Build Journal: My First Wide Panel Tweed Amp

[gabasa]

I'm just about to start building three amps and figured I'd document some of the process here. This will be my first 3x10 Bandmaster build, a narrow-panel 5E7. Also, I'm pretty excited to do my first wide-panel amp. It's going to be a 2x10 Super with a 5E4 circuit, because the goal for this one is to be a bigger 5E3.

I'm also working on a wide-panel octal Pro, a 5C5 circuit with 6SC7 preamp tubes, so there should be some cool photos to share. I think that Julian Lage used a 5C5 to record Nocturne, so that's pretty cool.

I just ordered all of my transformers from Soursound. I was really close to ordering a 2.67r OT for the Bandmaster to match the speaker load, but last minute I changed it to 4 Ohm because it's probably crucial to keeping the sound as authentic to the original as possible.

This should be a fun ride, wish me luck.

 

[screefer]

All luck!

I'm signed up for the 5C5.
This scheme?

 

[Uffepungen]

I can't wait to follow this along! The narrow panels we all know and love of course, but wide panels and TV panels are just a tad cooler, and you hardly ever see them.

Good choice!

 

[gabasa]

All luck!

I'm signed up for the 5C5.
This scheme?
View attachment 1110745

Yes, exactly that one, grid-leak and all!

 

[Timbresmith1]

Yes, exactly that one, grid-leak and all!

That one looks easy enough that even I could manage it

 

[gabasa]

I can't wait to follow this along! The narrow panels we all know and love of course, but wide panels and TV panels are just a tad cooler, and you hardly ever see them.

Good choice!

Thanks, the more I look at the old wide-panel amps, the more excited I get! They're beautiful, I love how the brown grill cloth is flush with the front face of the cabinet in wide panel amps; something I haven't paid much attention to before.

 

[gabasa]

That one looks easy enough that even I could manage it

There's hardly anything in this one, the paper is almost empty!

 

[2L man]

I was really close to ordering a 2.67r OT for the Bandmaster to match the speaker load, but last minute I changed it to 4 Ohm because it's probably crucial to keeping the sound as authentic to the original as possible.

Obviously this is what is called mismatch when Bandmaster is spoken. So would it be 6k for 4 ohm speaker and now using three 8 ohm parallel as 2,7 ohm the OT function comes 4,5k?

 

[gabasa]

Obviously this is what is called mismatch when Bandmaster is spoken. So would it be 6k for 4 ohm speaker and now using three 8 ohm parallel as 2,7 ohm the OT function comes 4,5k?

Yes, the reflected primary becomes 4k in this case.

 

[polloelastico]

Wide panels are a nice change. My last 5E3 and 54F were both wide panel cabinets. One from Armadillo and one from Guitar Cabinets Direct; both well made cabinets.

 

[gabasa]

I've been looking at the circuits and comparing them to vintage chassis pics online, because I'm trying to find if there are any component values in the schematics that are different that what Fender actually used in their amps.

Offhand, would anyone know if there are any inaccuracies in the 5E7 schematic? Knowing that the original 5F6A tweed Bassman schematics were different than Fender's real vintage 5F6A amps in a few places makes me want to double check this before I make a parts list. Anything like this in the 5E7?

I noticed that Fender's reissue 57 Bandmaster schematic is not exactly accurate to the originals, so I'm keeping away from that one and using the original drawing.

 

[gabasa]

Caught one! Regarding the 10M feedback resistor around V2 in the 5E7 schematic, in any pic I can find of an original 5E7 chassis, it looks like Fender used 4.7M.

 

[NTC]

Caught one! Regarding the 10M feedback resistor around V2 in the 5E7 schematic, in any pic I can find of an original 5E7 chassis, it looks like Fender used 4.7M.

This was always a bit puzzling - why would ONE resistor value be different on a chassis that is otherwise the same as the Pro and Super? Plugging in a different tube for V2 - that is simple.

On the other hand, bigger resistor = less feedback = more gain. They must have made SOME that way.

 

[gabasa]

This was always a bit puzzling - why would ONE resistor value be different on a chassis that is otherwise the same as the Pro and Super? Plugging in a different tube for V2 - that is simple.

On the other hand, bigger resistor = less feedback = more gain. They must have made SOME that way.

The OT into the 2.67r 3x10 load would make for a bolder, cleaner sounding amp then the Pro/Super. That's what Bryan Sours told me recently. I'm not sure, but if "bolder and cleaner" was Leo's design intent for the 5E7, then maybe a bit more NFB would push the amp a hair more in that direction? Fwiw, I've seen photos of tweed Pros that also used 4.7M, so I have no idea really.

 

[gabasa]

Here's my first pic ... the next ones will probably be when the transformers arrive. I got my hands on 8 6SC7 tubes that are apparently NOS/NIB. All I need is three to work, so I'm keeping my fingers crossed. Check out the chassis I'm using for the 5C5 build, it's sized properly and punched for octals! I found three of them online, but just using two as the 5E7 uses a different one.

 

[gabasa]

I'm considering buying some Garolite sheets and making the eyelet and backing boards out of them. 12"x12"x0.0625" sheets are large enough to make eyelet and backing boards for two amps, and they cost $14.33 per sheet at Grainger.

https://www.grainger.com/category/raw-materials/plastics/plastic-sheets-bars/garolite-lightweight-high-strength-sheets-bars?attrs=Material%7CGarolite+G-10%2FFR4&filters=attrs

 

[mountainhick]

I'm considering buying some Garolite sheets and making the eyelet and backing boards out of them. 12"x12"x0.0625" sheets are large enough to make eyelet and backing boards for two amps, and they cost $14.33 per sheet at Grainger.

https://www.grainger.com/category/raw-materials/plastics/plastic-sheets-bars/garolite-lightweight-high-strength-sheets-bars?attrs=Material%7CGarolite+G-10%2FFR4&filters=attrs

How is garolite different from https://www.tubesandmore.com/products/turret-board-blank-no-holes-black-g-10-11-78-x-7-116

 

[gabasa]

How is garolite different from https://www.tubesandmore.com/products/turret-board-blank-no-holes-black-g-10-11-78-x-7-116

That material is also Garolite, I think, because it's G-10. At industrial suppliers, you get to pick the thickness, and there are options for size as well as colour.

The options in your link are for 2mm and 3mm thicknesses, but I'm going to use 0.062", which is closer to 1.5mm, because that's more typically the thickness of eyelet boards.

I just noticed that McMaster Carr has a good selection:

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[Esquier]

When I use G10 I use standoffs so there's no point in wasting another piece of it for an insulator. If I was using the fibreboard that's also known as "fishpaper", I'll use a blank piece for an insulator cos it's sandwiched together and it's supposed to be wavy...