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

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

Post by Bieworm »

Daviedawg wrote:
Mon 04/06/20 2:15 am
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
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

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

Post by Bieworm »

Yamariv wrote:
Mon 04/06/20 8:52 am
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
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by colossal »

Bieworm wrote:
Mon 04/06/20 9:12 am
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.
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by Bieworm »

colossal wrote:
Mon 04/06/20 10:36 am
Bieworm wrote:
Mon 04/06/20 9:12 am
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.
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by Yamariv »

Any other tried recommendations for an 18Watt TMB?
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by JMPGuitars »

Yamariv wrote:
Tue 04/07/20 10:24 am
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.
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by 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?
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by JMPGuitars »

Yamariv wrote:
Tue 04/07/20 6:30 pm
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.
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

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

Post by JMPGuitars »

Daviedawg wrote:
Wed 04/08/20 2:23 am
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. ;)
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by 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? :D
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by JMPGuitars »

Yamariv wrote:
Wed 04/08/20 11:21 am
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? :D
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
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by zaphod_phil »

Yamariv wrote:
Wed 04/08/20 11:21 am
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? :D
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! :mrgreen:
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Re: First Test of 18 Watt build - Sounds great but has a steady loud hum - Help

Post by 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 :D

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!! :D 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!
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