On Tue, 24 May 2011 21:25:50 -0700, spamtrap1888 wrote:

On May 24, 6:38Â*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 - Â*so there is a much bigger drop in voltage,
Â*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?


I've installed several SS diode replacements for a valve rectifier.
Most notably the RTSSR from Ruby. Some musicians like sag in their
amps and you certainly won't get it from the RTSSR or a 5AR4.

It TOTALLY depends on the musician and I always cater to their ears.


--
Live Fast Die Young, Leave A Pretty Corpse