Originally Posted by Dave H

Most any modern speed control will have a BEC feature, battery eliminator circuit, so a separate receiver pack is not needed. According to the Tamiya website the 105 has a BEC. The 104 does not if I remember correctly, that model does need a receiver pack.

Just be sure the speed controller does brushed motors if that is what you have-want. Might want to get something that also does brushless, as it is an excellent upgrade.