Hi, I'm repairing an ancient AWA Record player for a mate, The input stage has a Grid-leak biased 6AV6 running at 85V. The grid resistor is 10M, input is a ceramic cartridge.
I've already converted the output stage from Back Bias to Cathode Bias, and it seems to be behaving. I'm just concerned that doing the same to the input stage may stuff up the loading of the ceramic cartridge - however, there is a pi pad of ~ 820K & a 500K vol pot between the cartridge and the input cap, so my guess it's not an issue. Perhaps lower distortion with Cathode bias?
I've already converted the output stage from Back Bias to Cathode Bias, and it seems to be behaving. I'm just concerned that doing the same to the input stage may stuff up the loading of the ceramic cartridge - however, there is a pi pad of ~ 820K & a 500K vol pot between the cartridge and the input cap, so my guess it's not an issue. Perhaps lower distortion with Cathode bias?
10M grid leak bias was the typical circuit for 6AV6. This tube was designed and tested to be fairly stable with a 10M grid leak bias. You can try cathode bias, but it probably will not make any real difference, unless you have a hum/noise pickup isse due to the high grid impedence or the 10M resistor has become noisy or drifted in value.