#124 Main Board Layout

[martin manning]

A bit more info.

I did a little analysis of the photos and came up with dimensions for the boards: I have the main board 2.75 x 7.5", and the filter board at 3.75 x 5.50".

These dimensions are based on the transformer mounting centers (3.00 x 3.75" for a Fender Twin), and the length of a 0.1uf Orange Drop (which is 1.30"). Between them, these two dimensions allow the length of the main board to be added up from the three photos ic-racer made a composite of. Each was adjusted to full scale and then measured from one end to a wire and from that same wire to another wire in the next photo, and finally to the other end in the next photo.

MPM

[talbany]

This is great talk about nailing it down.. I am also going to try and run the wires the same as well.. At least what I can make out.. This will no doubt take some time so Please be patient..I will keep an eye on this thread for more posts..Keep em coming



Tony VVT

[martin manning]

Here's my put at the rectifier and relay supply boards. My guess at the dimensions for both boards is 1.75 x 3.00.

MPM

PS: ic-racer, your bias supply filter cap is reversed in several of your schematics. (This is just nit-picking really, innit?)

[ic-racer]

Here's my put at the rectifier and relay supply boards. My guess at the dimensions for both boards is 1.75 x 3.00.

MPM

PS: ic-racer, your bias supply filter cap is reversed in several of your schematics. (This is just nit-picking really, innit?)

That freeware program only has that one type of capacitor, and I used it everywhere without regard to polarity. You are right, though, if I am showing a polarized icon I should have given it the correct orientation.

Excellent work on the dimensions!

[martin manning]

Looks like there were a few errors lingering in the FET portion of the #124 schematic. I suspect this had just been passed along, but looking at the pictures I see two 8K2 resistors.

I've been looking at the FET board as posted, the Ceriatone layout, your schematic, and the #0124 pictures.

I see the 8K2 source resistor in the pics, and note that Ceriatone has a 2K7 there. That's a pretty big difference... does Ceriatone use the same FET, and is it pretty certain that the original used an NTE452? The part number in the photo looks like it begins with "2N".

Also, I see that in your PC layout you haven't provided a trace to ground the case, and the real #0124 board maybe didn't either, given the position of the source resistor and the close spacing of the FET leads. Either way, what are the consequences?

The trimmer looks really big, too, maybe 0.5" square. It is marked 3386, which is 0.375" square. Maybe it's just the photo.

As an aside, what is the consensus on the FET pre-amp? My understanding is that this was intended to be a high-impedance input for acoustic pickups, but does it provide an advantage now? Many electric-acoustic instruments now have on-board pre-amps. What does it do when a conventional pickup is plugged in?

MPM

[ic-racer]

I looked at the FET board as posted, the Ceriatone layout, and the #0124 pictures. I see the 8K2 source resistor in the pics, and note that Ceriatone has a 2K7 there. That's a pretty big difference... does Ceriatone use the same FET, and is it pretty certain that the original used an NTE452?

I'm pretty sure Nik (who designed the Ceriatone) saw this FET schematic from Schematic Heaven. Note the comment on the bias resistor. I believe I asked Nik about it and he tried to bias it to be more useful with an electric guitar. Thus the 2k7 on the Ceriatone.

3 legs or 4 legs on the FET??

I know for sure the FET board on #40 has only 3 legs. I think the later amps all have 4-legged FETs but that is a guess because I honestly cannot see 4 legs on any picture I have. Every datasheet I have seen shows 4 legs also.

[martin manning]

Final update on the main board. I got to thinking that the original was probably laid out on graph paper, so taking the estimated overall dimensions as good I looked for some kind of fractional-inch pitch positioning of the eyelets. That seemed to help get things dialed in. I also moved the strain relief holes around to match the photos, and sized the large caps more or less correctly.

I'm calling this approximate scale now (as are all of the others I posted), since the overall dimensions are probably pretty close, and these are all probably good enough to use for drilling templates. The one exception is in the case of the trimmer pots, as I can't seem to find any specs for that large-size style of Bourns trimmer. (Anybody know what model number they are?)

MPM

Edit: small tweaks to trimmer size and shielded cable
Edit: OD input trimmer labeled 346K as measured (345.5K)

[ic-racer]

Nice!!!