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Last edited by PeterCapo on Tue Dec 01, 2020 12:28 pm; edited 1 time in total
Power consumption: Mark II vs. Mark III
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Last edited by PeterCapo on Tue Dec 01, 2020 12:28 pm; edited 1 time in total
danf- Posts : 58
Join date : 2009-01-19
Hi Peter,
The 5AR4/GZ34 filament draws 1.9 amps at 5V, while the 5U4 draws 3 amps at 5V. This 5 watt difference doesn't explain a 120W-240W fusing difference. EL34's draw 1.5 amp, 6550's draw 1.6 amps, also a small difference, but in the Mark II's favor.
The 5AR4/GZ34 warms up slowly because it has an indirectly heated cathode; the 5U4 warms up more quickly because it has a directly heated cathode. The GZ34 and the choke in the Mark III will reduce the surge currents, but I doubt that this is a big effect. Someone with power supply modeling software could check this out.
I think that it is likely that Dynaco just kept pushing the fuse value down to provide additional safety. Older equipment had no fuses at all, and the idea of fine tuning the fuse value may have entered slowly.
Dan
The 5AR4/GZ34 filament draws 1.9 amps at 5V, while the 5U4 draws 3 amps at 5V. This 5 watt difference doesn't explain a 120W-240W fusing difference. EL34's draw 1.5 amp, 6550's draw 1.6 amps, also a small difference, but in the Mark II's favor.
The 5AR4/GZ34 warms up slowly because it has an indirectly heated cathode; the 5U4 warms up more quickly because it has a directly heated cathode. The GZ34 and the choke in the Mark III will reduce the surge currents, but I doubt that this is a big effect. Someone with power supply modeling software could check this out.
I think that it is likely that Dynaco just kept pushing the fuse value down to provide additional safety. Older equipment had no fuses at all, and the idea of fine tuning the fuse value may have entered slowly.
Dan
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Last edited by PeterCapo on Tue Dec 01, 2020 12:28 pm; edited 1 time in total
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Last edited by PeterCapo on Tue Dec 01, 2020 12:28 pm; edited 1 time in total
danf- Posts : 58
Join date : 2009-01-19
Hi Peter,
To clarify, the rectifier current is at 5V, and the fuse current is at 120V. One amp at 120V corresponds to 120W, and one amp at 5V corresponds to 5W. Reflected back to the transformer primary, one amp at 5V would be 5/120 or 1/24 amp at 120V if the transformer is 100% efficient.
If the different fuses were used at the same time, I would lean to the power on surge current explanation. This could be tested or modeled if you really want to know.
Dan
To clarify, the rectifier current is at 5V, and the fuse current is at 120V. One amp at 120V corresponds to 120W, and one amp at 5V corresponds to 5W. Reflected back to the transformer primary, one amp at 5V would be 5/120 or 1/24 amp at 120V if the transformer is 100% efficient.
If the different fuses were used at the same time, I would lean to the power on surge current explanation. This could be tested or modeled if you really want to know.
Dan
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Last edited by PeterCapo on Tue Dec 01, 2020 12:28 pm; edited 1 time in total
danf- Posts : 58
Join date : 2009-01-19
Hi Peter,
I haven't used thermistors, but I am not sure that they will significantly change the peak current on turn on with a vacuum tube rectifier, even a 5U4. They will make a difference with a solid state rectifier. Someone more experienced with thermistors could comment. If you want to try a lower value fuse, go ahead and try it as is. Fuses are cheap, and if a 3 amp fuse blows we've learned something.
Dan
I haven't used thermistors, but I am not sure that they will significantly change the peak current on turn on with a vacuum tube rectifier, even a 5U4. They will make a difference with a solid state rectifier. Someone more experienced with thermistors could comment. If you want to try a lower value fuse, go ahead and try it as is. Fuses are cheap, and if a 3 amp fuse blows we've learned something.
Dan