Valve Wizard U-Boat SMD/TH hybrid

[induction]

Merlin Blencowe (aka Valve Wizard) has posted 3 versions of this circuit. This layout is for the latest version, which he has stated has the best performance. Additional information, including schematic and circuit explanation here.

I have built this but not tested it yet, so I have also not yet chosen a tracking resistor or trimmer setting.

Try to find physically small 10u caps near the trimmer. They're a bit squeezed because I found the newest schematic after I had already cut the board, and I had to adjust the layout after the fact. Mine are smallish but not tiny, and they fit fine.

Note:

Merlin wrote

Tracking is very dependent on the opamp used for the comparators (U4). I tried a lot of devices and found the LM833 to perform best. The NE5532 seems to be a good choice too. Other BJT-input opamps will work, but none quite gives the good tracking as the 833. A TL072 can also be used, but tracking is distinctly poorer, although adding resistor R19 helps.

Since I used a NE5532 (equivalent to LM833) for U4 (dual op-amp at lower right), I did not include R19, but it can be easily added for those who prefer to use a TL072 for U4. See schematic for component numbers.