View Full Version : 5U4 vs 5Y3 rectifier tubes

11-27-2006, 10:49 AM
Stupid question:

Is a 5u4 rectifier tube warmer sounding typically than a 5y3?

11-27-2006, 11:14 AM
It drops more voltage than a 5Y3, so it sags more and may sound a little "browner." But it also draws 3A on the filaments, so you can't just drop one in without verifying your PT can handle the load. Most other rectifiers draw 2A.

Bruce / Mission
11-27-2006, 12:54 PM
Steve I'd add that the voltage drop across a rectifier tube as it turns into B+ is semi-variable with the load after the recitifer and the load a 5U4 can carry is much greater then a 5Y3 so I think the 5U4 would drop less voltage in an amp built around a 5Y3.
What do you think?

11-27-2006, 12:55 PM
I don't know which tube data sheet s2amps is referring to, but @ the same current draw I think a 5Y3 will drop about 2x the voltage of a 5U4, and not only that, it's way deeper into the curve if you are seriously drawing current so it'll have a lot more sag.

Additionally, there are a variety of other important ratings that differ between the tubes so you should sub with care.

IME, a 5U4 sounds a lot stiffer than a 5Y3 in any amp that draws enough current to get their attention. A pair of 6V6's or EL84s will draw enough to show a marked difference in performance between a 5Y3 and a 5U4, not just in dynamic response (sag, punch) but also clean headroom and total power/volume.

11-27-2006, 06:39 PM
Bruce, I see where you are coming from, but I was thinking about it in a different way--swapping rectifiers and measuring the results. One of my amp models draws 125mA total for a pair of EL84s and ships with a 5Y3GT rectifier. I use a PT with a 3.25A filament tap so you can swap in a 5U4GB if you like. The B+ goes from 340VDC with a 5AR4 to 318VDC with a 5Y3 to 300VDC with a 5U4. The catch is it is a new production Sovtek 5Y3, which does not drop as much voltage as a true 5Y3.

Since we are talking TRUE 5Y3 here, I am in error in my earlier statement. Thanks for pointing that out.

11-27-2006, 07:17 PM
Thanks for all of your reponses!

Bruce / Mission
11-28-2006, 02:10 AM
"The catch is it is a new production Sovtek 5Y3, which does not drop as much voltage as a true 5Y3."

Right... I think the SOVTEK 5Y3GT is actually a Euro 5Z3, similar to a GZ30 and has much higher plate impedance then a good old American made 5Y3GT, So even though it also is rated at 125ma, the voltage drop across it would be less.
I find those SOVTEK 5Y3 tubes to be a good match for fixed biased class AB 6V6 or EL84 amps where you can dial in or out a certain amount of idle current and keep the higher voltage swing across the OT for more real power output.

07-03-2009, 01:49 PM
I have a sovtek 5Y3 in my 6G2/5E3 build it did raise the B a bit . I found one site that lists it at 140 mA but does not spec the voltage above a real 5Y3 . I also got a sovtek 5V4 which hoffman says is a real 5V4 and it is a 2 amp 5 volt 25V@ 175 mA where the real 5Y3 is 50V@125 mA . I thought of trying the 5V4 but feel it might raise my builds B+ and plate which is now at 410VDC.