Found these at http://www.parelectronics.com/index.php under one of the W4OP links at the top right of the page. Some of you may be familiar with the concept, but I sure wasn't. I was blown away but the idea of a paddle wheel indicator on an amp. Dale Parfitt (W4OP) is a fascinating fellow. 2 X 2C39. The object on the bottom center is a paddle wheel that gives confirmation that the water is indeed flowing. The black meters monitor cathode currents and the center meter is plate voltage. 250W typical output. 2x2c39 Internal view showing water jackets and plumbing. 4 X 2C39 water cooled. The 2 knobs tune the input and output while the meters monitor the 4 cathode currents and plate voltage. Once again, a flow meter on the bottom center. 4 X 2C39 again, showing plumbing and the 4 cathode bias supplies.