Most reliable current production 5AR4/GZ34?

[Rhodesplyr]

I know this question has been asked before, but, according to the search engine, it's been four years.

JJ, Sovtek, and Chinese appear to be the current offerings. (I know that Mullard, GE, and Sylvania are better, but expensive.)

I just removed a shorted Groove Tubes-labeled Sovtek 5AR4 from a client's Deluxe Reissue.

[greekie]

Any amp that has the standby switch between the rectifier tube and a choke and big capacitors is gonna kill that tube eventually. The biggest savior of rectifier tubes I have found, is to disconnect that standby switch.

YM2C

[big_teee]

Any amp that has the standby switch between the rectifier tube and a choke and big capacitors is gonna kill that tube eventually. The biggest savior of rectifier tubes I have found, is to disconnect that standby switch.

YM2C

An Amp without a Standby, Can be Pretty Un-Handy!

[imaradiostar]

Any amp that has the standby switch between the rectifier tube and a choke and big capacitors is gonna kill that tube eventually. The biggest savior of rectifier tubes I have found, is to disconnect that standby switch.

YM2C

Or...just connect a bleeder resistor across the standby to prevent the shock to the rectifier tube. It'll go a long way toward saving the rectifier. Sure, the amp won't be 100% silent but it'll prolong the rectifier.

jamie

[clyde1]

I've used them all and the winner is..........none of the above. A little series resistance would help some too.

[Rhodesplyr]

I'm going to conclude that the answer to my question is: No one knows. It's a total crapshoot :-)

[km6xz]

A 5AR4 is not a GZ34 regardless of what labels they have. The GZ34 version by Mullard was pretty unique, with very little forward drop.
Ruby Tube started making their own in China over 10 years ago that was close to the old Mullard and better than the 5AR4 tubes. It is a shame New Sensor captured the name and started confusing everyone with Mullard Tungsol knockoffs that are just not the same thing.
If you can't find a NOS GZ34 the only real replacement is the Ruby from Magic Parts.
I remember dissecting real GZ34 and doing full parameter testing to see how the old tubes performed and how they were made back in the late 90s. That data was used as a template for recreating the old style performance, but it is still not quite there, but a lot closer than the others.

[Rhodesplyr]

How is the Ruby Tubes GZ34 different from the TAD GZ34 or the generic Shuguang GZ34? Testing and selection?

At this point in time, as someone with a doctorate in literature with graduate work in linguistic history, I'd say that whether or not a GZ34 is a 5AR4 is matter of semantics not really worth debating. Yes, the Mullard version was the best. We all know this. The GE and Sylvania versions were also pretty good. I haven't heard anyone else on any other tube discussion list (I posed the question in other places) make the claim that the Ruby-branded tube was better than the old-stock General Electric or Sylvania versions. I'm guessing that those are the tubes you refer to when you write '5AR4' (?)

I predict that a semantic debate will now ensue, but, as someone who knows the difference between words and the things they refer to, I won't be participating. A Mullard 5AR4 works just as well in my amp as a Mullard GZ34 :-)

[km6xz]

The Ruby was modeled after the Mullard and was made in Tom's own factory there in China. Mullard's original GZ34 is different than a 5AR4 due to its cathode design and spacing which resulted in a lower impedance, and a lower forward drop voltage. It should have been classed a different tube designation because a circuit using it will have higher B+ which in some circuits would require either adjustments or slight modifications. The heater and cathode were spaced closer, in fact so close that the heater to cathode voltage tolerance was not as high as a spec 5AR4.
I tried to model the Mullard to find out what its real specs were and why it was different since all the players of GZ34 power amps preferred the Mullard over the others. After many months of testing samples and making incremental changes a final candidate was picked for production. Several other companies are buying that tube now for rebranding but since the source is not always the same, the one someone buys might be a normal 5AR4 copy or a the Mullard version that Ruby/Magic parts supplies. The Shuguang GZ34 is similar to the old US production 5AR4's and a fine tube, but with the higher forward drop and higher Z like the old ones.
Many of the tubes that have dual designations, like the 5AR4/GZ34 are one or the other but not both since they were different tubes. Patent cross licensing was common in the industry within the US but that did not occur internationally so many US or European tubes were patent work around models, to produce something that could replace the original but by using a non-infringing technology. When a major tech change occurred like when RCA patented the focus beam tubes the European makers had to come up with something that did not infringe but could be used for similiar purposes and be selected as OEM for similar consumer products. For a while RCA and its beam tube licensees were all alone and had the power tube market to themselves until a patent work around of using the very different performing tetrode in a way that mimicked the performance of the beam tubes, so the Kinkless Tetrodes were developed, now just known as KT-xx tubes as a way to avoid owing RCA royalties. But the cross licensing extended down to minor differences as well and the 5AR4 was a different stand alone tube than the GZ34 but for consumer products, they could be interchanged.
Measure the z of a regular 5AR4 and the original Mullard and you will see the Ruby is the closest to the Mullard. If your design works best with a bit slower(less stiffness in the supply and lower plate voltage) use the 5AR4 but if you want the tighter higher peak current and higher voltage of the Mullard, use that design tube. The results are difference for technical reasons you can measure, not magic dust that most tubes require for a particular sound. Personally, I like the sound of the lower voltage types, a rounder browner sound that is great for blues and jazz. Amps that used the original Mullard GZ34 had their own sound that was also great but different. The same technical traits could be had by other means however. Putting several diode sections in parallel would lower the z as well. Or changes to the filter topography. The GZ34 higher peak current allowed using either cap input or inductor input without much concern. But one thing to assure in a Mullard GZ34 optimized circuit, make sure the leakage between heater winding and anode supply was very low, the tight spacing of the heater and cathode meant it should not be used with a heater that was grounded anywhere.

[Rhodesplyr]

The heater and cathode were spaced closer, in fact so close that the heater to cathode voltage tolerance was not as high as a spec 5AR4.

But one thing to assure in a Mullard GZ34 optimized circuit, make sure the leakage between heater winding and anode supply was very low, the tight spacing of the heater and cathode meant it should not be used with a heater that was grounded anywhere.

On all datasheets of the GZ34 I've seen, the heater and cathode are directly internally connected at pin 8, so shouldn't the heater to cathode voltage be zero--or close to it? They obviously have to be used with a dedicated 5V heater winding.

The heaters are also internally connected to the cathode on the GZ30, GZ32, and GZ37. This is different from indirectly heated rectifiers like the 6X4 or EZxx tubes, where the cathode is isolated from the heater, but where heater-cathode shorts tend to be a significant failure mode. Of course, designers could thereby save the cost of an extra transformer winding.

[km6xz]

Yes, but notice, connected at a single point. which helps the shielding effect but raises the shorting potential since there is a potential difference between one end of the heater and any point on the cathode sheath. Mullard solved the problem with a different oxide that was tougher for the thickness. The cathode sheath is really compressed around the heater which increased thermionic efficiency. heater shorts are one of the most common rectifier failure modes. Notice the anode<>cathode spacing also is tighter. That is why a lot of people questioned applying the designation GZ34 on the tube. There were a lot of differences between various brand tubes in things like heater elements layouts where the licenses permitted deviation from the original but allowing the licensees to create a slightly different character and marketing point.

[Rhodesplyr]

Yes, but notice, connected at a single point. which helps the shielding effect but raises the shorting potential since there is a potential difference between one end of the heater and any point on the cathode sheath.

Yes, I did notice, before you pointed it out, that the heater and cathode are connected at a single point. Obviously, they have to be connected that way, or heater current would be divided between the heater and the cathode itself.

Ohm's Law tells me that the resistance of the heater during operation is around 2.6 Ohms. Unless the cathode is highly resistive itself, I fail to see where a large voltage potential between heater and cathode is liable to occur.

Thus, I fail to see how there's much potential, pun intended, for a large voltage difference to develop between the heater and cathode, unless the cathode is, itself, highly resistive. On the other hand, if the heater shorts, via mechanical failure of its insulation, to the cathode, it would create the situation I describe above of the heater being connected to the cathode at two points. At that point, the problem would be one of current flow rather than voltage difference.

[Wombaticus]

I'll take your word that true GZ34s may have had less voltage drop, but (at least in North America) line voltages are also considerably higher than back in the day, so it may be essentially a wash as far as B+. A small difference in sag is probably all you might have comparing Old-days GZ34 and modern 5AR4.

In any case, the voltage drop with either is small enough that there is a very marginal argument for using a GZ34 class tube to begin with....there's so little sag you might as well just go solid state for the recto.

[jmaf]

I know this question has been asked before, but, according to the search engine, it's been four years.

JJ, Sovtek, and Chinese appear to be the current offerings. (I know that Mullard, GE, and Sylvania are better, but expensive.)

I just removed a shorted Groove Tubes-labeled Sovtek 5AR4 from a client's Deluxe Reissue.

Never had issues with the current production Reflektor GZ34(Sovtek,EH) and JJ's(Czech?) also have been reliable so far. I did have problems with a bunch of EH 6v6's, it last year IIRC.

Have had issues with the Chinese rectifiers though, but I've heard they've improved quality since - don't have any evidence to support it.

My 2 cents on standby switches: you won't be able to find a single good reason to have them.
Quieting the amp dead quiet during gig breaks? Turn it off. Who the hell cares about waiting 20 seconds?
Saving tube life? Turn the amp off.
Preventing cathode stripping, not applying HT before it warms up? Blahhh...

[Bruce / Mission Amps]

Wait a sec'... wasn't Andres, of TAD, the actual German guy who worked with and or designed Tom's RUBY tubes in China?