G4003G...100 watts of wall shaking thunder

[ogberi]

Usually tube shields are mu-metal, and work by absorbing stray EM and converting it to heat like a shorted turn in a transformer. Aluminum should work, though I've never seen or heard of one made from aluminum. I'm interested to see how well it works! I knew an old timer, maybe 25 years ago, who made his own tube shields from large transformer EI lamintations. He'd cut the middle out of an E section, and run it through a sheet metal roller to make a tube, and solder it closed. He used piano wire to make spring clips to hold the shield down tight to the socket. The clips held onto the top of the shield, and went into holes in the chassis.

Dangit man, I got enough projects going on. You're making me wonder about building that 6AS7/6080 headphone amp I've been putting off for too long. :thinking::lmao:ondering:

 

[coolidge]

Usually tube shields are mu-metal, and work by absorbing stray EM and converting it to heat like a shorted turn in a transformer. Aluminum should work, though I've never seen or heard of one made from aluminum. I'm interested to see how well it works! I knew an old timer, maybe 25 years ago, who made his own tube shields from large transformer EI lamintations. He'd cut the middle out of an E section, and run it through a sheet metal roller to make a tube, and solder it closed. He used piano wire to make spring clips to hold the shield down tight to the socket. The clips held onto the top of the shield, and went into holes in the chassis.

Dangit man, I got enough projects going on. You're making me wonder about building that 6AS7/6080 headphone amp I've been putting off for too long. :thinking::lmao:ondering:

Embrace the tube amp sickness my brother. Black .125 thick board with plated through holes, hybrid turret/PCB.

 

[John Hasler]

Usually tube shields are mu-metal, and work by absorbing stray EM and converting it to heat like a shorted turn in a transformer. Aluminum should work, though I've never seen or heard of one made from aluminum. I'm interested to see how well it works! I knew an old timer, maybe 25 years ago, who made his own tube shields from large transformer EI lamintations. He'd cut the middle out of an E section, and run it through a sheet metal roller to make a tube, and solder it closed. He used piano wire to make spring clips to hold the shield down tight to the socket. The clips held onto the top of the shield, and went into holes in the chassis.

Dangit man, I got enough projects going on. You're making me wonder about building that 6AS7/6080 headphone amp I've been putting off for too long. :thinking::lmao:ondering:

Mu-metal is magnetic and shields against stray magnetic fields (i.e., from the power transformer) by having high permeability. It also shields against high frequency magnetic fields and electrical fields by being conductive. Ordinary steel will work nearly as well. Just make it thicker. Aluminum was often used for tube shields in applications where low frequency magnetic effects were not a concern but weight was. It provides less effective shielding against low frequency magnetic effects but is excellent for shielding against higher frequencies and against electrical fields.

In an audio amplifier your primary concern is probably 60-cycle hum. For that you want steel. Mu-metal would be preferable but sheet steel will help a lot.

If you want to go nuts over 60-cycle hum put the power supply in a seperate steel case and run DC for the filaments.

 

[John Hasler]

But - despite what the audiophools say, do not bother making big aluminum heatsinks for the tubes. It won't make one single bit of difference in how hard you can push them. Running the tube at it's absolute maximum ratings, you'll still be within the thermal limits of the glass, base, and socket. (unless it's a cheap recycled plastic socket from China. If it is, toss it and get a good ceramic China socket.) "heatsinking" the tubes is just a waste of a lot of nice aluminum.

It isn't just a waste. It's counterproductive. Glass tubes like those are cooled almost entirely by radiation (some heat is removed via convection from the glass). Sheathing them in aluminum will tend to reflect the heat back and make them run hotter. There is no advantage to shielding power amplifiers: the levels are too high for the effects of stray fields to matter.

 

[coolidge]

Guys mu-metal shielding is not required for reducing hum in this guitar amp. Its about proper amp design and layout and grounding. This 100 watt amp is silent with the volume on 4, and that's quite loud. With the volume on 8 again no hum but you do hear some white noise that says you better put some freaking ear plugs in. If you crank it full tilt to 10 and smell dust burning you might hear a slight hum but you better be playing in a foot ball stadium at that volume. And that's with AC powered pre-amp tubes, one could go with a DC power supply on the pre-amp to further reduce hum but I think that's overkill in this amp.

Now IF you were building a small amp in a cramped chassis with the transformers and components crammed together, the above may not hold true.

 

[wrmiller]

Ah...brings back memories. My first two years of electronics theory was tubes. My first ham set was all tubes. Yea, I'm that old...

 

[John Hasler]

Embrace the tube amp sickness my brother. Black .125 thick board with plated through holes, hybrid turret/PCB.

Do it right. Use point-to-point wiring on ceramic standoffs (or phenolic terminal strips if you're cheap like me).