5E3 trouble shooting

Snfoilhat

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That negative dc voltage measurement makes me think there is still a ground issue. It looks like you’re using the split ground scheme. I see buss heading toward the input jacks and presumably everything gets a ground reference there at a connection to the chassis.

But what about on the power side? Fender used to tie the red/yel center tap to the chassis and you’ve moved it to the negative end if the reservoir—that’s a good change for current flow, but that system still needs a ground reference by connecting to the chassis. Is there one?
 

Burning Fingers

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Rather than try guessing at what is wrong, you need to take a structured approach to troubleshooting.

Rob has an excellent troubleshooting guide at https://robrobinette.com/Tube_Guitar_Amp_Troubleshooting.htm

Basically you need to break down the possible cause of problems into stages and doing some diagnostic tests.

Those tests include:

Is the hum present with no lead plugged into an input socket ?

Does the hum increase with a guitar plugged in and the amp volume increased ?

Is the hum present with the first preamp tube removed ?.

Is the hum present with both preamp tubes removed ?.

Have you tried another pair of power tubes ?

Have you tried reversing the output transformer leads to the power tubes ?.

Let us know what you find in each step.
 

RickRogers

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On a positive note, I built and covered the cab this weekend while I waited for my guitar. I’m happy with the end product….. meaning the cab.

Here is a video of the nasty sound…. volume is turned up all the way up

 

2L man

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If you hear hum without playing or playing certain note you should be able to test if hum come from bad filtering flipping mains switch Off. Volume drop fast but if you hear hum quits immediately it is bad filtering or orienting of PT and OT. Possibly hum can come thru mains safety earth wire if other electricity users around cause lots of hum. This should be possible to test pulling mains plug and listening quieting sound.
 

RickRogers

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Rather than try guessing at what is wrong, you need to take a structured approach to troubleshooting.

Rob has an excellent troubleshooting guide at https://robrobinette.com/Tube_Guitar_Amp_Troubleshooting.htm

Basically you need to break down the possible cause of problems into stages and doing some diagnostic tests.

Those tests include:

Is the hum present with no lead plugged into an input socket ?

Does the hum increase with a guitar plugged in and the amp volume increased ?

Is the hum present with the first preamp tube removed ?.

Is the hum present with both preamp tubes removed ?.

Have you tried another pair of power tubes ?

Have you tried reversing the output transformer leads to the power tubes ?.

Let us know what you find in each step.
The hum goes away when I pull the second preamp tube out. I will have to order more power tubes to try them out. All of the guitar shops in town are out of power tubes….. figures.
 

Burning Fingers

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The hum goes away when I pull the second preamp tube out. I will have to order more power tubes to try them out. All of the guitar shops in town are out of power tubes….. figures.
While you wait for new power tubes :

Do you still have negative 13.4 volts DC on the power tube cathodes ( pin 8 ) with the power tubes removed?...I would expect zero volts AC or DC on those pins with no power tubes installed.

I am am leaning towards you having a bias problem and your power tubes are drawing way too much current.

The negative 13.4 volts could be masking an excessive current through the power tubes.

If there is a voltage there with no power tubes installed you need to find out why...have you moved the center tap wire from the cathode side of the cathode resistor to an earth point ?.

If you haven't moved then move it to an earth point and check Pin 8 again for any voltage with no power tube installed.
( I don't know if it is the HV center tap or the heater center tap but I assume it is the HV tap )

You could also measure for any voltage on that center tap wire when it is disconnected from anything
( with tubes out ).

Are the 2 x 220k grid leak resistors connected to the earth side of the cathode resistor ?

Any hum with the first preamp tube out and the second in ?
 

2L man

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The hum goes away when I pull the second preamp tube out. I will have to order more power tubes to try them out. All of the guitar shops in town are out of power tubes….. figures.
But pulling that tube will take away guitar sound as well :(

Test Mains frequency harmonics pulling notes to exact 120Hz, 240Hz and 480Hz and then sound might improve when signals cancel each other.

Best test is to find a note which you hear worst sound and then flip the Mains switch Off and you should hear about a second of quieting sound. If distortion immediately go away it is bad filtering because you took mains frequenzy away. Or half of the rectifier has failed which increase mains brum.
 

RickRogers

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While you wait for new power tubes :

Do you still have negative 13.4 volts DC on the power tube cathodes ( pin 8 ) with the power tubes removed?...I would expect zero volts AC or DC on those pins with no power tubes installed.

I am am leaning towards you having a bias problem and your power tubes are drawing way too much current.

The negative 13.4 volts could be masking an excessive current through the power tubes.

If there is a voltage there with no power tubes installed you need to find out why...have you moved the center tap wire from the cathode side of the cathode resistor to an earth point ?.

If you haven't moved then move it to an earth point and check Pin 8 again for any voltage with no power tube installed.
( I don't know if it is the HV center tap or the heater center tap but I assume it is the HV tap )

You could also measure for any voltage on that center tap wire when it is disconnected from anything
( with tubes out ).

Are the 2 x 220k grid leak resistors connected to the earth side of the cathode resistor ?

Any hum with the first preamp tube out and the second in ?
I moved the HV center tap wire to the earth point above B1. Pin 8 reads Zero with Power Tubes removed.

I did not measure the voltage of the center tap wire.

The 220k grid leak resistors are connected to earth on the preamp side as per the layout on Rob's website.

There is no signal or hum when either one of the preamp tubes are removed. It makes a slight crackle noise in the sockets however.
 

Burning Fingers

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I moved the HV center tap wire to the earth point above B1. Pin 8 reads Zero with Power Tubes removed.

I did not measure the voltage of the center tap wire.

The 220k grid leak resistors are connected to earth on the preamp side as per the layout on Rob's website.

There is no signal or hum when either one of the preamp tubes are removed. It makes a slight crackle noise in the sockets however.
With no preamp tubes in you will get no signal and usually no hum.

What's is like with all tubes in...still humming and low distorted volume or is it behaving itself?

The slight crackle can be sorted after you have got the power section working correctly.

Good that the negative 13.4 VD is gone from pin 8 on the power tubes and that the grid leak resistors are connected correctly.

Can you measure the voltage across the cathode resistor with the power tubes in...hopefully it will not jump up much from your previous measurement of positive 19 volts.
Also the B1 voltage
 
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RickRogers

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With no preamp tubes in you will get no signal and usually no hum.

What's is like with all tubes in...still humming and low distorted volume or is it behaving itself?

The slight crackle can be sorted after you have got the power section working correctly.

Good that the negative 13.4 VD is gone from pin 8 on the power tubes and that the grid leak resistors are connected correctly.

Can you measure the voltage across the cathode resistor with the power tubes in...hopefully it will not jump up much from your previous measurement of positive 19 volts.
All tubes in have a fairly loud hum even without a guitar cable pugged in. Also still has the low volume nasty sound like in the posted video. I will have to measure the cathode resistor when I get home later on. I ordered a new set of power tubes and a few new tube sockets. I saw one of the power tube sockets had a chip in the ceramic. They should all be here Friday.
 
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RickRogers

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The tech at one of the shops in town said he had some tubes he could sell. I paid WAY too much for some Groove Tubes and they might sound worse than the Electro-Harmonics I originally installed.

The cathode resistor is still reading 19v and B1 is at 369v.

The hum/buzz is still there and playing a guitar through it sounds nasty and very low volume.

I was hopeful the power tubes would solve the issue, but I must continue on.
 
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Burning Fingers

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The bias voltage and B1 voltage are in the ballpark for 90% dissipation for the power tubes which is about where I run My 5E3 amps at.

I have a Hotrod deluxe in my workshop that turned up today with the same symptoms as your amp is showing... bad hum and distorted low volume. I tried known good power tubes to no avail so that left the power supply caps as the likely suspects... connecting a 22uf 450 volt electro capacitor across the B1 capacitor stopped the hum and restored the volume. I replaced all the power supply caps as they were all IC branded and known to be unreliable. Hopefully you have a 450 volt electro capacitor 22uf to 47uf on hand that you can connect across the B1 cap to see if that stops the hum....make sure the orientation is correct.

I imagine that you are getting a bit frustrated with your build by now but patience is a requirement for working on tube amps as is a structured approach to trouble shooting...that's why I am only now suggesting connecting another electro cap across B1... I wanted you to get the voltages and current draw in the power section correct before suggesting any other actions.
 

RickRogers

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I'll try that later on today. I figured this is all part of the process especially since I am new to it. I hope this is it. My next solution I was seeing on Rob's website was to check the output transformer.
 

RickRogers

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I replaced the 3 filter caps and it didn’t really do anything different. The volume is still very low with a nasty sounding distortion. There is still a buzz/hum One interesting thing I did notice was that the input signal would completely be lost if both volume pots were at max. Signal would come back when I dial one back slightly.

One of the power tube sockets is a little loose. I notice a crack in the ceramic as well. I have ordered a few new tube sockets to replace it.
 

Burning Fingers

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Time to check the wiring of both preamp tubes and measure the Dc voltages on pins 1 ,6, 3 and 8 of V1 and V2 and pins 2 ,7 of V2.
Any DC on pin 2 or 7 of v2 usually means the coupling caps are shot.
Are the volume pots wired correctly ?.
 

RickRogers

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I took a week off and now back at it. I replaced the bad tube socket and the filter caps. There is no hum at all and it is now almost too clean. I suspect it was the tube socket the whole time. It had a crack all the way through when I pulled it out. The volume however is still very low even maxed out. The low normal channel also comes in and out like a wave. I know it’s not supposed to do that, but it could be a trippy effect with delay… haha.
 

Burning Fingers

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I took a week off and now back at it. I replaced the bad tube socket and the filter caps. There is no hum at all and it is now almost too clean. I suspect it was the tube socket the whole time. It had a crack all the way through when I pulled it out. The volume however is still very low even maxed out. The low normal channel also comes in and out like a wave. I know it’s not supposed to do that, but it could be a trippy effect with delay… haha.
No hum=good !

Is there any DC voltage on the volume pot wipers ( with volume set to halfway ) ?..any DC voltage there indicates one or both coupling caps are no good.
What are the voltages on pins 1 and 6 plus pin 3 and 8 of each preamp tube?
 

Burning Fingers

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I just had another look at the pictures you posted and I am a bit confused.
Do you have a volume pot for each channel and a tone pot that serves both channels ?
Do you have a master volume mod installed ?
Any other modifications ?
 

RickRogers

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I just had another look at the pictures you posted and I am a bit confused.
Do you have a volume pot for each channel and a tone pot that serves both channels ?
Do you have a master volume mod installed ?
Any other modifications ?
I scraped all the mods I was feeling ambitious with. The only change I made is a .022uf coupling cap on the bright channel instead of a .1uf. I wanted to see what it would sound like, but I’m probably going back to how it is meant to be. I swapped out both coupling caps already because I burned one with the soldering iron. I can get the voltage on the pots and pins tomorrow.
 




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