I used the 2SH27L battery tubes for portable radio operation. These tube were derived from the german RV2,4P700 tubes which were widely used by the germans in WWII. The russians made their own enclosure but kept the original design of the internal structure.
I added also the 2P29L power amplifier tubes to the amp. Both tubes have a heater voltage of approximately 2.2 Volts.

Because I had only the 5V USB power for running the tubes, I decided to use a BC548C transitor after an impedance changer, which was fed back by a 330k resistor. Doing so the overall loudness was significantly altered.

The overall weight of the amp was significantly reduced by using the BC548C transitors since no heavy output transformers where needed.

I use a powerbank with some USB PC loudspeaker feeding the amp by a Bluetooth module.

I hope you enjoyed this.