Help with weird noise -2203

[Jonsnothere]

Hello,
Purchased and built a kit from Triode Electronics based on their diagram. See product here

http://www.triodeelectronics.com/100wmarshkitv2.html

Video of the sound here, this is with no speaker connected just the amp itself squealing. In Hamilton Ontario Canada so this is on 120V mains.

https://youtu.be/oT6fO0Y2LjY

I thought it was a short, redid all the wires, thought it was interference, shielded all signal lines, thought it was tubes, checked all of them and fully functional to spec, thought I blew a transformer, checked all those and also at spec, flipped grounds all around and confirmed an accurate loop on the ground.

Plate voltage reading at 378, set bias at 31ma.
Sound does come out when I connect a speaker but it is amplifying that sound when the speaker connects, it does go away in the amp but then the speaker sounds similar, high pitch hum, signal does get through but is nominal.

See the wiring diagram, it doesn’t match much of the schematics I find for a Marshall 2203 with a MV mod, should note that switch I’m flicking is standby and the knob is the Master Volume, no other knobs affect this tone or sound.

Left on and the volume up blows the HT fuse.

Any and all help is appreciated.

[Randall]

This sounds like a HF oscillation. This is typically due to lead dress, or possibly try swapping OT primary wires from one side of output tubes to the other.

[Enzo]

Hi

NEVER operate a tube amp without a speaker or resistor load. It can cause the output transformer to damage itself.

I don't have sound on my computer, but if I had to guess unheard, I'd suspect you have the plate wires from the output transformer reversed. A quick way to find out is to disconnect that orange wire from the speaker selector switch back to the middle of the eyelet board. Just unsolder from the board and tape the end up. Did the noise stop?

[Jonsnothere]

Hi

NEVER operate a tube amp without a speaker or resistor load. It can cause the output transformer to damage itself.

I don't have sound on my computer, but if I had to guess unheard, I'd suspect you have the plate wires from the output transformer reversed. A quick way to find out is to disconnect that orange wire from the speaker selector switch back to the middle of the eyelet board. Just unsolder from the board and tape the end up. Did the noise stop?

Thanks for the tip,
There isn’t a speaker selector, just the resistance selector, is that what you mean?
I did notice on my traces that there was something feeding between the primary and secondary windings but once I disconnected the wires it was gone.
If it’s the orange resistance selector wire let me know, I’ll try that.

[Jonsnothere]

This sounds like a HF oscillation. This is typically due to lead dress, or possibly try swapping OT primary wires from one side of output tubes to the other.

Thanks Randall, I did swap tubes and that didn’t help.
What do you mean “lead dress” I don’t know this term

[Enzo]

Lead means wire, dress means arrangement. Lead dress means the physical routing and arrangement of the wiring. In other words keeping input and output wires away from each other. That sort of thing.

Speaker impedance selector switch.

[Jonsnothere]

Lead means wire, dress means arrangement. Lead dress means the physical routing and arrangement of the wiring. In other words keeping input and output wires away from each other. That sort of thing.

Speaker impedance selector switch.

Thanks Enzo!

Well I did map out the chassis myself and thought of that as a potential issue so I shielded as much signal wire as I knew could be interfered with.
Just at work but will lift that wire, I believe the orange is the 8ohm winding and from my wire traces that does sound extremely logical. Will post results this evening, thanks again and hope that’s it!

[Helmholtz]

The Triode layout shows 2 orange wires connected at the impedance selector. You should disconnect the longer one (being the NFB wire) which leads to the board.

But this is only a preliminary test to find out if the OT primary wires need to be reversed. If you prefer you may skip the test and directly reverse the OT primary wires (blue and red ) at the power tube sockets (pins #3).

Do you use the original Triode OT?

[Jonsnothere]

The Triode layout shows 2 orange wires connected at the impedance selector. You should disconnect the longer one (being the NFB wire) which leads to the board.

But this is only a preliminary test to find out if the OT primary wires need to be reversed. If you prefer you may skip the test and directly reverse the OT primary wires (blue and red ) at the power tube sockets (pins #3).

Do you use the original Triode OT?

All as spec per Triode except 0.1uF Presence cap, I replaced that with Nichicon as I blew it while testing but that makes sense as it’s right next to that same line... don’t get me started but that was the problem, their diagram is wrong, I thought so and now it works.

Huge thanks and holy shit is this loud!!

Will post a demo vid here and thanks again for the help!

[The Dude]

So, to be clear, the cap alone was the problem, or did you do something else?

[Jonsnothere]

It was that one line, I disconnected the line from the impedance selector

[Helmholtz]

It was that one line, I disconnected the line from the impedance selector

Sorry, not clear.
If you leave the longer orange wire disconnected, this will disable NFB and presence. Instead you should reverse the OT primary blue and red wires that lead to the power tube sockets.

[Jonsnothere]

Sorry, not clear.
If you leave the longer orange wire disconnected, this will disable NFB and presence. Instead you should reverse the OT primary blue and red wires that lead to the power tube sockets.

Ok can confirm, the presence is not working but sound did work. Master volume is fine but Volume knob also is unresponsive, I think that’s unrelated though.

So I should swap the blue/red wires on the pin 3 power tubes, then reconnect the 4ohm (orange) line from the impedance selector switch back to the 100k Presence resistor, is that correct?

Thanks again Helmholtz, super helpful here!

[Helmholtz]

So I should swap the blue/red wires on the pin 3 power tubes, then reconnect the 4ohm (orange) line from the impedance selector switch back to the 100k Presence resistor, is that correct

Correct.

[Enzo]

Let us be clear. Disconnecting the long orange wire was not the solution, it was a test. it is a hell of a lot easier to lift that one wire to see if NFB is the issue, than it is to rewire the tube sockets. Now that we know it WAS the issue the solution is to rewire those sockets.