Voltage multiplier for sealed, AC Quickie

[Dr. Toobz]

I would like to put my now disassembled Quickie into a nice sealed case for use with my Apple TV in one of my rooms (such as this: http://cgi.ebay.com/DIY-Audio-Aluminium-Chassis-Headphone-amp-Metal-case-01-/150448327532?pt=LH_DefaultDomain_0). Meaning, no exposed tubes or batteries on top, and no messing with having to open the case up every time I need to change batteries. So, I'm thinking of adapting the circuit for AC. Now, getting down to the 36-48VDC range should be easy enough with a cheap 120:24VAC or 120:12VAC transformer and a voltage multiplier. But that leaves the question of what to do with the filaments. I could run them in series at 3V, but that means going from whatever the secondary voltage is (let's say, 12VAC since that type of power transformer is readily available at Rat Shack) to 3VDC, either before the B+ rectifier bridge (i.e., as a second circuit) or afterward (by dropping the "high voltage" DC across a separate resistive divider). The second option seems even more wasteful, as there's more to drop. But I'm not sure either would work all that well.

Should I instead contact Edcor about making a custom 120:36:1.5V transformer? Or am I better off jury-rigging the filament supply from the B+ as discussed above?

(As for the tubes, I'm building each channel onto its own small circuit board, with the tube socket soldered on stiff wire "standoffs" and attached to the board, as to allow the tube to "lay" parallel to the board, resting on top of a piece of foam to damp any vibration. The cases I've seen aren't tall enough to allow the tubes to stand upright).

[Paul Joppa]

Note that the filament supplies are floating - you need three separate power supplies, two at 1.5v (or 3v; the tube allows either arrangement) plus a third at 36v or whatever you wish to run the tubes at.

Many companies make tiny, flat-pack PC mount power transformers with dual primary and dual secondary windings. One of these for the two heater supplies, and another for the high-voltage supply, would probably work well. I'd run them wired for 240v input (primaries in series) to reduce the radiated field. Just a thought.

[Dr. Toobz]

Darn - I conveniently forget that the filament supplies float. I'll look into your transformer idea - or, can just stick to batteries. I probably would only need to change them every few months, as the Quickie won't be used all that much (my main rig is in my music library). Of course, maybe now is the time to put my nascent skills to good use and design a simple 12AU7 or 6SN7 based headphone amp - with the IDHT's, I wouldn't have to worry about three power supplies! Or put some of my 6418 submini pentodes to good use - I've got a bunch of those and haven't found anything to do with them yet (I bought them hoping to build some effect pedals for my new guitar.)

[grufti]

I would go for the power supply that Paul suggested: cheap, easy, no hassle with batteries, no need to mess with a good amp.

[Paul Joppa]

This thread has me thinkin' ...  Perhaps a 24v AC wallwart could do high voltage duty, and one of those tiny PC mount flat-pak transformers with dual secondaries could power the heaters. Feed the 120v winding 24vAC and the transformer will be practically silent. Schottky bridges wouldn't wast too much voltage, and 1.2-v regulator chips are available (e.g. TI SN105125).

With a PC board designed to fit the battery holder mounting holes, it could become a micro-kit if there was enough interest.

[Dr. Toobz]

Count me in if you do a micro-kit....

Breadboarded some 6418's tonight. Interesting little things they are, but much less power (and not as good of sound) as the Quickie (tried them in series feed and parafeed with an Edcor transformer, both in triode and ultralinear mode, 27V B+). That's why I think I'm better off using my Quickie parts for my Apple TV headphone amp vs. building a new battery amp with the subminis. AC is so much more convenient, though.