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Thread: I love the 5e3. Just not mine! Please help.

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    I love the 5e3. Just not mine! Please help.

    Hello all!! Firstly I'm excited to be here around all of you. This is my first post but not my last. I've played guitar for 22 years and have owned a wide array of amps vintage and new. I'm currently running a '66 super reverb. Love it but I needed something smaller and not so powerful. I'm a fan of the tweed deluxe but don't have that money. So I saw the schematics and thought I could build that. Then saw kits. Mojotone was the only company to reach back to me so I bought theirs. Nice cab. Bought an original '56 Jensen for a song and found some good tubes.
    Build was fun and educational. My first but TOTALLY not my last.
    I did it because amp guts scare the crap out of me. I always think I'll shock myself to death. So precaution and awareness has been my motto.
    I don't know abbreviations too well or the names of the wires and inside of the amp. I build this with the mojotone schematics which is very very close to the original. I used no mods. Didn't exchange the tubes for other types.

    Ok, so with that, my problem:

    I get sound, yay!! What I don't get is my normal channel volume knob working and the 2nd normal input doesn't work. Checked solder. It's great. Pots, perfect.
    Secondly; my volume is stunningly low. Maxed out it's no louder than someone talking in conversation. Also there is a lacking low end.

    I put my multimeter on the power tube prongs? 1-8 and some got reading. Same for the pre amp ones. The filter caps are working. Is there anything I can do to aid you in your feedback?

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    Note: I put a bleeder resistor for each filter cap. No bueno? Should have used just one?

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    Hey, John, welcome to the forum! I hope you had good fun with your build, and continue to enjoy the build experience! Per your questions:

    I'm not sure if the schematic you have lists test points and voltages. If it doesn't probably your best bet is to start measuring AC and DC readings at each pin (that has something connected) on each pin of each tube. People can get an idea of voltages that are radically off from the norm. I hope your meter can select AC and DC so you can get separate readings at each point that you check.

    Also, I see some less than stellar soldering in you pics. That's OK, absolutely to be expected at this point in the game. I want to ask what wattage soldering iron are you using? Too small or too large can have adverse results on the quality of the build. Too small an iron - say 15W or less - can force you to apply the iron for an excessively long time in one spot. One result of that is that the joint may not have gotten hot enough, and is not conducting the way it should. Another possible result is that as the iron stays on the lead of a sensitive component (capacitor, say) for longer than it should, heat can travel into the component and cause damage. Too large an iron - say 50W or more (these are my numbers, others may disagree) - and you might as well take a blowtorch to the innards of the chassis.

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    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


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    Hey hey! 40watt iron. Didn't wanna go too high. My soldering does suck, but I was using wrong solder and after I changed it up? The points got much better. I'll get those readings.

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    For reference, I have attached the schematic and layout from mojotone.
    One simple thing I will mention, a very simple common mistake leading to very low volume is using the wrong speaker jack. I only mention this as I see evidence of the ext. spkr. jack having been used. Make sure the speaker connects to the jack with the 3 lugs, not the one with 2 lugs.

    As eschertron suggested, giving DC voltages is a good place to start. To simplify a bit, how about the DC voltages at pins 3 and 8 of all tubes except the 5Y3.
    List tube type, pin#, and DC voltage at that pin.
    Attached Files Attached Files

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    Def using the 3 prong speaker jack.

    12ay7 pins 3 and 8 = 0
    12ax7 pins 3 and 8= 0
    6v6 (on right) pin 8 is like 12 pin 3 is 210
    6v6 by the 5y3 is the same. Pin 3 is like 210 and pin 8 is like 12.

    Also, earlier I reversed the OT wires (brown and blue) to no avail. I can put em back to normal.

    Pins 3 and 8 for the 12ay and 12ax are just ground pins. Should they read anything?

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    Last edited by JohnRose81; 03-24-2014 at 02:00 AM.

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    210V at the 6V6 plates is quite low. What is at pin8 of the 5Y3?
    Pins 3 and 8 of the preamp tubes are not ground pins. What is the DC voltage at pin 1 and 6 of the preamp tubes?

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    Quote Originally Posted by JohnRose81 View Post
    12ay7 pins 3 and 8 = 0
    12ax7 pins 3 and 8= 0




    Also, earlier I reversed the OT wires (brown and blue) to no avail. I can put em back to normal.

    Pins 3 and 8 for the 12ay and 12ax are just ground pins. Should they read anything?

    According the schematic, the 12AY7 cathodes use a shared 820 ohm resistor to ground.
    And the 12AX7 cathode uses a 15K on the driver & the PI uses a 15K, 56K in series to ground.

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    Pin 8 on 5y3 is around 220. (Analog multimeter)
    12ay7 pin 1 is 70
    12ay7 pin 6 is 170
    12ax7 pin 1 is 90
    12ax7 pin 6 is 110

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    I really need to learn the flow through this circuit so I can understand what ya mean. I know what all those are but outside of that, no.

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    Are you very confident about the accuracy of that meter? Do you have another you can try? Or how about checking what it reads for AC voltage at your wall outlet.

    Another thing, you said no mods, but you also said you added bleeder resistors for the filter caps (that would be a mod ). What value and wattage did you use for the bleeders?

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    Yes. Calibrated.


    And yes, I suppose bleeders are a mod. 220 2w bleed resistors on each filter cap.

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    Quote Originally Posted by JohnRose81 View Post
    220 2w bleed resistors on each filter cap.
    I hope you mean 220K, otherwise remove them and repost the new voltage readings.

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    Haha. Yes 220k. I'm sorry.

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    With 6V6 tubes removed, what is the DC voltage at pin3 of 6V6 sockets?

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    Interesting. With tubes the filter caps read (from left to right) 250, 200, 150. Without they are all around 12. The 3 pins on the 6v6's are around 12 without tubes also. And for the record, I removed all tubes.

    Also, before all of this, I reversed the speaker wire since the Jensen didn't have a + or - marketing. So after looking at reference images, I know it's not that.

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    I take that back, my mistake. I had the wrong setting on the meter. All filters and 3 pins are Zero responsive with no tubes.

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    You have to have the 5Y3 in or you will get nothing.
    But before you put it in, check the AC voltage from one of the reds at the 5Y3 socket to ground.
    Then put the 5Y3 back in and check the DC on those filter caps leaving the other tubes removed.

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    Thank you for the quick responses. I get 220 at the red wire on the 5y3 socket with no tube. With a tube, all the 3 pins for the 6v6's are pegging my meter which goes to 300. I hear a slight static from the speaker when this happens.

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    What do you measure in AC volts from either side of the fuse holder to ground? And AC at either green of the pilot light to ground?

    I'm not sure which power transformer they are using but I think it should be (at the red) more like 320AC, not 220. Is there a number on it? Does it have multiple taps for export use or is it for 120V only?

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    I read 70 off the fuse tabs and zero on the light tabs. The power transformer is mojo 756 HTS-8051 9961403. 120v only.
    On my meter I have a ohm section. A v.mA section and a ac10v section. The v.mA goes to 250. That's what was being pegged. It's a M1015B I got from Home Depot.

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    Going to get a digital multimeter today so I can get more accurate readings! Yay for that.

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    Quote Originally Posted by JohnRose81 View Post
    I read 70 off the fuse tabs and zero on the light tabs.
    Quote Originally Posted by JohnRose81 View Post
    Going to get a digital multimeter today so I can get more accurate readings! Yay for that.
    Good, the voltage at the fuseholder should read 120V, or whatever is coming out of your wall outlet.
    So there are 3 possible reasons for the 70V reading:
    1) there really is only 70V at the fuseholder due to faulty wiring in the house or amp AC wiring.
    2) the meter is defective/inaccurate/damaged
    3) you are reading the wrong scale of the meter

    Whatever the case may be, you want a meter that can read more than 300V anyway.

    Edit: with new meter, repeat measurements from post #6

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    With regards to #1, is there anything I can do about this? Should I re-read with and without tubes? Would the speaker or guitar being plugged in change this value? If the volumes were turned up would this affect it?

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    Keep speaker attached at all times. Reread voltages from post #6 with tubes in.
    No point doing anything until you verify your meter.
    You can take it into a room where you know the outlets are working properly, check what the AC volts reading is at the outlet, does the meter read 120V? If you get a good 120V reading, the meter is not the problem.

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    So the multimeter is spot on. Put all the tubes in. Plugged the speaker up. Touched the 6 pin on all the tubes except the rectifier tube. The 6v6's registered zero. The preamp tubes popped really loud when I touched them. Once the ax7 read 120. But they just pop and make loud noises and read zero. Cold solder? I re soldered the wires back on the pins. No avail. Would it be the soldering of those wires on the fiberboard? I'll try. Any suggestions?

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  27. #27
    Supporting Member eschertron's Avatar
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    Quote Originally Posted by JohnRose81 View Post
    So the multimeter is spot on. Put all the tubes in. Plugged the speaker up. Touched the 6 pin on all the tubes except the rectifier tube. The 6v6's registered zero. The preamp tubes popped really loud when I touched them. Once the ax7 read 120. But they just pop and make loud noises and read zero. Cold solder? I re soldered the wires back on the pins. No avail. Would it be the soldering of those wires on the fiberboard? I'll try. Any suggestions?
    I think g-one wants you to get readings as per the pins you read in post number six, not necessarily on pin 6 of each tube. Having said that, pin 6 of the preamp tubes is a plate, so it is connected to the grid of the following tube. The popping sound is a good indication that signal is getting through!
    Can you AC versus DC volts on your meter? Selecting AC with no signal will give you zero on the pin 6 of the preamp tubes. With a test signal applied to the amp, AC on pin 6 would be a valuable number to have.

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    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


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    I don't know the names of the tubes but I started right to left calling the 12ay7 v1 and v5 is the 5y3
    F1 is the filter cap closest to the power supply and f3 is the on on the far right.


    V1 1:75 2:0 3:0 4:0 5:0 6:75 7:0 noise 8:0 9:0
    V2 1:100 2:0 3:0 4:0 5:0 6:125 7:5 8:25 9:0
    V3 2:0 3:210 4:190 5:0 6:0 7:0 8:10
    V4 2:0 3:210 4:190 5:0 6:0 7:0 8:10
    V5 2:210 4:0 6:0 8:210
    F1 210
    F2 190
    F3 145
    Fuse top post dc 0 ac 70
    Fuse bottom post dc 0 ac 7
    Light top post 0 for ac and dc
    Light lower post 0 for ac and dc

    Ac value on 12ay7 is 155 and ac value on 12ax7 is over 250. I can only go to 250

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    Maybe new power tubes are needed...

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    I take it that you are still using the same meter. For measuring the DC at pins 3 and 8 of the preamp tubes you need to switch to the 2.5 or 10 volt ranges.
    As to the 70V at the fuse, is the green wire of the AC cord connected to the chassis? What is the AC measurement from the white to the black of the AC cord?

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    Yes, sadly I couldn't get to Home Depot for a new multimeter. As soon as I get home around 5.30 EST I will recheck using the 2.5 and 10 volt ranges for those 2 pins on the pre-amp tubes.

    The green wire of the AC cord is attached to the chassis. I bolted it down.

    I'm unsure by your final question. How would I measure that. The black goes to the fuse and the white goes to the on/off switch. Are you wanting an AC reading of those two wires?

    Also, I'm using NOS tubes for my 6V6's. Old GE tubes. They tested fine, but I'm seeing that I shouldn't use NOS tubes there. If so, I can replace them if need be.

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    I see no reason why you shouldn't use NOS tubes there. Lots of folks run old 6V6's in their amps. In fact, when you get loud popping noises from touching preamp tubes, that is a good sign that there isn't a major problem with the power amp section (if there was, you wouldn't hear the pops).

    There could be an argument made that it'd be better to use cheap 6V6's when debugging the amp, so as not to potentially expose good expensive tubes to a fault situation, but if the power amp section of the amp is working (and it appears to be) then the NOS tubes are fine, IMO.

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    Quote Originally Posted by JohnRose81 View Post
    I'm unsure by your final question. How would I measure that. The black goes to the fuse and the white goes to the on/off switch. Are you wanting an AC reading of those two wires?
    Looking for the AC voltage between those 2. So one probe to the black, other probe to the white.

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    Hey hey. So I bought a digital reader. Screen is blow fun. Too late to return it so I'll do that tomorrow. I did get a couple readings like the filter caps are like 420 for the first one.

    I got to your two wires and it was like 120. I can't remember. But I rechecked with the analog one and it read 60 if I was on the 300 setting and it read 120 of I was on the 250 setting. My analog is a m1015b if you want a screen shot of what I'm talking about.

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    Also, if I have just the rectifier tube in, my filter caps show a much higher reading. Also, my normal channel volume pot is scratchy and cuts in and out I'm noticing. I've only been using the bright channel. Never thought about it.

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