Crack;Bottlehead OTL

[Nebby]

That's running cool by pass lab standards

[Beefy]

Well, the heater on the 6080 alone is dissipating 15W. And guessing up to 50mA through the tube itself, so the 3k plate resistors are dropping up to 7.5W each for another 15W, and some more heat from the plates themselves. That is an absolute minimum 30W total, before we even consider the heat dissipation from the power supply, transformer, and the 12AU7.

So imagine a 30W lightbulb in a similar sized box, and think how hot that would get......

[EDIT] Actually a bit less than 50mA through the 6080, but still a total of about 25W from that tube alone.

[ironbut]

Yeah, if the amps running for an hour and it hasn't snapped a fuse, I wouldn't worry about that. You might consider putting some taller feet on it. I've been using mine to burn in a new pair of headphones running it 24/7 for the past week. When I do that, I usually put the amp on 1/4th inch squares of wood to increase the air flow from underneath. That seems to decrease the heat by about a half. I've got some cheapo rubber feet that I keep meaning to install on mine that doubles the height from the supplied ones.

[guzziguy]

What do people say on the Bottlehead forum? I suspect that they might have a bit more experience with this amp than the people here do, the exception being Steve.

[Nebby]

First attempt at staining wood: spotty.

I used the Minwax pre-stain treatment but I think I should have just gone for some thinned shellac. The question now is whether to try a second coat to even it out or give up and sand it back down for a fresh start?

[Nebby]

[Beefy]

I'm no woodworker, but perhaps a very light sand then a second coat?

When I do mine, I am just going to use several coats of teak oil. Always goes on easy, and very easy to 'top up' without risking of ruining the finish.

[Nebby]

I'm shooting for a dark color scheme with an anodized (or painted if the quote is too high) black top plate and dark-ish stain otherwise I would have gone with a simple light finish like teak oil or something similar.

I'll give it a light sanding tomorrow and see if some careful application of the stain can even it out.

[n_maher]

Anodizing is likely to be a $100+ expense unless you can piggyback on a much larger order. I'd give some thought to trying to find a local powder coat shop and see what they'd charge. I think that'd made a sweet finish for a top panel like that. Otherwise break out the rattle can and be sure to use an appropriate primer/etcher for the aluminum.

[Nebby]

I was originally planning to get it powder coated locally, but the shop quoted me $125 to do a 6x10 panel. That's why I'm now looking to see if I can get in on a larger order with an anodizing company. Worst case I'll go with the rattle can (already bought some just in case)

What do you use to find local services? I'm not getting very many hits via google.

[Mister X]

What do you use to find local services?

Did you try the phone book?

I found when googling it usually helps to add the city or zip code.

[ironbut]

With dark stains on soft woods it's pretty hard to avoid those kinds of blotches. The softer spots just suck up the pigment so you end up with twice as much stain in those places. One way to reduce that effect is to sand the crap out of the wood with 220 grit or higher. Things like UV rays and crap in the air will "wear" the softer areas on the outside layer increasing the differences in the wood density and opening up more pores which result in blotching. Be careful to "always" sand with the direction of the grain. Crossgraining forms crosshatched scratches which aways stain twice as dark making them stand out. From your picture it looks like you may have crossgrained the outside corners or not removed enough stain. Of course, folks do that on purpose sometimes to give the "aged shellac" look.

Different stains also help. I like gel stains. Gel stains don't penetrate into the wood as deeply. Like most stains, you apply it and wipe off almost all of it. There are several companies that make it but "Old Masters" is pretty good, comes in lots of colors and you can usually buy it in small cans. As far as stain types go, I think you like what you're used to though.

The key to getting good results is to try your entire process on the inside of the base. Now that you're at the point where you're considering sanding and starting all over you need to take a spot inside and do what you've done on the outside of the base to find the best method of getting back to square one. That's one nice thing about the way the chassis plate just sits on the base. You can do anything you want and not have to worry about masking anything off.

So, once you have a decent sized patch of the inside just like the outside, experiment away. If you can't find a way to rescue what you already have on the outside, you'll be able to see the best way to get rid of it on your sample.

[Nebby]

The corner darkness is caused by an admittedly poor job of masking tape clamping, after I finished gluing I found that there was slight cracks at the corners and thats where a lot of stain ended up. After looking at the frame again, it seems like the first panel I did turned out best, on that panel I had let the wood conditioner driver sit for a longer period of time so I think the root cause of the splotching might be a combination of crossgraining sanding and uneven drying of the wood conditioner.

Mister X: Thanks for the idea, I'll need to find a phone book first as I don't even have one

[Beefy]

I was originally planning to get it powder coated locally, but the shop quoted me $125 to do a 6x10 panel. That's why I'm now looking to see if I can get in on a larger order with an anodizing company. Worst case I'll go with the rattle can (already bought some just in case)

Why not just get an FPE panel for it? Works out cheaper...... Crack Panels from Front Panel Express - How to Order

Though I would probably try and get hold of the FPD file and get rid of the Mickey-Mouse font they use, amongst other modifications.

[Mister X]

What color do you have in mind for the top?

If you're thinking about doing it black I would almost be inclined to do a piano black style finish on it.

It's pretty easy to spray the paint, wet sand, wet sand, spray again if needed, wet sand, wet sand and then clear coat it (there are a ton of case modding tutorials out there if needed).

Just takes a lot of drying time...

[Nebby]

I'm going with a black top. I do think piano black is nice, but dust and fingerprints become very obvious with it but even so, now that you mention piano black it is tempting. I was personally thinking more along the lines of a satin finish for the top plate or brushed finish in the case of anodized black. Honestly, I was just hoping to do something different than a simple spray coat but was surprised by the quote for powder coating; I didn't expect it to cost nearly so much. If the anodizing quote is similar (which I'm going to guess it will) I'm going to spray the panel myself. Heck, if I had my own house I'd already have bought a DIY anodizing kit and went to town with the panel.

Beefy: I'm trying to stay with the stock case setup because I know if start dipping my hands into FPE, I can't just let it go with only getting a color change. Too tempting!

Any ideas on where can I get etching primer? Last time I painted a Hifi2000 panel I simply used an all-surfaces primer and didn't use an etcher.

[Nebby]

Found where to get etching primer: amazingly enough (automotive) paint suppliers carry them.

[dsavitsk]

If the anodizing quote is similar (which I'm going to guess it will) I'm going to spray the panel myself. Heck, if I had my own house I'd already have bought a DIY anodizing kit and went to town with the panel.

It's worth calling around, but most anodizers are slop shops used to doing 50000 pieces or more per run where per piece quality is not that important. Finding someone willing to take care of your stuff and not charge a ton is difficult.

If you want anodized, you'll probably get the best results for the least money having CamExpert/FPE mill a new plate out of pre-anodized stock. The edges won't be anodized then, but you can embed the plate in a rabbet cut in the wood so it won't show. The quality of the anodizing will be a lot higher. And, if you want brushed, they can special order brushed/anodized material. If you don't want to measure, send the precut sheet to Heinz and I'm sure he can just replicate it for you.

[Nebby]

Ironically enough there's a full machine shop and paint/plating shop at work that definitely do top notch work, but their hourly rates are likely well above my budget.

Thanks for the info dsavitsk, I'll think about getting a custom panel done from FPE. Once I start that though, it'll be a good opportunity to look into mods/improvements for the Crack beyond the Speedball. Might as well since I'm getting a custom top panel, right?

I did look into DIY powder coating and it actually doesn't seem too difficult aside from finding an oven large enough to contain your workpiece; given how much of electronics DIY involves metal panels I think in the long run it might make more sense to invest in such a system (assuming it really is as easy as the documentation I've read says).

[spritzer]

To powdercoat a piece like that here wouldn't cost more than 20$ and that's with 25.5% VAT.

[Nebby]

I called around and found a small powder coating shop with a reasonable price, should be interesting to see how it turns out. Powder coating it also works out well since I can get the transformer bell done at the same time.

I was surprised to find that minimum order charges were about even for both powder coating and anodizing services, $75 and $100 being the most common.

[Beefy]

Once I start that though, it'll be a good opportunity to look into mods/improvements for the Crack beyond the Speedball. Might as well since I'm getting a custom top panel, right?

There aren't that many things that you can mod/improve, and certainly very few that require top panel alterations.

The sensible upgrade list as I see it in order of priority is Speedball, output caps, volume pot, input connectors. Maybe headphone jack as well. So for the top panel you would only need to get the correct key location for the pot, and correct hole size for the input and output connectors.

Anything more than that is probably pretty pointless from a cost/benefit standpoint.

[Nebby]

Then I've already covered the gamut of sensible upgrades with what I have now Just didn't know if there were any other worthwhile changes that could be done without going overboard, so I was wondering out loud as it were.

[luvdunhill]

I called around and found a small powder coating shop with a reasonable price, should be interesting to see how it turns out. Powder coating it also works out well since I can get the transformer bell done at the same time.

I was surprised to find that minimum order charges were about even for both powder coating and anodizing services, $75 and $100 being the most common.

group buy?

[Nebby]

We'll see if their work is good first, then if it is we can contemplate that option if people are interested. Shame they didn't have satin black, only semi-gloss black...close enough I suppose.