thesharpener wrote:This contradict's another_jim's statement...
I'm considering a Strega for my next machine, so I always closely follow these discussions. I'm curious what data exists to help prospective owners decide if they want to modify their machine or not?
I suppose another_jim can clarify what exactly he meant in his statement about temperature management, but I suppose he was referring to the group head not being thermally connected to the boiler for heating (like wiht a thermosiphon) and relying a pair of electrical heating elements that go inside of it. They are denoted by number 14 on page 23 in the manual http://img.web.mdsnet.it/bezzera/allegati_articoli/58db7625bb2f3_strega%209942051.03%20gb%20ed07.14%20rev00.pdf
The operating temperature is controlled by a "THERMIC SAFETY DEVICE 250V 95°C AUTOMATIC", item 12. This thermostat is also embedded in the group, close to the heating elements, and stops the heating of the group when it reaches 95C. The heating resumes when the temperature drops to around 80C-85C if I remember correctly.
When you turn on the machine, you have no way of knowing when the group head reaches to 95C, nor would you know where in the "temperature window" you are at any given time, unless you attach some kind of thermometer to it.
Now that I have replaced the thermostat with a very precise temperature sensor and a PID controller, I can see when the group actually reaches the set temperature, and it keeps it there within 0.1C . When I turn my machine on at ambient 20C, the boiler gets fully up to the pressure while the group head is still around 65C. I have to wait a bit longer for it to reach 90C, which I usually use with the light roasts.
Another benefit for me was the ease of adjusting the brew temperature via PID controller. I used to open up the top lid of the machine and regulate boiler's pressurestat to control the brew temperature (you change the temperature of the boiler to impact the temperature of the water going through the heat exchanger). But this gives you a more rough control, and is certainly tedious. I dropped the screws into the machine on more than one occasion, and had to completely take the cover off to get them.
In the end, I lived happily with my machine for 4 years before PID-ing it, it makes very decent coffee once you get the hang of it. PID-ing definitely makes it better, but everyone decides for themselves if it is worth it. I just loved the process itself, making something with my own hands that worked well.