15-05-2020, 10:03 AM
(This post was last modified: 15-05-2020, 10:03 AM by Mike Watterson.)
The heater power is related to the electron emission needed. The anode and even g1 is too far away. Sometimes the visible outer "can" isn't the anode but a screen. Also to a small extent the insulation, some valves can only be used near the earthy end of a series chain. A power rectifier on the same heater supply as the rest of the valves or the mad 115V heater rectifier valves used in some USA mains/battery sets needs more insulation. Compare warm up times of a parallel and series mains radio. Some series sets are nearly a minute. A direct filament needs much less power, hence older rectifiers using a filamentary cathode and a separate winding. Most direct Triodes started off as battery valves, at the output stage the hum issue isn't so severe on a direct triode. Hence battery valve sets are basically instant on, when on battery, but ones with valve rectifier for mains can seem slow.
You see the variation in filament current needed with anode current required most clearly on the Telefunken Y8 metal can parallel only battery valves from the 1940s. They were far more "efficient" than the RCA B7G, because the 1T4 filament current is artificially high at 50mA to allow series operation.
Some mains signal valves are deliberately 6.3V and 300mA, or two 6.3V @ 150ma (for 12V cars OR 300 mA series chains to suit series or parallel.
It's obvious on the audio power out and power rectifiers, over 1A on 6.3V for some (1.5A for EL34 and 1.27 A for KT66), The UL84 is 100mA and 45V (4.5W), the EL86 is 6.3V 0.76 A, surprisingly 4.8W, apparently the same valve with a different heater. I'd have thought the UL84 would need more. Comparison of heater power of a selection of series and parallel power valves with otherwise the same spec would be interesting. You'd imagine the UL84 is the 100mA version of an EL84, but allegedly not.
I'd thought a stereo amp with no mains transformers and PL509 or PL519 in push - pull was an interesting idea to save a big transformer. Four of those alone is 160V @ 300mA for the heaters.
You could have switches to triodise, feed screen grids from audio transformer or not, vary cross-over and feedback, maybe even parallelise for more 2nd harmonics instead of push-pull (which cancels most of the second harmonic). Lots of scope for experimentation.
Use a voltage doubler to have about 600V HT, or a tripler for 900V direct from the mains?
I shall dismember and photograph more dead valves
You see the variation in filament current needed with anode current required most clearly on the Telefunken Y8 metal can parallel only battery valves from the 1940s. They were far more "efficient" than the RCA B7G, because the 1T4 filament current is artificially high at 50mA to allow series operation.
Some mains signal valves are deliberately 6.3V and 300mA, or two 6.3V @ 150ma (for 12V cars OR 300 mA series chains to suit series or parallel.
It's obvious on the audio power out and power rectifiers, over 1A on 6.3V for some (1.5A for EL34 and 1.27 A for KT66), The UL84 is 100mA and 45V (4.5W), the EL86 is 6.3V 0.76 A, surprisingly 4.8W, apparently the same valve with a different heater. I'd have thought the UL84 would need more. Comparison of heater power of a selection of series and parallel power valves with otherwise the same spec would be interesting. You'd imagine the UL84 is the 100mA version of an EL84, but allegedly not.
I'd thought a stereo amp with no mains transformers and PL509 or PL519 in push - pull was an interesting idea to save a big transformer. Four of those alone is 160V @ 300mA for the heaters.
You could have switches to triodise, feed screen grids from audio transformer or not, vary cross-over and feedback, maybe even parallelise for more 2nd harmonics instead of push-pull (which cancels most of the second harmonic). Lots of scope for experimentation.
Use a voltage doubler to have about 600V HT, or a tripler for 900V direct from the mains?
I shall dismember and photograph more dead valves
