A quick thanks to Martinh for getting the parts from Farnell for me to get my dimmer running again.
Back to the roast.
This was a roast of Hill & Valley's Bourbon Espresso pre-blend.
I managed to slow the initial part of the roast down well taking about 6 minutes to get to 300F, then I wound up the power, and found that as I had predicted from the uncontrolled roast the other day getting 3 minutes from 300F to 380F took full power. From 380F I wanted around 10 degrees F per minute to the end of the roast. This is where things became tricky
First I forgot to add time to the timer
(it is still in circuit, but I think I'll take it out), so it went on to cooling about 1 minute into 1st crack 
I quickly wound more time on so I only lost about 10F of temp, still, not good. At around 420F the temp rise was really slowing, and I struggleg to get to second crack. I think I heard a couple of pops, but not sure, but the temp stalled at 435F. The beans looked OK, so I hit the heat off.
When I dumped them they look a good medium to dark, and there are a couple of besns with divots out, so some must have hit 2nd crack.
I'm rather diisapointed that I struggled to reach 2nd crack, as I managed 460F bean temp the other day. Perhaps there is a small voltage loss through the dimmer (should be almost nothing), but this confirms my fears that at higher temperatures the Imex's heat loss is close to it's heat in. There is certainly much more heat overhead with my Rival popper.
I am running without a chaff collector at the moment, and lots of chaff collects on the grill for the re-cycled air so maybe this is restricting the warm exhaust air from getting re-cycled and restricting obtainable chamber temp. Having said this I guess you get the same effect from the chaff collector, maybe?
Having preached that you don't need a variac for popper control, use a dimmer instead, the Imex would benefit from a variac, so that you could increase the supply voltage SLIGHTLY to healp the heating. This is of coarse not really recommended
.
I'm not giving up yet, as I think this could be a great roasting tool.
Next step, maybe some heatproof insulation round the outside of the roast chamber, this would help keep the heat in, and keep the noise down!
More likely is a transformer kit so I can make a step up transformer and get a few more volts to the imex, and keep the dimmer. This will still be a cheaper ans smaller solution than a varic.
I'll keep you posted
