Millett "Starving Student" hybrid amp - Page 32

Try holding the amp case with one hand (assuming it is metal and grounded) and cupping your other hand around the right tube. If the hum goes away your tube is probably picking up interference from something close by. Something closer to the right tube.

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holland: great information. Thanks for posting! I think I ended up with some 100V caps, and somewhere around here I think I have some values larger than the 470uF as well. This project seems like a great place to tweak and enjoy.

Thanks for the help. I'm using a plastic case right now, but I will try cupping my hand around the tube and see if it does anything. Would using a metal case help? I'm pretty sure I don't have and cold joints since I was very careful when I was soldering. I'll report back later.

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I tried shielding it, but the hum was still there. I will try using it in a different location tomorrow.

I replaced the tube on the side that was humming more, and that reduced the humming. I can listen to it now. The humming is not noticeable when there is music, but is present when there's no music playing.

FIY, the Cisco power adapter is available from two Amazon sellers here:
Amazon.com: CISCO PSA18U-480C /34-1977-03 Power Supply for Aironet Access Point or VOIP Phone: Electronics

Just $4.50 plus shipping. I wasnt even going to build the Starving Student Millet, but I couldnt resist ordering the PSU

This may be crazy but is there a way to modify this design to use 5963 tubes? I wondered why people hadn't made modifications to this design with different tubes? I am not experienced/wise enough to do this but would appreciate if someone else had some suggestions.

Although not specific to the 5963, this was answered by Dsavitsk in Post #116.

So I couldn't get rid of the hum, but I don't hear it at all when a song's on. I'm adjusting to the tube sound (coming from a Mini3, so it sounds quite different), but I like it.

The MOSFETs were getting too hot for my liking so I switched out the heatsinks for these guys GPU heatsink. The MOSFETs barely get warm with them on. Not sure if it'll cause any interference, but it was already humming anyways so it couldn't hurt

Pictures?! That's gotta look kinda funky...

I doesn't look too bad, here's with one heatsink on.

This amp pairs really well with my AD700, but I gotta say it doesn't sound so good with my iM716

A couple of things might help, but one of them may not be very easy to do:

1. There's a reason why Pete spec'd a copper PCB even for a Point-to-Point Bill Of Materials. The bare copper provides a ground sink for the circuit that minimizes hum. This might be very important with an all-plastic case.

2. Do you have R3 and R9 tied directly to the gate legs of the MOSFETs? Pete and Nate both have mentioned a couple of times that might induce oscillation if that isn't done. It's hard to say if that attributes to the hum, but my guess is that it will definitely cause more noise.

3. One reason the heat sinks might run too hot is that they're upside down. The center-notch in the heat sink is meant to provide better cooling by allowing induced air circulation underneath the sink, through the legs of the MOSFET, and up vertically along the entire height of the sink.

#2 and #3 are fairly easy to do. #1 is not so easy. One suggestion might be to find a large copper rod - you might find them at Home Depot. Either an electrical panel grounding rod or a small section of copper tubing might work. Cut it to fit the length of your case (the more metal the better). Nestle it at the back of the case top and run all ground wires to that rod. Just a guess - I'm not sure if it will work, though.

One other comment, it doesn't look like that build uses the BOM heat sinks. The one on the left looks a lot thinner than mine, that's for sure, which would certainly contribute to higher temps.

Good call, Nate! That's definitely a half-inch thick sink - not nearly enough at this voltage and current.