does anyone recognise this fault? Audio link

[bibio]

Hello,

I recently finished building a 5F1 style kit amp for a friend.  I upgraded some of the components but all values were kept the same.
It sounded great and worked perfectly.
After a few weeks, it started to develop this noise after around 15mins of use:

https://vocaroo.com/i/s1HtgRzWCPc6

As you can hear from the link there is a lot of hum and a popping sound.
Unfortunately, I'll be away for the next month so won't be able to inspect it.
The sound is quite unique, does this ring a bell with anyone?
Strange it only happens after 10-15 of use, sort of implies its heat-related????
When it was built it had all brand new components fitted.  Cathode, screen and plate currents all verified and dissipation checked.
I'm quite confident it's not a dry joint or lose connection but open to all possibilities.
Could anyone hazard a guess at a potential cause of the issue?
All help much appreciated.

[jjasilli]

Might be bad tube or RF interference.

[Willabe]

Strange it only happens after 10-15 of use, sort of implies its heat-related????

I'm quite confident it's not a dry joint or lose connection but open to all possibilities.
Could anyone hazard a guess at a potential cause of the issue?
All help much appreciated.

Yes, heat is a good guess.

Tube could be bad, but doesn't revel itself until after getting hot, grid/cathode/heater alignment could move with heat.

I know you think your solder connections are good but, could be bad solder joint, common for this to revel itself after heating up. Hum and popping are common symptoms.         

[bibio]

Hi Guys,

Thanks for the response.
It's a difficult one to identify with the limited information.
Equally frustrating I can't start fault finding right now!
You know that feeling when you can't wait to solve a problem.......
Not exactly sleepless nights but lots of wondering, did I make a mistake????

[DummyLoad]

sounds like arcing. is the 5Y3 healthy? cold solder joint?


--pete