Because of my continual bantering of Oatley to produce a K272X which had filament batteries and powered by 18V the K272C has been developed. The K272B will probably never see the light of day being a big improvement over the K272A but not being an 18V amp and not having separate filament batteries. I liked the "B" having seperate filament resistors and thought it sounded very good in a headphone amp I built up. I think Oatley had the K272B PCBs produced but just not packaged as kits at this point. My suggestion to them was to sell the PCB for the "B" only at a reduced price and let the constructor supply his own parts. I have no answer back on this at the moment.
Blow the trumpets and roll the drums the K272C is here. I believe it will go into production. I have been sent what I think is a prototype or first run compete unit. Looks good. Big filament batteries and 18V ready. It may be a week or so before I have it as a complete portable HP unit but I am very excited to try it. I still have the K272B and as I said love it.
Oatley have included in the kit the OPA2134 high performance Fet front-ended OPAMP chip. Two leds monitor battery health. One led will indicate when the 18V is fallen to 14V by first growing dull then finally going out. Another led, monitoring the filament voltage, goes out when the filament batteries fall to 1.4V (from just over 3).
The biggest improvement is the 18V supply. Some K7272s hissed and I think it was because the driver chip (OPA2134 or PT2308) was running on too lower voltage. Also with the higher voltage across the driver chip a greater dynamic headroom should be available. I would have liked the tubes to also have a 18V HT but it appears from the cct. that there is only 9V across the tubes. Oh well.
Attachment:
K272C.jpg
Login
Register
FAQ
