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PostPosted: Sun May 19, 2019 10:38 pm 
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Hello, I recently finished my TMB build, which was my first ever amp building project. I needed some help from this forum along the way, so thank you all! I loves the challenge, it works fine, and sounds really good, but it does not have as much gain as I expected on the TMB channel, even with the gain knob maxed, unless I crank up the volume to impractical levels (or boost the input with a pedal.) Additionally, some of the voltages, particularly on the V2 pins, are pretty low. Do you think these issues are related? Should I troubleshoot the low voltages before pursuing some of the modifications to increase the gain? I have attached the sheet with the tested voltages listed, as well as a photo of the layout. (You will notice some third-party components. I damaged some components during the build and ordered some replacements from amplifiedparts.com) I also attached a photo of the new cabinet I built, also my first. (Craftsmanship is quite rough if you look closely, but it turned out looking pretty cool from a distance!! I am workingon the cab now...) Thanks for any help and advice. -Trey


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voltages.jpeg
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final head.jpeg
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PostPosted: Wed May 29, 2019 5:00 pm 
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Anyone have any ideas? I'm stumped. Thanks.


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PostPosted: Wed May 29, 2019 7:31 pm 
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Disclaimer: Haven't built this amp. That being said, your voltages from rectifier tube look to be where they need to be and most seem to be within +/- 10% ,but the ones you have for V1, V2 and V3 some of them look kinda low. V1 and V2 are gain stages so you may be losing gain there. Have you done all the usual things(checked solder joints, tube swapping)? Again, just guessing, YMMV. Hoping a more experienced builder will chime in. And if you want, you can PM Stephen (Coco) thru User Control Panel. He wants you to have working amp and is always willing to help. Sorry that I don't have any better suggestions or help. :(

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PostPosted: Thu May 30, 2019 4:36 pm 
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Finished speaker cab (almost- still needs a handle and another lower rear panel.)


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PostPosted: Thu May 30, 2019 8:23 pm 
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I made three yellow circles
Two wires (make sure there going to the right place).
Turret reheat and solder. (check all your solder joints again)

Lower voltage would probably not mean lower gain


Take 2


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PostPosted: Fri May 31, 2019 10:26 am 
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The cabinet looks good! The voltages are not that bad.
The TMB has the most gain of all the 18 watts. The amount is determined by the cathode / bypass cap and plate resistor combination.
Try to get your voltages close, redo grounds, turret connections, confirm connections, component values (measure if possible) etc. around the suspect area.

If the voltage around a specific tube is lower, the voltage drop will be less, so the drive to the next stage will be less and will sound like lower gain since it is not pushing as hard.


It can also be a result of the 12AX7 tubes you have. Some have more amplification actor than others.
check this out and see what you have.

https://www.cedist.com/tech-corner/12ax7-comparison-current-made-tubes

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PostPosted: Fri May 31, 2019 8:46 pm 
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Trey, did Sazafraz or Coco's advice help? I'm always curious to find out how a problem was solved. Helps me and others so if there's a fix for a problem, it'll be out there.

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