09-09-2019, 06:41 PM
Hi Amie,. a good subject to study and all the answers will be on the tube books site, even if a lot of digging will be required.
The approximate way is to look in a valve data book. This will give a value for Ra (anode load impedance) as well as Rl (load inpedance). This is normally lower, and is the figure about which your output transformer is designed to match to the loudspeaker. The valve data books then show the anode to anode load impedance for a pair of valves in push pull. This figure is usually twice that of a single ended system.
If you parallel valves to reduce impedance further then ohms law applies; 2 valves in parallel 1/2 impedance, 3 in parallel 1/3 impedance.
Note that this applies to valves operating on sensibly the same DC conditions. If the Dc conditions change then the values of Ra and hence Rl will also change. The tubebooks website will explain how.
Good luck, Ed
The approximate way is to look in a valve data book. This will give a value for Ra (anode load impedance) as well as Rl (load inpedance). This is normally lower, and is the figure about which your output transformer is designed to match to the loudspeaker. The valve data books then show the anode to anode load impedance for a pair of valves in push pull. This figure is usually twice that of a single ended system.
If you parallel valves to reduce impedance further then ohms law applies; 2 valves in parallel 1/2 impedance, 3 in parallel 1/3 impedance.
Note that this applies to valves operating on sensibly the same DC conditions. If the Dc conditions change then the values of Ra and hence Rl will also change. The tubebooks website will explain how.
Good luck, Ed
