I wanted to leave the subject line general as Mapletree is a small outfit that makes several amps and if anyone has one they can post in this thread.
My particular amp is the Ear+ HDII. I am going to post some specs, which I hope I have copied correctly. Some tube amps seem to have really underwhelming specs, but I guess that is the nature of tubes.
Power at 32 Ohms is 70mW
Frequency Response is 10hz to 20Khz at -1 Db
Gain at 1 kHz via HiZ output is 10DB’s. Approximately 3 Db’s lower at LowZ
Phase structure is non-inverting
Tubes supplied are 2x12B4A (NOS) and 1x12AX7/5751 (new)
Input impedance is 25K Ohms at minimum
Output impedance is 3.5 Ohms
Recommened headphone impedance is 30 to 600 Ohms
Power Consumption is 35 Watts
History is 2002 - 2019 (latest edition)
Here are some pics from the weekend. It is supposed to be finished in a few days.
They probably can’t buy a readily available transformer with both windings, separate heater transformers are pretty typical. The fact they rectify it to DC is kind of interesting, that and the cathode follower output stage, should make it relatively quiet.
It’s a very interesting design, they are using 2 identical transformers. First one to get from 120VAC to 10VAC and then a reversed one to get 240VAC from the 10VAC. It’s a clever way of wiring those transformers. I haven’t seen many tube amplifier diagrams, but the ones I’ve seen use a single transformer with a main winding that gets the high voltage output, and a secondary winding for the tube heaters.