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5U4G equivalents...

jt1stcav

jt1stcav

Up and Coming Bottlehead
Was curious...I have a Mullard GZ30 that replaces the Chinese 5Z4GT on my preamp, and thought it'd be nice to find a Mullard equivalent for the venerable Sylvania 5U4G rectifier that's used on my 300B amp. After a Google search I first spotted a Mullard GZ32 that stated it was a 5U4G equivalent. Then on another site there was a Mullard GZ37, and on yet another site a GZ31! Not all of these Mullard rectifiers can be an equivalent for the 5U4G, can they? I can't seem to find a straight answer anywhere I look...maybe someone here would know. Being a tube-noob, I'd hate to use the wrong rectifier and possibly muck things up!

Your comments are all appreciated...thanks.
 
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I have a bunch of these tubes 5u4gb some nos and some used. one older 5u4 (need to test) I only have an emissions tester but if you want one just pay shipping.
 
Mullard GZ33

The GZ33 "falls" between the GZ34 and the GZ37 in its capabilities. It's much less sought than the other two, so it's way cheaper but from what I hear is superior.

MikE
 
Rock, thanks for the offer. I'm not really in need of a 5U4G since I have an excellent '51 Sylvania 5U4G in place right now. Just thought a matching Mullard for my amp (like the GZ30 in my pre) would be kinda cool is all.

MikE, I'm confused about your statement...I can't use either of these Mullard rectifiers for my amp, can I? The amp's schematics actually call for a Chinese 5Z3PAT (or a 5U4G, says the manufacturer), and I would assume only one Mullard rectifier would be an equivalent to the 5U4G, or am I wrong? From what I've read so far (if I'm understanding it correctly) is that a little sag that the 5U4G provides at startup is a good thing that it isn't rough on the output and drivers...I don't even know if this matters or makes any sense. But can you just choose a certain rectifier within a given circuit and it should operate satisfactorily?
 
Here's the BEZ Model T3B 300B SET schematic: what do you make of it, if anything?

EDIT: It's a 120V version obviously. Wonder why it only shows one 300B instead of two for a stereo 2-channel layout?
 
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Jim,

There are a lot of rectifiers with the same pinout as the 5U4. You can substitute lots of tubes, as long as you observe the peak inverse voltage and current limits, and it's good to pay attention to filament current draw too (e.g. replacing a 5AR4 with 5R4 or 5U4 adds another amp @ 5v = 5 watts current draw).

The specs for tubes are readily available on many web sites, so you can do a comparison of options that way.

I mention this because for some folks it's fun to begin to "own" the process of understanding different tube options. Your question is a great place to start!
 
Thanks, tubino, for the info, although it falls on deaf ears I'm afraid. I'm not technically inclined, therefore I wouldn't understand the proper electrical components and their measurements in any given circuit. How to choose the right rectifier for my amp's circuitry is beyond my grasp (unless I just leave well enough alone and continue using the NOS Sylvania 5U4G).
 
Jim,

Many Schematics only show one channel of the audio circuit the other channel is just a mirror. I see he sent the schematic right to you when you asked I figured he would. You may want to drop him a line and ask him what different rectifiers would work okay in his amp since the schematic doesn't give you any specs for heater current draw. I bet many of the Mullard GZ series will work in the amp.

Craig
 
You only have 390V per plate on that rectifier and, AND the 5U4G is the lowest voltage rated of the 5U4s. There are many tubes that you can use as many have higher ratings than a 5U4G and almost every octal rectifier of high enough ratings will fit right in. For instance a 5AR4/GZ34 will have a different basing diagram even though the pinouts are the same. You could drop one of those in there no problem.
I checked the voltage rating for a 5V4G and it is higher than a 5U4G and it is a soft start.

Now if you check voltage draws and drops you might not find that all pigs are equal, but every amp will be built with a lot of tolerances in its componants so I doubt there is anything to worry about.

You pull up the data on these other tubes and compare them to a 5U4G and if the max plate voltages and the inverse volts meet or exceed those of the 5U4G then the tube will not fail because of that. How much the draw, drop and inverse can change the B+ I will leave to someone else.

I would say that using a soft start will be better for the amp in the long run. Email about using a 5V4. They don't cost much, have the ST shape and will help your 300Bs to last longer.
 
Originally posted by Thatch_Ear
I would say that using a soft start will be better for the amp in the long run. Email about using a 5V4. They don't cost much, have the ST shape and will help your 300Bs to last longer.
Click to expand...
Ditto everything Thatch said. The indirectly-heated 5AR4 and 5V4 give you the somewhat slower ramp-up of B+. You shave a few watts of fil. juice (no big deal, but a little help to run it cooler).

A 5AR4, though, will have a significantly lower voltage drop than a 5U4. I measured this once in a circuit, and the 5AR4 gives you something like 30+ volts more (depending on how worn the tubes are). I never compared 5V4 by measurement, but I guarantee it will have a greater drop than 5AR4.

I'd probably drop a 5V4 in without much worry and get the softstart, but an email to the manufacturer is a smart move. Incidentally, it's not unusual to find a tube labeled 5AR4 that is really a 5V4. The honest-to-gosh 5AR4 was designed using damper diode plates -- which is why it is a gnarly tube that can handle some current and has low dropout.

People who don't want to pay up to $40+ for a Mullard 5AR4 can design gear to use a pair of high-current 6volt damper diodes (e.g. 6CJ3) and get the same or better performance at low cost. :) That's an audio cheapskate tip for ya.
 
Mullard GZ33

The Mullard equivalent for the 5u4 is the GZ33. I only mentioned the other tube because you did. MikE
 
Swapping rectifier tubes

Sometimes a particular amp or preamp defies conventional wisdom about which tube sounds best. Friend of mine was selling an amp that used multiple 5AR4s per monoblock, and because of the massive filter capacitance right after the rectifiers, it ate up the tubes. He popped in 5R4s and was surprised to find he PREFERRED that sound.

When you model PS behavior, it's not hard to see that adding resistance in the right place can provide damping and cure ringing. That's just one mechanism that might be at work.
 
Craig, Thatch, MikE, tubino...thanks so much for your time helping in explaining this situation to me; I truely appreciate it. The best course of action for now would be to contact Edmund Lam and see what he has to say about a Mullard equivalent to the 5U4G. I will take into account everything you've told me thus far, and if I can squeeze any amount of pure clean tone from my amp (and longevity for the other tubes) due to a rectifier swap, then this search will all be worth it!
 
Mullard GZ34 and GZ37 can be used...

Just got an e-mail from Mr. Lam and the GZ34 and GZ37 can be used in place of the 5U4G without difficulty. That solves this lil' mystery!;)
 
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