18 Watt TMB Build

[professormudd]

Greetings,

After having put together a few Fenders and a few Dumbles, I thought it was time to try something British. After checking out some videos and letting my ears lead the way, I have decided to start with a build that follows the Mojotone 18 Watt TMB schematic. I will not be purchasing a kit, however. I prefer to sleuth for parts on my own.

So far I have ordered chassis, transformers (Hammond PT 290PAZ and OT 1750PA), capacitors, and potentiometers. The rest, I believe, I already have on hand.

I am very much looking forward to this build. I will be using this thread as my build log.

Initial question:

• Is shielded cable advised for the input jacks? Anywhere else?

[alkuz1961]

Initial question:

• Is shielded cable advised for the input jacks? Anywhere else?

I built this amplifier once, and I did not use a shielded cable anywhere. There have never been any problems with noise.

[ViperDoc]

If you haven’t already, check out www.18watt.com for some great resources on 18 watt British builds.

[professormudd]

I built this amplifier once, and I did not use a shielded cable anywhere. There have never been any problems with noise.

Thanks! I prefer to avoid working with shielded cable primarily because it is a giant pain in the ass.

If you haven’t already, check out www.18watt.com for some great resources on 18 watt British builds.

Thanks, will do.

[professormudd]

Welp, hit my first mishap.... I cracked the faceplate

Oh well, onward and upward. I got the passive components soldered to the board. I still need to hit the hardware store for some M3 screws so I can mount the tube sockets, cap clamps, and power inlet. Once they're mounted I'll get to wiring. Good times.

[dgrainger]

Would a drop of thin superglue wick in and fuse that back together, or just cause a mess?

[Colossal]

Would a drop of thin superglue wick in and fuse that back together, or just cause a mess?

The solvent will likely cause the acrylic to craze (getting worse), and it will attack the gold paint on the back

[professormudd]

Would a drop of thin superglue wick in and fuse that back together, or just cause a mess?

I don't know, but I doubt it will help. I think the best thing for me to do is leave it alone. I might one day buy another faceplate, but until then, this one will be scarred. I will come up with a good story about flying beer bottles or something to tell the grandchildren if they ever ask.

[alkuz1961]

In cell phone repair shops there are special liquid adhesives for masking cracks. There are also similar sealant for repairing cars windows.
I myself have seen some of these methods in action, and the result is really impressive. But I think that in reality, not everything is as simple as shown in the clip.

[professormudd]

In cell phone repair shops there are special liquid adhesives for masking cracks. There are also similar sealant for repairing cars windows.
I myself have seen some of these methods in action, and the result is really impressive. But I think that in reality, not everything is as simple as shown in the clip.

I had a car windshield repaired with epoxy once. It was a pretty impressive result. Like Colossus said up there, though, I worry about the plexiglass/acrylic reacting with the chemical(s) in a way that causes more damage. I might look more into it later on.

[wpaulvogel]

I’m not sure about the TMB circuit in the 18 watt Marshall but I prefer the standard tremolo version myself. Blending the two channels creates lots of funky phases in the tones. The EL84’s are really easy to overdrive in the tremolo amps. I can only imagine how much overdrive can be had with the TMB circuit. I have one with 4 EL84 output tubes also. It makes 30 watts.

[professormudd]

I believe I've completed wiring this thing. I'll give it a thorough inspection prior to powering up for the first time.

[professormudd]

I’m not sure about the TMB circuit in the 18 watt Marshall but I prefer the standard tremolo version myself. Blending the two channels creates lots of funky phases in the tones. The EL84’s are really easy to overdrive in the tremolo amps. I can only imagine how much overdrive can be had with the TMB circuit. I have one with 4 EL84 output tubes also. It makes 30 watts.

The video demos I've seen on YouTube of this circuit sounded nice, but who knows how this one really sounds until I fire it up. Hopefully I don't run into the phasing issues you mentioned.

[professormudd]

My initial power on went smooth. The clean channel works as expected. The volume and tone both do what their labels say they do. The TMB channel may need some closer evaluation. I did not get to spend too much time turning knobs, but I am getting noise while sweeping the volume/gain and the master pots and the overdrive starts to get "fizzy" or "sizzle" (something with z's) a bit when I crank the gain passed 2 o'clock or so. The scratchiness sounds a bit more like voltage than debris. Does anyone have any thoughts on these symptoms?

Minor inconveniences aside, man this amp is loud.

[professormudd]

Okay, so when I turn up the gain or the master it starts to oscillate once it gets to about 7-8. It does this even without an instrument plugged into the front. I am suspecting a lead dress issue and will proceed with chopsticking.