Installed the rest of the hardware on the back of the chassis.


Next thing I wanted to do was build a little turretboard for the diode rectifier, so I made a drilling template.


I then installed the turrets and soldered the diodes onto them. The bottom left and right turrets gets connected to the high voltage taps on the power transformer and the bottom centre turret is where the rectified voltage appears. You only actually need two diodes for this to work but I'm using two in series per side so that the voltage rating goes up to 2000V, this is just a safeguard for my transformer in case one of them decides to fail to a short.


...and installed the rectifier on the chassis. The socket below the board is for the valve rectifier.

I wired the rectifiers to the switch but I haven't soldered anything yet. The top right solder tab on the pic is where the bias supply is going to be tapped. I still need to install a resistor of some unknown size between that tab and the centre tab below it so that the bias supply voltage can be lower when the switch is set to valve rectification i.e. the centre tab and the top tab (as you see it) is connected to each other when the amp is set to solid state rectification and the bottom / centre tabs are connected when set to valve rectification. The centre tabs gets the high voltage supply. So when the valve rectifier is active, that supply still has a path to the bias supply through the resistor (its not there right now), when the solid state rectifier is active the resistor is short circuited.



Here's another angle.


Tomorrow I will add more things to the valve sockets (screen stoppers, plate resistors, bias resistors), wire the jacks, impedance switch, mains fuse, choke and output transformer then I'll start the turretboard. Once I've made sure the layout is fine and have actually MADE the turretboard (drill, install turrets) then the rest will go quite quickly. Its the pondering, planning and measuring over and over that takes so long.

Lots of people looking but nobody saying anything, I'll keep posting. Feel free to leave comments ?

I took some better pictures, because, you deserve it if you're still looking at this thread.

Out of curiosity, isn't that cap you mounted on the chassis inside perhaps a bit close to the transformer? Might induce some EMI noise or something? Dunno?

But it really looks good so far! Wonder why no turret board yet? Probably still drilling holes ?

Eujean wrote: Out of curiosity, isn't that cap you mounted on the chassis inside perhaps a bit close to the transformer? Might induce some EMI noise or something? Dunno?

But it really looks good so far! Wonder why no turret board yet? Probably still drilling holes ?

Who knows, it can't really go anywhere else so that'll have to do. I think it'll be ok because that cap is the filter cap for the screens on the power tubes and then an extra stage on the way to the preamp where it will get filterered some more. So 1. I'm hoping the signals are strong enough to overpower any noise I get here and not be audible and 2. I assume it'll be the same noise on both power tubes (common mode) and hence get cancelled out in the output transformer (this is one big advantage of push-pull amps). I'll bugfix if I have noise but I think it'll be ok. This is not a high gain amp so my lead-dress can be a bit shoddy, compared to things like Trainwreck Express or Soldano SLO et al.

Turretboard is the last thing I need to do and I'll start tomorrow. I've decided to only drill the necessary holes ?

Here's the schematic if anyone is interested:




Links to fullsize images:
http://www.drtube.com/schematics/marshall/1987u.gif
http://www.drtube.com/schematics/marshall/1986u.gif

Mine will be both, in a sense. One difference is that I'm not using 50µF caps throughout, mine will be 50/50, 32/32 and 32/32 instead.

It's looking sweet!

Don't think the cap near the transformer will be an issue. Mine is in a similar location and was installed there from the factory.

Finished a layout sketch. Just making sure I'm not going to stuff this up, only have one piece of brown phenolic.



I must also measure the standoff spacings, because my board is non-standard layout and non-standard size I need to drill new holes for the board's standoffs.

Checked the turretboard layout today, found a mistake. I'll check it once more before I take the drill out, tomorrow.

Layout with components


Drill Template


Soon...

I also want to see what communica has in the line of lugs I can attach to the can capacitor's legs, they don't have nice rings to solder to.

Here's some more progress photos. I think they're fairly self-explanatory ?

Eujean wrote: Is it just me or does it feel incomplete with only the required holes drilled ?

I'm sure the extra unused holes will play a super-important part in shaping the tone.....

I'm not going to risk it any further with the drilling, I only have a handheld drill so it is pretty tricky getting the holes to line up perfectly. The open holes are for the standoffs and the wires that connects the board to the rest of the amp ?

Lookin good!

This was a lot of work. Flyleads in place, needs soldering.

Completed board


Checking whether the newly drilled standoff holes are ok.


Flyleads


I think it's going to look pretty nice though

Looking good.

petercornell wrote: Looking good.

Thanks! I got distracted by real life things this weekend, so more will follow later and tomorrow.

I got as far as this today, maybe I can fire it up in the morning ?



The flyleads off the board are not soldered to the chassis yet, I'll do that in the morning, that's all thats still needed.

ez wrote: I got as far as this today, maybe I can fire it up in the morning ?



The flyleads off the board are not soldered to the chassis yet, I'll do that in the morning, that's all thats still needed.

Looking super neat, nice work ez!

Fingers crossed for the play testing ?

V8 wrote: Looking super neat, nice work ez!

Fingers crossed for the play testing ?

Thanks a lot ?

Many events today though, Star Wars and dogwalks and dinners (with booze, no ampy ampy) so it looks unlikely that today will be both Star Wars and 68 Plexi day ? Maybe, would be nice.