Check the listing for details. Crystal Ovens used in Moseley Model 505 Transmitters. Condition: Used. Listed at 29.00 USD. Crystal Ovens used in Moseley Model 505 Transmitters These oven units are very high end, high stability, proportion operated crystal ovens that accommodate one FT-243 size crystal. (Crystals at frequencies as noted on the ovens are available in a separate ebay listing.) The heating element is nominally 12 volts but ordinarily temperature regulated via a proportional controller in the area of 3.7 to 4.3 volts DC such as set via the circuit used by Moseley (see pictures) in the associated 505 transmitter. If you want high crystal stability, this is your solution. These 505 crystal ovens are quite special and unique and near impossible to acquire as a replacement part. If you want to operate your 505 into the future, you should have a spare oven.