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New Production 5AR4 Reviews

Isn't an ST70 pretty hard on the stock 5AR4 anyway? I'd imagine a 120 would be even worse. Honestly applications like this are begging for dual rectifiers or some sand in the box. Hang a voltmeter on the B+ line sometime when you're jamming. If the meter dips and sags, you need more current capacity. Analog meters will tell the story, you'll see the needle dance if something is going on. B+ sag can be useful on a guitar amp, but its really not something you want on a hifi amp.
 
I leave my meters off on the ST-120 when I'm listening, but I have turned them on every now and then for a peek, and they just barely dance an mA or two when it's really hittin' it. You'd expect some fluctuation, and I wouldn't consider that bad - we're talking Porcupine Tree tickling 100+ db into some fairly inefficient speakers.

And ya ... a 5AR4 is being asked to work pretty hard in this amp, but the only real impact is tube life. Bob provides them as the stock tube with the kit.

Because of the power demand, I'd expect the very best rectifier for the ST-120 would probably be a GZ-37 variant, even more so with the KT120's installed, but they're expensive. Main reason a lot of folk migrate to the GZ68 copper cap, but I find those a bit sterile sounding compared to any tube rectifier I've tried. A good NOS Mullard GZ-37 will set you back several times the cost of the copper cap, but the new production re-issues are going for around $100. Been thinking on one of those as they're a more robust tube and should last a lot longer in the bigger amps. Then again, I could get three of the 5AR4 reissues for the same price, so is longevity really an issue here?
 
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I found a good deal on some GZ37's and bought them up. Then I looked up the specs and they have a maximum input cap of 4 uF. I have seen them used with up to 8 uF caps. I found that the GZ33 is a better candidate for the ST-70, it looks the same, but will allow up to a 60 uF max input cap. It does require more filament current than a 5AR4 tube but uses less than a 5U4 and has a slow warm up. I had some diodes in series with my 5AR4 (Diode Mod) but they added noise so I removed them.
 
The 5AR4/GZ34 is an indirectly heated rectifier with a 5 volt heater at 1.9A. The Mullard and GE are generally rated at 450V @ 250mA; modern Chinese won't handle that voltage or current for long; the Russian and Eastern European are better than the Chinese. The voltage drop by the rectifier is about 17V.

The 5Y3 is an indirectly heated rectifier with a 5V heater at 2A. They are rated for 350V @ 125mA.

The 5U4GB is a directly heated rectifier rated at 5V and 3A. They are rated for 275mA @ 450V with a voltage drop of about 35V. Since some power transformers are only rated for 2A, this 3A rectifier will stress the power transformer, make it run hot, and possibly damage it. The 5V3A is an uprated 5U4GB that is well worth looking for if your equipment can use a 5U4GB.

The 5AU4/5V3 are my favorite rectifiers; they are uprated 5U4GB that can handle even more current. They are rated for 350mA @ 450V with a voltage drop of about 35V. Notice: the 5AU4 and 5V3 have a current ratings of 3.8A, almost twice the current for which the ST70 transformer is rated, for example. These robust tubes were made for color television sets. I use them where I can.

The 5R4GYB is a directly heated rectifier rated at 5V and 2A; so it will work fine in an amp rated for a 2A rectifier like a ST70. It is rated at 250mA at 900V so will be coasting in most equipment. It drops about 40V so the plate voltage will be slightly less.
 
gadget73 said:
Shucks, I was hoping for a nice blue color. Odd as it sounds, nuclear material under water makes a lovely bright blue glow. Cherenkov radiation is the fancy name for it, but it looks quite cool. The brightness of the glow around individual sections directly relates to the activity level.
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Then you want the 866 in my opinion the coolest looking tube on the planet.

I am so happy the I can get some new 5R4's they are used in one of the 3 power supplies on both my Viking 1, and Viking II transmitters.
 
Just bought a NOS Mullard GZ37 ... I feel so dirty after starting a thread about the 5AR4 ... and somebody's gonna end up with coal in their Christmas stocking, but it won't be me ... :D

Those can pass a bunch more current, so I should get some more grunt out of the deal. I've heard a lot of good from folk with bigger amps. I do know the requirements of my ST120 and my tube preferences do tend to push the GZ34 variants pretty hard.

Doesn't put me out of the market for the new production 5AR4's though ... me being a certifiable roller keeps me poor.
 
Cap rolling, Tube rolling and Porcupine Tree?
You sound like my kind of audio guy Skizo.
Porcupine Tree is the only band since Zappa that I've seen more than three times.
Me and my earplugs that is.
 
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buglegirl said:
Hiya,

There is some confusion in the thread about what is a fat bottle 5V4GA which is alleged to be a 5AR4 re-labeled.

Relabeled "Philips" 5V4GA Tube ..

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Original "Sylvania/Philips" 5AR4/GZ34 Tube ..

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I bought into these relabels before they became known. Now they are selling about 3/4 of what a NOS Mullard goes for in some cases.

You are better off finding Japanese "Mullard Tooled" variants if you desire NOS over current production IMHO.

Frannie
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I remember Toshiba as having a particularly good one, I wonder if it was crafted on the Mullard machinery.
 
audiodon said:
Porcupine Tree is the only band since Zappa that I've seen more than three times.
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Three for me too ... once right here in my hometown, opening for Coheed & Cambria ... that one tore the roof off da house! NOBODY does the "wall of sound" like PT ... Some of my favorite test tracks ... Russia on Ice, Tinto Brass, Wedding Nails, and .3 If the system can handle those, it can handle anything.
 
Ah. On the DVD-A of Deadwing, there's a song called "Halflight" that I love. It's also on the Anesthetize concert Blu-Ray.
My PT test tracks:
Vinyl:
1. In Absentia - The Sound of Muzak
2. Fear of a Blank Planet - Cheating the Polygraph

Digital:
Storm Corrosion - Akerfeld & Wilson - Lock Howl
Deadwing - The Start of Something Beautiful

Sorry . . . back to the rectifiers!
 
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Tom Bavis said:
I don't think that's the "big bottle" Philips tube he's referring to... Philps bought Sylvania and continued manufacturing some of their tubes - 6DJ8, 6L6 and 5AR4 among them. When the military wanted spare 5V4 tubes, they relabeled some 5AR4s. When they needed 5881s, they stuffed 6L6GCs into the shorter bottles.
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I read the same thing about military 1625s and the 6L6 guts, especially after the war was over, and they were just finishing off contracts.
 
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