Rectifier tubes?

I don't know where Tomryan buy 5U4GB, most of them are under $15 each on ebay. I got them as low as $5

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.