5F6A heater voltage, hum and volume problem

[vincenzo]

Hi, I've several problem with this amp. Hum is this:
 

I tried to remove V1 and hum is still there, I remove V2 and hum is stille there slightly quieter, I remove V3 and hum is disappeared. Then I swap V2 and V3 without changes, so I tried other new tubes on V3 and hum is disappeared but volume is decreased about 50% less. Then, I tried all my 12ax7 in V3 and no changes. I decided to reading voltages:
 B+ 410VDC
 
 V1
 pin1 210-220
 pin3 1.8
 pin6 215-225
 pin8 1.8
 
 V2
 pin1 188-190
 pin3 1.1
 pin6 328
 pin8 188
 
 V3
 pin1 271
 pin3 18
 pin6 375
 pin8 18
 
 V4
 pin4 420
 pin5 408
 pin6 -45
 pin7 408
 
 V5
 pin4 408
 pin5 408
 pin6 -45
 pin7 405
 
 In the same moment:
 
 wall voltage 213VAC
 heaters unloaded 5.95
 heaters loaded 4.6
 
 
 I noticed that fuse holder that contain 4A fuse for heaters wires were hot, I do not know if it is normal.I think that problem is around V3 or too low heater voltage. I do not know what dropping heaters voltage.
 

[tubenit]

What power transformer are you using?  What are the specs for the transformer? 

What kind of power tubes are you using?   6L6/5881?

[vincenzo]

PT is a Hammond 290DEX. Power tubes is 6L6GC
Update
Heater voltage is resolved. The problem was a bad fuse holder.
Also I change a V3 tube and now amp has right volume but remain to fix hum

[shooter]

check wires, especially from tonestack area

[vincenzo]

It seems that the cause of the hum is heater wires. I got up heater wire from V2 with a chopstick and hum has significantly reduced but not completely gone.
 What can I do to get better? Are they too close to signal wires? Can Heater elevation resolve?

Also I noticed that if I touch or move V2 grid wire at pin2 amp has scratch noise and pop. If I touch with a chopstick this wire amp has pop

[tubenit]

I am thinking your heater wiring may be too close to the bare wires that you have on V1, V2 & V3 sockets?  Don't know that to be the problem, but perhaps it could be?   It's not that the wires are bare, it's that they may be too close?

I use "above" heater wiring even on my tweed style amp chassis and they are very quiet at idle. 

Maybe if you had the heater wires floating above and then coming down on the sockets in a way that is not so close to those bare wires, it might be quieter?

The other thing you might consider is do you need more B+ filtering? 

With respect, Tubenit

[sluckey]

wall voltage 213VAC
 heaters unloaded 5.95
 heaters loaded 4.6

Why is your wall voltage so low? That PT is expecting 240VAC. Your low wall voltage is causing your heater voltage to be very low, maybe too low for proper tube operation. I would be very concerned if my filament voltage was only 4.6. Is this maybe a meter issue?

Also, do you have the filament center tap connected to chassis ground?

[vincenzo]

wall voltage 213VAC
 heaters unloaded 5.95
 heaters loaded 4.6

Why is your wall voltage so low? That PT is expecting 240VAC. Your low wall voltage is causing your heater voltage to be very low, maybe too low for proper tube operation. I would be very concerned if my filament voltage was only 4.6. Is this maybe a meter issue?

Also, do you have the filament center tap connected to chassis ground?

In Italy wall voltage is much instable, it varies from 207 to 230. Anyway, low heater voltage is resolved. It was a bad fuse holder. Also I added a voltage stabilizer that keeps voltage at 230V with 6% tolerance. Now heaters voltage varies from 5.8 to 6.2V and yes, filament are center tap to ground

[shooter]

this wire amp has pop

usually bad solder connection, loose socket pin, that sorta thing

[Willabe]

Also, do you have the filament center tap connected to chassis ground?

[vincenzo]

I am thinking your heater wiring may be too close to the bare wires that you have on V1, V2 & V3 sockets?  Don't know that to be the problem, but perhaps it could be?   It's not that the wires are bare, it's that they may be too close?

I use "above" heater wiring even on my tweed style amp chassis and they are very quiet at idle. 

Maybe if you had the heater wires floating above and then coming down on the sockets in a way that is not so close to those bare wires, it might be quieter?

The other thing you might consider is do you need more B+ filtering? 

With respect, Tubenit

I'll try to lift heater wires far above bare wires.
 What do you mean about "more" B+ filtering? Increase filter cap value?

[Willabe]

Also, do you have the filament center tap connected to chassis ground?

This is very important. Please verify if you have the heater CT grounded or have a faux wired and grounded.   

Would hate to see you spend the time moving the heater wires on top of the sockets when it was just no heater CT or faux CT.

[vincenzo]

Also, do you have the filament center tap connected to chassis ground?

This is very important. Please verify if you have the heater CT grounded or have a faux wired and grounded.   

Would hate to see you spend the time moving the heater wires on top of the sockets when it was just no heater CT or faux CT.

Thank's Willabe, yes, I have the heater center tap firmly to ground.
I suspect that my main problem is bad solder joints every where. I would be tempted to unsolder all components and resolder it.
I hate having this V2 grid wire at pin 2 that pop and scratch when I touch and move it.
Do you think it's better to concentrate to it or unsolder all components?

[John]

I hate having this V2 grid wire at pin 2 that pop and scratch when I touch and move it.Do you think it's better to concentrate to it or unsolder all components?

That seems like the place to look. Re flow solder joint at pin, if that doesn't fix it replace the wire itself - it may be broken inside the insulation somewhere.

[Ed_Chambley]

Since you photo only shows the tube side, in a tweed chassis it is easy to get a high voltage component near a Pot.  This causes noise.  Your heater wiring could be better.  I would look for the problem first.  Yes, you filter question is upping the Large Caps, but I have built many old tweeds using the lower value caps and this has never been an issue.


Sounds like motorboating, power tubes especially, bad solder joint on new filter caps or elsewhere, loose components and/or circuit board, choke going bad.  The hum broken up by static sounds like a tube or a plate resistor.


You can check your Cathode voltage on the power tubes and connect the center tap to elevate the heaters.  I have checked and heater elevation gets more quiet between 60 and 70 VDC, but I have had a lot of success with simply connecting the center tap to cathodes with 20 to 30 VDC.


Pull your tubes one at a time to find out which one is causing the hum.  If it is coming from a tube filament, it should get quiet when you pull the tube where it is originating.


Also, read this http://www.valvewizard.co.uk/heater.html


It will show you a very neat way to run your heater wires and also give input on what may be your noise.

[vincenzo]

Since you photo only shows the tube side, in a tweed chassis it is easy to get a high voltage component near a Pot.  This causes noise.  Your heater wiring could be better.  I would look for the problem first.  Yes, you filter question is upping the Large Caps, but I have built many old tweeds using the lower value caps and this has never been an issue.


Sounds like motorboating, power tubes especially, bad solder joint on new filter caps or elsewhere, loose components and/or circuit board, choke going bad.  The hum broken up by static sounds like a tube or a plate resistor.
This scenario is drastic even if in fact static sound was caused by smarthphone. The problem is that when I use chopstick sometimes I get pop or scratch noise, sometimes no.

You can check your Cathode voltage on the power tubes and connect the center tap to elevate the heaters.  I have checked and heater elevation gets more quiet between 60 and 70 VDC, but I have had a lot of success with simply connecting the center tap to cathodes with 20 to 30 VDC.

Do you mean connect heater CT directly to power tubes cathode?

Pull your tubes one at a time to find out which one is causing the hum.  If it is coming from a tube filament, it should get quiet when you pull the tube where it is originating.I tried to raise up heater wires around preamp tubes and hum is significantly decreased. Anyway I get pop and static sound around V3 pin2 grid wire and sometimes when I touch V1 couplind cap and circuit board. This makes it difficult for me to understand.
I need to be followed step by step, please.


Also, read this http://www.valvewizard.co.uk/heater.html


It will show you a very neat way to run your heater wires and also give input on what may be your noise.

[Ed_Chambley]

You shouldn't have to do anything different, like elevating the heaters.  You are not cathode bias, so your cathode is grounded.  I missed this.  If you have this hum and moving your heater wires makes if change and if you get pops whit a wooden chopstick, then you should know where to begin.

[vincenzo]

Update
I think I've solved it. The problem was a bad or cold solder joint on V1 coupling cap. Now the amp is quiet, it have not popping when I touch board or other components.
What I do not understand is how, this problem, caused all these noises. Indeed, sometimes, he made the preamp tubes microphonic and caused popping everywhere.

[tubenit]

Congratulations on getting it resolved and sticking with it!  Bravo!   

And I appreciate your taking the time to share your success!

With respect, Tubenit

[Ed_Chambley]

Update
I think I've solved it. The problem was a bad or cold solder joint on V1 coupling cap. Now the amp is quiet, it have not popping when I touch board or other components.
What I do not understand is how, this problem, caused all these noises. Indeed, sometimes, he made the preamp tubes microphonic and caused popping everywhere.

The problem was a V1.  The reason it was a problem is because any noise at V1 gets amplified a lot.  A coupling cap is supposed to block DC, but since I did not see it I cannot be sure.  I can surely tell you this.  If you have poor lead dress and solder joints all that current that should go to the next stage, but if it cannot it lives in the chassis.  The current in am amp when running (EMF, Electromotive Force) will "find" the least path of resistance.  A Plate poorly soldered to a coupling cap results in sending current inside the amp.  It doesn't just go away.  If the current escaping has a closer connection, it will couple to it, just like a transformer does with primary and secondaries.


Most Fender amps have around 180 VDC provided to V1 on the plate.  The cap should block the DC, but not if it is not soldered in place.  This electricity will find a path.


Lot of guys believe they can just put an amp together and as long as your layout matches the schematic, you are fine.  Not the  case at all.  There is a reason people use the term proven layout.  Glad you got it.

[PRR]

> a bad or cold solder joint on V1 coupling cap. .... What I do not understand is how, this problem, caused all these noises

An early telephone was based on "loose contact". If a circuit has a barely-touching electrical connection, shaking it (even talking at it) makes audio vibrations in the circuit.

This was Grey's Patent. Bell's Patent (which became super-valuable) used a different principle. Neither was a good telephone. Grey's microphone only made distorted "sound"; slightly intelligible but nasty. Bell's microphone was clean but very-very weak. Interestingly the "carbon microphone" used for almost a century "was" a loose-contact device, but instead of one loose contacts it had hundreds (powdered carbon, actually selected coal dust).

So it wasn't the tube being microphonic, but a connection TO the tube.

[vincenzo]

Well, I have to say that the merit is not mine, but yours alone and for this I thank you.

I am grateful also for the explanation.
This forum is full of really prepared and available people.
Thank's