Chassis Layout

[JJH0906]

Hey group,

I have revised my initial chassis layout for my build and would appreciate any constructive criticism of how this looks. I hope the details of the location of the components make sense but feel free to pass along words of wisdom or ask for any clarification!

ChassisLayout_20220301.pdf

[johnnyreece]

I don't suppose it looks all that unconventional. I'm just curious about needing (what appears to be) four triodes for a FX in/out, plus two more for a line out. Got a schematic? I'm not saying it won't work; just curious about driving the 6L6s with only two gain stages.

[JJH0906]

The Effects Loop and Line Out circuit were derived from Merlin Blencowe's Amp Design book:

Blencowe_ParallelFxLoop.jpg

Blencowe_LineOut.jpg

[johnnyreece]

Gotcha. It appears you only need to use four triodes for that (three for the loop; one for the line out). That might get you a couple more gain stages, or whatever you might like. Shoot, maybe tremolo? EF86 Channel? I dunno. Just trying to be helpful!

[JJH0906]

No, this is pretty much what I'm looking for, not really trying to add anything else.

The premise of my question was if the layout seems fairly legit. It's sort of based off the Fender Super Reverb layout but that is very linear and uses a 24"X8" chassis. So, I've scrunched things up a bit (because I have no idea what I'm doing) and used a 17" long chassis and the components absorb alot of real estate in that form factor.

[johnnyreece]

Well, in that case you can save a tube. You could combine U4 (which will only use one triode) with U7 (which will also only use one triode). That would also save you some space. In essence, you'd be using the two tubes originally for the vibrato channel, and using them for F/X loop and Line out. I think you'll really start to see whether it will work out when you start to lay out the board. That's where things start to get a bit tricky.

[erwin_ve]

Maybe put the tube sockets on the other side of the chassis away from the pots?
Potential hum in this configuration.

[JJH0906]

Well, in that case you can save a tube. You could combine U4 (which will only use one triode) with U7 (which will also only use one triode). That would also save you some space. In essence, you'd be using the two tubes originally for the vibrato channel, and using them for F/X loop and Line out. I think you'll really start to see whether it will work out when you start to lay out the board. That's where things start to get a bit tricky.

I have heard of this practice but I wasn't sure how any kind of induced interference might be brought through the tube when mixing things up like that. It definitely would be a space saving idea.

The components are intended to be mounted with turret board construction, so that is the next step, as you say. See how all that's going to line up with the external components and determine how bad it's going to get!

[JJH0906]

Maybe put the tube sockets on the other side of the chassis away from the pots?
Potential hum in this configuration.

I'll see how that shakes out. I was going to try to bridge the external components, like the pots and valves sockets, to the internal components by making his direct connections as possible. So moving the valves may not work out if I go that direction.

[pdf64]

What kind of cab is it going in, eg valves down combo, valves up head?

[JJH0906]

What kind of cab is it going in, eg valves down combo, valves up head?

Sorry, I didn't make note of that did I?

I intend for the chassis to be on the bottom, with a valves pointing upwards. This will likely be mounted in a head, with a speaker cabinet separate below. I was going to do a combo but understandably with the valves pointing up arrangement, it makes it a lot more challenging to get the controls in a comfortable place.

Plus that way I can move the amplifier around to a different cabinet with different speakers.

[bepone]

tubes to the phase invertwr can stay in front, preamp tubes in front are in all the meanings advanced build level, tubes from pi to the rectifier need to go back. output trafo pull around on free space when you sort the tubes out

[thetragichero]

for line out i never use a tube, just a voltage divider off the output transformer like this: https://www.thetubestore.com/lib/thetub ... ematic.pdf
two resistors is much nicer than a triode and a bunch of other components, and depending on where the jacks are located can even be done point-to-point

[JJH0906]

for line out i never use a tube, just a voltage divider off the output transformer like this: https://www.thetubestore.com/lib/thetub ... ematic.pdf
two resistors is much nicer than a triode and a bunch of other components, and depending on where the jacks are located can even be done point-to-point

Thanks for this comment! After hearing back from some of the great comments, I was thinking about getting rid of the tube portion of the line out signal. I really would like one for interface purposes, but I think you are right, using tubes and a bunch of stuff to do that seems a bit much.

[thetragichero]

if you're going into an interface, replacing the 'top' resistor in the voltage divider with a resistor and pot (wired as a rheostat) will give you a bit more volume control in the event that your interface does not want such a hot input signal (did this for a fella for his amp). the OTHER thing to keep in mind is that guitar speakers are REALLY CRAPPY for full range audio, so they knock off a bunch of junk frequencies that sound absolutely awful so some sort of speaker sim/impulse response is absolutely mandatory if you're going to be recording from the line out (i'm sure you can bypass the 'lower' resistor with a cap if you want to make a fixed low pass filter, but you'll still likely want some sort of speaker sim on there)

the *other* good reason to have your line out just an attenuated feed from the output transformer is that you'll then capture whatever tone the output tubes are adding