Strange Blackstar MKiii issue

[gibsonfan159]

I picked up a new HT club 50w MKiii head a year ago. It has two channels, each with a boost selection, and a 5w setting. Great amp until about 4 months ago when I started noticing volume fluctuations on both the 50w and the attenuated 5w settings. Now, on the 50w setting, the boosted setting is quieter than the normal setting and the gain sounds the same either way. Also the clean channel has noticeable overdrive no matter how low you set the volumes.

Switching to the 5w setting actually increases volume, but the boost switches seem to be operating normally. Which leads me to believe the normal 50w setting is jacked up in some manner. I'm hoping a tube replacement might be an easy fix but I don't feel that lucky. I have emailed Blackstar but no reply yet.

 

[gearJunkie]

I'm hoping a tube replacement might be an easy fix

Sounds like a tube issue. Before buying any tubes, try swapping the positions of your preamp tubes, and then your power amp tubes, testing the amp between each change.

If the amps behavior changes, replacing tubes should remedy the issue.

Good luck and be careful. Make sure your amp is powered off and unplugged before swapping tubes. Do not open the amp chassis unless you are familiar with how to safely discharge and test the filter caps for residual voltages.