuck H]

OK. Then your original plan is best. Obviously trying not to step on your own toes is the goal.

[tubeswell]

So the heater wires won't get in the way when soldering to leads to the tubes?

Depends whether you do 'overhead style' heater wiring, or 'tucked in the corner style'. I do the latter for tweed chassis type builds, in which case I wire the heaters in first (straight after the tube sockets are mounted). But for brown/BF style chassis, I wire overhead heaters in last.

Also if you want to get finickity, where you have octal PP output stage in your amp, wire the opposing tube's heater pins in reverse to each other (i.e.; for 6V6/6L6 etc, pin 2 of one socket to pin 7 of the other socket, and vice versa). This helps with canceling out output stage heater hum in the primary of a PP OT (because any of the VAC cycle from the heaters that happens to get through and ride on the signal, will be in opposing phase in the opposite sides of the OT primary). Elevating the heaters also helps in this regard.

[JoeM]

The output PP stage should have the heaters in phase, not out of phase.

From the ValveWizard site:

"Valves in push-pull or in balanced stages (such as long tailed pairs using separate valves) should have their heaters wired in phase. Any noise induced will then be common mode and rejected by the stage (mostly). Valves in parallel single-ended stages should have their heaters wires out of phase for mutual cancellation. Using two different colours for the heater wires will make this easier"

[tubeswell]

I stand corrected (thanks Joe)

[MarkF786]

Depends whether you do 'overhead style' heater wiring, or 'tucked in the corner style'. I do the latter for tweed chassis type builds, in which case I wire the heaters in first (straight after the tube sockets are mounted). But for brown/BF style chassis, I wire overhead heaters in last.

Thanks for the feedback. To help my education, is there a reason to do the heater wires differently depending on the amp, or is it just to match the original? I figure either way would be functionally equivalent. Heck, some amps don't even use twisted wire, like the Soldano SLO using bus wire run straight (and that's a high-gain amp which you'd think would be noisy as hell), so there seems to be many ways to skin the cat.

I've read some contradicting info on wiring the heaters regarding in-phase and out-of-phase, so I'm not sure what's the right answer. This amp is single-ended with only one tube so I don't need to worry about it now, but my OCD nature will ensure I wire all the pre-amp tubes in-phase.

[tubeswell]

... is there a reason to do the heater wires differently depending on the amp, or is it just to match the original?

Overhead heater wires keep the heater circuit well clear of the signal wires. On the other hand, if you've got room to tuck the heater wires into the corner of the chassis, that can make the main board easier to get in and out. JM2CW