5u4 and 5y3 instead of 5ar4 tube rectifier

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5u4 and 5y3 instead of 5ar4 tube rectifier

Postby chieftain on Sun Dec 07, 2003 10:56 pm

hi guys,
i know that we can put a 5u4 and a 5y3 tube retifier instead of a 5ar4 one, but is there differences? i think that 5u4 and 5y3 have a lower voltage so it will be less hard on the transformer, right? is there any difference sound wise? finally, if changing the tube rectifier for a lower one, does the amp need a new biasing? thanks a lot guys for the help. olivier
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Re: 5u4 and 5y3 instead of 5ar4 tube rectifier

Postby Da Mule on Sun Dec 07, 2003 11:46 pm

Be careful substituting a 5U4 in an amp not designed for it. 5U4's draw 3 amps, while 5Y3's and 5AR4's draw only 2 amps. If the supply winding from you PT can't handle it, you could have problems. I'v heard that 5V4's are a good approximation of a 5U4 (between a 5Y3 and 5AR4 in voltage drop) that draws 2 amps.

Other than that, the best thing to do is experiment and see what sounds best to you.

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Re: 5u4 and 5y3 instead of 5ar4 tube rectifier

Postby johnnysavant on Sun Dec 14, 2003 10:42 pm

I'd be VERY careful. It depends on the amp. If your amp has no standby switch, then do not use a 5U4 or 5Y3. They are directly heated and will slam your tubes with B+ before they are warmed up.

A 5AR4/GZ34 is indirectly heated, which means it has a built-in time delay befoe it puts out B+ to the plates of the other tubes.

You can substitute a 5V4 safely for a 5AR4 if you want a little more sag. I run one in my JMI AC30. The 5V4 is designed like the 5AR4, but with lower voltage and less current output.

If you do have a standby switch, Steve is right about the current draw on the 5U4. The problem with a 5Y3 is that it only puts out 125 mA of current vs. 225mA for a 5AR4 and 175mA for a 5V4 at normal RMS voltages). For some amps 125 mA is not enough to run everything. So, again, it depends on the amp. A 5Y3 usually will be enough for a two channel amp running a pair of 6V6s or EL84s. But I wouldn't put a 5Y3 in a two channel amp that runs a pair of 6L6s or EL34s unless the manufacturer says it's OK.
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Re: 5u4 and 5y3 instead of 5ar4 tube rectifier

Postby Jeffery on Sat Dec 20, 2003 5:38 pm

So are you saying the 5V4 is indirectly heated ?
What difference in tone,headroom,& gain would there be using it over a GZ34 ?
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Re: 5u4 and 5y3 instead of 5ar4 tube rectifier

Postby johnnysavant on Sun Dec 21, 2003 4:01 am

Yes, a 5V4 is indirectly heated like a GZ34. The 5V4 puts ~25 volts less to the plates and has a little more sag. What it does to your amp depends on how it's designed. Normally, the amp will run a little cooler, which will extend tube life. It will also be slightly "browner" sounding, with a little more sustain and dynamic sensitivity. More sag and less voltage on the plates will more than likely mean less headroom. In other words, it will break up a little bit easier. On some amps the changes are subtle; on others quite audible.

I use a 5V4 on my 65 JMI AC30 and I love it. I don't think I'll ever change back to a GZ34.

You just have to try it and see if you like it.
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Re: 5u4 and 5y3 instead of 5ar4 tube rectifier

Postby jonathan horne on Sun Dec 21, 2003 3:36 pm

Another rectifier tube to consider is the 5T4. Electrically its very close to the 5U4 but its heater will only draw 2 amp instead of three. They never made a glass version only metal. They are available and cheap.

When selecting a rectifier for an amp you need to consider how much current it will be asked to provide. If the tube cannot keep up with the amps needs you get arcing on the plates and possible damage to the amp.
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Re: 5u4 and 5y3 instead of 5ar4 tube rectifier

Postby johnnysavant on Sun Dec 21, 2003 5:20 pm

A 5T4? Interesting. But they are directly heated also.
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