NOS 5U4GBs are dirt cheap. $5-$10 each. Cheaper than the new ones. Shop around on ebay and try several different flavors for little investment. RCA, Sylvania, Tung Sol etc. Just look at the ones offered for carefully. Do they appear to be NOS. Original boxes; JAN military boxes; etc. Don't mess with the used crap at these prices. Have fun. If your amp can use 5U4Gs (225ma vs. 275ma) you might want to look into these. More expensive, but in my Cary SLI-80 much better sonically. Also, if your amp can use the 5U4Gs, look into some NOS 5AS4s. A pair of Mullard 5AS4s worked magic in my amp. Good luck!
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I cannot speak from experience with this exact product but in general, NOS tubes are far superior to new stocks.
My luck with NOS 5U4GB has obviously been better than yours. My first choice would be Sylvania Gold Brand with old Tung Sol running a close second. My tests and reliability results were (as I remember) with Tube Research GT 400 and Mike Elliott's EASE Magnum.
Here is a link to BWS tube who has them in stock.
Man, maybe I've been overpaying for the Jan, Ken-Rad, and RCA used tubes! Anywhere from $65.00 to $85.00 and two of them looked well used. I also bought a tube that was advertised as NOS but came pretty well worn. This was from a private individual. Think I'll give BWS a try.
Is the 274B a drop in replacement for 5U4GB?
I'm kinda new at this so if what I say isn't true, somebody jump in and say so.
I have an Audio Note Kit 1. The biggest change I have noticed so far was going from a Raytheon 5U4gb to a 2/59 US Army Coke bottle RCA 5U4G
I think the 5U4G and 5U4GB are interchangeable
I also like the JAN Sylvania 5931. This is also one of the coolest looking tubes I have. This sucker has 3 micas and a "girder" in it. Huge base also.
Hi Tom Ryan. Most Nos 5au4's and subs are readibly available, easy to source and relatively inexpensive. If you can ascertain the voltage requirements of the rectifier in the airtight, you have many options available to you. Rectifiers "DO" make a difference and in many circuits... it can even be quite dramatic. The most important parameter here is to make sure each side of a full wave rectifier is tightly matched and the tube itself should test no less than 95%.Good Subs for a 5au4 would include.... 5aw4,5ax4,5t4, 5v4, 5y3,5z4,5as4,,5931 and their euro equivalents. I like the old st shaped 5v4g in particular here for a sub. Hope this helps.
I have bought two recs which were highly recommended by my amp's importer as being far superior to that which came with amp. I shopped around (at 3 different sources) and located two of the highly prized NOS - thus the high price. I have to say that both tubes sound the same and I can't tell a difference, except between the one which came standard and a $20.00 new one. That is to say, the NOS tubes sound superb and have improved the musical performance of my Air Tight in a very meaningful way. Have to say I don't fully understand why a change in retifier tubes would make such a difference but it does. I just need to find someone who can test my existing tubes as I think one of them is slowly dying.
Hi Tonryan. Chriskeating's post above is an appropriate one regarding ramp up time. Does the airtight have a standby switch? Indirectly heated rectifiers vary in ramp up time in comparison to directly heated rectifiers. This lag time will prevent cathode stripping of the other tubes in your amp. Regarding sound of rectifiers.... While it may be difficult for some people to comprehend,like input tubes,driver tubes,and output tubes... rectifiers do make a difference and can have a major influence on the sound of the amplifier or preamplifier. If the amp or preamp employs a vacuum tube for rectification... it should be the first logical place to start regarding tube rolling for voicing ones system, as they can [and do] have a major influence. One can invest in expensive nos tubes for the input or outputs and only hear minimal changes in tonal balance,bass drive, frequency extention etc when a weak, unbalanced or mediocre rectifier is employed in the circuit,and then wonder what all the fuss is about with nos tubes! Swap out the sovtek or weak rectifier for a strong nos one and be prepared for a whole higher order here[ WOWZA]. The Western Electric 274b..... unlike the majority of Western Electric manufactured tubes, the 274b rectifier is grossly overrated and overpriced, you can find far better for less coin [much less]. The same can be said for a good many of the English rectifiers[mullard excluded here]... like the fabelled U-52. Typically... any early US and Canadian made coke bottle style 5u4g from the 40's will transform your amplifier to a whole higher order as long as both halves are close and the tube test strong. The original Tung-sol coke bottle being my particular favorite of the bunch. The RCA, sylvania, GE and many branded 5u4g coke bottles will simply stomp on any of the current equivalents.
Ecc. - I actually have 5 recs., two new ones (both a bit rough sounding) and three NOS all of which "stomp on" the new new tubes. My favorite of these in order are:
1) Sylvania - 1943
2) RCA - 1955
3) Ken Rad - 1940s
I'm afraid the RCA is nearing it's end, though. It arrived in used condition and was not NOS as advertised. However, it has provided wonderful music for the last 2 years and I don't regret the $85.00 spent.
Unfortunately, the Air Tight does not have a soft start feature so I have a shelf full of input and rectifiers tubes. However, I'm still using the WE 300B output tubes that came with amp three years ago and they spec out fine, at least by my amp's own bias meter.
Hi Tomryan. Forget about changing out your rectifier as both the Sylvania and Kenrad 5u4g's are terrific and should last a long time. While I have never had the pleasure of hearing the Air Tight 300b with the Western Electric tubes in it, after hearing a pair of their 2's. I am most certain it would be something very special indeed.
Does GZ34 and GZ37 are the same?
According to the Tube Substitution Handbook the following tubes can be substituted for each other.
GZ34, 5AR4, 52KU, U54, GZ37, and U54.
5AR4 shows the following are also compatible, U77, 5U4GB, 5AS4, 5AU4 and 5V3A
There is also an antique tube, the CV378 (British) which is excellent. I have a couple of them myself.
Last, if you want something cheap but decent there is a Chinese rectifier called 5C3PJ that subs perfectly. I bought some on line for $3.00 each a couple of years ago.
Have fun experimenting, you never know what will sound best until you experiment.
I just did search on the 5C3PJ and came up empty. Do you have a link to where you bought them? Thanks!
Correction, number is 5Z3PJ, keyboard fumble. Ebay has them at high price, maybe worth it to try one out and if you need quantity go elsewhere.
Most websites in English language look high, the one site that was close in price I have no experience with. Exercise common sense, post results if you test.
I have use both GZ37's and GZ34's in my amp. With the GZ34's the B+ is 425v and the amp has a very taught, muscular robust sound. With the GZ37's the B+ is 400v and the sound is more relaxed with more breath and ease but also slightly softer around the edges.
Not sure what causes the difference in sound. Is it the difference in B+ or is it the different tube? I am guessing its the difference in B+.