2nd Gen Build Started (that didn’t take long…)

[Raoul Duke]

Been working on the cab over the past couple of days and should have it done tomorrow - then I’ll throw up a pic. The pig suede definitely handles differently than tolex - but I’m happy with the results. Just need to finish the aluminum trim.

I was looking over the data sheet for my Hammond 290EX to get familiar with it and saw that it has the heater CT and and internal ground. I was especially concerned about the internal ground when I replaced the studs - using spare screws to push the old one out and new one in; effectively end to end to ensure the lug stayed on the stud. It was pretty obvious where the ground was because three stud/screws had plastic bushings and one had internal tooth washers. Anyhoo, on to my question:

I was planning on using the artificial center tap for the heaters and wrapping the HCT and isolating it, but have read that with internal grounded PTs - I ought to ground it at the HV/filter ground. Some posts have also indicated that using the heater CT is preferable to the ACT. My question is: which pieces of info are correct for this build? There must be a rule of thumb on this?

Thanks!

[sluckey]

Why are you replacing the transformer bolts?

I was planning on using the artificial center tap for the heaters and wrapping the HCT and isolating it, but have read that with internal grounded PTs...

That internal ground (gray wire) is simply a shield. It has nothing to do with heater CT. Just connect the gray wire to chassis and proceed with your artificial center tap for heaters as planned.

https://www.hammfg.com/files/parts/pdf/ ... 1697661948

[Raoul Duke]

Thanks for the advice!
I replaced the bolts because they protruded about an inch above the chassis and prevented me from using the 12v regulated 2nd gen board as well as being really close to the caps and leads on that board. I thought about cutting them down, but this solution seemed quicker and neater - and bought me the clearance I needed. Kind of an oddball situation I imagine - but I tried to cover every base when doing it.

The gray wire doesn’t actually have a lead that runs outside the transformer. Based on what I can tell, it makes its connection to chassis through the bolt that has the tooth washers (I think?).

So clip/wrap/isolate the heater CT then?

Thanks again!

[martin manning]

That Hammond data sheet is a bit inconsistent. It shows a gray lead in the schematic but not in the illustration. Most transformers now have nylon insulators on both ends of the bolts to avoid making a closed circuit. It could be that the shield ground is now made by way of that star washer.

[Raoul Duke]

Ok, cab is done - back to the part I don’t know squat about, lol:
Mock up to check fit:

IMG_0194.jpeg

Final (on top of 102):

IMG_0195.jpeg

On to finishing up the power section and hopefully testing that soon.

[martin manning]

Looks fantastic! Big space on the right side begging for a logo badge of some kind, Like Dr. Gonzo, or Gonzo Overdrive.

[erwin_ve]

Ok, cab is done - back to the part I don’t know squat about, lol:
Mock up to check fit:
IMG_0194.jpeg
Final (on top of 102):
IMG_0195.jpeg

On to finishing up the power section and hopefully testing that soon.

Stunning looks!

[Raoul Duke]

Ha! I like it Martin! Thank you for the compliment!

Just sitting here looking at my speaker stash and trying to decide which I’ll try first: an EV-12L or an Altec 417 that I forgot I have. Any suggestions?

Tried both of them with 102 the other day and they really brought out the brightness. Also tried an old Celestion Creamback 12-65, which was better - but the WGS ET65 actually sounds the best with that circuit (or at least my version of it).

So much to figure out, lol…

[Raoul Duke]

Ok, cab is done - back to the part I don’t know squat about, lol:
Mock up to check fit:
IMG_0194.jpeg
Final (on top of 102):
IMG_0195.jpeg

On to finishing up the power section and hopefully testing that soon.

Stunning looks!

Thank you Erwin, your chassis looks right at home there!
I hope I can make it sound good when the time comes.

[ijedouglas]

Ha! I like it Martin! Thank you for the compliment!

Just sitting here looking at my speaker stash and trying to decide which I’ll try first: an EV-12L or an Altec 417 that I forgot I have. Any suggestions?

Tried both of them with 102 the other day and they really brought out the brightness. Also tried an old Celestion Creamback 12-65, which was better - but the WGS ET65 actually sounds the best with that circuit (or at least my version of it).

So much to figure out, lol…

My vote is the 12L. The 12S is also a great sounding speaker with these type of amps

[Raoul Duke]

Thanks Ian, I’ve been keeping an eye out for one on your advice

I have these two here already so I figured I’d start with those - but if a decent 12S shows up - I’m on it for sure.

[ijedouglas]

Thanks Ian, I’ve been keeping an eye out for one on your advice

I have these two here already so I figured I’d start with those - but if a decent 12S shows up - I’m on it for sure.

I think you will be very happy with the 12L. Each to his own but I think the EVs are so transparent, they really let the amp shine.

[Raoul Duke]

Quick question:

Looking at the layout, it looks like B+3, 4, 5 are grounded with the HV and B+1 is grounded at the power tubes. Should I follow that or use the grounding points from the 4th gen? I looked at the schematic and it doesn’t seem to indicate where - just shows “ground”. I imagine there’s a best practice for this but wasn’t sure if one ground scheme works better than the other for this build.

Thanks in advance!

[martin manning]

I seems to work fine either way, but I would ground the PI filter with the screen filter, and both preamp filters at the input on principle.

[Raoul Duke]

That sounds like 4th gen to me
The “funny” thing is that I’ve read about keeping the nodes’ grounds separate (either Merlin or Aiken; or both) - but because HAD is HAD - I second guess these principles just because I wonder if he created a circuit that might be the exception to the rule. That’s when I start asking, lol.

Thanks Martin!