On May 24, 6:38*pm, "Phil Allison" wrote:
"Arfa Daily"



What do you think about subbing the 5AR4 with a 5U4?

Never tried it, but looking at the specs, they look rather different from
one another, see -

http://www.r-type.org/exhib/aaa0997.htm

http://www.r-type.org/exhib/aaa0504.htm

** Useless info.

The big difference between the 5AR4 and the 5U4 is in amount of voltage drop
across each diode when conducting.

The 5AR4 is uses an indirectly heated cathode, close coupled to each plate
and the voltage drop is very low, about 35 volts at 700mA peak.

The 5U4 uses a directly heated cathode with lotsa space between the plates
and the cathodes - *so there is a much bigger drop in voltage, *more like
100 volts at peak current.

So, if you drop a 5U4 in place of a 5AR4 - expect to lose 60 to 70 volts DC
straight off the B+.

Also, the 5AR4 is rated to work reliably with a large filter cap on the
cathodes ( 60 uF) compared to the 5U4 ( 40uF).

So the proposed sub is bad news all around.


Considering that the vacuum tube rectifier was the first tube to be
eliminated (in receiving sets at least), why not replace it with a
semiconductor diode circuit? What effect would it have on the
amplifier's sound?