New 1987 Build Marshalling Forward.

[Lummox]

My first Marshall style build, but I'm sure not my last.

[IMG:384:576]http://i.imgur.com/ddX7S2J.png[/img]

[IMG:384:576]http://i.imgur.com/ceZPG5L.png[/img]

[IMG:576:384]http://i.imgur.com/usvguQk.png[/img]

Now I'm trying to decide between Lar/Mar and Rich for the MV circuit. I've read a bunch of threads on both of them, and they both seem pretty usable.
Anyone have strong feelings either way ?

[trane34]

None of the above? I like a clean and loud plexi though. Maybe let it break in and see what you have. That way you can tell what the master does when you install it.

[Lummox]

Yeah, I'm gonna play it straight for a while, at least until it gets broken in. I love a clean (ish) plexi too. Unfortunately, I rarely get gigs where I can let 'er rip these days.

[dariez75]

I've built JTM45 with both PPIMV and after all I've decided to hold installed Lar/Mar

[dariez75]

Please post some audio clip

[Colossal]

Good job Lummox. Always nice to see another Marshall roar to life.

[Lummox]

Hmm, not quite roaring to life just yet... Getting some weird readings on the meter, and the output is weak and distorted.

Here are the readings I'm getting.

V1 P1 = 163 P2 = xxxx P3 = 0.95 P4 = 3.14 P5 = 3.14 P6 = 214 P7 =xxxx P8 = 1.8 P9 = 3.14

V2 P1 = 175 P2 = xxxx P3 = 0.99 P4 = 3.14 P5 = 3.14 P6 = 299 P7 = 176 P8 = 177 P9 = 3.14

V3 P1 = 345 P2 = xxxx P3 = 5.0 P4 = 3.17 P5 = 3.17 P6 = 345 P7 = xxxx P8 = 5.0 P9 = 3.17

V4 P1 = Grd P3 = 3.17 P3 = 438 P4 = 433 P5 = - 40 P6 = 438 P7 = 3.17 P8 = Grd

V5 P1 = Grd P3 = 3.17 P3 = 438 P4 = 433 P5 = - 40 P6 = 437 P7 = 3.17 P8 = Grd




Rectifier = AC 330 (+) 439 AC330

I'm going to go over the phase inverter circuit, but what are some other things to look for ?

[maxwedge]

V3 isn't right. Did you use a 470k when it should be a 470 ohm resistor? I did that once and had the same symptoms that you have.
The v3 plate voltages should be a lot lower and the cathode voltages higher.

[Lummox]

V3 isn't right. Did you use a 470k when it should be a 470 ohm resistor? I did that once and had the same symptoms that you have.
The v3 plate voltages should be a lot lower and the cathode voltages higher.

Guilty as charged. You can see it plain as day in my 3rd picture. Once I corrected that, everything settled down nicely. Now I'm just trying to eradicate a bit of hum, but it sounds glorious,otherwise.

[maxwedge]

I can't see the colors well enough in the pictures. Too small for me!
Watch your grid wires and keep them away, as possible, from the heater and plate wires. Especially v2a

[julian1107]

Hi!
Did you twisted you heater wires? (I can't really see that in the photos)
I mean, something like this: [img:900:675]http://www.charlestonarea.com/octane/2- ... eaters.jpg[/img]
What layout did you use? Check if you have a good grounding scheme.

If you could upload some bigger and clearer photos of your build it would be awesome and it would be easier for everyone else to help you.

Ps: Sorry for my poor level of english, it's not my first language

[Joe Popp]

I recently knocked out my hum by going with the "Larry" grounding scheme. It took a while to so it but I have the quietest amp I've even built!

Congrats on your build!

[Lummox]

I did twist the heater wires, but maybe not so nicely as Julian's. I was using the stock grounding scheme, with the buss running along the pots, and it was quite noisy. I snipped the buss wire, separating the presence control, and desoldered the lead from the cap on the back of the pot, and ran the ground from the presence pot to F1, and it made a world of difference.
It's amazingly quiet now.I played it for about an hour last night, and it sounded amazing, until the first power tube started redplating... Looks like I'm going back over everything.

[julian1107]

Joe, could you post the link to Larry's gound scheme so I can take a look? Thanks

Lummox, post some pictures of how you solved the grounding/hum issue.

The photo I posted earlier wasn't mine, it was just an example I took from this post: http://www.diyaudio.com/forums/tubes-va ... -ugly.html there's a lot of info on how to wire the filaments.



Julián T. Schönfeld

[Lummox]

Here's a shot of my filaments. On my next build, I'll try twisting them right to the sockets.
[IMG:960:720]http://i.imgur.com/S9eqfeU.jpg[/img]

This is the back of the presence pot, you can see where I cut the buss wire, and lifted the cap leads off the back of the pot. The ground wire(blue) connects to the first filter cap ground.
[IMG:960:720]http://i.imgur.com/utH7KOS.jpg[/img]

Sorry for the crappy pics, these were taken with my phone.