Tweed/BF Princeton

[sgbrewing]

Hey, hope all is well!

I'm planning a build that started out as a 5f2a but now with a BF tonestack and NF.

This will be mostly used at home as a pedal platform for Kingsley pedals to get a good sound at low volume at home. I decided to use power scaling on the power amp only to be able to get the amp working a bit while clean and not just cracked on with the volume control. I also decided against the VVR/Mosfet type power scaling as I dont want to worry about failing Mosfets.

I have had a custom power transformer made from http://www.transformerequipment.co.uk/ for £113 delivered, If you are in the UK and need a custom spec transformer, I would definitely recommend them!

The transformer has 2 secondaries:
250 - 110 - 55 - 25 - 0 at 75mA
250 - 0 at 75mA

This should yield me: 5, 1, 0.25 & 0.05W

The multiple powered secondary will be switched by a rotary switch and feeding a bridge rectifier and then the power section. The seperate 250v will feed into a seperate bridge rectifier and then the pre amp.
As there isn't sag with a SE amp, I've used a large reservoir cap for reduced hum and bass response, using 30uF for the rest for bass handling also.

Have a raw princeton cab on the way that I shall be covering with the cool paisley fabric :D

I've done some tests and using Titebond works well to glue the fabric to wood with no seeping through the fabric. I did try using a satin poly varnish over it, but it darkened the fabric way too much and made it look pretty smudged. I then tried using multiple coats of shellac (1:4 cut) and that worked really well, didnt darken it too much but sealed off the fabric and firmed it up, so will be using that on the cab!

For tubes I have some mil spec brimar 6v6 and 12ax7

And for the speaker I shall be using a Celestion G10 Greenback, probably not the most popular choice for this type of amp, but I just love the greenback speaker! I have broken it in using a 15hz signal for 24 hours.

I shall be updating my progress and parts come in and the build progresses 😁

If someone could check over my layout for stupid mistakes, I would greatly appreciate it! 😊

Cheers! 🍻

[sluckey]

A schematic would be very helpful for verifying your layout.

[Latole]

Yes schematic is a must.

[sgbrewing]

I shall draw one up over the next few days.

I did forgot to include the ground on the V1a cathode after the fat switch on the layout, I shall alter that!

[Latole]

It is better to start with a schematic before a layout.

[sgbrewing]

It’s just a blackface champ schematic, just with power switching and tweed transformers so I didn’t think it was worth it 

[sgbrewing]

It’s essentially this:

https://el34world.com/charts/Schematics/files/Fender/Fender_champ_aa764_schematic.pdf

[PRR]

It’s just a blackface champ schematic, just with power switching and tweed transformers so I didn’t think it was worth it 

Well, surely not the rectifiers! And maybe I need another 11 hours sleep but they don't look right on your pictorial. Don't diode-stripes go to cap-pluses?

Minor point:
> 250 - 110 - 55 - 25 - 0 at 75mA
> 250 - 0 at 75mA
You didn't need that second winding (which did not need to be 75mA, but maybe that's the least they would spec). But it's all bought and paid for now.

[sgbrewing]

It’s just a blackface champ schematic, just with power switching and tweed transformers so I didn’t think it was worth it 

Well, surely not the rectifiers! And maybe I need another 11 hours sleep but they don't look right on your pictorial. Don't diode-stripes go to cap-pluses?

Minor point:
> 250 - 110 - 55 - 25 - 0 at 75mA
> 250 - 0 at 75mA
You didn't need that second winding (which did not need to be 75mA, but maybe that's the least they would spec). But it's all bought and paid for now.

Well spotted  thanks!

Yea obviously not the power switching but the rest is pretty much dead on minus a few component values.

I was advised by the transformer manufacturer that it would be better having a seperate 250v winding for the pre amp as switching on a lower winding would drop the 250v down.