I’m quite inexperienced when it comes to forum posting, so please accept my apologies for all the blunders I’m bound to make. I’ve been lurking on this forum for around a year now and I have to say that I’ve learned a tremendous amount, so it about time I made a contribution.
Now if it could be blackened a little bit.......
If only. I’ll just have to pretend they’re using really good coal on a really cold day and its being fired by a really good fireman! Can’t have everything.
I did dabble with the smoke some years ago but it was fairly uninspiring as it would not produce a decent 'puff' of smoke. Would you care to provide details of your home-made units?
The smoke units are really simple; the only problem is the enclosures. The heaters are two 15ohm heaters wired in parallel. They get their power direct from the track via a zero crossover relay. I also put a 2amp nano fuse in-line, just in case. I don’t understand electronics, but I’m told the zero cross over relay is needed to avoid excessive voltage spikes, which I dare say wouldn’t be too good for the decoder. The relays are available from
www.7mmlocomotives.co.uk//index.php?option=com_virtuemart&page=shop.browse&category_id=7&Itemid=52
I started off using the Peter Clark Smoke Units
www.peterclarkkits.com/smoke-units--lighting-kits.html
but these seem to be primarily aimed at diesels or at least larger steam locos. I cut off all the electronic stuff and reduced the size of the fan and chamber. I replaced it with a brass unit but I guess I could have just cut down the original mazak arrangement.
This was fine for the Safety Valve Unit and the next couple of photos show how I mounted it in the Firebox.
Trying to get a square assembly into a round smokebox wasn’t going to work very well, so I machined up a special round unit.
The material is PTFE. It machines quite well, has a very low thermal transfer rate and quite a high melting point. Having made the round unit I thought I might as well make a ‘proper’ one for the Safety Valves.
If anyone is interested, I would publish my drawings for the two units.
I'm in the process of building one of these locos and am interested as to where you sited the speaker and zimo chip.
I’ve put two identical speakers in the loco, one at the front as shown in the photo, and one in the coal bunker.
Both point down to the track and are ‘in phase’. I came across an interesting article regarding speaker and sound.
www.youtube.com/watch?v=j4kgLeDltxg
Well worth a look. I carried out some trials myself as I didn’t really believe that a speaker would actually be better when it’s not mounted in an enclosure, but it’s all true.
Remember that my loco is S7, so I’ve got a bit more room between the frames. I think it would still be possible to put the same speaker in a ‘normal’ loco but it would have to be cut down to fit.
I can’t take a photo of the bunker speaker because the body is back with Warren Haywood. Warren painted it initially and did an absolutely superb job. Unfortunately, when I was doing a bit of maintenance work on the chassis, I caught the side of the body and it fell of my workbench onto the floor! OMG, I can tell you it’s not a pleasant feeling when you pick it up off the floor and examine the damage. The roof had sprung off, the bunker was folded up towards the firebox and the rear steps were very badly bent. Anyway, it’s now repaired, albeit, nowhere near as good as it was originally and it’s back with Warren for him to produce another miracle. I’ve shown a photo of the coal which covers the bunker speaker. Although it does muffle the sound a bit, it’s quite surprising how much it lets out.
Where you put the decoder is very dependent on what decoder you fit. This photo shows the size difference between the larger MX696 and my failed MX645. The ‘package’ for the MX696 also includes two zero cross over relays and two nano fuses.
The only place for the MX696 is in the boiler which is why I’ve cut it way so much and fitted a much lower profile motor/gearbox than specified by MOK. When I originally used the MX645 I fitted it in between the frames under the cab. Quite a good arrangement, so it’s a shame that I had to change to the larger version.
I'm about half way through my next engine which is an MOK 8F.
Regards
Steve