Superlite TMB First build

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Len24
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Superlite TMB First build

Post by Len24 »

Hello. Hi-ya

By the end of summer i bought a homemade 18W amp. The guy who was selling it advertised it as a 18watt Marshall clone without the tremolo channel (instead there was TMB). I guess the amp was ok build because it worked. One day i started to notice that i couldnt get preamp distortion from the amp (when i cranked the preamp and left master volume kind of low it would only get pretty loud but there was little of breakup. Only when i maxed out the preamp and master it started to distort). What im trying to say is that the MV had to be cranked for preamp to work. Watching some videos on youtube from the other builders i have seen that they did not have this problem. The amp was dirt cheap (the guy sold me fully loaded chassis with cabinet and speaker with cabinet for 200$) and i was aware i would have to invest in it to sound like it should. I swapped the speaker and tubes and even though it sounded better still it felt like something was holding back the preamp volume, like it was having too much of a clean headroom and it sounded dull.

Upon further inspection into the chassis i have found a wire jungle. There was no turret board, components were hanging in air while some of them were soldered directly to tube sockets and the tube sockets looked like rotten teeth. I could not compare it to any 18w layout as the components were having some crazy values (can capacitor was 200+100+50uF)

I replaced everything except the chassis, output and power transformer and rebuild it following this layout

http://rh-tech.org/public/18-Watt/18W_S ... ut_new.jpg" onclick="window.open(this.href);return false;

I did almost everything stock with the layout except 0.01 cap before and after 33uF capacitor i have placed 0.1uF and instead of 500uF i have placed a 470uF cap (i only replaced them because that was available to me at the time).

So finally, whats the problem ?

When i powered the amp tubes light up and the status led was lit but after one second it went dead (did i mention this is my first tube amp build, and while soldering the board i have foolishly removed the resistor from the status indicator). Other than the status indicator not working the fuse did not blow and the tubes stay lit, and while there is some amount of hum coming from the speaker the sound from my guitar does not.

only when i max the preamp volume, master volume and treble some high frequencies bleed through to the speaker and fade away like tiny sounds. Sounds like there is a massive block somewhere in the circuit. There was no burning smell and no smoke when i powered the amp and as i can see the components on board look fine.

Sorry for the long writeup but as i checked everything and compared the layout of my build with the layout from this forum i really have no idea what might went wrong so any suggestion is more than welcome.

thanks in advance.
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rock_mumbles
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Re: Superlite TMB First build

Post by rock_mumbles »

First thing is check all of the resitances on the board to ground
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Len24
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Re: Superlite TMB First build

Post by Len24 »

Did it last night and there is almost none. I even singled out resistors and checked them out just to find that most of them are dead. Hope the sozo capacitors and the filters are holding up but cannot be sure because i only have multimeter to work with. I think it wouldnt be wise for me to touch this thing till my spare parts (including pilot lamp) arrive. As far as the situation has gone so rotten from the start i guess this is going to be a loooong build for me.
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Len24
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Re: Superlite TMB First build

Post by Len24 »

Len24 wrote:Did it last night and there is almost none. I even singled out resistors and checked them out just to find that most of them are dead. Hope the sozo capacitors and the filters are holding up but cannot be sure because i only have multimeter to work with. I think it wouldnt be wise for me to touch this thing till my spare parts (including pilot lamp) arrive. As far as the situation has gone so rotten from the start i guess this is going to be a loooong build for me :cry: .
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Len24
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Re: Superlite TMB First build

Post by Len24 »

Well, after a couple of weeks of wait, my new beautiful power transformer arrived and it did give life to this amp indeed.

Sounds amazing except i am having issues with treble, middle and volume pot.

At first, it happened when i would adjust master volume beyond half (about six or seven) and then it started to, if i am not mistaken, manifest like a high pitched whistle. Almost impossible to play with master volume after halfway.

Then i removed the master volume from the circuit.
Removed two wires from center and right lug and left the ground and pot in chassis. The wire from the board which was connected from the master volume to the 0.01 cap instead i connected that wire to treble center lug.

Problems i am having with this is now when i adjust gain which is now the only volume in the amp, again after halfway on the pot it starts to throw out that same high pitch whistle type of sound but now the same thing happens with treble and middle pots only bass i can crank all the way to ten with no issues.

I have found out on couple of forums that this way i could turn MV into non-MV amp. Must have done something wrong. The strange part is that even when the volume pot is on zero i can still play and get really clean and thin sound coming out of the speaker.

With that said, i would really like that the amp to be non-MV. Can it be done ?

I have attached the layout which i followed for my build.


I did almost everything stock from the layout except i used 47uF cap instead of 50uF and my PT delivers 290v instead of 275v.

Could it be too much voltage ?


Thanks for any suggestions.
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JMPGuitars
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Re: Superlite TMB First build

Post by JMPGuitars »

The MV is not your enemy, or the source of your troubles. The layout you used is also not the standard method people would be referring to as a MV to be added or removed from an 18 watt circuit.

First, I would return the pots to stock (including the MV), and make sure the solder connections are solid.

Second, one thing I would NOT do, is follow the grounding scheme as shown in the drawing you linked. The input jack should have its own independent ground point, and the preamp and power amp sections should have their grounds isolated from each other. Doing a full "star ground" as shown in that layout can contribute to high-pitch squealing and other noise issues.

Third, take some detailed photos of your build so we can see what it looks like. Get good shots from different angles.

Finally, after the pots are returned to stock, and the grounding is corrected, take some voltage readings and share them here. You can use the template from the downloads section if you want: http://18watt.com/storage/18_watt_volta ... mplate.doc" onclick="window.open(this.href);return false;

The voltage readings will tell us more about what's going on with your distortion and headroom than anything else can.

Side note: 47uF or 50uF are basically the same thing. If you consider that they're probably 10% or 20% caps, that means they can be off by as much as 5 to 10uF depending on their specs. So don't worry about that cap value, as long as the voltage requirements are correct.
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mehfuzhoss
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Re: Superlite TMB First build

Post by mehfuzhoss »

speaking from a general consensus, usually a non master volume amp will start to distort right after the headroom is run out, so basically the amp will get a tad bit louder at the breakup point and will just and add more and more compression/squish from the OT being loaded with signal.
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TriodeLuvr
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Re: Superlite TMB First build

Post by TriodeLuvr »

Len24 wrote:
Tue 02/17/15 5:26 pm
The strange part is that even when the volume pot is on zero i can still play and get really clean and thin sound coming out of the speaker.
Either the pot is defective or (more likely) you have a grounding problem.

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