Later versions of the 21st Century/Motorworks M5A1 Stuart had dual frequencies in the form of a toggle switch-one side of the switch was 27 MHz, the other 49 MHz. Typical RC toy freqs. These later versions also had a volume control knob. The original machines were quite noisy prompting a normal indoor conversation to degrade into a shouting match. Outside, the noise dissipated enough so as not be such a nuisance but it was still pretty loud.

Thanks for all the discourse on the old M5 Stuart. I may just have to hold on to mine. Bought one on clearance after the 2003 Christmas season and had lost all interest in it until now.

Here is a good site for M5 upgrades- [link=http://www.armorpax.com/Armorpax/armorpax%20home.htm]ARMORPAX[/link]

My favorite M5 conversion is this particular item which used to be hosted on Armorpax but is now seen on Customrcmodels.com. Builder is "Dave from the UK". As you can see it has a ubiquitous smoke generator installed to good effect.