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

[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

[JMPGuitars]

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

Ignore the worm (or eat it if it's from a tequila bottle). You'll hear the video when I post it. There's plenty of sag from the power transformers, which is maybe why the lack of a sag resistor isn't as noticeable. I dunno, you can be the judge when you see the video.

[Yamariv]

Cool thanks! So why is it called a Lite? Is it missing something or is it just a name for an 18 Watt TMB? This version would have more gain than the stock 18 Watt right?

[JMPGuitars]

Cool thanks! So why is it called a Lite? Is it missing something or is it just a name for an 18 Watt TMB? This version would have more gain than the stock 18 Watt right?

I believe he called it the superlite because it has only 4 tubes with a lot going on. I dunno, I could be wrong, ask ZP. The Lite series was named lite because they are single channel versions of the classic 18W. They usually have 5 tubes with the rectifier.

With a cascaded preamp tube, the preamp has more gain, and can have overall more gain. It's very tweakable though depending on how you use the gain and volume knobs. You benefit from both preamp and power amp gain.

BTW- I'm going to post a small change to the layout, to move the preamp decoupling cap closer to the preamp cathode resistor/cap. I'll probably have that up later today.

EDIT: The new layout is up.

Thanks,
Josh

[zaphod_phil]

Cool thanks! So why is it called a Lite? Is it missing something or is it just a name for an 18 Watt TMB? This version would have more gain than the stock 18 Watt right?

It’s called Lite or SuperLite because it’s a single-channel version, which is simpler and uses less tubes than a Classic 18W or TMB amp. Based on that philosophy, it’s not supposed to have a tube rectifier. UF4007 rectifiers with a sag resistor will do exactly the same job. So it only needs a total of 4 valves. And yes, it has plenty of gain available!

[Yamariv]

Just thought I'd update you guys, the amp is finally fixed and working as it should. I ended up totally rewiring the amp and converted it to a TMB circuit that was recommended here

The more I played the original amp I found it had an odd sounding wooshy distortion to it, hard to explain unless you heard it, add in the hum and I figured the TMB design would cure that.

When I played the new TMB it sounded horrible, the clean channel was super distorted in the same wooshy sound as before, something was definitely not right and I still had the low hum. Since I had already changed literally everything in the amp, I started to wonder if the output transformer could be failing..Some forum posts I found online seem to describe similar sounds to a failing output transformer. I was using an old Hammond Organ OT so I figured why not order one and try it, had nothing to loose.

Well, that was the problem all along!! Hum is gone, all channels sound great, wooshy distortion is long gone!! The amp is one of the quietest I have at idle, forgot it was on the other day! I've also finally heard the sound the 18 Watt is supposed to make..finally it's done!

Just thought I'd pass the fix along in case it can help someone else with a faulty OT. Thanks for all your help guys!

[JMPGuitars]

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

All tube voltages are measured in DC, except the AC voltage going to the rectifier tube. In the case of the EZ81, that's Pins 1 and 7. Everything else on the tubes is DCV.

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.

I don't know if you saw the thread, but I posted my demo: viewtopic.php?f=4&t=25615

Well, that was the problem all along!! Hum is gone, all channels sound great, wooshy distortion is long gone!! The amp is one of the quietest I have at idle, forgot it was on the other day! I've also finally heard the sound the 18 Watt is supposed to make..finally it's done!

Just thought I'd pass the fix along in case it can help someone else with a faulty OT. Thanks for all your help guys!

Glad you sorted it out! Would you say the "wooshy" distortion had an almost phaser-like effect to it?

Thanks,
Josh

[Yamariv]

Yes, that's a great way to describe it actually!! The clean channel after the TMB mod sounded horrible, not clean at all and very bad sounding distortion, never heard anything like that before

Was actually just playing my TMB with my Junior which has the hottest pickup I own. Sounds friggen glorious!! Nice crisp and clear tones, very saggy vintagey distortion that you'd expect from a 60's design. Love it!

[Yamariv]

Just saw your video link and checked it out, sounds awesome! Very smart to put the switch on the front! I never use my standby so I should have done that! lol

I did do a solid state witch at the back but going to solid state brings me to 400vdc which makes me a bit nervous to run the amp that high. At least the option is there. Also did a Mojotone effects loop and a tone cut knob to load her up with all the options incase I ever want to gig it

[JMPGuitars]

Yes, that's a great way to describe it actually!! The clean channel after the TMB mod sounded horrible, not clean at all and very bad sounding distortion, never heard anything like that before

Yuck. I think I'm in the same boat. I've done a million things to chase the problem with a build (all the while thinking it's the OT), but I chased other things down because it isn't usually the OT that's the answer.

I think I'm gonna swap out the OT and see if it's cured.

Just saw your video link and checked it out, sounds awesome! Very smart to put the switch on the front! I never use my standby so I should have done that! lol

I did do a solid state witch at the back but going to solid state brings me to 400vdc which makes me a bit nervous to run the amp that high. At least the option is there. Also did a Mojotone effects loop and a tone cut knob to load her up with all the options incase I ever want to gig it

Thanks! Get yourself some 5W zeners, and run some in series to get the B+ voltages where you want them. I have both the amps in that video with two different strings of zener diodes each to adjust the B+ lines to where they are. Keep in mind that doing this puts the zeners before the first filter cap (actually before the standby switch), so they won't drop their rated value.

Thanks,
Josh

[Yamariv]

I'm a bit confused, you have an amp that is doing the Phazer sound? You're thinking it's the OT or something else?

Ahh Zeneers, I may have to do that next time I have it open then, thanks! My rectified B+ is a tad high at 355 but I'm fine with that. Just flipping over to the 1N1007 diodes I put in bumps that to 400v! Eeek! Is there a way to just drop the Diode part of the B+? I'm guessing put them inline after the switch I put in to toggle back and forth? If I ran it at 400v and had some robust EL84's in there, could I actually run it like that safely?

I'm not too worried about using the solid state diodes though as I have other amps to do the tighter sound. I love the way the TMB sounds vintagey with the tube rectification!