18Watt.com

Some more progress today. I wire prepped and connected the pots, and PCB.

Looks real awesome... I'm jealous

Bieworm wrote: ↑

Mon 02/15/21 4:49 pm

Looks real awesome... I'm jealous

Thanks!

I will be selling the boards after this is built/tested. You can get one if you don't think 2 Trem TMBs is enough. lol

Then again, this build is 36W EL34, and I don't think you have one of those.

Very tempting...

Nice. Very professional!

Josh, dude... one of these days you can line up with the famous boutique builders. Switching to rugged PCB boards and all.. bogner style amp building. You might think otherwise but I really like the build quality of them bogners

I designed a PCB to simplify the (already pretty simple) footswitch I built. This will be stupid simple, mount the parts, and drill a few holes in a box. I'll probably have them in 2 or 3 weeks.

I'd like to applaud you for the pcb-turret post combo. One of my frustrations with a number of the folks selling amp pcb's to DIY'ers right now is that they make it pure pcb. There are some connections that are just more efficient to do (and modify) with turrets.

turtle441 wrote: ↑

Tue 02/16/21 9:50 am

I'd like to applaud you for the pcb-turret post combo. One of my frustrations with a number of the folks selling amp pcb's to DIY'ers right now is that they make it pure pcb. There are some connections that are just more efficient to do (and modify) with turrets.

Thanks! I agree, there's a LOT of mistakes on the PCB designs for guitar amps out there (plenty of issues with some of the turret/eyelet boards out there too). You may notice that I made the use of turrets optional, so people can go either way. Another important factor is to leave the tube sockets separate to avoid any unneeded stress on the PCB.

After I finish this build and test it all out, I'll be making the boards available for sale to anybody interested.

Thanks,
Josh

That looks great!

A little more progress...

More wire prep: Sockets wired up:
Thanks,
Josh

Rear jacks and shielded connections are in: Here's a close up of how I do the rear jacks:

You probably noticed my FX loop isn't connected. I do that last after the amp is tested and verified. I don't want to disconnect the FX loop while troubleshooting if there's noise or oscillations, so I wait to connect it when that's all sorted. Then if there's an issue after installing the FX loop, I've likely narrowed down the source.

When I have more time, I'll start by highlighter verifying the build, then power up and test it out.

Thanks,
Josh

Nice job man!!
Can't wait to hear the demo (s)

Did you put a .022µF cap in the first fase shift position of the tremolo? It's bigger in physical size...

Btw, I found out that putting a 12at7 in the PI the volume is substantially less compared to a 12ax7. Sounds equally great, but makes it a little better suited for bedroom level playing. Thought I'd share it...

Bieworm wrote: ↑

Fri 02/19/21 12:50 pm

Nice job man!!
Can't wait to hear the demo (s)

Did you put a .022µF cap in the first fase shift position of the tremolo? It's bigger in physical size...

Btw, I found out that putting a 12at7 in the PI the volume is substantially less compared to a 12ax7. Sounds equally great, but makes it a little better suited for bedroom level playing. Thought I'd share it...

Thanks!

Yes, I decided to try out the .022µF cap there. It's also possible that the next version of this PCB will make the capacitance there switchable by adding a second .01µF in parallel. And by possible, I mean already designed and ordered.

Do you have an attenuator? If so, do this test if you want: record a few demos- 1. with the 12AT7 cranking the power tube distortion; 2. with the same and an attenuator; 3 with a 12AX7 and attenuator; and 4. a 12AX7 and no attenuator.

That will give you a better idea of how the tones compare. Of course if it sounds good to you, it's good anyway. So you could skip all that if you're not curious.

That was the logic next step .. switchable cap

About the AT vs AX .. ofcourse the AX sounds way better, but to tame it you "could" deal with the compromise.. only at home. Maybe add an extra PI tube and make that switchable

Bieworm wrote: ↑

Fri 02/19/21 12:50 pm

Btw, I found out that putting a 12at7 in the PI the volume is substantially less compared to a 12ax7.

That surprises me. According to the math (simulator), the difference in this application is only about 2.5 dB. Are you using the "standard" Marshall PI circuit?

Jack

TriodeLuvr wrote: ↑

Fri 02/19/21 5:22 pm

Bieworm wrote: ↑

Fri 02/19/21 12:50 pm

Btw, I found out that putting a 12at7 in the PI the volume is substantially less compared to a 12ax7.

That surprises me. According to the math (simulator), the difference in this application is only about 2.5 dB. Are you using the "standard" Marshall PI circuit?

Jack

Yes standard PI.. but only playing on lowish volume it's pretty noticable.

The gain of a LTP is equal to the gain of a single gain stage for a given tube. The mu of a 12AX7 is 100 and the mu of a 12AT7 is 60. So that's why the 12AT7 LTP is lower volume.

Here is a soundclip of my tremolo TMB reverb on full blast. Volume and gain on 10. Incredible how it cleans up on the guitar volume pot!!!

https://www.dropbox.com/s/23h9ol4lwyy9r ... t.m4a?dl=0


And here is my rockin'bird .. same deal, but creamier.. the tremolo TMB is nastier and superior to my taste.

https://www.dropbox.com/s/4ztce46vyo1e8 ... t.m4a?dl=0

After highlighter testing, I tested the voltages, and everything looks great, except my B+ is slightly low because I used a 3.3K instead of a 2.2K. I'll swap that out when I get some more 2.2Ks in stock (or find the ones I swear I ordered ). I also need to up the wattage on the cathode bias resistor, that thing is fairly hot. After I do that, I'll do some more testing, and then add the FX loop.

BTW- I'm slightly surprised nobody noticed that I didn't solder the ground wire on the intensity pot. Good thing I check connections during highlighter testing.