Help on my Green Board Blues Junior

Discussion in 'Amp Central Station' started by Bomberman977, Jun 23, 2020.

  1. Bomberman977

    Bomberman977 TDPRI Member

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    Yeah its very weird when I took down all those zeros, I think I’m just measuring it wrong possibly. Ground on the chassis and measure with the other lead on the pin right? Its a weird issue cause the amp is fully functional just has that buzz like a spring or something vibrating and hissing. Probably not worth going to a tech over quite yet for me personally. I know what the layout of the amp is and where everything is connected I’m just not sure of the function of said resistors :( I’ll keep tinkering
     
  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Yup - ground to chassis, other lead on the pin. Should be all there is to it.

    A lot of those should be zeros, or darn close, like pins 2 and 7 on the 12ax7s. I'd expect a bit more than 1V on pins 3 and 8, but sure, 1V is fine. Pins 4/5/9 would all be AC for the heaters, so we don't care about those on the 12ax7s either.
     
  3. saltyseadog

    saltyseadog Tele-Meister

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    This is a post of mine copied from a thread I had here earlier this year and which the clever people here helped me solve on my own as I could not get my Rev C green board made in the USA BJr' to the local tech due to the Covid 19 pandemic isolation. As my tube board had been repaired a couple of times since I bought the amp in 1998 and had gone again I found a link on Reverb to a guy selling stronger replacement boards and bought one which I had some problems with. Anyway after I had it fixed with the help of the guys here I posted the following DC test voltages which tied with the ones the board maker had on his installation info.


    Quote:
    While I had the back off I took it as a good opportunity to redo the testing using my new Fluke 101. Testing with all tubes removed, amp controls off and the amp switched on I got 373.5 on pins 1&6 on V1, 373.5 on pin 6 on V2 and 373.5 on pins 1&6 on V3. On the power tubes I got 11.48 on pin 2 and 377 on pins 7&9 this was the same on both the V4 and V5 power tubes. This all more or less compared with the checksheet reading the pcb board maker had supplied except his quoted 360 where I was getting the 370+ readings. On reinserting the tubes and with the controls still all at 0 on the amp I switched it on again and redid the tests. This time I got 162 on pins 1&6 on V1, 159 on pin 6 on V2 but got a reading of 200 on pins 1&6 on V3. Like I say the amp is sounding better than it ever has in the 20+yrs I have owned it but just thought I should mention it to you guys in case it might be of concern that the V3 tube was higher. quote"
     
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  4. Bomberman977

    Bomberman977 TDPRI Member

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    9FA4E130-12B6-4BD7-BE60-D3125FBDF82D.jpeg
    Ok so my first picture was with the tubes installed they are more or less consistent with your values at each pin. I think they are just lower voltages due to me having a 33k bias resistor installed leading to a voltage drop on the tubes. This picture is what I found with the tubes uninstalled, also more or less consistent when taking the voltage drop into account due to the bias resistor. I think the next move would be replacing the two resistors on my tube board as they are reading 23 instead of 47 and replacing the V3 ribbon cable and re soldering those connections again to make sure theres no cracks in the solder once again. As I tested the amp, it seems like all this fiddling around has reduced that noise issue, its still present but its getting better. This leads me to believe it could be a connection with the ribbon cable as thats been the only thing moving throughout this process. I also noticed when I get my fingers close to the ribbon cable a hum is produced. I’m not sure if thats related at all to the buzz. Anyways, I’ll replace the V3 ribbon cable and direct wire to the tube and replace those resistors and see what happens. Thanks again for the help all.
     
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  5. saltyseadog

    saltyseadog Tele-Meister

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    Also the fact that I am in the UK where we use 240v AC for lights sockets as standard and I believe you use 110v in the USA may have a bearing but either way the figures for both our amps are very similar.
     
  6. Bomberman977

    Bomberman977 TDPRI Member

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    848FB8D7-187D-4BD5-B39E-CE10EE862818.jpeg
    So the amp seems to be doing better the more I tinker with it. I keep trying things till it works out. So I put the tubes in and measured voltages at each pin and this time measured DC and AC on each pin (see picture). Only thing that is a cause for concern is the AC voltage on pins 7 and 9 on the power tubes. Must be some weird glitch in the multimeter as the multimeter only goes to 600 Vac and the wire used to connect to the pins is only rated for 600 so it would have degraded by now I’m assuming. Anyways maybe something is up with those numbers?

    Edit:

    Had to do a little research again, turns out I don't remember that much about electronics from my undergraduate college classes as I thought. In terms of AC/DC, I think those AC numbers are irrelevant on those pins, as I believe that the DC is all that matters (correct me if I'm wrong). Also to test this I took my meter to a 9V battery which supplies 9Vdc obviously, but when the meter is set for AC the meter reads 20Vac which is an irrelevant number and likely why those voltages were so high when reading AC on the power tubes. Also probably why these wires aren't failing, and I don't think this amp is even able to generate that large of a AC voltage anyways.
     
    Last edited: Jun 25, 2020
  7. Gonza_Sz

    Gonza_Sz TDPRI Member

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    Hey, I'm having the same issue on a Deluxe Reverb Boutique amp, it works fine until you crank the volume knob above 6 or 7, then the reverb circuit makes this fuzzy noise. If I disconnect the reverb tank it goes away, but it is not the reverb tank itself as I tried changing it and it does the same noise.

    Were you able to solve this?
     
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  8. Bomberman977

    Bomberman977 TDPRI Member

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    Hey! Yes I was able to solve it. I ended replacing all the ribbon cables and faulty parts until it ran quiet again. Also just recently built a new cabinet for it. Sounds great, and I'm really excited about it.

    In regards to you Deluxe Reverb. I'm not too familiar with this circuit. I know the older blues juniors had a faulty reverb circuit when it first came out so I had to purchase a mod to get rid of the noise from the reverb circuit. I'm wondering if this is a similar problem that you are having. Might want to search around online and see if that is a common problem, because when it had the faulty circuit I would also have a hiss either increasing the volume or the reverb controls. Hopefully this helps!
     
  9. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    DR and BJ have completely different reverb circuits, so there isn't likely to be much overlap here. Might be good to post a new thread @Gonza_Sz
     
  10. Gonza_Sz

    Gonza_Sz TDPRI Member

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    The problem itself is not a hiss. It just happens when you crank up the volume knob, if it is above 6/10 will only happen when strumming heavily on some chords or notes, but above 8/10 it will do it every single time you play something on the guitar. It sounds like if a plastic bag was attached to the speaker.

    Bomberman977 I'm glad you were able to solve it! It means there is some light at the end of the tunnel.

    I'll probably start a new thread, as it is an electrical problem and the amps have different circuits. This was the only place over the internet where I could find someone having a similar problem to mine.
     
  11. chet again

    chet again Friend of Leo's

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    This is why I don't like the PCB board amps.
     
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