Any reason Not to shield the 12AU7?

[Strikkflypilot]

Might be a stupid question,but I want my Mainline all black on top.
Any reason shielding all tubes with anodized black shields would be a bad thing?

 

[Grainger49]

It won't hurt it.  The aluminum will draw heat off of it.  So it might give longer life?

 

[Strikkflypilot]

Thanks, Grainger.
I think it will look cool and add a little safety, don't want burnt prying little fingers, also thinking of adding a grounded metal mesh to the bottom of the mainline for safety reasons, will connect it to ground with locking washers, crimped connector AND solder, and then connect to the grounding screw with a big fat stranded wire for mobility.

 

[Paul Birkeland]

It's no big deal to put a shield on the 12AU7.  We don't put one on because it's not in a particularly sensitive position.  IIRC, the 6C45PI tubes get quite a bit hotter than the 12AU7.

The 12"x12" base has a recess on the bottom, so a 12"x12" aluminum plate can be fabricated as a bottom plate.  Mesh is a nice idea, but generally not very stiff.  A thin piece of aluminum will work nicely, and you can glue in some small mounting blocks in each corner to keep the plate in place.  A little drain wire from the grounding screw by the IEC inlet on the Mainline that attaches to the plate would satisfy the safety conscious. 

-PB

 

[Strikkflypilot]

Thank You very much for the reply, PB,
I wasn't aware of the recess.
I was thinking mesh for ventilation, but if a plate is ok, then that's great!

 

[Paul Birkeland]

Yes, I would add some holes to it, however.

You may also need to add larger holes where the heatsinks pop through, as they are pretty close to the bottom of the amplifier.

-PB

 

[Strikkflypilot]

Very good. Gives me quite a few ideas

 

[Paul Joppa]

Sometimes you can find perforated plate inexpensively - usually it's "decorative" but check out a large hardware stode - always fun to go browsing.

 

[Strikkflypilot]

Thanks for all the answers.
Really looking forward to this build.
It is already underway from San Fransisco

 

[Chris65]

Another option would be an acrylic/perspex base, like Blumentstein bases:

 

[Strikkflypilot]

Oh man, so many choices

 

[NightFlight]

Why the bottom plate at all? Little fingers?

As for the 12AU7, Mine reads 46oC while the 6C45Pi's read 36oC at the center of the tube body.  Different 12AU7's run at different temperatures as well. One 12AU7 I tested ran 10oC lower. 

I have also tested to see if the shields draw more heat away.  Allowing them to come up to temperature I would removing them and quickly test again only to find no difference.  I've heard no difference with and without, but I'm still acclimating to the sound of this amp so I might be off there. I run without shields.

 

[swich401]

I have also tested to see if the shields draw more heat away.  Allowing them to come up to temperature I would removing them and quickly test again only to find no difference.  I've heard no difference with and without, but I'm still acclimating to the sound of this amp so I might be off there. I run without shields.

Having the tube shields in place for the 6C45s is also a precaution against radio-frequency pickup in the tubes which could result in high frequency oscillation. 6C45 tube oscillation can make the output of an amp containing this tube sound "hard", or have harsher treble. Best to keep the tube shield in place in my opinion.