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Vertical 6EM7 Portable Amp
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Author:  Suncalc [ 09 Mar 2015, 23:04 ]
Post subject:  Vertical 6EM7 Portable Amp

UPDATE - June 2015 - See the 6EM7 Single-Ended Triode (SET) Vertical Amplifier project page for more details.

So, I've been working on a couple of different small amps (as I mentioned here) and I finished one of them today. And this amp is just a little bit different from what one normally sees. Let me explain.

I decided a while back that I needed to take a different tack with respect to my amp chassis. Things just seemed to be getting a little too predictable. After discussing the matter with my son (he studies human design as one of his hobbies), we decided that it would be interesting to change the default form factor from planer to vertical. So I laid out a plan for a big 807 triode strapped amp in the new form factor. However, before tackling the main project I decided to prototype the idea in a smaller package. This would allow me to study the issues associated with this type of build so that I have a better idea of how to attack to big amp. So this amp, is really all about the chassis design. Well, mostly about the chassis design.

For the electrical design, I settled on the V2 version of the 6EM7 amp that I designed for Mark way back in October 2011 and modified in December 2013. And while building it, I even ended up modified the power supply design somewhat. First let me show you how it looks.
Finished Front.jpg

Finished Right.jpg

Finished Left.jpg

The chassis is all black walnut with several coats of Birchwood Casey "True Oil" finish. It then has a couple coats of a quality furniture wax applied to give it a slightly aged look. The handle is a reinforced leather amp handle for easy portability. The amp weighs in at 22.8 pounds (minus the power cord).

In this design the tubes fit in little cubby holes made of the same walnut as the chassis for the sides and back and aluminum plate (painted black) on the top and bottom. Each cubby has vent holes in the top. The back plate has vent holes at the top so that the natural convection airflow is in through the front, up inside the amp, and out the back vents at the top. The amp also sports dual current meters to monitor the power stage cathode current in each tube. Power switch and indicator light (with amp jewel) are on the front along with the master volume control. The lower tube is a 6CA4 rectifier for the power supply. Various electrical connections are on the sides. Overall the amp is 17-1/2" tall (not counting the feet), 12" wide at the widest point, and 7-1/4" deep. This compact size will allow this amp to sit on the back of a desk, or on a book shelf, without taking up an undue amount of space (only 7-14"x12").

The amp sounds great. It is dead quiet at full volume with a paused iPod attached. It has a special split filter power supply for each channel that gives it an unbelievably deep and wide sound stage. Every instrument and vocal shows up in it own position while listening. Here is a picture of the amp playing it's first music.
Finished First Music.jpg

I consider this amp to be a great success. It sounds wonderful, it looks good, and I have learned a whole set of lessons for attacking this type of design. Now when I attack the big 807 Triode Strapped amp, I'll know exactly how to proceed for best results.

So what do people think of the approach? Let me know.

Author:  thehoj [ 09 Mar 2015, 23:12 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Looks stunning, I'm impressed with your woodworking skills.

What sort of current meters are those, and how are they hooked up?

Also, I'm interested in how you did the power supply, is it 2 completely seperate rails after the rectifier?

Author:  Geek [ 10 Mar 2015, 01:05 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Beautiful! :beerchug:

Author:  ToddD [ 10 Mar 2015, 13:15 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

That looks really cool!
Love the walnut.

Author:  laurie54 [ 10 Mar 2015, 18:47 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

A beautiful amp, completely different approach, and good on you for thinking out of the box Matt.

Author:  Les [ 10 Mar 2015, 21:32 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Very nice, Matt. Very cool, indeed.

Author:  mwhouston [ 11 Mar 2015, 07:42 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Love the retro look and the use of nice lumber. How about a shot of the guts?

Author:  RossD [ 11 Mar 2015, 07:53 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

Very nice!

Author:  Suncalc [ 11 Mar 2015, 19:49 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

mwhouston wrote:
How about a shot of the guts?
The guts are scary. One of the things I've learned is that when you build in three dimensions, you really have to THINK about wire routing. I believe I did ok, but I'll do much better next time in the 807 amp.

Here is an overview of the insides of the amp:

Here is a view through the "bottom" of the amp:

And here is a look at the upper cubby with the two 6EM7s before being installed in the chassis:

In spite of the look of the wires, the amp is dead quiet at full volume, driven by the iPod on pause, and with my ear right next to the speaker. Right now the plates one the power stages are running a little over rated dissipation but I'll install a new dropping resistor this week to get the voltages back in line.

Author:  mwhouston [ 12 Mar 2015, 04:31 ]
Post subject:  Re: Vertical 6EM7 Portable Amp

There's nothing wrong with that wiring. Beats a PCB. I'm stuck on Class Ds currently but can't wait to get back to tube-a-licious builds.

Real nice Matt. Not sure I can follow up but I'll give it a try.

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