05-07-2015, 07:52 AM
(This post was last modified: 05-07-2015, 08:05 AM by Radio Fixer.)
I'm with Mark here. Its years since I got out the last AVO 8, it was good in its time but I find it clumsy (bench space again!) and error prone in reading, but that's just because I don't use it enough.
Like the scale changing meter Alan, a neat piece of design by someone. As to measuring anode volts and impedance loading well rarely do that ... HT and cathode volts tell me all I need to know. Its sometimes useful to measure (digital meter is easier) the primary resistance of the output transformer (or halves of for push pull) so that from the voltage across them, the valve current(s) can be calculated for stages that don't have cathode resistors. These are often biased by resistors or a choke or field coil in the -ve HT rail. Old hands will have been doing this for years of course but I put it in just for those new to the art.
Its handy to look at the Trader Sheet or Service Info voltages and currents but I don't really need those either. Interestingly all the radios I look at have valve parameters the same as the AVO valve tester settings (another piece of kit, never stops does it
). Just use those figures after testing the valves.
Gary
Like the scale changing meter Alan, a neat piece of design by someone. As to measuring anode volts and impedance loading well rarely do that ... HT and cathode volts tell me all I need to know. Its sometimes useful to measure (digital meter is easier) the primary resistance of the output transformer (or halves of for push pull) so that from the voltage across them, the valve current(s) can be calculated for stages that don't have cathode resistors. These are often biased by resistors or a choke or field coil in the -ve HT rail. Old hands will have been doing this for years of course but I put it in just for those new to the art.
Its handy to look at the Trader Sheet or Service Info voltages and currents but I don't really need those either. Interestingly all the radios I look at have valve parameters the same as the AVO valve tester settings (another piece of kit, never stops does it
). Just use those figures after testing the valves.Gary
