thickness requirement for making chassis from scratch

[Amryan]

I'm quiet new member in this forum soI need guidance from all seniors in this forum. I plan to build Fender twin reverb Blackface. I confuse about the chassis thickness that it needs to make the chassis since in Australia there couldn't find any already made chassis for Fender Twin Reverb even if there is one, I have to import from USA which is gonna cost a lot. And since the PT and OT for fender twin reverb are heavy so I don't know Aluminium or Steel and which thickness should I choose.

[Tom Phillips]

As a reference point, I have a 1979 Fender Super Reverb chassis here and it is made of 18 Gauge (0.050 inch thick) steel. I believe that the Twin Reverb chassis is the same thickness.
Cheers,
Tom

[Amryan]

As a reference point, I have a 1979 Fender Super Reverb chassis here and it is made of 18 Gauge (0.050 inch thick) steel. I believe that the Twin Reverb chassis is the same thickness.
Cheers,
Tom

Thank you very much Tom for your information as a big reference for me.

[soundguruman]

I'm quiet new member in this forum soI need guidance from all seniors in this forum. I plan to build Fender twin reverb Blackface. I confuse about the chassis thickness that it needs to make the chassis since in Australia there couldn't find any already made chassis for Fender Twin Reverb even if there is one, I have to import from USA which is gonna cost a lot. And since the PT and OT for fender twin reverb are heavy so I don't know Aluminium or Steel and which thickness should I choose.

Aluminum is a bad choice. Even Mesa Boogie stopped using aluminum chassis, guess why?
It don't hold up to the challenge of rock & roll. It is a very poor conductor of electricity (because it oxidizes when contacting dissimilar metal)
(you are connecting the Earth Wire to: "that?")

And so, the best choice is galvanized steel. It is in fact the world wide standard...

[Amryan]

Aluminum is a bad choice. Even Mesa Boogie stopped using aluminum chassis, guess why?
It don't hold up to the challenge of rock & roll. It is a very poor conductor of electricity (because it oxidizes when contacting dissimilar metal)
(you are connecting the Earth Wire to: "that?")

And so, the best choice is galvanized steel. It is in fact the world wide standard...

Thank you soundguruman. But which thickness should I choose? Is 18 gauge good enough to withstand the weight or do we need more than 18 gauge? And why in some diy store they offered the chassis with aluminum?

[J M Fahey]

Aluminum 2mm will be fine, can be worked with simple tools and needs no treatment at all, either galvanizing or painting.
For series production metal shops with all the big shears, folders, presses and spot resitance solder machines steel is actually far cheaper, but for the home builder it's the exact opposite.

FWIW here's one of my Plexi 50W clones, of which I made hundreds; homemade chassis out of 1.5mm Aluminum.
2mm is far stronger.

[Amryan]

Aluminum 2mm will be fine, can be worked with simple tools and needs no treatment at all, either galvanizing or painting.
For series production metal shops with all the big shears, folders, presses and spot resitance solder machines steel is actually far cheaper, but for the home builder it's the exact opposite.

FWIW here's one of my Plexi 50W clones, of which I made hundreds; homemade chassis out of 1.5mm Aluminum.
2mm is far stronger.
[ATTACH=CONFIG]26698[/ATTACH]

thank you J M Fahey for sharing your experience in amp building. can the aluminium withstand the Transformers. Especially for big Watt Power Transformers

[J M Fahey]

Basically yes.
Of course you must make a sensible design, with the exact same materials things can be made better or worse.
Imagine a "Marshall type" chassis like the one I use.
The easy to make "C" (or "U") shaped chassis is the weakest one, because it´s an open frame, imagine it on a table, open (inner) side down.
If you push down in the middle, it will bend down somewhat, depending on thickness and pressure.
I'll make a drawing showing how it can be made *much* stronger with very simple reinforcement.
Hard to say in words, very easy to see.
Stay tuned.

[Amryan]

Basically yes.
Of course you must make a sensible design, with the exact same materials things can be made better or worse.
Imagine a "Marshall type" chassis like the one I use.
The easy to make "C" (or "U") shaped chassis is the weakest one, because it´s an open frame, imagine it on a table, open (inner) side down.
If you push down in the middle, it will bend down somewhat, depending on thickness and pressure.
I'll make a drawing showing how it can be made *much* stronger with very simple reinforcement.
Hard to say in words, very easy to see.
Stay tuned.

I will stay tuned…. can't wait to know how you can make the aluminum chassis stronger with simple reinforcement

[loudthud]

Juan, it looks like you mounted the output transformer on the preamp end of the chassis. Are the wires routed above the chassis over to the output tubes? Did you ever make a 100W version of that amp?

[J M Fahey]

Juan, it looks like you mounted the output transformer on the preamp end of the chassis. Are the wires routed above the chassis over to the output tubes? Did you ever make a 100W version of that amp?

Hi loudthud.
No , the lesser of two evils was mounting the power transformer in the preamp end.

Reasons:
1) it's WAY easier to avoid 50 Hz interference than high frequency one.

2) say, 5 pF stray capacitance coupling fixed level 50Hz interference into a high impedance point is nil; same capacitance coupling full bandwidth audio and with lots of gain involved can be a nightmare.

3) power wires travel along the chassis underside but inside a grounded aluminum U channel.

4) plate to OT windings connections are very short and straight, radiating as little as possible inside the chassis cavity.

5) I only offer them in 50W.

I consider 30 to 50w the "perfect" general purpose power for tube amps, allowing beautiful, fat, creamy power tube distortion, without resorting to tone killing Master controls (buzzy) or passive attenuators (dull/dry) .

While less power than that can carry lack of headroom.

I mean acoustically matching a regular energetic drummer; greybeards playing Blues in a Club situation can do very well with 15/20W.
As is, Soundmen yell at it when plugged into a 4 x 12"

The PCB I made allows building a Plexi/JTM45/AC50/TweedBassman with small changes and a Normal Blackface channel with a little extra tweaking.

This amp is meant as a "Tube Base", guys can play as-is or bring their own pedals, which are used between guitar and input; Efx loops don't make sense in this configuration (at least in my book)

On the back you'll see the "3 AM" switch, a fixed compensated PPI attenuator which kills power down to less than 500 mW, for bedroom/small appartment use, but keeps audible sound warm and full.
Much more useful than any "5W" amp and flipping it off you are stage ready again.

Don't believe in Mojo so I took the good parts of Classic, simple amps and freely modified what I thought would simplify it or make for easier construction.

So the power transformer has a single 340V secondary rectified with 4 x 1N4007, and 2 filament windings: a 6.3V one for power tubes and a 12.6V one which *can* be used straight for 12AX_ but usually is rectified and filtered.

*Or* supplies raw +/-16V for Op Amp clean boosters inside, if a customer asks for some extra gain.
Avoiding hum/hiss/popcorn/microphonics which can come with an extra triode gain stage or complicate my life.

I don't sell many of these, relative to my bread and butter SS amps, but they have a loyal following, who need a reliable versatile tube "sound brick" around which they can build their own sound.

Almost forgot: bias is capacitively derived from 340VAC, and (heresy!!) is Zener regulated.

[g1]

I'll make a drawing showing how it can be made *much* stronger with very simple reinforcement.
Hard to say in words, very easy to see.
Stay tuned.

It doesn't have to be pretty, just functional drawing, thanks!

[J M Fahey]

If I could had draw and scan, you'd already have it, but my parallel scanner misses an old W98 machine I had for that purpose and refuses to work with more modern systems.
So it's drawing on Corel or something and converting to .png for posting .

[Tom Phillips]

...So it's drawing on Corel or something and converting to .png for posting .

Or, for a quick drawing, I've sketched with pencil & paper and photographed the page. Works great.
Merry Christmas,
Tom