Roger has inspired the creative impulse to attempt a DIY project. After doing a lot of research for an affordable power tube that is affordable and of high quality, settled on the 6883B tube for this project. The 6883B is the 12 volt version of the 6146B tube. Its still readily available, reasonable cost, and very well built.
The 6146 is a RF transmitting tube. Early attempts to use the tube for audio and guitar were less than stellar. RCA made a theater amp in the 50's that employed the 6146, with less than good results. So, RCA converted these units to the 6550 tube. In 1964, RCA introduced the 6146B, which was a complete re-design of the 6146. RCA claimed 33% increase in output power, along with increased reliability. Although it was not always a drop in replacement for some of the older transmitters, it proved to be more reliable than than older 6146 tubes for units that were designed from the ground up to use it.
The key to using this type of tube is to make sure one pays attention to the screen voltages. For the 6146/6883B tube, this means a separate screen supply not to exceed 250 volts. As long as that is followed, the tube should work flawlessly a s a push/pull output tube. Designs can get up to 100 watts from a pair. There is a gent in the Philippines who has made quad mono blocks that output 200 watts a channel. I also like the "dark heater" feature, which is supposed to increase longevity and run the tubes cooler.
The input tubes will be a pair of 6BL7 TV tubes. They have similar characteristics to 6SN7, expect they are a much stouter tube (they were vertical deflection tubes back in the day). Expect to have this done late 2014/early 2015.
Thanks to Roger for providing the spark to try and build another DIY product.