Rectifier tubes?

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.

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.

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.