Hy i have very similar amp , 6an8s for the small tubes it was 6L6 out puts but some one converted it to 6bg6ga out put tubes ----amp works and has great sound when it warms up , very warm , very pleased but amp has a small back ground hum when idle , and i would like to fix this , but not sure what to do , mabey increase a cap value , but would like input on this ---------not much or many on line , for this one , uses 5u4 rectify too . has run light , on /off switch and speaker jacks - this amp has way better sound then my maggies it has mcintosh type sound , and i do have a pair of MC30s - but it has this hum issue that i need help with , its not a lot , not real bad , but its there and you really only hear it a quite times in music or at idle with no input signal , ive tried ground ing chassy and reversing the power plug , no go ! --- could it be because of the out put tube switch ? should i put it back to 6L6 ? please help ! have another sylvania console tube amp that i use on my multi tube amp system just to power my jbl 2404h tweeters its a el84 amp similar to a maggie it works great to power the compression tweeters in my four way system , the mcintosh mc 30s power just the jbl 2012h ten inch lower mids , a maggie 8802 powers the jbl midrange 2445 horns with 2380 lens --- if i can get that hum out of the sylvania it could be a back up to power my lower mids or a replacement for my maggie 8802 to get a bit moor power to the mid range horns ---------electronic crossover is a sony tad888 , all thanks to my late uncle watts ------------a solid state amp powers the 15 inch 16 ohm JBL woofers