WHY ALUMINIUM CHASSIS?

[M Fowler]

deleted

[drz400]

Interesting that on an "Ultrphonics mod" he spaces the OT transformer away from the chassis with a thick shim. So he must think there is something to it, or maybe just a quicker way of getting components/wires further away from the OT. Have also understood that because a steel chassis is ferromagnetic the transformer can induce a hum into the chassis.

I wonder if the "shim" is actually as an interface plate between the already drilled chassis and a new transformer with different mounting bolt centers.... I would suspect that to be the case, and it would save HAD from having to drill a vintage, steel (although galvanized, not stainless) Fender chassis.

Gil

On the 2 I saw the Transformers were stock BF Bassman, so he raised the stock transformer by a healthy amount, I believe it was .5" phenolic
No reason for an interface shim.

[glasman]

Is it possible that HAD felt that the steel chassis used in the Fender amps would "screw" with the magnetic properties of the OPT? Of course, it could be for a completely different reason .

[FUCHSAUDIO]

Is it possible that HAD felt that the steel chassis used in the Fender amps would "screw" with the magnetic properties of the OPT? Of course, it could be for a completely different reason .

Agreed, they're called "magnetic lines of force" and steel couples them better than aluminum, which has no ferric properties....

[glasman]

FWIW, when I built my Zingaro prototype I used a generic princeton reverb chassis (steel) I purchased from Mojotone. I used my "normal" grounding scheme for the proto and I got to relearn everything I thought I knew about ground loops . HMMMMMMMMMMMMMMMMMMMMMMM

[David Root]

HMMMMMM! indeed. I am starting on a +/- #13 ODS 50W combo w/out reverb, something between earlier and #40 and I'm using a Mojo steel BFPR chassis, no doubt the same item you described.

The only thing I have determined for sure about it is that the old Altec 417B I have put in the cabinet will take care of the period tone!

Perhaps a standard galactic star ground system is in order here, although HAD never used it.

Opinions?

Would be useful as I'm currently planning two multiple can caps, one for plate/screen, the other for PI/preamp. This arrangement allows me space to put in an FX loop (yes it ain't original but it would be nice!).

[glasman]

Suffice to say, I spent a lot of time with a taper reamer and installing isolating washers at several key locations. Input jack, send and return jacks etc etc etc.

HMMMMMM! indeed. I am starting on a +/- #13 ODS 50W combo w/out reverb, something between earlier and #40 and I'm using a Mojo steel BFPR chassis, no doubt the same item you described.

The only thing I have determined for sure about it is that the old Altec 417B I have put in the cabinet will take care of the period tone!

Perhaps a standard galactic star ground system is in order here, although HAD never used it.

Opinions?

Would be useful as I'm currently planning two multiple can caps, one for plate/screen, the other for PI/preamp. This arrangement allows me space to put in an FX loop (yes it ain't original but it would be nice!).

[heisthl]

I use 2 grounds in a steel chassis, one for B+1, B+2, speaker jacks and the relay supply and the other (by the input jack) for everything else (including pre out/Power/in and/or send and return jacks, reverb tanks,presence cap etc.). Works great with no hum or ground loop issues.

[David Root]

Thank you Gentlemen! Sounds like a two point star ground with all jacks insulated from the chassis.

I have lots of those neat black fiber shoulder washers ready to go! (I don't care for plastic jacks either).

[heisthl]

Thank you Gentlemen! Sounds like a two point star ground with all jacks insulated from the chassis.

I have lots of those neat black fiber shoulder washers ready to go! (I don't care for plastic jacks either).

The input jack and the speaker jacks don't need isolation, but isolate everything else.

[thyx]

"WHY ALUMINIUM CHASSIS?"

*BURP* WHY NOT!!!?

[BobW]

Why AL chassis? It's easier to drill and does not support electromagnetic induction. Keeping your power current paths away from your signal current paths minimizes noise.

[glasman]

oh and it is lighter ......