I am in desperate need of some help. I would be very appreciative of anyone who can help me solve a problem with vacuum tube headphone amp hum.
First, some background. I built the following headphone amp and it works perfectly, no hum.https://www.aliexpress.com/item/32898304278.html?spm=a2g0s.90423220.127.116.11c484c4dfhenE9
Next I got more ambitious and built the following headphone amp:https://headwizememorial.wordpress.com/2018/03/20/a-single-ended-otl-amplifier-for-dynamic-headphone...
This second headphone is almost identical to the first. The amp part I built is exactly as in the Headwize link. The power supply for the filament is identical to the one from aliexpress. The high voltage power supply is a custom based on a bridge rectifier, followed by 47uf cap, followed by 50 ohm voltage dropping resistor, followed by 330uf cap, followed by 50 ohm voltage dropping resistor followed by 47uf cap. I have separate transformers for both filament and high voltage. The negative of both transformers is connected to circuit ground. The high voltage supply is on a separate board. The filament supply is on the same board, but on the other side of the board. the filament transformer is about 2 inches from the 6AS7.
The problem is that the Headwize amp has a severe hum. The hum is the same no matter what the volume is set to. The hum starts about 30 seconds after power on. If i turn the power off, the music continues to play for a few seconds without any hum. Also, I tried using 4 D batteries for the filament supply and the hum went away.
I have tried everything I can think of to solve this problem with no success, so as I said in the beginning I would greatly appreciate any help I can get. I used high end parts in the Headwize amp, hoping to have a better sound than the aliexpress one.