AX84 Moonlight Amp Build Project

[Marcel]

Yep... certainly is useful.... One part that I had to temporarily substitute is available on the Evacto site... I'll peruse the rest of the site before I put an order in just in case I find something else I need/desire....

[DrNomis_44]

I think what I will do for this amp build is order a chassis and cover from Evatco to build the amp on, instead of going with my original plan of using a diecast aluminium box bought from Jaycar, Evatco stock some really nice tagboards that I could use to build the amp circuitry on, also, I've figured out that if I add one 12AX7 valve to the valve line-up, I will be able to create something like a 1 channel Marshall Plexi preamp, and still keep the EF86 valve, should be a pretty gainy amp once it's finished.


These are the tagboards/tagstrips I'm thinking of going with:

https://www.evatco.com.au/tag-strip-28-x-2


I'll see if I can create a hand-drawn schematic of the Moonlight amp with the "Plexi" mods to the stock preamp circuit tomorrow, so stay tuned.

[Marcel]

Those tagstrips look very similar to what I used in my AC15 build.

I could get up to 3 leads into the holes on each side of each lug/tag which made things a lot easier on real estate consumption... 6 component wires per tag and then the huge hole in the middle for big multistranded cables from underneath came in very handy ...

My only concern was voltage rating between lugs wasn't specified by my supplier, so I ended up leaving lugs vacant when next to any lug with any sort of anode voltage or higher HT on it... Low voltage lugs like cathodes or decoupled tone components I felt were fine when next to earth lugs.

[DrNomis_44]

Those tagstrips look very similar to what I used in my AC15 build.

I could get up to 3 leads into the holes on each side of each lug/tag which made things a lot easier on real estate consumption... 6 component wires per tag and then the huge hole in the middle for big multistranded cables from underneath came in very handy ...

My only concern was voltage rating between lugs wasn't specified by my supplier, so I ended up leaving lugs vacant when next to any lug with any sort of anode voltage or higher HT on it... Low voltage lugs like cathodes or decoupled tone components I felt were fine when next to earth lugs.

Yep, that would be a concern, you definitely don't want the voltage between two adjacent tags to end up exceeding the dielectric-strength of the insulating material and causing a leak, especially if one tag happens to be the one with the negative grid-bias supply for one of the power valves, I'm not sure what the dielectric-strength of Phenolic is, I think it's something like 300V DC or so per so many milimeters, or I could be wrong, on the other hand FR4 Fibreglass will definitely have a higher dielectric-strength.

From looking at the pic of the tagstrips from Evatco, it looks like they're made using FR4 Fibreglass.

Edit (04/05/2023):

Seeing as I just recently ordered a set of 10 of these 28 X 2 tagboards from Evatco, I can confirm that they do indeed use 1.5mm thick (roughly) FR4 Fiberglass as the insulating material, the tags themselves looked to be tin-plated and fastened to the insulating material via brass eyelets with an inside diameter of about 3 or 4mm, this is actually a good and useful thing since brass is solderable so you could use the brass eyelets as well as the tags for mounting components and wires, this gives you more layout options.

[artyone]

One of my first tube amps was the Moonlight, it seemed fair as Simcha Delft (the original designer) had first printed the DIY thing in our NZ musician magazine. I even got one of Simcha's output trannies that he winds himself as he lives here in NZ so why not. I haven't fired it up for years but when I do it's through a cab with 4 x 12's which are alnico magnets, paper cones with a few ribs... found a guy in Christchurch in the South Island had a whole bunch of NOS stuff like this. The only thing I changed was using a valve rectifier and a choke as the old radio power transformer I used had the wrong voltage but by using the voltage drop in the rectifier and the choke I got into the ballpark required.

If this is still a goer, Marcel, I can get Simchas email, and you might even be able to get a output tranny from him.

[DrNomis_44]

The first time I tried building a Moonlight amp I had a go at winding my own output transformer, using the laminations and bobbin from an Audio Transformer that was intended for use in 100V PA speaker line applications, winding each layer of the primary winding and separating them with plastic adhesive tape was the most time-consuming part of it, if I remember things right, the primary winding from the centre-tap to each end measured about 27 ohms on my Digital Multimeter, I wasn't sure if it would actually work, but I tried it anyway, and it actually worked first go, I was surprised at how loud my Moonlight amp was, when I overdrove the amp to get the 6SN7 tube to distort, the sound was really smooth.

I don't remember how many turns there were that made up the primary winding, my memory's a bit rusty.

[DrNomis_44]

Update:


Seeing as I'm really in the mood for doing some diy amp builds this year, I thought I would pop-by the AX84 website and gather together as much info as possible on the AX84 Moonlight amp, this will be a real fun build for this year, well, at least it'll give me something "constructive" to do anyway, so yes, this build is scheduled for this year.



And, as luck would have it, I managed to scrounge a spare EF86, 12AX7, and 6SN7GT that I can use in my AX84 Moonlight build, next fortnight I'm going to pop-by my local Jaycar Electronics store and buy a diecast aluminium box I can use as a chassis for my build, and maybe some other bits and pieces that I'll need, will also order some other bits from Evatco too.