trinityamps.com

Mitch, thanks for your continued dedication and extremely prompt replies! I looked at all of my photos after reading your suggestion that the wires were reversed and was convinced you were right, in spite of having traced all of the leads on final inspection. BUT alas, after cracking it open one more time and in spite of what the pics look like, things were actually connected correctly. I did my best to send the wires to less populated areas but didn't see any change. The mystery continues...

Not really surprised that the wiring is OK. If the wires were reversed, I think you would have known long ago because the tone stack wouldn't work as expected. They do look reversed in your photo, though!

Not really sure what to suggest next. Maybe change C6. It's interesting that the treble issue doesn't happen with the overdrive engaged. Does it matter where the master volume control is set when you hear the treble control act up?

Just checked for your Master Vol question--if the master is above about 5 o'clock (aka dimed), the treble knob issue as shown in the YouTube video doesn't happen when turning the Treble knob. Alternately, if Treble is maxed and has already gone past the "pop" into the attenuated territory and you rotate the Master from below 5 o'clock to above it, there's a less drastic static burst noise that occurs when the knob passes 5 o'clock. These are all pretty extreme settings!

I went ahead and ordered a .001 replacement for C6 in an Amplified Parts order I just happened to be placing, so we'll see if that has any effect!

So, I changed the C6 capacitor a while back with no effect. I've just been living with this slight issue and going on with my life, but I've also been learning a lot about amp design and construction and completing more projects: a 5F1, a Princeton Reverb, and a 6G3. Yesterday I came across an older D-Lab video where he diagnoses a Princeton experiencing an extremely similar issue using an oscilloscope. He describes the issue as parasitic oscillation/distortion--the fix? Grid stopper resistors. But the Triwatt already has one on each power tube. I'm wondering if there's more than one way to combat this issue, especially since he claims that the issue shortens power tube life.

I just read through this thread and I have the exact same thing happening with my build. I noticed it when I first took the amp through its paces, and figured that since I likely would never run treble all the way up like that, it wasn't something I wanted to chase down. The overall performance of the amp seems fine other than that.

At this point, my suggestion is to review your lead dress. Shortening, Separating wires and crossing wires at 90 degrees. I've not had this issue in my builds.
Check out the picture for clues.



and here's a large hi res picture

http://www.trinityamps.com/ForumGallery/trinity/triwatt/circuit_board.jpg

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hi Stephen and PharmRock, thanks for the replies, and sorry I'm a couple months late--in fact, I somehow missed Stephen's reply to review lead dress until I came back to follow up. I'm about to embark on an 18-Watt build and wanted to resolve any lingering issues with my Triwatt to start from a clean slate. That, and the laziness of not wanting to unpack the chassis and poke around was holding me up!

Stephen--I came to the same conclusion without seeing your post after gaining much more amp-building and troubleshooting experience during the lockdown (7 more amps, to be exact!): LEAD DRESS. I found I was able to eliminate the pop by snuffing the V1A plate resistor with a .1uf capacitor, so I started chopsticking leads around V1, V2, and V3. I was able to get a little joy with the chopstick on the V3A plate/grid wires, so I went through all 3 tubes' plate and grid wires, shortening most of them, getting more space between them, and crossing as cleanly as possible as Stephen suggests. Et voila, no more pop!

Revisiting the layout, I have to say Stephen has done a very good job of showing you where the wires should be--the closer you follow that, the better your chances are of avoiding any oscillation issues. As someone who marveled at the precision of other users' Triwatt builds here and attempted a similar look, my build style has progressed to the point that I really don't care if all the wires are making their way around the chassis at 90-degree angles--the ability to see/access everything, and a cleaner lead dress has become the focus, which doesn't necessarily translate to visual precision all the time (not to knock those out there who've achieved both a quiet amp AND such a stunning look .


I would recommend you try and sort it out, if possible, since there's potential it's oscillating below that point on the knob too. Since the oscillation is often above our hearing range, it means the amp is constantly amplifying the oscillating signal, causing potential unnecessary wear and tear on your transformers and tubes. Then again, it may not be a practical problem--unfortunately I've got an obsessive personality so I find it really hard to let stuff like this go!! Hope you're enjoying your Triwatt.

Which version of the FC12 are you using ceramic or almico?

Thanks,
Kev

Ceramic. Far as I know the original Fanes were ceramic.