Amp Chassis Materials

[Julio Emilio Jimenez Nava]

Hi!

I'm planning to build a amp, so the first thing I want to have is the chassis.
I was reading that the material used to make the chassis can affect the tone of the amp.
For example: Fender used steel and Marshall used aluminum.

As an engineering student I'm aware of the magnetic properties of different metals,and that transformers work
to due magnetic fields, so I want to be sure I'm using the right one.

I want a Fender style amp and I was wondering if any of the members of the forum have made any research
on this. Wich type of steel was Fender using in the 60's to manufacture their chassis? Wich is the
closest substitution material I could use today?

Hope someone can help me out.

Thanks!

[stingray_65]

It's my belief (opinion) that it makes no difference at all.

Stray magnetic eddy currents CAN influence parts and wires that lay below the chassis, however the MOST likely outcome of that is uncontrolled oscillation and not a tone enhancing godsend.

Lead dress is your friend in those circumstances, That is to say routing your internal wires in such a way to avoid crosstalk and magnetic interference.

A lot of guitar amp lore  comes from the audiophiles and HiFi crowd. When they build an amp the strive to make the circuit as clean and un-distorted as humanly possible. Going to extremes to achieve these results are par for the course.

A guitar amp on the other hand purposefully colors and distorts the incoming signal then feeds in into an often undersized OT and then to a speaker of limited range.

Esoteric changes and nuances of different brand parts no doubt can subtly alter the tone and mojo of a guitar amp. You will have greater, more dramatic result by changing a value of a component than you will by changing brands or materials.

I'm not saying just throw some parts in a box!  A lot of us amp builders do make certain mods  that weren't on vintage amps, but they are usually modifications done to improve reliability, reduce hum, or deliberate circuit mods to enhance voicing.

You have to keep in mind, Leo Fender designed some of the finest amps ever and built them out of the cheapest parts he could muster!

You say you are planning  to build an amp. a Fender to boot, but what model?

OH!, Welcome to the friendliest forum anywhere on the net. You'll be in great hands here.

Fender used plain old sheet metal for their chassis' 

I use 16ga when I build mine, but I like a stiff chassis, especially for 35 watts and up, the transformers get heavy. Smaller amps you could get by with 18ga, but I feel it is kind of flimsy.

Most prefer aluminum. I seem to always use 5052 alloy, It's nice and easy to machine and cut but It has a grain to it so watch how you orient your bends.

It kind of sounds like you want a particular vintage sound, remember if you build it with all new parts, It will sound like that vintage amp did when it was new, and not like it would sound after 30,40 or 50+yrs of play and abuse.

Any how, give us a clue as to what direction you want to go and the guys here would be happy to lead you down a sane path to tooby sweetness.

Ray

[Rev D]

 The only group of builders I'm real aware that specify only aluminum (and even then its those most wanting to copy exactly his formula) are the Trainwreck guys. They did it because the designer did it and they do believe it makes a difference. That said that amp is on the ragged edge of being unstable anyway, so I'm sure anything a person can do to try and give them an edge in stabilizing it would be a good thing. Examples however have been built with steel chassis's so I'm not sure its a necessity even then.
 I'm not sure why Marshall used aluminum, if you look at nearly all they're amps after many years the transformers are leaning in from buckling the top of the chassis. I suspect Leo designed his amps from a price standpoint and had a good deal on steel chassis's and just went with it. This proved wise in his case from a durability standpoint as most of his amps are probably still on the road with the exception of those that had accidents or were destroyed by wood be amp molesters who decided they needed to be something besides a Fender amp. 
 As far as Fender amps, being low to mid gain amps you could use whatever you wanted and I doubt you'll hear much of a difference. I broke tradition and used a aluminum chassis on a tweed deluxe I built and it still very much sounds like a tweed deluxe, in that amp with its small chassis and light transformers it wouldn't matter. If I were building a larger Fender head or combo amp with beefy transformers I'd very much look at using likewise beefy chassis materials. I agree also with Stingray_65 about this being quite possibly the friendliest amp forum on the net, welcome and good luck with your project!

Regards,

Don

[billcreller]

I built 5 exact dimension chassis, using both steel and aluminum.  Same layout of tubes & iron etc, and couldn't hear any difference between them.  Just an observation...

[RicharD]

From a purely "tone" point of view, how the chassis is mounted in a combo and it's relationship to the speaker is a lot more important than what the chassis is made out of, especially in a high gain amp.  Electronically, shielding in the audio range could be be tin foil or 1/4" steel and you're not gonna hear a difference.  Mechanically steel is tougher inch for inch than aluminum, but thick (1/8") aluminum is pretty dang cool stuff.  You might let your metal tools decide which material to use.

[PRR]

The USA has lots of iron, South California had lots of war surplus tooling, stock chassis were mostly steel, Fender went with steel even on proprietary chassis.

It is much easier to bend and drill aluminum. England does not have such huge amounts of iron nor such a large market, much tooling was lost in the war. Somehow they had Aluminium which is easy to work. A lot of England's notable post-war products were "alloy". Jaguar Six. Comet airliner. MG-B bonnet.

[Geezer]

I really doubt I could "hear" a difference in steel vs aluminum, and even if I could, that difference would be a matter of opinion as to whether one was "better" than the other.......

I use aluminum because it's easy to work with, and my local metal shop has lots of scrap pieces that are enconomical to bend into my chassis designs.
I use a 3-piece design (basically a flat 0.080 sheet folded on 2 sides into a long u-channel) and use oak or poplar to enclose the ends. Cheap and sturdy.

G

[tubeswell]

'nother vote for ally if you're fabricating your own chassis (because its easier to tool).

[Willabe]

The USA has lots of iron, South California had lots of war surplus tooling, stock chassis were mostly steel, Fender went with steel even on proprietary chassis.

It is much easier to bend and drill aluminum. England does not have such huge amounts of iron nor such a large market, much tooling was lost in the war. Somehow they had Aluminium which is easy to work. A lot of England's notable post-war products were "alloy". Jaguar Six. Comet airliner. MG-B bonnet.

I know this already about you PRR, but I'm still amazed at the fact that, you sir are a walking library! Where did/do you find the time to sleep - - AND - - read as much as you have, let alone live a life!        


                                               Hats off to PRR, thanks for sharing with us!        


      
              Brad, (I need to read more) Willabe        

[Merlin]

England does not have such huge amounts of iron nor such a large market, much tooling was lost in the war. Somehow they had Aluminium which is easy to work. A lot of England's notable post-war products were "alloy". Jaguar Six. Comet airliner. MG-B bonnet.

I don't think this is true; this island is practically made out of coal and iron ore. After the war we didn't blink an eye at using thousands of tons of iron to build steam engines, when the rest of the world had long gone over to diesel. I don't think much tooling was lost in the war either, as there was plenty outside London. (Plus we talking about the 1960s; it's not as if Marshall was operating out of the blitz rubble).

The use of aluminium in engineering was more a matter of strength-to-weight. Whereas the US has always been happy to build big, heavy things with giant engines, we had to be more economical with fuel (we didn't really strike oil until the 60s), so we naturally developed smaller, more efficient things.

I expect Marshall used whatever metal happened to be recommended/ available from his local supplier. He wasn't quite in the same league as Rolls Royce... I'm visiting the Marshall factory tomorrow, so I'll see if anyone knows.

[PRR]

> amazed

Merlin (the man, not the engine) will correct me.

FWIW, the Jaguar OHC Six is iron block under the alloy head (not counting a few race specials). But in confirming that, I learned that some of Jaguar's tooling was world war ONE naval surplus job-work machinery, and its decline after only 50 years has been blamed for the decline in Jaguar engine excellence after the heady 1950s (there were plenty of other reasons).

[tubeswell]

I'm visiting the Marshall factory tomorrow, so I'll see if anyone knows.

IIRC, I'm pretty sure that Enzo told me once how he used to be an amp tech at Marshall a few decades ago, he may know something.

[loogie]

The real question here is who was Lucas, The Prince of Darkness?

[spacelabstudio]

I had an amp tech tell me one time that a steel chassis will interact with and affect the magnetic fields generated in the output transformer and that the steel will sound better.  I'm skeptical, but have done no experiment that could discredit or corroborate that claim.  I have no doubt, actually, that the OP and the chassis do interact with each other, but the real question is whether that interaction leads to audible differences between steel and aluminum.  My best guess is maybe but probably not enough to matter.  Cork sniffers might disagree.

[Merlin]

OK, I went to Marshall today. They said Jim was making his chassis by hand at the time, and he used aluminium because it was easier to bend accurately (they still have the original bending brake). When he made the first 100 watts he then realised it wasn't up to the job and switched to steel, which they have used ever since.

[Rev D]

 That's pretty accurate, from a Marshall site when I queried "when did Marshall switch to steel chassis?", I only did this because I remember seeing early marshall 100 watt amps (and I stress early as in the first couple years which would make sense I'm sure they hand bent the first few years just from a standpoint of low production numbers) that had the transformers all flattening the chassis and they're leaning in. Thanks for filling in the gap on why Marshall did what it did, it makes sense for what was then a small builder before they became a foundation of an amp that was on every stage in the late 60's early 70's (I should say on harder rock and edgier bands, the Country folks were just fine with they're Fenders and now twangier offshoots of Vox circuited amps, not EVERY STAGE EVERYWHERE) and still on many stages today. From a Marshall forum here's a quote on when the steel amps were merged into production:

"Alloy 100watt was from 65-66 with folded edges, '67 with block end and mid '67 steel with single cap up top late 68 added the preamp can up top and 69 all caps up top"

Regards,

Don