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I am restoring an Ampeg B18N. This is an amp for a major studio here in NYC and was really hurting. At first they just wanted the speaker replaced, but then I uncovered all KINDS of stuff, like poorly piggybacked filter caps hanging out inside the amp with the most piss-poor wiring job, blobbed solder joints, frayed AC cord, death cap still in there (with a 3-wire cable!)... just pitiful. And the wrong rectifier tube to top it all off.
I replaced the caps with the proper filter can and a series cap network for the first B+ cap, plus the bias cap and diode. I also replaced the rectifier tube with the proper 5AR4, as well as a new pair of Sovtek 7027A's and a new Sovtek 7199 driver/PI. The 6SL7's installed were Sovtek and looked relatively new, so I left them alone.
After I got it all together, this thing hummed like a bastard! The hum balance control was doing some weird things, with several nulls across it's travel. I checked and rechecked my work and all grounds and got NOWHERE! I kept pulling my hair out on this and then thought "Let me try another 7199". I have a bunch of NOS Sylvania's in stock. So I did, and BINGO!..... 75% of the hum was gone. The other 25%? The f***in' "relatively new" 6SL7's! Two new ones, an adjustment of the hum balance control, and the amp was DEAD quiet. Oh yeah, like any good B18N, it sounds just SUPER!
So much for new tubes, huh?
I replaced the caps with the proper filter can and a series cap network for the first B+ cap, plus the bias cap and diode. I also replaced the rectifier tube with the proper 5AR4, as well as a new pair of Sovtek 7027A's and a new Sovtek 7199 driver/PI. The 6SL7's installed were Sovtek and looked relatively new, so I left them alone.
After I got it all together, this thing hummed like a bastard! The hum balance control was doing some weird things, with several nulls across it's travel. I checked and rechecked my work and all grounds and got NOWHERE! I kept pulling my hair out on this and then thought "Let me try another 7199". I have a bunch of NOS Sylvania's in stock. So I did, and BINGO!..... 75% of the hum was gone. The other 25%? The f***in' "relatively new" 6SL7's! Two new ones, an adjustment of the hum balance control, and the amp was DEAD quiet. Oh yeah, like any good B18N, it sounds just SUPER!
So much for new tubes, huh?
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