The Next Amp: A 15W 6V6 Project Featuring Toroids

The latest “One-of-a-Kind” amplifier project uses a 2:1 Toroidal Step-Up Transformer with a voltage-doubler rectifier tube. The Toroid is rated for 200mA and the doubler/rectifier is rated for 100mA which is a perfect match.

The 6V6 tubes at the output of the A/B class amplifier stage are rated at 12W, but there are Soviet-Era Mil versions that can give you 15W without red-plating. Under the heaviest loads, the 100mA DC max rating would be approached but never exceeded (remember, tubes don’t have specs, they have “ratings”. )

The choke is also toroidal. The beauty of the toroids is that they are superior transformers and chokes and don’t have the obscene markup of the commercially available transformers manufactured as replacements for classic amplifiers of the past. The power transformers are much lighter since they do not have the step-down windings needed for the filament voltages of the tubes.

The FYF Jr. uses an independent filament transformer with a 12.6 VAC, center-tapped secondary to supply separate filament supply lines for the pre and power stages. The Rectifier diodes typically have 5 VAC filament voltages which is the case for the rectifier/doubler of the FYF Jr. However, the doubler filament can also take a 25 VDC source which can be derived from the 12.6 VAC secondary using 2, solid-state Schottky rectifier diodes which have a minimal voltage drop. (As low as 150mV) Within 10% of the rated voltage is more than sufficient. An added feature of the DC filament voltage is decreased 60 cycle hum. The DC line choke may not even be necessary which would increase the reach of the applied plate voltage. (415 VDC for the Power Amp stage is optimal.)