First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

[zaphod_phil]

Another thing I'd recommend separating is that bundle of wires shown in the middle of the picture you posted. They will all radiate into each other like that. You should replace them with solid core wire that you can bend tidily to shape, and run separate lengths between the points you need to connect. Shielded wire is instead recommended for any longer stretches, with the braid connected to the ground buss at one end only.

[Yamariv]

Good point, that bundle of wires is for the master volume. As soon as I finish the 5E3 build in a couple of days, I'm going to bring the 18 Watt to the bench to mod a few things and redo a few others.

I'm going to redo the entire heater wire (not looking forward to that ) and I'm going to move the master to the front of the amp. That will be a win win as the wires will be much shorter and having the master underneath in the cab is a pain in the butt.

What's the consensus on add a choke to the 18 watt? I have a spare one out of an EL84 Organ Chassis I was thinking of trying

[colossal]

What's the consensus on add a choke to the 18 watt? I have a spare one out of an EL84 Organ Chassis I was thinking of trying

You can try it and it will likely change the feel of the amp (for better or worse) but I wouldn't do so as a means to fix your noise problem by brute force. Your issue is most certainly lead dress related. 18W amps should be very quiet at idle. Matchless amps, specifically the Spitfire, is closest to an 18W topology and uses a choke in the power supply, FWIW.

[Yamariv]

For sure, makes sense about the lead dress. I was more just curious about a choke on its own, what will it do exactly, tighten up the sag? Not sure if I want to loose any sag so maybe I should wait to try a choke and do it down the road just for an experiment.

[colossal]

For sure, makes sense about the lead dress. I was more just curious about a choke on its own, what will it do exactly, tighten up the sag? Not sure if I want to loose any sag so maybe I should wait to try a choke and do it down the road just for an experiment.

Depends on the inductance and DC resistance of the choke. Chokes resist changes in current. Think of them as frequency dependent resistors where a resistor provides the same voltage drop at all frequencies. A choke will provide much better DC regulation with a greater reduction in AC ripple. You could certainly try it. The magic of the 18W is in its touch sensitivity which, in part, is contributed to by the 2k2 resistor feeding the screens. EL84s draw a fair amount of screen current on large transients and the voltage drop across that resistor will cause some compression. Matchless amps have low DCR chokes (screen voltage is very close to plate voltage) and are biased very hotly, so will sag less, giving them a stiffer feel and more zingy tone. This may or may not float your boat, but it won't be an 18W anymore.

[Yamariv]

Makes sense, thanks for the explanation! Given that, I don't think I will put it in just yet, I'm going to focus on the hum fixing first then maybe down the road I'll pop the choke in for curiosity sake since it's easy to install and remove. I definitely don't want to loose the 18 watt feel.

[zaphod_phil]

that bundle of wires is for the master volume.

If that's a Post-PI MV, I trust you realize that with a classic 18W, it will just delay the onset of breakup,rather than work as you would probably expect an MV to work. An attenuator or VVR is the best MV for an 18W.

[Yamariv]

Yeah, it's a PPMV.. I'm not sure I know what you mean, it's not the most ideal master for that amp?

I spent the afternoon moving a few things around, chopsticking and completely redoing the heater wires on the amp and am frustrated as the noise is still there and just as strong. I've put the amp in the corner for a couple days to rethink my plan. I'm also not very happy with the sound of the amp..maybe it's the Tube Depot version or just the 18 Watt characteristics but I find it very Middy with very little clarity / clean overdrive. I'm not expecting it to be a high gain amp but as it is right now the most it will do is a weak crunch sound on the normal and the Tremolo barely breaks up at all.

Just starting to research other versions and need some advice. Are the TMB models usually designed with more gain on tap? If that's the case, then maybe a TMB model would be better, which is the most proven layout you guys would recommend?

[Bieworm]

Yeah, it's a PPMV.. I'm not sure I know what you mean, it's not the most ideal master for that amp?

I spent the afternoon moving a few things around, chopsticking and completely redoing the heater wires on the amp and am frustrated as the noise is still there and just as strong. I've put the amp in the corner for a couple days to rethink my plan. I'm also not very happy with the sound of the amp..maybe it's the Tube Depot version or just the 18 Watt characteristics but I find it very Middy with very little clarity / clean overdrive. I'm not expecting it to be a high gain amp but as it is right now the most it will do is a weak crunch sound on the normal and the Tremolo barely breaks up at all.

Just starting to research other versions and need some advice. Are the TMB models usually designed with more gain on tap? If that's the case, then maybe a TMB model would be better, which is the most proven layout you guys would recommend?

I had a very hummy TMB tremolo build. Turned out to be the power tubes. It is hum free after the swap.

Of you want gain, just build the TMB tremolo. It's endless gain on that one..

[Daviedawg]

Your description of the sound from the 18 watt is far from what I would expect. It is possible (likely even) that the hum and poor performance are caused by the same issue. A break from it is a good idea. But don't forget or give up on it.

Dd

[Bieworm]

Your description of the sound from the 18 watt is far from what I would expect. It is possible (likely even) that the hum and poor performance are caused by the same issue. A break from it is a good idea. But don't forget or give up on it.

Dd

at first with my classic 18W I had a 120R resistor and 500uf bias cap on the power stage. On that combination mine broke up all right!!!
this was my very first voltage chart. Afterwards I ruined my Powertransformer by tweaking and building the TMB tremolo. So now I have another PT from another brand. The voltage chart her was with a Hammond
NOTE: the gridvoltage on V2 were probably aroudn 50V..I didn't know any better back then, so I measured on DC instead of AC
PAZ290.

18W classic first voltage chart.jpg

[Yamariv]

Whats the best tried and true 18 Watt TMB layout you guys would recommend? I think I'm just going to shot gun it and redo it into a TMB with a bit higher gain

[Bieworm]

Whats the best tried and true 18 Watt TMB layout you guys would recommend? I think I'm just going to shot gun it and redo it into a TMB with a bit higher gain

I find this very decent and clean:
https://www.tube-town.net/cms/?DIY/Amps/TT_18_TMB

But ask Josh ... he'll have one for sure

[colossal]

I find this very decent and clean:
https://www.tube-town.net/cms/?DIY/Amps/TT_18_TMB

Note the dropping resistors in the power supply and the stated voltages for the phase inverter and preamp. Not a Lite IIb. They are probably going for more and earlier onset of distortion.

[Bieworm]

I find this very decent and clean:
https://www.tube-town.net/cms/?DIY/Amps/TT_18_TMB

Note the dropping resistors in the power supply and the stated voltages for the phase inverter and preamp. Not a Lite IIb. They are probably going for more and earlier onset of distortion.

I was under the impression the OP was after that? Early breakup...
Being near Germany I found myself ordering most of my parts there at Tubetown. Their prices are really ok and short + sure delivery time. I find their photos showing also super neatly wired amps

But that was just examplairy .. me thinks you guys here have to deliver the proper layout/schematic.

[Yamariv]

Any other tried recommendations for an 18Watt TMB?

[JMPGuitars]

Any other tried recommendations for an 18Watt TMB?

My favorite is the Superlite TMB: viewtopic.php?f=25&t=24430

I recently uploaded some new docs on the top of that page, that's the version I recommend. Zaphod_Phil designed the circuit, and that new version of the docs incorporates his intended designs (some versions strayed away from this). Also included is the correct ground scheme, and the Paul Ruby Mod.

[Yamariv]

Cool thanks for the other suggestion! I keep seeing Superlight on this forum, why is it called that?

I see the link you attached has no Rectifier tube, is there a version that does in the TMB format?

[JMPGuitars]

Cool thanks for the other suggestion! I keep seeing Superlight on this forum, why is it called that?

I see the link you attached has no Rectifier tube, is there a version that does in the TMB format?

You can build the Superlite TMB with a tube rectifier. Use the rectifier section from my Lite IIb(ish) drawing: files/JMPGuitars_18_Watt_Lite_2b_Layout.pdf

The rectifier isn't that important between the two types. Pick which rectifier you feel like building, and build it.

Probably within a week I'll post a demo comparing an 18 Watt amp I made with a switchable rectifier. Even with a 20V higher B+ on the solid state rec, there's barely any noticeable difference. No sag resistor on the SS rec either, so it's even weirder how close it is.

[Daviedawg]

Looking forward to that Josh. My 18 watt is ss rectified and every once in a while this little thought worm gets going suggesting a valve rectifier. So it will be really of great value. All my recently built amps have valve rectifiers even my valve reverb unit. So the 18 watt is an oddity here.

Dd