5E3 Amp Whistling - Bright 1 Jack

[paul-e-mann]

Set your digital multimeter DMM to measure V DC 200V range, clip the black probe to the chassis and the red probe at the V3&4 6V6 pin 8 node.
Switch the amp on, allow it a few minutes to warm up and stabilise, then take the reading.

FYI a circuit node is an equivoltage point where 2 or more circuit elements meet aka connect.
Usually represented on a schematic by a dots on the lines linking stuff together.
The above node also includes one end of the cathode resistor and its bypass cap.
So you can clip on to whichever lug / lead etc of any of those 4 nodal points is most convenient

20.5 VDC

 

[paul-e-mann]

Exactly, the point is to compare current flows when the amp is idling normally to when it’s acting up.
To that end, output valve cathode voltage is missing

I measured everything normal and acting up and voltages dont change.

 

[BlueX]

So I figure while I'm in here I'll tackle another peculiarity thats going on. The amp makes some noise now and then while I'm playing and I tap the amp to make it stop, I thought maybe a dodgy tube so I tried isolating one at a time but that wasnt it. I dont see any more loose connections anywhere either. I'm able to duplicate the problem by tapping on the chassis, see below video. Any thoughts?

Have you tried replacing, or moving, tubes?

Might be another bad solder joint, that's not visible (not sure how to find it, if so).

 

[paul-e-mann]

Have you tried replacing, or moving, tubes?

Might be another bad solder joint, that's not visible (not sure how to find it, if so).

Yeah I already pulled all tubes, replaced each one at a time.

 

[paul-e-mann]

I'm out of ideas to get this working right, been awhile since I looked at it, the amp works and then it doesnt work, when it doesnt work all I gotta do is give it a smack and its working again. I'm thinking I might reflow every solder joint, they all look good but I must be missing something. This sound like a realistic plan?

 

[Chris-in-LA]

I'm out of ideas to get this working right, been awhile since I looked at it, the amp works and then it doesnt work, when it doesnt work all I gotta do is give it a smack and its working again. I'm thinking I might reflow every solder joint, they all look good but I must be missing something. This sound like a realistic plan?

Yes

 

[Pete Farrington]

For most typical builds, of equal importance to the soldered connections are the mechanical ones, mainly to the chassis.
They need to be torqued up, with a good sharp star washer between the soldered connection lug (or whatever) and the chassis metal.

 

[2L man]

Have you installed insulation washers to input jacks? If there are how do three of them get the Reference for Signal? One jack SR seem to be wired to potentiometer case.

When it began making the noise does either Volume have any effect to the noise?

There can come noise when input impedance come high for example when jack switch fails. Or 1M resistor fails. Volume potentiometer is on input triode output so it should have definite effect to this noise.

When one input jack switch has failed often it is in the jack which stop the noise when guitar cable is inserted to it when guitar bring some impedance to the input.

 

[paul-e-mann]

For most typical builds, of equal importance to the soldered connections are the mechanical ones, mainly to the chassis.
They need to be torqued up, with a good sharp star washer between the soldered connection lug (or whatever) and the chassis metal.

Everything is tight

 

[paul-e-mann]

Have you installed insulation washers to input jacks? If there are how do three of them get the Reference for Signal? One jack SR seem to be wired to potentiometer case.

When it began making the noise does either Volume have any effect to the noise?

There can come noise when input impedance come high for example when jack switch fails. Or 1M resistor fails. Volume potentiometer is on input triode output so it should have definite effect to this noise.

When one input jack switch has failed often it is in the jack which stop the noise when guitar cable is inserted to it when guitar bring some impedance to the input.

All the jacks are grounded together and one is then connected to grounding bus on the pots (plus all jacks are grounded to chassis). The original problem is fixed, it was a grounded solder joint that broke loose, now I just get a random noise that can be fixed by smacking the amp (see post #14), I can smack the amp and make it come back too.

Also I can have amp on with no cable or guitar connected and after awhile it will make noise on its own, then I tap the amp to make it stop.

 

[GAStan]

Have you tried to pull V1 and/or V2 to see if it will still make the sound?

 

[Resident 217]

 

[paul-e-mann]

Have you tried to pull V1 and/or V2 to see if it will still make the sound?

Pull the tubes and just let it idle? I have but just to get startup measurements but I didn't leave them out long, and I had also replaced the tubes with spares which didn't make a difference.

 

[paul-e-mann]

View attachment 144963

Yes they are close it's a very tight space and where they sit was the best position, but with cable plugged in they don't touch anything.

 

[2L man]

I always make wires as short as possible because I think "lifting Circuit Board" is impossible even wires are longer. I do not solder any wires under the board because on top side they are more accessible.

First you should shorten wires between both double 68k "grid blocks" and input tube control grids because now they are very long. The length between grid block and control grid is most sensitive for extermal Electromagnetism. Now they are very close the Chassis*** I always solder 68k direct to tube socket where they block the best forming a low pass RC filter with control grid Miller capacitance. I often use a shielded cable as well. This also save CB room for other use.

***The layout you have used make HV currents flow "wildly" thru chassis and thru potentiometer cases which make amp more prone to many kind noises!

Mains Electrics was make safer about 50 years ago when mains Safety Earth came mandatory in new buildings. When SE wire run parallel with Hot and Neutral there inevitably come EM noise so it is best to lessen possibility for interaction with amp (secondary) circuit not using Chassis for operative current. It has been forbid in electric regulations since SE introducion because it increase noise to mains.

 

[paul-e-mann]

I always make wires as short as possible because I think "lifting Circuit Board" is impossible even wires are longer. I do not solder any wires under the board because on top side they are more accessible.

First you should shorten wires between both double 68k "grid blocks" and input tube control grids because now they are very long. The length between grid block and control grid is most sensitive for extermal Electromagnetism. Now they are very close the Chassis*** I always solder 68k direct to tube socket where they block the best forming a low pass RC filter with control grid Miller capacitance. I often use a shielded cable as well. This also save CB room for other use.

***The layout you have used make HV currents flow "wildly" thru chassis and thru potentiometer cases which make amp more prone to many kind noises!

Mains Electrics was make safer about 50 years ago when mains Safety Earth came mandatory in new buildings. When SE wire run parallel with Hot and Neutral there inevitably come EM noise so it is best to lessen possibility for interaction with amp (secondary) circuit not using Chassis for operative current. It has been forbid in electric regulations since SE introducion because it increase noise to mains.

Yes I've been told by a couple members to shorten my wires but I haven't cuz the amp is dead quiet and sounds great and has for the past year until this problem arose, I don't think shortening wires will fix the problem. I don't like the wires under the board, that I wish I didn't do, also I don't like the cloth covered wire the kit came with it's very messy and brittle. I think if I were to shorten the wires I would all out replace them with better wire and move the wire from the back to the front. Also I've been told my grounding is not very good and all of it should be routed directly to the chassis. But again, with all these flaws the amp sounded good and dead quiet for a year. So I'm kind of at a stand still here, if I can't get this noise resolved I may eventually pull the amp apart and start over, which I don't really want to do.

 

[Chris-in-LA]

Tapping makes the sound come and go, use your chopstick on every wire, cap, resistor and solder connection until you isolate the area where the sound is coming from.

 

[GAStan]

When I suggested pulling v1 or v2 yes I meant to leave it out and try to replicate the sound. This would help isolate where the sound is originating. If you pull v1 and can still replicate the sound then it is originating after v1. You can also disable a single triode by using a jumper to ground its input (after coupling cap before grid stopper). If you can isolate the section of the amp where the noise is originating you can focus on only those components.

 

[2L man]

Yes I've been told by a couple members to shorten my wires but I haven't cuz the amp is dead quiet and sounds great and has for the past year until this problem arose, I don't think shortening wires will fix the problem. I don't like the wires under the board, that I wish I didn't do, also I don't like the cloth covered wire the kit came with it's very messy and brittle. I think if I were to shorten the wires I would all out replace them with better wire and move the wire from the back to the front. Also I've been told my grounding is not very good and all of it should be routed directly to the chassis. But again, with all these flaws the amp sounded good and dead quiet for a year. So I'm kind of at a stand still here, if I can't get this noise resolved I may eventually pull the amp apart and start over, which I don't really want to do.

You could tack solder wire shorting other input jack and use only one. Removing filament voltage on pin 4 or pin 5 on input which you not use and triode stop amplifying. Tack soldering a wire from grid to 0V is good method to stop triode amplifying.

Then if there does not come oscillation anymore you know it is the input circuit which cause the oscillation.

There was a video where turning both pre amp volumes did produce whistling noise. Master volume did produce lower frequency noise and pre amp volumes were about 5. That noise is quite typical when input jack is open. If you have new 6,3m plug you could test inserting it to all four inputs and observe noise. If there in one input where inserting plug increase noise only little then that jack switch might be bad. Instrument cable without quitar bring much more noise. If you do not have unused plug a short cable which is used to connect pedals should increase noise much less than instrument cable so test it.

When amp function normally and you turn all volumes 10 do you hear any mains frequench hum or other noises?

If you don't find a good fix which stop the oscollation then using perhaps two hours changing few wires and shortening input wires and installing grid blocks to tube socket is well wasted time

 

[paul-e-mann]

I've decided to rebuild this amp. I want to replace all the fabric covered wire, what should I get, what gauge, what colors, and where can I get a good deal on wire?

I want to redo all the grounding, I was told by many people here the grounding is not good, what do I need to do?