[trackball02]

Can 5u4g tube be used in place of a 5AR4?
Thanks.

[Tom Alverson]

Can 5u4g tube be used in place of a 5AR4?
Thanks.

It would probably "work" but I would not recommend it.  The 5U4 draws more filament current which could be hard on the power transformer and there is more voltage drop in the 5U4 so your amp would put out a little less power. 

[trackball02]

Thanks for the information.

What can you tell me about the Philips 5R4GYS Upscale audio that is being sold as a 5AR4 replacement?

[Tom Alverson]

Thanks for the information.

What can you tell me about the Philips 5R4GYS Upscale audio that is being sold as a 5AR4 replacement?

If you  scroll down a little on the link below you will see a nice chart that someone worked up on the different rectifier tubes.  It appears that the 5R4GYS is just a higher voltage version of the 5U4 with even more voltage drop.  The filament current is only a little higher than the 5AR4 but because of the greater voltage drop the amp would put out even less power than the 5U4.  I would stick withthe 5AR4 but I would add the extra silicon diodes in series with the tube rectifiers as that will improve the reliability. 

http://dynacotubeaudio.forumotion.com/t1649-philips-5r4gys-rectifier

[trackball02]

Thanks Tom for the information. The link is interesting reading.

[Lefty052347]

I would second Tom's advice.  If you are unhappy with the Sovtek 5AR4, try an NOS 5AR4.  I have been using a Mullard in my Ultravalve since 2010 without any problems.

Regards,
Dean

[thorman]

 I was using a NOS Mullard 5AR4 in my Power supply Modwright ( Oppo 105 w/ Modwright Truthmods ) and I eventually removed the Mullard due to being too warm a thick.....I ordered the Upscale Audio Phillips 5R4GY and after about 50 hours or so I found no longer use the Mullard 5AR4. I do suppose it is System dependent, but for me it was a night and day improvement. The Upscale Audio Phillips 5R4GY is neutral and quick with very good quick and tight low end......I can no longer go back to the Mullard.....

[avahifi]

Replacing an 5AR4 with a 5R4GY in an amplifier designed for a 5AR4 simply lowers the B+ voltage, turns down the output tubes, may make the bias adjustment go out of range low, lowers the power capability, provides a higher then design load on the filament circuit, and increases the distortion.

Not recommended with an Ultravalve or Ultimate 70, although some may like the sonic results with other designs.  Changing tube types without an understanding of the circuit or making measurements is like testing tires without a pressure gauge.

Installing an appropriate diode in series with each lead of the transformer B+ supply will unload the 5AR4, using it essentially just for its slow turn on effect and maintaining the appropriate voltage drop for design B+ voltage under load and improve 5AR4 service life.  Recommended.  Standard on Ultravalve amps.

Frank Van Alstine