Need 5E3 Build Troubleshooting Help

paul-e-mann

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So...when you pulled the power tubes and tried one at a time, did you actually try the scenario of just leaving both power tubes out? That's a fast test that would've told you if at least one power tube is bad if the limiter bulb was now softly glowing. ? I've forgotten what I've read, but you've verified your speaker and connections since you need one connected with all tubes in, right? Also, a Fender usually has you wire the output jack so it shorts should the speaker cable be jerked out. Kind of a failsafe for the output transformer vs. the open circuit which you really never want at the speaker jack. Check everything,...measure it.

Also, I can't get a good visual on the rectifier socket with the stray wiring. Can you post a photo of that? Specifically peek and verify what transformer wire colors are on pin 2 & 8...should be black and white going direct from the transformer for the 5vac according to the transformer wiring chart on the transformer.
The bulb doesnt light with the power tubes out. The bulb lights with either of the power tubes in and in either socket. I had a speaker connected to the amp during this test.

The output wires of the OT (green 8 ohms, yellow 0) yellow wire connected to the speaker jack sleeve and switch terminal, green wire connected to the tip terminal, then green jumper from tip terminal to the extension speaker jack tip terminal.

The rectifier socket, from the PT 5V black wire on pin 8 and white wire on pin 2, also on pin 8 is a red wire to the standby switch, pin 4 and 6 have the green 340V wires.

YGaELd0.jpg
 

paul-e-mann

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@Pete Farrington do I have the speaker jacks wired correctly?

The output wires of the OT (green 8 ohms, yellow 0) yellow wire connected to the speaker jack sleeve and switch terminal, green wire connected to the tip terminal, then green jumper from tip terminal to the extension speaker jack tip terminal.
 

Guitar-Rocker

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You will want to also have a ground reference from the speaker jack sleeve to a bolted or soldered connection point.

Take all of the tubes out, power the amp up with the speaker connected and check terminals 4 & 6 on the rectifier tube socket. You should see after you've changed your high side wall tap to 125V, the listed voltage of 340V AC from pin 4 to pin 6. Do not measure to ground

Also check voltage on the rectifier socket from pin 2 to pin 8, should read @5V AC. Then check across pin 4 or pin 5 to pin 9 at the first preamp tube, should read higher than 6.3V Ac because again with no tubes in there is no load to lower the AC voltage to the proper range. If all 3 AC tests are normal, shut down the amp and put in the rectifier tube and take some more readings.

With the speaker connected, rectifier tube in, and amp is on, read your DC voltage at the head of your burnt resistor (which should also be the OT CT). It may be high due to no power tubes in the amp for load, maybe 20% higher. Read downstream of that burnt resistor and see how many volts DC you dropped, then read the down stream DC voltage of the preamp dropping resistor. All of these are measured to ground

You pass these tests and maybe your B+ rail is functioning properly. Any of these fail, then correct your wiring. Prove these, then with a know good set of power tubes you can test further.
 

myersbw

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As others have said, the 120 to 125V tap is fine. And, two more things...be sure you're plugging into the speaker jack and not the extension jack (which will leave the OT shorted if the main speaker jack is not used). Don't assume that 4.7K resistor is "still good" because it measures good with a meter. A meter applies a small voltage to measure the resistance. The live circuit is an extremely large voltage. Liken it to 9 volts vs. lightning. You can touch a 9 V battery to your body and not feel a thing. To your tongue and a mild tingle. Lightning is a different story. Thus, that resistor can be carbonizing internally. The small voltage from a meter likely won't jump the carbon short spot until it's complete...but, go apply full voltage...the electrical potential has no problem migrating across compromised areas internally. Thus, for high voltage it likely appears as a short...or greatly reduced value...at this point. I had one 100K 12ax7 plate resistor do this. Measured ok. I thought I was crazy replacing it...but, it solved the problem.

I'd also recommend investing in an inexpensive LCR meter and check all your caps out. Don't know what soldering iron/wattage you're using, but it takes some heat to solder turrets. I normally use high heat and work fast...and...use small aluminum alligator clips on cap leads to help prevent compromising the caps with too much heat. I also measure every component before and after I install it. The little things help make a completed build work the first time.

Dress your wires, replace the 4.7K, clip excessive wire at solder points, once you have new tubes, leave those out and power up with the preamp tubes in....make a chart of each tube (V1, V2...) in grid form and note ac and dc voltages at each tube socket pin. Then post it here.

The better path, like Ken suggested, take it to a tech that will solve it and show you the issues. If you're "that close" it shouldn't be an outrageous price. Also, the LCR meter can measure some of those parts in circuit. Just remove all tubes to break open some connectivity. Make certain the speaker cable and speaker coil is solid and without question.

Yep, troubleshooting can be a major pain in the butt! Do not assume or take shortcuts. Make sure power supply large cap voltages are drained before starting in the tracing process.

And, given this wasn't a Mojo kit...I'm now interested in where exactly you found it. I'd like to see a link and look into that one a bit more.
 

Pete Farrington

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do I have the speaker jacks wired correctly?

Your description sounds right.

check terminals 4 & 6 on the rectifier tube socket. You should see after you've changed your high side wall tap to 125V, the listed voltage of 340V AC from pin 4 to pin 6. Do not measure to ground
340-0-340 = 680V across the whole winding, ie pin4 to pin6 of the rectifier.
 
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paul-e-mann

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As others have said, the 120 to 125V tap is fine. And, two more things...be sure you're plugging into the speaker jack and not the extension jack (which will leave the OT shorted if the main speaker jack is not used). Don't assume that 4.7K resistor is "still good" because it measures good with a meter. A meter applies a small voltage to measure the resistance. The live circuit is an extremely large voltage. Liken it to 9 volts vs. lightning. You can touch a 9 V battery to your body and not feel a thing. To your tongue and a mild tingle. Lightning is a different story. Thus, that resistor can be carbonizing internally. The small voltage from a meter likely won't jump the carbon short spot until it's complete...but, go apply full voltage...the electrical potential has no problem migrating across compromised areas internally. Thus, for high voltage it likely appears as a short...or greatly reduced value...at this point. I had one 100K 12ax7 plate resistor do this. Measured ok. I thought I was crazy replacing it...but, it solved the problem.

I'd also recommend investing in an inexpensive LCR meter and check all your caps out. Don't know what soldering iron/wattage you're using, but it takes some heat to solder turrets. I normally use high heat and work fast...and...use small aluminum alligator clips on cap leads to help prevent compromising the caps with too much heat. I also measure every component before and after I install it. The little things help make a completed build work the first time.

Dress your wires, replace the 4.7K, clip excessive wire at solder points, once you have new tubes, leave those out and power up with the preamp tubes in....make a chart of each tube (V1, V2...) in grid form and note ac and dc voltages at each tube socket pin. Then post it here.

The better path, like Ken suggested, take it to a tech that will solve it and show you the issues. If you're "that close" it shouldn't be an outrageous price. Also, the LCR meter can measure some of those parts in circuit. Just remove all tubes to break open some connectivity. Make certain the speaker cable and speaker coil is solid and without question.

Yep, troubleshooting can be a major pain in the butt! Do not assume or take shortcuts. Make sure power supply large cap voltages are drained before starting in the tracing process.

And, given this wasn't a Mojo kit...I'm now interested in where exactly you found it. I'd like to see a link and look into that one a bit more.
 

paul-e-mann

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I'm hanging tight waiting on parts, I'll be back at it in a couple days. :yesway:

Thanks everybody for your help, its been a great learning experience and exactly what I wanted out of it. :yesway:
 
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myersbw

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Yep...definitely measure all components...you can't always trust a color code. I've been burned by that a couple times, thus I always measure parts I'm about to install -and- I take an exacto knife and do light scrapes on the component leads to break through any oxidation. I'm a bit redundant on precautions, but it leads to good builds...THAT makes it all worth the extra time spent.
 

paul-e-mann

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Cool I just nabbed a Jensen C12Q for cheap off Reverb for the amp. :yesway:

No resistors man, they were supposed to be delivered yesterday, I got the tubes though! Just ordered some more resistors for Friday delivery, lets see which come first the ones I ordered a week ago ebay or the ones I ordered today amazon!
 
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paul-e-mann

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You will want to also have a ground reference from the speaker jack sleeve to a bolted or soldered connection point.

Take all of the tubes out, power the amp up with the speaker connected and check terminals 4 & 6 on the rectifier tube socket. You should see after you've changed your high side wall tap to 125V, the listed voltage of 340V AC from pin 4 to pin 6. Do not measure to ground

Also check voltage on the rectifier socket from pin 2 to pin 8, should read @5V AC. Then check across pin 4 or pin 5 to pin 9 at the first preamp tube, should read higher than 6.3V Ac because again with no tubes in there is no load to lower the AC voltage to the proper range. If all 3 AC tests are normal, shut down the amp and put in the rectifier tube and take some more readings.

With the speaker connected, rectifier tube in, and amp is on, read your DC voltage at the head of your burnt resistor (which should also be the OT CT). It may be high due to no power tubes in the amp for load, maybe 20% higher. Read downstream of that burnt resistor and see how many volts DC you dropped, then read the down stream DC voltage of the preamp dropping resistor. All of these are measured to ground

You pass these tests and maybe your B+ rail is functioning properly. Any of these fail, then correct your wiring. Prove these, then with a know good set of power tubes you can test further.

As others have said, the 120 to 125V tap is fine. And, two more things...be sure you're plugging into the speaker jack and not the extension jack (which will leave the OT shorted if the main speaker jack is not used). Don't assume that 4.7K resistor is "still good" because it measures good with a meter. A meter applies a small voltage to measure the resistance. The live circuit is an extremely large voltage. Liken it to 9 volts vs. lightning. You can touch a 9 V battery to your body and not feel a thing. To your tongue and a mild tingle. Lightning is a different story. Thus, that resistor can be carbonizing internally. The small voltage from a meter likely won't jump the carbon short spot until it's complete...but, go apply full voltage...the electrical potential has no problem migrating across compromised areas internally. Thus, for high voltage it likely appears as a short...or greatly reduced value...at this point. I had one 100K 12ax7 plate resistor do this. Measured ok. I thought I was crazy replacing it...but, it solved the problem.

I'd also recommend investing in an inexpensive LCR meter and check all your caps out. Don't know what soldering iron/wattage you're using, but it takes some heat to solder turrets. I normally use high heat and work fast...and...use small aluminum alligator clips on cap leads to help prevent compromising the caps with too much heat. I also measure every component before and after I install it. The little things help make a completed build work the first time.

Dress your wires, replace the 4.7K, clip excessive wire at solder points, once you have new tubes, leave those out and power up with the preamp tubes in....make a chart of each tube (V1, V2...) in grid form and note ac and dc voltages at each tube socket pin. Then post it here.

The better path, like Ken suggested, take it to a tech that will solve it and show you the issues. If you're "that close" it shouldn't be an outrageous price. Also, the LCR meter can measure some of those parts in circuit. Just remove all tubes to break open some connectivity. Make certain the speaker cable and speaker coil is solid and without question.

Yep, troubleshooting can be a major pain in the butt! Do not assume or take shortcuts. Make sure power supply large cap voltages are drained before starting in the tracing process.

And, given this wasn't a Mojo kit...I'm now interested in where exactly you found it. I'd like to see a link and look into that one a bit more.

Your description sounds right.


340-0-340 = 680V across the whole winding, ie pin4 to pin6 of the rectifier.
I put in the new resistor and tested all AC and DC voltages on all tubes and connections in the chassis and on the board, all voltages measure correctly. I also added duct tape to the chassis beneath the board so no chance of under wires shorting on the chassis (solder joints under the board are solid). I'm still getting the same result, with amp in play mode with speaker plugged in, the bulb limiter lights indicating a problem. I have new power tubes, I get the same result with both sets of tubes so I suspect the original tubes are probably good. Only thing I havent done yet is shorten and clean up the transformer leads which I will do, I didnt think long leads would matter for this test at the moment, I'll straighten them out tonight and try again. Anything else I should be looking at? Here's a recap of where I'm at:

- All caps and resistors measured correctly before installation.
- All transformer leads measured and identified.
- All solder joints solid, nothing touching each other.
- All AC and DC voltages measured correctly on tube sockets.
- All AC and DC voltages measured correctly in chassis and board.
- Light bulb limiter stays lit with power tubes installed in play mode.
 
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william vogel

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I put in the new resistor and tested all AC and DC voltages on all tubes and connections in the chassis and on the board, all voltages measure correctly. I also added duct tape to the chassis beneath the board so no chance of under wires shorting on the chassis (solder joints under the board are solid). I'm still getting the same result, with amp in play mode with speaker plugged in, the bulb limiter lights indicating a problem. I have new power tubes, I get the same result with both sets of tubes so I suspect the original tubes are probably good. Only thing I havent done yet is shorten and clean up the transformer leads which I will do, I didnt think long leads would matter for this test at the moment, I'll straighten them out tonight and try again. Anything else I should be looking at? Here's a recap of where I'm at:

- All caps and resistors measured correctly before installation.
- All transformer leads measured and identified.
- All solder joints solid, nothing touching each other.
- All AC and DC voltages measured correctly on tube sockets.
- All AC and DC voltages measured correctly in chassis and board.
- Light bulb limiter stays lit with power tubes installed in play mode.
Lit bright?
 

william vogel

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Not fully bright, more on the dimmer side. 60 watt bulb.
What is the mains voltage that you measure in the amp at the power switch? With the current limiter in place it’s going to be lower than 120 volts because there’s a voltage drop across the bulb filament. What voltage is at the power switch?
 

paul-e-mann

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What is the mains voltage that you measure in the amp at the power switch? With the current limiter in place it’s going to be lower than 120 volts because there’s a voltage drop across the bulb filament. What voltage is at the power switch?
About 103 volts through the bulb limiter. Plug the amp direct I get 120 volts.
 
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william vogel

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About 103 volts through the bulb limiter. Plug the amp direct I get 120 volts.
That’s with the tubes in place? At 103 volts, it’s dropping about 17 volts on the bulb. A 60 watt bulb. It’s about 15% bulb or 9 watts. I don’t think you have a serious problem. It’s not a dead short by any means. You need to measure the voltage drop across the 4.7k resistor. You also need to measure the b+ voltage. This has to be done quickly. If you’re dropping all the b+ across the 4.7k resistor, you’re short is between it and the preamp plate resistors (100k’s).
 

paul-e-mann

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That’s with the tubes in place? At 103 volts, it’s dropping about 17 volts on the bulb. A 60 watt bulb. It’s about 15% bulb or 9 watts. I don’t think you have a serious problem. It’s not a dead short by any means. You need to measure the voltage drop across the 4.7k resistor. You also need to measure the b+ voltage. This has to be done quickly. If you’re dropping all the b+ across the 4.7k resistor, you’re short is between it and the preamp plate resistors (100k’s).
I dont have the lingo entirely down, b+ voltage is what?

100k's look solid, the wires underneath connected to them look solid, their connections to the preamp tubes look solid.
 

william vogel

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I dont have the lingo entirely down, b+ voltage is what?

100k's look solid, the wires underneath connected to them look solid, their connections to the preamp tubes look solid.
The high voltage at the first filter capacitor.
 

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