Question about non-functioning of my G3-Blues Amp (V2-section isn't right). In prespective, my second 'G3-Rock project' worked fine and without any complaints...

  • Hi there guys (F/M) at MadAmp,

    Unmistakenly I purchased my G3-Blues (DIY-kit) Aug 2020 from Musikding. To 'build' my own tube-amp was a long-dreamed wish on my 'todo'-list. So MD provided me a affordable dream 8) . As I'm the proud owner of a real home-studio for about 30 years (mainly producing my own albums; about 18 until now 8o ), I'm rather familiar to some soldering and constructing. It's fair to admit that constructing my own tube-amp was a great challenge. Therefore, I first tested my skills with a few FX-pedals (also from MusikDing!).

    In short, after finishing the construction process of my G3-Blues and when it came to measuring all the voltage-values were within the 10%-margins. However, all the problems leading to a non-functioning amp were related to the V2-section (see the attachment).
    These V2-values were on the one hand totally different from the given values or otherwise even in the minus (value at VII-3 was (-)16 Volts; weird <X ). Of course, I thoroughly checked ánd measured every part over-and-over again, but I wasn't able to detect what the underlying problem was (in other 'projects' my analytical and scientifically trained mind will help me very well :rolleyes: ). Based on my measurements, can you help me with this nice, little amp to give it a voice in real life ?( ? Do you have any suggestions?

    To place my questionary in the right perspective. Please note that a few months later I also purchased the G3-Rock version. And after assembling and measuring without any problems, I found out that all measurements were in a very tight and secure 1-2% margin. Except for one V2-connection which felt in a still very acceptable 10% margin. In other words: Yes, I am capable of constructing your DIY-kits. My second MadAmp G3 (Rock-version) sounded as a typical tube-amp with that recognisable edge of mild driven tubes :D .
    If there is something to complain, the sound is a bit on the thin side. But that can be explained by my own choice to opt for a small 8 inch speaker (Jensen) and an - indeed! - homemade housing of 'good quality' 12 mm plywood (see picture). In fact, I'm also proud on this effort. Excellent DIY-kit! And that statement to your department brings me back to my question to find out what went wrong with my G3-Blues project. Hope to hear from you soon. Thanks and musical greetings,

    Dr. Coen Raad
    (aka Dr. Coenobite)
    Leiderdorp - NL

  • Hi and welcome to the forum!
    Interstingly the voltage ratio between A/B/C is fine though the voltages are way off. It's hard to determine remotely what exactly is wrong with the circuit around V2, but I'm pretty sure that it's resistor values (did you measure them before soldering?) and/or wiring. So you should first of all measure the resistors (with V2 being removed) and post any values that seem to be wrong ;) You also have an issue with V3 (cathode voltage 0V), so you have to check R20/C11. Btw: Did you check/measure the ground wiring? If a conncetion to ground is missing, this might result in weird voltages...

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