For RG re crackle painting boxes

[Lord Tim of Wah]

Hi
I'm in the UK where products are sometimes differently labeled. Can I ask is the Rustoleum Hard-Hat white you use over the primer Mat (Flat) or High Gloss? I assume Mat. And for how long and at what temperature do you bake the primer and Rustoleum coats? Also what kind of auto metallic paint are you using? Over here I can get acrylic or polyester I believe. I could probably get nitro-cellulose from a specialist paint merchant but auto stores no longer carry nitro-cellulose because of pollution.

Thanks for your tip on testing germanium transistors; I'll try that. Is there anything wrong with new production germaniums? I can easily and cheaply get hold of AC128 AC127 and AC188, but these are the new ones (still in TO-1 cases) the AC128 has its emitter marked with a red dot, the AC127 has a little flange/tab thing. If I measure the HFe on my DMM I get very peculiar results: AC128 measures 11-13, the AC127 over 200 as I recall (yes i did put the PNP in the PNP socket and the NPN in the NPN).

Thanks for your help guys

[Brett Clark]

On the AC128, try reversing the collector and emitter leads.

I don't know about UK parts, but on old US Ge transistors, the dot marks the collector, not the emitter.

[R.G.]

It's almost neither gloss nor mat. I picked it up at a hardware store because it was advertised as being hard and tough. Think of it as something you might spray on construction equipment. There was a yellow hard hat prominently displayed on the label.

The overcoat was acrylic lacquer. The lacquer part is important. What's really happening is that the undercoat is (I think) a high-solids synthetic enamel. Once the ename has dried, you spray on lacquer.

The lacquer solvent in the spray on lacquer cracks the surface film and bores through the opened crack down toward the underlying metal, in the process using up the available solvent, so the damage stays mostly where the cracks start. The first coat of lacquer dries and then protects the enamel from succeeding coats of lacquer solvent, so you get the clear overcoat buildup for gloss and depth.

I don't think that the exact curing time and temperature of the underlying enamel is critical - I hope not because I didn't control that very well. I just let it dry to non-tacky, baked it for a while at under 200F, then sometime in the next day or so sprayed on the car lacquer.

I hope that helps.

[Lord Tim of Wah]

Thanks Brett and RG - very helpful

I bought a spray can of Rustoleum white - it also has the yellow 'hard-hat' on the label. It cals itself Mat - the alternative white Rustoleum was 'High Gloss' so I can assume yours wasn't that one. I can easily get acrylic lacquer here so I should be in business.

I plan to put polyurethene clear lacquer over the top as it is the most hard wearing , but I suppose I better check the compatibility with acrylic.

Thanks again

[brett]

Concerning the transistors.  Sounds right for the AC127.  It's a less leaky and higher gain device than the AC128.  200 is probably the top of the range for them, there's lots with 120 to 150 hFE.  Perfect for making NPN fuzzfaces.  Don't know why they're not more popular.

[Lord Tim of Wah]

Thanks Gentlemen
I am getting a new meter next week (a Wavetek Meterman LCR55 as it's the only one I can find in the UK that measures inductance) and will try the transistors on that. My cheapo DMM I don't think is up to the job as the trannie socket seems dodgy. When I can get it to work many of the AC128s measure about 95 when I first put em in and creep up to 106 or so if I hold em there. The others measure wildly varying amounts (up into the thousands!).
I intend to try to calculate the leakage of each next week and try to get a proper indication of the gain.

And the dot DID indicate the collector - thanks Brett

[Ge_Whiz]

the AC128s measure about 95 when I first put em in and creep up to 106 or so if I hold em there.

That's your explanation. The leakage (and apparent gain) increases as the transistor warms up, even just in the fingers.