paradoxper
Headphoneus Supremus
Here is Thomas Mayer's take:
I never understand why people plug different types of rectifiers which are not compatible.
You should always use the rectifier for which a circuit is designed and optimised.
Example:
a 5U4 is designed to deliver more current than a 274. It can also handle a bigger capacitive load in the filter than a 274 ( actually 10 times more)
And it draws 3A filament current instead of 2A.
When you plug in a 274 this happens or can happen
Due to the lower current draw in the filament, the power transformer will deliver more filament voltage to the tube (voltage regulation in the transformer)
This will result in over voltage on the filament which can shorten tube life
A 274 is designed to work into max 4uF capacitive load. if it is loaded more it can flash over at turn on.
If the circuit draws the full current a 5U4 can deliver, the 274 will exceed max specs.
The other way around if you plug a 5U4 into a circuit designed for 274, it will draw 50% more current on the filament winding which can cause the filament transformer to overheat. It will also result in a drop of the filament voltage which again can shorten tube life.
Then both tubes have a different internal voltage drop at the same current which results in different voltages to the amplifier circuit. Most of the differences heard are probably due to the circuit behaving differently with different supply voltages. This point is much more pronounced when swapping between directly heated rectifiers like 5U4 and 274 and indirectly heated rectifiers like GZ34, GZ37, etc. The latter have much less voltage drop and using these will result in significantly higher voltage to the circuit which can cause damage if the design asks for a directly heated rectifier. The other way around the directly heated rectifiers will not give the slow ramp up of voltage to the circuit which an indirectly heated one does.
Unless the designer knows exactly what he is doing and designs the circuit so that it can cover all these points it is a bad idea to swap these against each other. Then on the other hand if the designer claims that the circuit can use both he probably does not know what he is doing or simply does this for marketing reasons to serve the current trend of tube rolling.
So a complex issue. And my opinion and experience with this (I should not say this as a manufacturer of rectifier tubes): A well designed amp will not change it’s sound appreciably when you use different brands of rectifiers or if the rectifier ages. If it does it is probably sensitive to the supply voltage to the amplifier circuits."
I never understand why people plug different types of rectifiers which are not compatible.
You should always use the rectifier for which a circuit is designed and optimised.
Example:
a 5U4 is designed to deliver more current than a 274. It can also handle a bigger capacitive load in the filter than a 274 ( actually 10 times more)
And it draws 3A filament current instead of 2A.
When you plug in a 274 this happens or can happen
Due to the lower current draw in the filament, the power transformer will deliver more filament voltage to the tube (voltage regulation in the transformer)
This will result in over voltage on the filament which can shorten tube life
A 274 is designed to work into max 4uF capacitive load. if it is loaded more it can flash over at turn on.
If the circuit draws the full current a 5U4 can deliver, the 274 will exceed max specs.
The other way around if you plug a 5U4 into a circuit designed for 274, it will draw 50% more current on the filament winding which can cause the filament transformer to overheat. It will also result in a drop of the filament voltage which again can shorten tube life.
Then both tubes have a different internal voltage drop at the same current which results in different voltages to the amplifier circuit. Most of the differences heard are probably due to the circuit behaving differently with different supply voltages. This point is much more pronounced when swapping between directly heated rectifiers like 5U4 and 274 and indirectly heated rectifiers like GZ34, GZ37, etc. The latter have much less voltage drop and using these will result in significantly higher voltage to the circuit which can cause damage if the design asks for a directly heated rectifier. The other way around the directly heated rectifiers will not give the slow ramp up of voltage to the circuit which an indirectly heated one does.
Unless the designer knows exactly what he is doing and designs the circuit so that it can cover all these points it is a bad idea to swap these against each other. Then on the other hand if the designer claims that the circuit can use both he probably does not know what he is doing or simply does this for marketing reasons to serve the current trend of tube rolling.
So a complex issue. And my opinion and experience with this (I should not say this as a manufacturer of rectifier tubes): A well designed amp will not change it’s sound appreciably when you use different brands of rectifiers or if the rectifier ages. If it does it is probably sensitive to the supply voltage to the amplifier circuits."
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