AO-43 to Silver Jubilee

[dorrisant]

So I have this chassis and I need to build something with it, right? Why not a Silver Jubilee?

I stripped everything off the chassis for a good cleaning. Stripped all the way to the blank chassis.

I decided to one up Nik... I used the Ceriatone layout for the basis of my own layout. Maybe not as quick as he his though. I need the narrow layout for the confines of this chassis, so mine is narrow like Nik's but I incorporated the relay in the preamp board like the Marshall original. I used the schematic from the original 2550 with a few deviations: Added a resonance control and changed the presence control to the "non-scratchy" type but with a reverse audio taper pot. Please take a look and let me know if these look correct.

I will use separate switches for the channel switching and clipping instead of the push-pull pots. I added an LED for the clipping switch as well.

I'm using 6V6s along with a GZ34/5AR4. This will require changing the values of the filter caps. I'm thinking a 32/32 paralleled cap can for the reservoir, and moving the choke over to supply the screens. Does anyone know what kind of current this choke will handle? Enough to supply the screens and preamp? If it will work, I will move it closer to the associated filter caps. If not, I'll get another one and locate it there.

Has anyone run 6V6s in an AO-43? If so, what voltage was on the plates?

By the way, I can make these board sets on the CNC. If anyone is interested, PM me. More later...

EDIT 5-16-23: I added files for the board... a pdf can be used for 1:1. Let me know if there are any other file forms needed. I can probably export and post. I added the DIYLC file for this... couldn't post it as a .diy file so I zipped it.

EDIT 6-8-23: I built this one again and tried to correct the errors I found. The layout files have been updated. I have included the 2250 schematic... Follow this but deviate where the layout differs. As an example, the bias feed resistor dropping AC to the rectifier was actually was 47k as opposed to the 220k shown in the schematic. I've also added voltages using a 5Y3 rectifier.

[joeboo88]

Looks like fun one Tony
I believe Sluckey used a ao43 for his plexi6v6 project. His website should have the schematic with voltages to help you
Sluckeyamps.com
Good luck with the build!

[dorrisant]

I forgot about that one... I'll go look it up. Thanks!

[andresound]

Presently going to use same iron for a Tweedle Dee build, also 6v6

[dorrisant]

I had a chance to cut the new holes in the old chassis today. You can see the choke holes and octals are different. Also made new mount holes for the noval sockets. Opened up the cap-can holes as well. I'm gonna put a plate on the top of the amp along with faceplate and backplate to hide all of the ugliness. Board fits like a glove... I love having a CNC in the shop!

Pics make it look like the front and back panels have been bent... not so. Just an optical illusion.

[dorrisant]

Here's some pics with the new top plate I made today... I had to move the choke forward, away from the rectifier and power tube. Still may be too close though. We'll see.

[dorrisant]

I forgot to post the Hammond TX data I collected:

PT @ 120 vac
640 vac @ 130mA (320-0-320) = Tan - Yel/Red - Tan
6.3 vac @ 2.5A (3.6-0-3.6) = Org - Grn - Org
5.8 vac @ ?A = Yel - Yel

OT = 7k @ 8Ω

Choke = 12.07H, 477 DCΩ

[joeboo88]

Wow you don't screw around. that was fast work and looks good.
Love the top cover plate. Almost a shame to hide the chassis in a box?

[sluckey]

PT @ 120 vac
640 vac @ 130mA (320-0-320) = Tan - Yel/Red - Tan
6.3 vac @ 2.5A (3.6-0-3.6) = Org - Grn - Org
5.8 vac @ ?A = Yel - Yel

The 5V winding should be good for 3A since the amp used a 5U4. Where did you get these PT specs?

[dorrisant]

PT @ 120 vac
640 vac @ 130mA (320-0-320) = Tan - Yel/Red - Tan
6.3 vac @ 2.5A (3.6-0-3.6) = Org - Grn - Org
5.8 vac @ ?A = Yel - Yel

The 5V winding should be good for 3A since the amp used a 5U4. Where did you get these PT specs?

I can't find the link to that info, but I do remember reading it in a conversion thread. I wonder about the validity though... the L-100 service manual shows 160mA for the HT winding.

[sluckey]

I was just curious because I've repurposed several AO-43s. Never saw any transformer info other than what's on the service manual schematic. Good iron though. I really like it.

[andresound]

I am sure I saw somewhere, that the PT was 160ma and 315-0-315. Will look for it

[andresound]

Here you go from the service manual.

[dorrisant]

Here are a few updated pictures... Plates are finished. Wired everything under the main board. I'm waiting for another fuse holder for the HT and two more pots that I will swap out when they arrive. Order will drop tomorrow. More later.

I have no idea why the previews are upside down... They look fine when opened though.

[studiodunn]

Looks awesome! I love the etch and style of all the plates. I'm assuming you have Laser?