Re: Valve testing unexpected high emission?
Hello Dave, most likely PO - parasitic oscillation. Often happens with power valves & high-slope valves. Heaps of Forum info - see "Search". AVO VCM's, and particularly CT160's, are prone to this phenomenon. Heaps more "Search" info on fitment of Ferrite beads.
Tektronix & other major players might well have used "Burn-in" racks for valves, but this isn't recommended for use with one's valve testers, particularly expensive AVO's.
As for wee ECC type double triodes - 81's & 88's are two a penny, but 83's can be jolly expensive & E88CC's, E288CC can cost a fortune. I wouldn't put then anywhere near "burning-in" apparatus. Also many of them are Vg sensitive - get that wrong & "flash bang wollop" ! This happens with VCM's & other V/T's when folk believe that "Corse & Fine Ia" or other bridge balancing pots control Ia. Wrong, once under "Test", only the Vg(Delta Vg) pot controls Ia, and mA/V(delta Vg) pot to a much lesser degree.
Regards, David
|