YAOB (yet another one-zero-two build)

[Structo]

I went back and looked at your pictures.

It's hard to tell depth but the heater wires over your power tubes look like they are up against the screen resistors.

Re-check all your heater wiring dress and make sure it is up and away from everything else.

Also, when you recorded the hum, did you have a guitar plugged in?

[aflynt]

I went back and looked at your pictures.

It's hard to tell depth but the heater wires over your power tubes look like they are up against the screen resistors.

Re-check all your heater wiring dress and make sure it is up and away from everything else.

Also, when you recorded the hum, did you have a guitar plugged in?

I'm pretty sure I tried moving the power tube heaters further back, but with no audible reduction in hum. I'll give it another shot tonight. I'm not sure if the guitar was plugged in or not, but the amp makes the exact same sound with it plugged or unplugged.

Thanks again,
-Aaron

[boldaslove6789]

I went back and looked at your pictures.

It's hard to tell depth but the heater wires over your power tubes look like they are up against the screen resistors.

Re-check all your heater wiring dress and make sure it is up and away from everything else.

Also, when you recorded the hum, did you have a guitar plugged in?

I'm pretty sure I tried moving the power tube heaters further back, but with no audible reduction in hum. I'll give it another shot tonight. I'm not sure if the guitar was plugged in or not, but the amp makes the exact same sound with it plugged or unplugged.

Thanks again,
-Aaron

I know this seems crazy but, have you checked your speaker cable? I've had a Cord that drove me nuts trying to find this just audible hum. It turned out it was a bad connection from the factory. Since then I've switched to using George l's Speaker cable ends and either thick 18 awg Copper braided "Lamp Cord", or I really dig Evidence Audio Lyric cable. And I put them together myself, no solder, great connection. Better to check it out now, just incase.

[aflynt]

Interesting. I'll try some different speaker cables. I didn't realize George Ls made them. I'm using some that I put together using Neutrik ends and some 12 gauge wire I bought off Amazon.

[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]

-Aaron

[talbany]

I reinstalled the old Power Transformer (low B+ Quad Reverb) and discovered that the amp still hums in a similar way, just not as loud. Now I'm beginning to wonder if it always hummed but I just didn't notice it until the new higher B+ PT made it more obvious. Anyway... I put the new PT back in. For now I'll just see if I can live with the buzz.

Thanks for the help everyone!
-Aaron

[aflynt]

I reinstalled the old Power Transformer (low B+ Quad Reverb) and discovered that the amp still hums in a similar way, just not as loud. Now I'm beginning to wonder if it always hummed but I just didn't notice it until the new higher B+ PT made it more obvious. Anyway... I put the new PT back in. For now I'll just see if I can live with the buzz.

Thanks for the help everyone!
-Aaron

Sorry, man. I didn't mean to offend or annoy. I truly appreciate all the help I'm getting here. I definitely do want to get to the bottom of this and hope that my DIY hobbyist bumbling isn't turning this amazing forum into amateur hour.

-Aaron

[Mark]

The hum increases with preamp gain, IE: with all the amp controls off there is no hum. With only the master up there is no hum. On the clean channel, turning up the tone controls or volume increases the hum. The hum is loudest on overdrive also increasing with gain and volume.

I'd try strumming a chord and turn the power (not standby) off, this will turn the AC heaters off and the caps will still be charged. Does the hum stop and you clearly hear the guitar till the caps fully discharge?

If this is the case, then ac from your heaters is getting into the audio.

I'd be firstly looking for a bad valve and then I'd be measuring the AC on the rails.

If the hum continues with the power switch off then I'd be looking for a bad earth connection.

I'm thinking the hum can only be on the supply rail or the earth rail, unless of course you have a bad pre-amp tube.

[aflynt]

I've just seen this thread and I'm wondering if the hum is from the laminations of the power transformer or an AC signal in the power supply being amplified?

Thank's for the help!

Q: Does the amp hum if it is on standby?

The transformer itself does, but not through the speakers.

Q: Have you worked out where the hum is present in the amp?

talbany helped me out a great deal in isolating this to the preamp section.

Q: If you remove the PI tube does the hum go away?

Yes. Completely.

Q: If hum is still in the amp are you sure it isn't coming from one of the power tubes?

I did try replacing them and the hum remained the same. I also swapped in different preamp tubes with the same results.

-Aaron

[aflynt]

I'd try strumming a chord and turn the power (not standby) off, this will turn the AC heaters off and the caps will still be charged. Does the hum stop and you clearly hear the guitar till the caps fully discharge?

If this is the case, then ac from your heaters is getting into the audio.

I'd be firstly looking for a bad valve and then I'd be measuring the AC on the rails.

If the hum continues with the power switch off then I'd be looking for a bad earth connection.

I'm thinking the hum can only be on the supply rail or the earth rail, unless of course you have a bad pre-amp tube.

It was kind of tricky to test, but the hum does indeed go away if I turn off the power switch while still playing.

-Aaron

[Mark]

Then the problem is caused by the heaters.

Have you replaced any pre-amp tubes?

I have had hum come from pre-amp tubes. I'd probably swap V1 and V2 and see if there is still hum in the clean channel.

The next thing I'd do it pull V1 (clean channel pre-amp tube) and see if the hum goes away in both clean and distorted modes. The idea being to isolate the location of the hum.

[aflynt]

Then the problem is caused by the heaters.

Have you replaced any pre-amp tubes?

I have had hum come from pre-amp tubes. I'd probably swap V1 and V2 and see if there is still hum in the clean channel.

The next thing I'd do it pull V1 (clean channel pre-amp tube) and see if the hum goes away in both clean and distorted modes. The idea being to isolate the location of the hum.

I've tried different preamp tubes without any change to the hum level. The hum does go away in clean or overdrive if I remove V1.

-Aaron

[aflynt]

Here are some more detailed pictures of the heaters.

[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]
[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]
[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]
[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]
[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]
[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]
[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]
[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]

-Aaron

[Mark]

So the problem has to be in the first stage. You did say the volume control effects the hum?

Does the hum go away when you turn the clean volume control to zero (fully counter clockwise)?

If you get a lead and short the wiper of the clean volume to ground does this effect the hum more than turning the control to zero?

I ask as I've had issues with dodgy Alpha pots.

The thing to work out is which triode is it coming from?

[Dr d]

You might also double check your power tube heaters. With them being both green, it would be easy to accidently wire them out of phase....worth a quick look.

[martin manning]

If the hum disappears with the PI tube pulled then it can't be coming from the power tubes. I don't like the look of the heater wires running up against the snubber caps on V2. Can you bend the caps out to put some distance between them and the heater wires?