5U4 replacement

[Charlie]

Can anybody recommend a good 5U4 replacement for a Stiletto? I am looking for something greasy w/ a lot of sag and lower output is fine as well.

Also do I need to worry about using a non-Mesa brand tube?

 

[Elpelotero]

the mesa 5u4gb has a good amount of sag. I don't know if this is what you're using now though

 

[ThunderMonkey]

Any ol' fat Coke bottle 5U4 will do ! nice and greasy with plenty of sag or a 5Y3 = fat and greasy sag.

 

[Charlie]

Is the 5Y3 a direct replacement for the 5U4?

I bought the amp used but I'm pretty sure it has the stock 5u4gb tubes in it.

Also, I read somewhere that you have to re-bias the amp if you change rectifier tubes is this true? If so I'll probably stick with a Mesa replacement.

 

[ThunderMonkey]

The 5Y3 has the same current rise time as a 5U4G ( .44 of a second) but a lot less voltage, @ 303.00 So yeah, it would work.
Plenty of grease, I would think !

 

[Charlie]

Well I found this on the net and it seems like it isn't a proper substitution:

What is important in rectifier substitution is peak inverse voltage and
anode current capabilitities. The 5Y3 is a medium-power tube with a rating
of 1400 PIV and average anode current of 150 mA. The 5U4 is a "meatier" tube
that shares the same pinout and filament voltages. It has a PIV of 1550 and
average anode current of 350 mA. The only drawbacks of the 5U4 are 1)
slightly incresed voltage drop. The 5U4 will drop 5 to 10 volts more across
itself than the 5Y3. 2) It's physically larger. It may not fit well enough
in some applications to have enough cooling air around it. Despite these two
drawbacks, the 5U4 is an excellent replacement for the 5Y3. But as you can
see from the sspecs, the other way round is a no-no. The 5V4 is very much
akin to the 5Y3 in specs (25 mA more anode current), but it is a
heater/cathode type tube instead of a filament type like the 5Y3 and 5U4. it
will work fine, they're just harder to find. The 5Y3 and 5U4 were the most
popular rectifiers made, period.

Take from here:

http://www.zeni.net/pipermail/hammond/2002-February/019188.html

 

[Russ]

Interesting. So how does the GZ34 relate to the 5U4 in those terms?

 

[ThunderMonkey]

Interesting. So how does the GZ34 relate to the 5U4 in those terms?

ss diodes run @ .01 of a second rise time with @449.08 volts :shock: - the fastest, tightest and highest power obviously. Almost instant.

GZ34's are the fastest REC tube as far as rise time, .02 of a second, pretty damn fast with @ 413.90 volts current supply.

5U4-G takes .44 (almost half a second) for current to rise and puts out @ 357.06 volts - definitely the reason you can feel the sag with a 5U4G.

my learnins ! 8)

 

[Charlie]

So am I correct in saying that a 5y3 is *not* a replacement for the 5u4?

It is not listed as a substitute for any of the amps that use the 5u4...

 

[Russ]

Sounds like a reasonable assumption to me.

 

[Charlie]

So is it ok for me to use a non-Mesa 5U4 tube? Do these rectifier tubes need to be matched/biased with each other?