Blackstar Amp with Noises + Other Issue

[iamthesuck]

I have a Blackstar Club 40 Mk 2, and I noticed a couple issues I'd like to get your input on. I heard some weird noises, one day it was a rapid ticking sound that only showed up with lots of distortion, either from the amp or just the pedals. I eliminated all pedals from the signal chain, and it was still present. Volume didn't seem to affect it, but only distortion. This was on the 4w power reduction setting. I turned it off and left it alone. A few days later I tried it on the 40W setting, and after a few minutes I heard a loud noise, like a hum, come through on all channels, even after I unplugged all the pedals, and it persisted. I turned the amp off, and I noticed the power indicator light dimmed very slowly, which is not something I noticed before. I was pretty sure it was the tubes, but with the power light, I became concerned it could be some kind of issue with the transformer or power section of the amp. Repairing this amp is pretty difficult, so I'd appreciate any thoughts you guys have.

[The Dude]

Power indicator dimming slowly is normal. It's caps discharging. I wouldn't be concerned about it. I'd first try tube substitution. Eliminate the easy things first.

[Mick Bailey]

+1. Eliminate any tube issues before proceeding.

These amps can be challenging for an experienced engineer, so give us some idea of your skill level so that we can advise you further. A common problem with earlier versions of these amps is the PCB becoming conductive - particularly around the pads of the MOSFET phase inverter pair. Crackling, rustling, distortion, volume fluctuation and hum are symptoms (in any combination), but other faults cause the same symptoms, so you can't make any assumptions. If you're confident in working on a live tube amp then taking measurements to check the PI is straightforward, but one probe slip could cause far more damage either to the amp or to yourself.

[Jon Snell]

If you have the HFP830 fitted or anything other than IRF830, in the phase splitter, replace the pair as these get noisy or do odd things.
Always ensure the HT has totally discharged before looking at them. FETs can damage easily.