Mark IV Sound Fades out then Back in.

[clk102293]

I've been having an issue lately where the sound from my Mark IV will fade out after about 20 minutes of playing then back in after about a minute. This happens on all channels as well as Tweed Power and Full power. I've changed the tubes, eliminated all pedals (Guitar straight to amp), and switching cables, but nothing seems to remedy the issue.

Does anyone have any ideas? I would greatly appreciate any suggestions.

 

[BlackBoxy]

Hi,

i Would check all solder around tube sockets , they dry up and makes micro shorts when tube are hot !

and give a check to heater Power supply ! bring it to a tech

regards