On Wed, 25 May 2011 11:38:28 +1000, 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.

Not for those looking for more sag. I have a couple clients running
variacs to get that kind of sag sound with a GZ tube.



--
Live Fast Die Young, Leave A Pretty Corpse