Noob wants to build his first Wreck. Request guidance.

[Matthews Guitars]

APD shows 9 PTs in stock as of right now. Excuse me....8.

[wpaulvogel]

A Hammond 272JX also is a great Express power transformer. It produces the exact voltages. 402 volts @ 38mA bias per EL34.

[Roe]

My first build was a ceriatone express kit. I was guided by an experienced tech. The only problem was oscillation that disappeared once the OT primaries were reversed. The amp sounds great and is stable, although I've tweaked it in the last 15-16 years

[Matthews Guitars]

I guess I'm committed now, since I've bought both the required transformers.

Next, to take a basic chassis drawing to my local sheet metal shop and have him form up a chassis out of his heaviest gauge aluminum.

I've got everything I need to punch out all the features myself.

[Matthews Guitars]

Can someone post a CLEAR dimensioned chassis diagram? All the ones I've seen so far are heavily compressed to the point that dimensions are in some cases unreadable.

[johnnyreece]

I hadn't seen it mentioned yet, but since you were talking about transformer placement, have you heard about the headphone trick? If not, see here: https://ampgarage.com/forum/viewtopic.php?t=27502

Edit: Whoops...didn't answer the chassis question. How about this? http://ampgarage.com/forum/files/Trainwreck_Chassis.pdf

[wpaulvogel]

Can someone post a CLEAR dimensioned chassis diagram? All the ones I've seen so far are heavily compressed to the point that dimensions are in some cases unreadable.

The chassis is 17 inches x 8 inches by 2 inches.

[gktamps]

wpaulvogel and ViperDoc - thank you!

I have built a couple of cabinets but that curly maple one and the other ones in that shot that look the best were commissioned by me and built by a fine woodworker. I don't have the tools,talent, or time to do work that nice!

[gktamps]

Next, to take a basic chassis drawing to my local sheet metal shop and have him form up a chassis out of his heaviest gauge aluminum.

For your consideration, many folks believe that the thin Bud chassis contributes to the tone of the Express. I haven't used any, but am considering doing one more build with a Bud chassis. All of my builds so far have been with chassis either from Allyn or RJ, and they are thicker, but differ from each other in a few ways.

[ChopSauce]

How thick the Bud chassis?

[gktamps]

Info I have is 0.050".
Thin enough to cause Ken to use dowels between transformers and beneath, but otherwise thick enough to suffice as history shows.
Pretty sure the weatherstripping Ken used in the open space of the chassis was because the thinner chassis resonated otherwise.

[Matthews Guitars]

I may be setting myself up for a lower level of success, or even failure, but my concept is to be faithful to the schematic and parts choices (within limits, I'm not going to spend a mint for out-of-production NOS capacitors that are very rare) but as for the layout...I'm going to make a change. The power transformer and output transformer will be as far apart as possible and of course will be oriented in different planes. I want no possibility of transformer coupled interactions. But I'll make it with the idea in mind that the transformer that is moved can be relocated to its "correct" position if it doesn't work out.

[martin manning]

Power up the PT on your bench and put the OT in position with headphones or your DMM clipped to the 16 ohm secondary. You should be able to verify that positioning the OT as in the originals is quiet. I did a 2204 Marshall in the same style as the Express linked above, and they are both quiet.

[gktamps]

I agree with Martin. I have one built by another fellow that hums, but for my builds I've always been able to shift them a mm here and there using the headphone method and they do not hum any more than if they were separated. As a result, I think there should be no need to separate them, despite conventional wisdom.

[Matthews Guitars]

I'd never heard of the headphone trick before but it makes perfect sense and I'll use it.

Actually I'll hook up the transformer to my o-scope and exploit its high sensitivity to optimize the positioning.