• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Front Panel Express finishes

Had two different panels made up with this vendor, to see what kind of craftsmanship and finish I could get. To say the least, I am extremely satisfied. The holes are perfect, and everything smooth and perfectly aligned (as much as my drawing dictates, of course). The time and effort in using punches, drills, and cutting fluid has come to an abrupt end !

Now, my issue comes down to finish. One panel I had constructed with raw aluminum, the other anodized. Both have their merits, I suppose. Here are my dilemmas:

1) Anodized finish: Long lasting, durable finish. No oxidation or need to clearcoat. However, the bottom side of the panel is nonconductive, which I like using for a ground plane. For instance, ceramic caps from heater pins to chassis, or shields of dual triodes. Only solution I can come up with here is to sand/buff the surface down to bare metal for conductivity.

2) Raw finish: Good conductivity on the bottom surface, nice finish on the top. However, with light polishing (say, with Mother's) will the finish remain oxidation-free for an extended period of time? Even though the amp will be indoors, raw aluminum is very reactive with oxygen.

3) Raw finish with alodine coating. Is this conductive? If not, I'm somewhat at point 1.

4) With any of these above methods, I can copper and silver plate the aluminum, so can end up with a permanent conductive surface. Silver oxidizes quite easily also, but it's easy to polish and restore to a very conductive surface. My thought was to have a silver surface on the bottom for conductivity purposes, and whatever permanent and oxidation-free surface is practical on the top surface.

What finishes have you chosen, and how has it held up long term ?
You could pick locations where you would like to attach your grounds and use a mill bit to spot face the region. This cuts through the anodizing to reveal the base aluminum. Thus you have a region that allows conductivity, while still having most of the plate protected. From my experience, you would be better off with alodine, not anodizing. It is a stronger surface finish. I work with a lot of aluminum like this, the anodizing scratches easily, especially black. Then you really can't get the scratches out. You would have to check with the metal shop or plater to confirm, but I think that alodine is conductive also.


You know, sometimes it just helps to read a little further. From the Front Panel Express website:

Anodized aluminum/chromated (reverse side pictured)
Available thicknesses: 2.0 mm / 2.5 mm / 3.0 mm / 4.0 mm.
The front is natural anodized. The reverse side is chromated and thereby conductive, making it suitable for EMC applications.

Fantastic. That's EXACTLY what I need. Front is clear anodized, for a nice finish and durable life. Rear is alodine (which is basically a chromating process, thereby conductive). So, I just spent $135 on a piece of aluminum that really has little value. Serves me right.
Picture of the panel attached. Not a very good picture with the flash, but you get a good idea of the cutting precision. From their website, they do not guarantee the finish of raw aluminum, so the very light scratches are there, but are exaggerated in the picture. From what I have seen with their colored anodizing, the finish is superb.

All in all, the price is low given the labor and chemicals it would take me to build something similar.


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That would be a power supply only, my friend. For a Karna amp, http://www.nutshellhifi.com/Karna.gif

Two 500V supplies for output stages, and two 400V supplies for driver and input stages. Electraprint power trannies. Hammond chokes. ASC motor runs. 6DE4 dampers. I wanted to avoid a 4 chassis design, and managed to squeeze both power supplies in one. The supply will sit in the rack, the monoblocks will sit underneath each speaker.

I know in general where I'm going with the amp proper, but haven't concluded the final design yet. I'll have more questions for the forum gurus when I get the power supply completed, and start testing the individual stages.

Wenge wood will be the chassis for the power supply, and curly bubinga for the monoblocks. Can't wait to see the final product.
JoshK said:
my PSU transformers should arrive in a week or two (ordered from Onetics).


Let me know how you like them. I am considering O-netics for the output transformers (digs deep into pockets).

I will say, however, I am very happy with the Electraprints. They are extremely quiet, in comparision to the typical Hammonds, and have very good (5%) regulation. Beefy trannies.


2007-11-02 2:15 am
Any advice on powder coating an aluminum top plate? I need a deep red/burgundy top plate to use on a gold tone Koa base, and the only way I'm going to get the color I want is either custom powder coating or car paint. Should I go for the raw aluminum, or something clear anodized. Will the powder coating heat destroy a chromated finish on the underside?




2007-09-08 4:32 am
zigzagflux said:

No. Power coating is an electrolytic process, and doesn't require heat. You can actually tape the areas you don't want coated, and put the plate through the process. Pull the tape off when you're done. I would think this would work just peachy.
every powder coating process I've ever seen has a baking step where the powder is permanently adhered after spraying the powder.

At the risk of irritating Josh, Jack at ElectraPrint is probably as good as you can get for power.

PM Lynn Olson for his current view of the filament situation for the DHT's. We do have filaments powers with near absolute balance between halves of the secondary windings and extremely good shielding. Josh will get his in about a week and can report.

O-Netics is as good as you can get for the audio output transformers. This includes the interstage devices.

Tribute is still the best sounding input splitter transformer, but very costly. Sowter has a very good unit also. When I get to i,t we will also have a very good input splitter, based upon the preamp outputs we have.

Lundahl has some very good small signal transformers that can also be used as input splitters.

On a different note, all transformers are going up in price pretty dramatically. Materials pricing has doubled for all items, with one material having risen by 1700% in 4 years (M6 core) and the copper base price up 400% in 2 years. Not an excuse here, just a warning of what to expect.

Being this is my thread, I guess I can threadjack a little. If it goes anywhere, I could start another thread.

Thanks for your reply, Bud. It is an honor to have you provide advice.

BudP said:
ElectraPrint is probably as good as you can get for power.

That is comforting. I want the best that I can afford, and Jack's prices, while high, were justified given the quality. I ordered shielded trannies, too, because I know how you and Lynn feel about shielding and keeping heater supply separate from power supply, which is what I did. O yes, I definitely read and take your(s) advice.

PM Lynn Olson for his current view of the filament situation for the DHT's

I will do that; at the risk of getting flogged with boos, I have already built and tested 4 regulated DC supplies for the output stage. But I am always open to try, if the benefits of AC outweigh the annoying hum. Was careful to use split bobbin transformers and common mode chokes; we shall see.

O-Netics is as good as you can get for the audio output transformers. This includes the interstage devices.

I believe you. I have not yet bought the iron for the amp proper, as there are a few paths of the design I am considering. However, you will definitely be considered for the iron. Lundahl's 1620AM would be your competition with me. Kevin at K&K is a great supplier of iron, service, and moral support.

Materials pricing has doubled for all items

You ain't kidding. Even more surprising is the fact that most mining company stocks are in the toilet. Patience, patience.