You need the Heavy Steam decoder, because it can be programmed to represent a 4-cylinder ariticulated engine.
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IIRC the four-cylinder steam option - where the sound of the two sets of drivers goes in and out of sync - should only be used if you replaced the low-pressure front cylinders to create a "simplified" engine. I think the replacement cylinders are included with the Spectrum 2-6-6-2.
As built (and as the model comes out of the box), the high-pressure steam went to the smaller rear cylinders first, the exhaust low-pressure steam then was used by the larger front cylinders, then exhausted out the stack. I believe in this true "Mallet" configuration, the two sets of drivers would always be in sync.
In the simplified version, where all four cylinders get high-pressure steam directly from the boiler, the two sets of drivers are independent of each other and can slip in-and-out of sync.
Anyway, I'd still probably opt for the "heavy" steam option for sound for this engine, but if you got a good deal somewhere on a "medium" sound decoder, that would probably work fine too - unless you've installed the high-pressure replacement cylinders.
(Interstingly, the much smaller Mantua/Model Power logging 2-6-6-2 has all four cylinders the same size, so should probably get the "heavy" sound decoder too!!
wjstix wrote: IIRC the four-cylinder steam option - where the sound of the two sets of drivers goes in and out of sync - should only be used if you replaced the low-pressure front cylinders to create a "simplified" engine. I think the replacement cylinders are included with the Spectrum 2-6-6-2. As built (and as the model comes out of the box), the high-pressure steam went to the smaller rear cylinders first, the exhaust low-pressure steam then was used by the larger front cylinders, then exhausted out the stack. I believe in this true "Mallet" configuration, the two sets of drivers would always be in sync. In the simplified version, where all four cylinders get high-pressure steam directly from the boiler, the two sets of drivers are independent of each other and can slip in-and-out of sync. Anyway, I'd still probably opt for the "heavy" steam option for sound for this engine, but if you got a good deal somewhere on a "medium" sound decoder, that would probably work fine too - unless you've installed the high-pressure replacement cylinders. (Interstingly, the much smaller Mantua/Model Power logging 2-6-6-2 has all four cylinders the same size, so should probably get the "heavy" sound decoder too!!
The Spectrum 2-6-6-2 is a replica of the USRA "light" compound 2-6-6-2. My Spectrum 2-6-6-2, recently purchased from Micromark, came assembled with large low-pressure front cylinders and smaller high-pressure rear cylinders per the prototype, no high-pressure front cylinders as replacements.
From a recent discussion thread on simple and compound behavior, I understand that the two sets of cylinders on a compound could go out of "sync" from time to time (chuffs from front and rear sets not fixed time intervals in relation to each other) but would tend to be in sync most of the time. The explanation was that the rear cylinder exhausts are supplied to the front cylinders on each side through piping and chambers on each side that constitute plenums, with admittance of this exhaust steam from the plenums to the low-pressure front cylinders and the subsequent front cylinder exhaust chuffs being determined by the position of the front cylinder piston valves. Movement of the front set of drivers different from the rear set of drivers e.g. slippage, would change the position of the front set of piston valves relative to the rear set of piston valves and hence change the chuff time intervals between the rear and front cylinders.
It would be interesting to hear examples of simple and compound steam under various conditions. Presumably the sound equipped Spectrum 2-6-6-2's that are scheduled for release will reflect compound behavior. I'm waiting for reviews.
Isambard
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picked up the light tsunami today and cut out the dsd-100lc from the 2-8-0. Yep, that's what I wanted. everything's there that I sorta got used to from the qsi steamers. got more tweaking to do but looks like no problems. I don't know which whistle I'm using, just the one that sounds to my liking. I've got a heavy tsunami on b.o. for the 2-6-6-2 and yes mine only came with the cylinders installed too, no spares. it'll be fun to get the tsunami in it I'll say. good arrticle about the 2-6-6-2. take care and thanks again. this maybe should be a new thread, talking about the 2-8-0 and all, but this may wrap it up anyway. if not then, yo, we can always do a new thread.
I could be remembering wrong about the cylinders, might have been my Life-Like 2-8-8-2 that came with both...or maybe you could order the high-pressure cylinders as replacement parts or something??