Tysen
Active Member
Hey folks!
I have an early version of the 400c (no dual tone knobs). I recently had a tech (who will go nameless) restore it (caps, out of spec resistors, and selenium rectifier)...I got it back and it worked fine for literally 2 weeks. This was back in November. While working, it produced a lot of noise which I read prior to the restoration was normal for this unit.
Well, now I have a pre that produces barely audible distorted noise, even at full volume.
I've completed a couple of projects since then and I feel confident I can fix this. I also feel confident I can perform dcgilliespie's mods, but not without help from this great community!
So, I'm starting this thread to document the mods in case I run into problems.
Here's my starting point:
I'll be starting the restoration on Wednesday, but I hope to gather base voltage readings beforehand to see if I can pinpoint my current problem of almost inaudible distorted output. I know it's not the rest of system because everything else works with my passive pre in place. I also should point out that the distorted sound happened somewhat gradually—at first it was a volume imbalance so I swapped tubes between V3 & V6 thinking that my 12AT7s were fried. The imbalance remained. I'm nervous to put in another new set of my 12AT7s and risk killing them too...
Dave suggested that I inspect the integrity of the tape monitor jacks. Which I still need to do. I also will try cleaning the volume pots to see if that helps.
Cheers!
—Tysen
I have an early version of the 400c (no dual tone knobs). I recently had a tech (who will go nameless) restore it (caps, out of spec resistors, and selenium rectifier)...I got it back and it worked fine for literally 2 weeks. This was back in November. While working, it produced a lot of noise which I read prior to the restoration was normal for this unit.
Well, now I have a pre that produces barely audible distorted noise, even at full volume.
I've completed a couple of projects since then and I feel confident I can fix this. I also feel confident I can perform dcgilliespie's mods, but not without help from this great community!
So, I'm starting this thread to document the mods in case I run into problems.
Here's my starting point:
I'll be starting the restoration on Wednesday, but I hope to gather base voltage readings beforehand to see if I can pinpoint my current problem of almost inaudible distorted output. I know it's not the rest of system because everything else works with my passive pre in place. I also should point out that the distorted sound happened somewhat gradually—at first it was a volume imbalance so I swapped tubes between V3 & V6 thinking that my 12AT7s were fried. The imbalance remained. I'm nervous to put in another new set of my 12AT7s and risk killing them too...
Dave suggested that I inspect the integrity of the tape monitor jacks. Which I still need to do. I also will try cleaning the volume pots to see if that helps.
Cheers!
—Tysen