G3 Build Fail

    HI, I've just finished my G3 build and it doesn't work. I'm not terribly surprised as my electrical knowledge and skills are close to zero, however, I would like to get it going obviously!. There are some serious discrepancies on measurements, so much so that I stopped measuring at #9 on the checklist to switch off the amp 'in case'.

    First off, the switch light comes on but the tubes do not heat up (no glow from any tubes).

    Readings taken are as follows (check #/item/should be/is):

    1/wall plug/230/225
    2/V3-4+5/6.5/7
    3/BR1-~+~/208/223
    4/(A) lug 21 t/260/310
    5/(B) lug 18 t/237/310
    6/(C) lug 18b/225/310
    7/V1-1/225/311
    8/V1-3/81/300
    9/V1-6/105/262

    When I tried to measure V1-7 the meter went wild, climbing past 500 then back to low numbers and back again. One other qualification, when I first plugged in I got smoke from resistor R22 between the four large capacitors so I switched off immediately. I checked the build, and found I had connected capacitor D1 with wrong polarity. I reconnected, checked the resistor (it read correct value so I didn't change it). So this could be related to/my problem. Does anyone have any suggestions or observations?

    Many thanks, Raslo

    Sorry chaps, I meant 'diode' D1. I connected D1 diode with the wrong polarity so I then reconnected it correctly. I don't know how to check for diode damage so I'm about to google it right now....

    Raslo

    OK, so almost a week and no replies, so as an alternative can anyone point me towards another site/forum/source where I can ask for help? No disrespect intended, just need to get things fixed. Thanks.

    The reason why you didn't get any reply might be because of your first statement.

    Zitat von raslo

    HI, I've just finished my G3 build and it doesn't work. I'm not terribly surprised as my electrical knowledge and skills are close to zero, however, I would like to get it going obviously!


    This completely disqualifies you from working on any tube circuit. The voltages are not just "ouch", they are deadly. I know quite of lot of very experienced DIYers who happily refuse working any kind of tube circuit because of the immense care you have take in order to work safely.

    I am glad to hear that you seem to be rather alive still. Even if I am quite sure that this is not the answer you want to hear: Take you amp to an experienced tube amp technician and ask for help.

    Nobody here wants to be responsible if you fry yourself after following a certain advice.

    Get a professional, stick around and learn. Once you are very sure what you are doing, continue working on these amps for yourself.

    Hi and welcome to the forum!
    As Quiddel explained, please take care of the high and harmful voltages! Disconnect the amp from the wall outlet and measure the voltages at A, B and C (shall be 0V before starting to work in the amp!

    I generally support his view that you should try to find somebody reasonably educated at your place to support you fixing the problem. But in the meantime we can try to determine what the status of your G3 Blues is...

    So when you tried to measure the voltages, was this with tubes? And do I understand it correctly that the do not heat up (not glowing )? If this is the case, you will hardly get any reasonable voltages, so this is the first thing to fix...

    Zitat von Quiddel

    This completely disqualifies you from working on any tube circuit.

    Your arrogance is noted, as is your apparent desire to exclude new-comers from the elite and obviously highly-intellectual arena of electrical assembly. But I accept responsibility for perhaps misdirecting you, as I am assuming my definition of "close to zero" is further away from zero than your definition. This is my third tube amp build, and my first failure. And I am very aware of the dangers involved. I am also intrigued by your suggestion "Get a professional, stick around and learn" - this sounds an impractical proposition for an amateur builder. Equally "[once] you are very sure...." (I liked the "very"). Most of the new things we try in life (like learning to drive a car, for example), the first time we try we are never 'very' sure; we have done our homework, we are aware of the theory, but until we try we are never very sure. Like building an amp. But most times the experienced amongst us are willing to help the inexperienced. Not so here it seems.

    Yes, I was offended by your response. If this is the attitude of the community on this forum - stick together, lads - then I simply choose to leave. There is nothing to learn here.

    @MAD

    Thank you for your supportive reply and apologies for my terse response to Qiddel. When I made the measurements it was with the tubes in place, and they did not heat up (did not glow). So I was not surprised to get unreasonable readings, but I was - am - at a loss to know why.

    Please forgive me, but I am really quite soured by Quiddel's post. I prefer to resolve this issue somewhere other than this forum.

    No offence taken. :) I'm happy to point out again that my intention was not to demoralise you from learning new things, but rather to make very sure you understand the apparent danger of these high DC voltages and that it's crucial to know the security rules when working on a tube circuit. This forum cannot replace a solid education in how to work with high voltages.

    As you bring up the example of learning how do drive a car, it's exactly what I wrote before. You go to a driving school and have a driving instructor next to you, because it is dangerous and potentially lethal to drive a car without knowing the safety rules or how to operate it properly. You can't learn this in an online forum neither.

    So, in case it's really your third amp and you actually have knowledge of how to work on tube circuits, it is good practicte (and well expected) to post clear photos of front and back of the board and the schematic of your project. People don't wanna search the schematics for each post they see here in the forum. That's probably the other reason why you didn't get a lot of constructive replies in the first place. :)

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