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5u4g rectifier OK in simple SE?

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I am piecing together the parts for a simple SE build. I have some 5u4g rectifiers around from another amp and am wondering if they can be used as a direct replacement for the 5ar4? Do any other parts needs to be changed to accomodate it?

I have swapped it into another amp that speced the 5ar4 and it was fine, the 5u4 does not have the slow start feature of the 5ar4 so it is a bit tougher on the tubes.
I've used the 5U4 in my Simple SE. As you point out, it is a directly heated tube and does not provide the slow start of a 5AR4. It will be harder on the tubes, and especially the power supply capacitors at each startup.

If my power transformer were rated 750VCT or less, and my power supply caps were rated 500WVDC or higher (with at least 550V surge) I'd probably use the 5U4 and not worry to much. Overall, however, I think the 5AR4 is a better choice.

If you plan to use the 5U4 on a regular basis, I might recommend substituting a smaller capacitor for C1. I think the standard parts list calls for a 47uF cap at this location. I'd probably try a 22uF instead.
Maybe - it's not a direct replacement for a 5AR4.

5U4 will drop about 25 more volts than 5AR4. It also takes an extra amp of filament current. I don't think your tubes will care whether or not it has a separate cathode, I wouldn't worry about that.

In theory, C1 can be larger for a 5AR4 than a 5U4; in practice, old U.S. made 5U4's are pretty tough beasts so I wouldn't worry much about the C values. I've never killed a 5U4, and it hasn't been from lack of effort.


edit: the only rectifier tubes I've ever killed were 5AR4's and that Sovtek "5Y3", and I wasn't even trying to kill those ....
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Thanks for the replies, I will likely give both a try and see how it goes. I do like the large coke bottle shape of the 5u4, it definitely fills out the chassis nicely.

get serious dude, and try one of these: :rolleyes:

274A Data sheet. Emission Labs.

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