Dominator II Build (Dumbleator II)

[rccolgan]

Thanks, Guy! The build doesn't look so pretty at the moment lol trying to figure out the source of the hum. I used a pair of UF5408 to drop the voltage down a little with the heaters. They have a vF of 1.7v and I had a few laying around.

I just tried your trick DC elevating the heaters using 1M/100k & .22uF cap and no change

Rafael thinks it's a ground loop and I just might not have found the magic combination yet of ground lugs and circuit isolation.

I have a 12vDC power supply coming from Amazon tomorrow so I can power the tube heaters to help diagnose. I'm struggling here with the last 10% ha.

[Guy77]

Thanks, Guy! The build doesn't look so pretty at the moment lol trying to figure out the source of the hum. I used a pair of UF5408 to drop the voltage down a little with the heaters. They have a vF of 1.7v and I had a few laying around.

I just tried your trick DC elevating the heaters using 1M/100k & .22uF cap and no change

Rafael thinks it's a ground loop and I just might not have found the magic combination yet of ground lugs and circuit isolation.

I have a 12vDC power supply coming from Amazon tomorrow so I can power the tube heaters to help diagnose. I'm struggling here with the last 10% ha.

Hi Ryan. Thanks for the info on the diodes.
Sorry to hear that didnt reduce noise. I actually went lower than 1M for the first resistor. I ended up changing it to 720k.
Since your B+ is even lower than the amp I used that on (445v B+) you probably need to use a resistor smaller than 1M.

Cheers
Guy

[rccolgan]

Thanks, Guy! The build doesn't look so pretty at the moment lol trying to figure out the source of the hum. I used a pair of UF5408 to drop the voltage down a little with the heaters. They have a vF of 1.7v and I had a few laying around.

I just tried your trick DC elevating the heaters using 1M/100k & .22uF cap and no change

Rafael thinks it's a ground loop and I just might not have found the magic combination yet of ground lugs and circuit isolation.

I have a 12vDC power supply coming from Amazon tomorrow so I can power the tube heaters to help diagnose. I'm struggling here with the last 10% ha.

Hi Ryan. Thanks for the info on the diodes.
Sorry to hear that didnt reduce noise. I actually went lower than 1M for the first resistor. I ended up changing it to 720k.
Since your B+ is even lower than the amp I used that on (445v B+) you probably need to use a resistor smaller than 1M.

Cheers
Guy

Thanks again, Guy! I really appreciate the assistance. You're right, I should have checked my DC offset before coming back to the forum because I definitely didn't have the right offset. Now I'm sitting at ~62vdc DC offset using 500k+ 100k/22.uf and the hum is still there.. so maddening!! It's gotta be somewhere else but this is all good for the process of elimination. Thanks again for chiming in! I should have new things to respond with once I get the DC power supply in tomorrow to test.

[dbharris]

Ryan,

Do you just have the 2 star grounds now on either end of the power board? Is the ground plane on your 1/4 jack pcb split or is it all connected together? Also wanted to confirm you scraped the chassis to bare aluminum under your grounding points.

I looked back at your build and Charlie Wilson's and I am thinking your grounding scene is different from HAD's.

-Dan

[rccolgan]

Ryan,

Do you just have the 2 star grounds now on either end of the power board? Is the ground plane on your 1/4 jack pcb split or is it all connected together? Also wanted to confirm you scraped the chassis to bare aluminum under your grounding points.

I looked back at your build and Charlie Wilson's and I am thinking your grounding scene is different from HAD's.

-Dan

Hey Dan.. You just read my mind.. I'm looking at Charlie's photo and I'm not sure why I didn't just follow that grounding scheme from the beginning... The 1/4 jack PCB is not split (all together like buss bar) Same with the front controls... I did scrape down the powder to bare metal with my Dremel at least

I understand my next assignment now... Time to rebuild this thing.

[dbharris]

That should sort you out. Also pay attention to the filter cap grounds.

Good luck!