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.

Absolutely. Thanks, Ecclectique and everyone else. I have four different rec. tubes and each makes the amp sound different and two make it sound better. Now I just need to find someone local (Southeast Michigan area) who has a tube tester I can hire to find out what condition they're in.

tomryan,
The 274B is most likely a drop in, but there are instances where it is not viable. It comes on quicker than the 5U4. The folks at Sophia can help with that advice. I use a softstart with my stuff, so it is not an issue.

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.