power transformer for SE micro amp?

[alange5]

I'm planning on building a single-ended micro amp based on the "Deluxe Micro" project (https://robrobinette.com/Deluxe_Micro.htm) with a 12AU7 output stage and a reverb driver as an OT.  Using a diode rectifier, the project recommends a PT with approximately 250-0-250 secondary for about 400v B+.


I'm building the amp in an old radio chassis, and plan on using a LM3914 to control a LED bar as a volume display mounted behind the original tuner window.  I'm using a dual pot to control volume and LED sequence simultaneously.  If I get a PT with a 5V winding, can it be used to power the LM3914?  Alternatively, could I use the 6.3v winding as long as current is within spec? And will either option introduce noise being so closely wired to the volume pot and/or heaters?


Here's a LM3914 datasheet:
http://www.ti.com/lit/ds/symlink/lm3914.pdf


Here's the PT I'm considering if I use the 5V winding:
https://www.tubesandmore.com/sites/default/files/associated_files/p-t270dx.pdf


And if I can get away with using the 6.3V winding, I'd save a few dollars and use this:
https://www.tubesandmore.com/sites/default/files/associated_files/p-t269jx.pdf




Or maybe I'm totally missing the mark and there's a better way to power the IC?  Any input is much appreciated

[shooter]

if I can get away with using the 6.3V winding

That should work, as long as you ISOLTAE from ground, look at bottom off this page and see how Doug does his relay boards.  5Vac tap should also work, but you probably can't use a 7805 since your input volts will be close to output.

[PRR]

> using a LM3914 to control a LED bar as a volume display mounted behind the original tuner window.  I'm using a dual pot

Bah. Move the tuning dial-cord over to the pot shaft. Does the same thing, no electrons. (OK, that may need mechanical cleverness, and typically the tuning shaft is turned-down to a smaller diameter to make the dial-travel work out right.)

> could I use the 6.3v winding

Heater AC should "float". Trying to get grounded DC from it usually throws big DC buzz into heater lines near sensitive audio points.

But hey. The LM391X chip can eat 12VDC. The tubes will eat 12V DC. Making 12VDC out of 6VAC is tricky, and also it needs to be VERY clean to route near preamp nodes. We have the technology.

[alange5]

Bah. Move the tuning dial-cord over to the pot shaft. Does the same thing, no electrons.

I stared at that dial cord long and hard trying to come up with something unique for the tuner panel.  My brain started itching, so I gave up and ordered some LED strips.

Heater AC should "float". Trying to get grounded DC from it usually throws big DC buzz into heater lines near sensitive audio points.

would this be the case with a bridge rectifier? Could I use this 5V regulated supply on the LED's and use an artificial center tap for the filaments? 

[PRR]

> Could I use this

Only if NONE of the "5V" stuff goes to ground. If it does, it makes any "artificial center tap" moot.

And BTW, no need to regulate. I would drop the raw 8V on the LM391x. It don't care. The LEDs won't even flicker if you let the '391x regulate their current.

"Normally" we want our "other stuff" to do something groundy. However I am realizing that if you have a floating pot, and a '391x, and the output is just lights, NONE of that has to be tied to ground. So raw 8VDC from the 6VAC heater winding may work fine.

[alange5]

Alright, I'll give it a go!  I appreciate the advice.  I'll post back with results when I return from vacation in a week or so.