Building the Audio Note Kit 1 SET amp...

Rebbi, I hope your problem turns out to be just a tube, that being the ideal, then it wouldn't have been something you've done.

I'm going to have to bite the bullet myself, and send my Class D Audio amp back to them to fix a screw-up of mine. I enlarged the solder holes in the amp module for LED's that go on the front of the amp. I haven't been able to get them going (I removed all of the conductor traces around the hole when I drilled, duh! I've been trying to fix it, but no dice). The amp still works though, and sounds great.

Tom, at Class D said send it back in he'll fix it for free. I use it as back-up to the SET 300B. I can't recommend Class D Audio highly enough, their CDA amps sound amazing, and work great in the case of tube failure, you still have tunes, and at a very reasonable price.

Hope your AN returns soon, with a clean bill of health.

Regards,
Dan

Dan ,
First watt SS, 300b SET and class D. Different flavors for your Tannoys, I'm sure you're having a ball.😃😃
Charles,

Rebbi, I spent a little while looking at the photo of the underside of the chassis of your build, which you provided on the "Finishing Touches" page of your blog, looking for anything amiss that might account for the problem.

Although it's hard to tell from the photo, the one thing I question is the value of the 3.3K resistors which connect to the grids of each of the 300B's. I can't reconcile the color code bands appearing on the resistors in the photo with that value. The band that appears to be gold in color, at the end of each resistor closest to the top of the photo, would correspond to the +/- tolerance, which is unimportant. Reading the other bands upwards from the bottom, though, I would expect to most likely see orange-orange-black-brown, or (less likely) just three bands colored orange-orange-red. It appears, though, that the band just below the tolerance band is black, which would correspond to a much lower resistance value.

If the resistor value is much lower than the 3.3K the design calls for, it could very well account for the symptoms you've described, due to a lack of what is called "grid stopping". (See especially the paragraph near the bottom which begins with "The main reason for limiting grid-current is to reduce blocking distortion").

Also, regarding the possibility of a defective tube, fwiw I'll mention that based on a look at the schematic it appears that the only tubes which can affect both channels are the 6SN7 input tube, and the 5U4/274B rectifier.

Best regards,
-- Al

Almarg,
Can you be more specific where in the photo you are looking? Is this on the hard wired TAG strip or elsewhere?
Thanks!!

Yes, the two green colored resistors going from the TAG strip to each of the 300B sockets.

-- Al