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Added DC CFollower after pentode 6J7GT V1 stage - getting some high pitch squeal
I am having some oscillations/squeal when I turn the tone pot basically off or full one, after adding a cathode follower after a V1 6J7GT tube. I wanted to keep the amp all octal, and am using a 6SN7 as the preamp cathode follower, and it plays great otherwise, it just has that high pitched squeal. I just finished the amp a few nights ago, and checked out some other tubes which didn't change the squealing. I didn't check the power tubes/6V6's though, but I don't remember ever having one of those go micro...
This is the Filmosound 156 amp version H14. I gutted the extra 6V6, took out the choke in there for the light tube, and added an octal socket where the 4pin light socket was located. The 6J7GT has the top grid that has a copper cover with a shielded cable that goes to the input jack. I added The DC Coupled Cathode Follower taken from Valve Wizard's web site.
Could it be that I have too much gain now, and should just take the cathode follower out, and leave it at the one stage and keep it at that? That was what I had originally planned anyway?!? I just wanted a bit more ooomph from this amp. I did move a wire going to the volume pot and it did quiet down a bit, so maybe I missed a capacitor as looking at the schematic A55 looks like a 100pF may be missing in my design. I will check tonight, am just tossing this out there to see what anyone might think. I have included the original amp schematic and cathode follower I used. I did tweak the values a little on the follower but now much. I cut into the circuit on the schematic just after the 6J7 tube cap A384. Thanks for any help on this.
JRL
This is the Filmosound 156 amp version H14. I gutted the extra 6V6, took out the choke in there for the light tube, and added an octal socket where the 4pin light socket was located. The 6J7GT has the top grid that has a copper cover with a shielded cable that goes to the input jack. I added The DC Coupled Cathode Follower taken from Valve Wizard's web site.
Could it be that I have too much gain now, and should just take the cathode follower out, and leave it at the one stage and keep it at that? That was what I had originally planned anyway?!? I just wanted a bit more ooomph from this amp. I did move a wire going to the volume pot and it did quiet down a bit, so maybe I missed a capacitor as looking at the schematic A55 looks like a 100pF may be missing in my design. I will check tonight, am just tossing this out there to see what anyone might think. I have included the original amp schematic and cathode follower I used. I did tweak the values a little on the follower but now much. I cut into the circuit on the schematic just after the 6J7 tube cap A384. Thanks for any help on this.
JRL
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