All started after I built and listened to the First Watt F4 and liked it very much. The original F4 has 6 power mosfets per channel, draws about 160W and weights about 35 lbs, delivering 25 current buffered W per channel at 8ohms (2.58Ax2.58Ax8 ohms/2= 26.6 W). Then I built the Mark Audio 7.3A speakers and thought of pairing them with an amp that will deliver enough power to listen up to 90 dB levels. From my previous experience with the 4P1L – F4 integrated, I learned that a 16-20 dB gain it is plenty to drive the F4. The output impedance of the 6H30’s is even lower than the 4P1L’s, so no issues of driving capability nor gain. Actually I needed a little more gain as my small FLAC player has a lower output compared to a CD player. I chose 6H30 for multiple reasons: very linear, low Rplate, good gain and overall low PSU demands. PSU uses Antek 160V/50VA main transformer, FRED rectifiers, choke 157G and a 555 based 30 seconds HV time delay circuit. A hand made PCB holds the noval socket, the RC cathode bias, the grid resistors and the coupling caps. Separate PCBs are used for each anode load DN2540 based cascode CCS. 6H30 runs at about 125V/20mA.
I used a standard aluminum enclosure from Ebay and modified the top plate to fit all the pre-amplifier components. The (so called) mini F4 has only 4 power mosfets per channel and each runs at 300mA…this provides a 1.2×1.2×8/2=5.76 W pure class A with the heatsinks at reasonable temperature. At this size of the enclosure (wxlxh 9.5″x10″x5″) everything fits tight and weights 20 lbs. I am very happy that it fits well on my working desk.
The combination of the Mark Audio MTL Alpair 7.3A (design by Bob Brines) and the Mini F4-6H30 pre integrated sounds awesome: great dynamics specific to F4, low distorsion from the 6H30 and pleasant sound from the Alpair ( lows are excellent enough considering the size of the driver, mids are well defined and highs are awesome..this driver can go up to 30kHz…very unique).