813 Amp Project

June 6, 2006: 813 grid bias testing. Several circuits appeared in the early 1960's for grounded grid configurations for 813 tubes. All had different grid bias arrangements so I decided to test this RF deck using an adjustable bias circuit. Thanks to Roger, W1AX, I had a copy of the November 1959 issue of GE Ham News which described their approach and I incorporated that type of circuit into this test setup.

As cautioned by Bob, G3XNG, I was very careful to tie the 813 chassis back to the -HV supply and ground all exposed cabinets while conducting these tests!!

CLICK ON PICTURES TO ENLARGE

		June 6, 2006: 813 grid bias testing. Several circuits appeared in the early 1960's for grounded grid configurations for 813 tubes. All had different grid bias arrangements so I decided to test this RF deck using an adjustable bias circuit. Thanks to Roger, W1AX, I had a copy of the November 1959 issue of GE Ham News which described their approach and I incorporated that type of circuit into this test setup. As cautioned by Bob, G3XNG, I was very careful to tie the 813 chassis back to the -HV supply and ground all exposed cabinets while conducting these tests!! CLICK ON PICTURES TO ENLARGE
		June 7, 2006: First RF test with the 813 RF deck and 866 power supply. 813 bias was adjusted to just allow some plate current without RF present. Operating frequency was 14 MHz. A power output of 425 watts was measured at an operating plate voltage of 2050 VDC and plate current of 290 mA. The input coupling network needs adjustment as the SWR between the driver and 813 amp is about 2.5:1. But initial tests are encouraging. Movie