Need 5E3 Build Troubleshooting Help

Im247frogs

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Measured from the + end of the first filter cap to chassis ground, You should have like 350 volts dc there. Google Weber Typical 5E3 Voltages chart. Forget the current limiter-bulb for now as long as nothing is smoking anymore and it hasn't flashed super-bright.
 

Im247frogs

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Just to reiterate and I assume this is already known to you, Just make sure when checking voltages w the amp on, only do it w one hand. Don't rest your other hand on the chassis at all. I usually sit on my non-probing hand. If you're going to be flipping the amp on and off testing it you have to make sure the fliter caps show less than 30 Volts dc before working/soldering in the amp, or it's your ass. Making a voltage draining jumper tool dohickey is essential along w the light bulb limiter. The AC line cord should be pulled and the caps drained every time your done testing, before you go into the chassis, especially if you're going to walk away for a bit. Check the voltages again before you stick you hand(s) in again the next time you come back to it. Just develop a rigorous habit regarding high voltage while you're starting out.
In other words, dont find out what B+ is the hard way...
 

paul-e-mann

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Measured from the + end of the first filter cap to chassis ground, You should have like 350 volts dc there. Google Weber Typical 5E3 Voltages chart. Forget the current limiter-bulb for now as long as nothing is smoking anymore and it hasn't flashed super-bright.
Right, the limiter is lowering voltages, its also keeping that 4.7k resistor from smoking. I have the Weber voltages chart, the problem is I cant keep the power on long enough to take measurements without burning up that resistor.
 

paul-e-mann

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Just to reiterate and I assume this is already known to you, Just make sure when checking voltages w the amp on, only do it w one hand. Don't rest your other hand on the chassis at all. I usually sit on my non-probing hand. If you're going to be flipping the amp on and off testing it you have to make sure the fliter caps show less than 30 Volts dc before working/soldering in the amp, or it's your ass. Making a voltage draining jumper tool dohickey is essential along w the light bulb limiter. The AC line cord should be pulled and the caps drained every time your done testing, before you go into the chassis, especially if you're going to walk away for a bit. Check the voltages again before you stick you hand(s) in again the next time you come back to it. Just develop a rigorous habit regarding high voltage while you're starting out.
In other words, dont find out what B+ is the hard way...
Yup I'm doing these things :yesway:
 

william vogel

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Yup I'm doing these things :yesway:
Measure the voltage drop across the 4.7k resistor! If it’s the total voltage, meaning you have 0 volts on one end of the resistor, the short is between the 4.7 k and the 22k.
 

paul-e-mann

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Measure the voltage drop across the 4.7k resistor! If it’s the total voltage, meaning you have 0 volts on one end of the resistor, the short is between the 4.7 k and the 22k.
187v at the front end of the 4.7k and 0 on the other end, power is not passing to the 22k. Why wont the power pass through the 4.7k? The solder joint looks good. The back looks good.

mqyJDmB.jpg


oX8pd2u.jpg
 
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william vogel

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187v at the front end of the 4.7k and 0 on the other end, power is not passing to the 22k. Why wont the power pass through the 4.7k? The solder joint looks good. The back looks good.

mqyJDmB.jpg


oX8pd2u.jpg
Remove the capacitor between the 4.7k and the 22k. Problem found. The capacitor must be defective.
 

paul-e-mann

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Here's an update, I did some further testing with the power tubes, it seems I have at least 1 bad power tube, Ive moved it from socket to socket and the bulb lights up without a doubt, the other tube seems to be ok, this is not what I experienced earlier today. So I did the same test with my 2nd pair of tubes and they both seem to be ok so I took off the limiter and power it straight up and its holding steady, measured all the voltages and they are good. Plugged a guitar in and all jacks and knobs work. Success! :yesway:
 

paul-e-mann

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Its been running steady for about 40 minutes, its loud as F----! Quiet as can be and nice tones :yesway:

I have parts for a master volume mod, I also wanted to try building a JohnH attenuator. I'm waiting for some shrink tubing in the mail then I can finish tidying up the wires and I'm done, just gotta build an enclosure for it. :yesway:

Thank you again for everybody's help, I learned alot from some of who I consider the smartest people in the amp tech business. Thanks again! :yesway:
 

Springfield Scooter

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Its been running steady for about 40 minutes, its loud as F----! Quiet as can be and nice tones :yesway:

I have parts for a master volume mod, I also wanted to try building a JohnH attenuator. I'm waiting for some shrink tubing in the mail then I can finish tidying up the wires and I'm done, just gotta build an enclosure for it. :yesway:

Thank you again for everybody's help, I learned alot from some of who I consider the smartest people in the amp tech business. Thanks again! :yesway:
Congratulations!
 

william vogel

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Do yourself a favor and get some spare tubes, its good to have them. I'll send you a cheap and good source, no need to pay $55 for a pair.
Glad you got it figured out. I forgot you were good without the tubes in and shorted with tubes. I’m getting together a 5E3 build now. I just tested my transformers (Heyboer). I’m modifying it with a long tailed pair phase inverter vs the stock cathodyne just to see what it’s like. I’ll post pictures as I progress.
 

paul-e-mann

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Spent some more time with it, its very touch sensitive and sounds amazing through greenbacks. Its tough to get any gain out of it at reasonable volume so I'll be putting in a pre phase inverter master volume soon as per the Rob Robinette mods page: https://robrobinette.com/5e3_Modifications.htm#Add_Master_Volume

Rob has some interesting mods like the "Lead Channel" mod that will voice a channel with Marshall lead style tone, he's says it will be more pedal friendly. Another mod is the "High Gain Channel" mod that will scream without a boost pedal, I'm thinking of adding these both along with the PPIMV. His favorite mod is the "3 Way Switched Feedback" mod which adds more clean head room, thats his favorite it doesnt interest me, this amp is already super loud and clean I cant imagine needing it to be even more clean than it already is.

I'm waiting for a cable strain relief thingy and zip ties to be delivered so I can button up the insides, then I'll start looking at the mods starting with the PPIMV, maybe I dont need the other mods the amp is sounding good as is. :yesway:
 
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paul-e-mann

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Congratulations @paul-e-mann!

I guess Rob Robinette's advice here has been vindicated: "Always suspect a bad tube."

Those mods sound good, but I would make sure you get everything you can out of the stock 5E3 circuit first. It is a classic for a reason.
Ive been playing it through different cabs with different speakers and it sounds really cool, plus I have a Jensen C12Q on its way to try, I might just leave it stock and add a master volume. :yesway:
 

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paul-e-mann

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Glad you got it sorted.
We said at the beginning it was related to screens hook up.
Did you redo the mains grounding to ensure it is safe?
I will redo all the grounding, I just need a plan which I havent found yet.
 

paul-e-mann

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Hope it works out, let us know what you make of it.
Bear in mind that with only 2 common cathode gain stages before the master volume, you may need to add a boost pedal of some sort to get an acceptable depth of overdrive.
A Rangemaster type treble booster can work out great for that.
Now that I've cut my teeth on building maybe I'll build a Rangemaster pedal. :yesway:
 

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