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Originally Posted by SemiAudiophile /img/forum/go_quote.gif
1 GE/National 12B4A 12B4-A tube - NOS New In Box - eBay (item 360229798544 end time Feb-25-10 19:12:18 PST)
I bought some NOS National 12B4A's off ebay a few days ago. They look identical to the red label GE's posted by mraroyo in terms of construction and were re-branded for National according to the seller. They made a noticeable improvement on my amp sounding a bit smoother and mellower. Though I'm not sure if it's because that they were new or that my previous RCA 12B4A's were old and worn out (they were stock and had them since day one). The new National's sure have a nice glow to them though. My amp looks almost new again.
I'm actually considered buying a backup pair just in case..as there are only 5 left.
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I also purchased a pair of the 12B4A tubes from that same eBay sale. Due to back-to-back snow storms in and around my neck of the woods, they just arrived late this week. I've been running them in my Ear+ HD amp for a few days now, driving my HF2's, and here's what I've heard:
1) The first thing I notice is more space in the music. By this I mean two things: a) more space between musical voices and b) the larger ambient space in which all musical voices are located is substantially larger. The greater spatial dimension adds to a more relaxed, natural and credibly lifelike sound, to my ear.
2) The next thing I notice is a quieter background. There was not any audible background sound, such as hiss, with the RCA NOS 12B4A's I've been using, but, when the music makes a transition from many instruments playing at a moderate to loud volume to silence, or to a few instruments making soft, quiet sounds, the contrast is quite a bit more striking. Also, this leads to the easier hearing of quieter sonic events. So, it makes for a more detailed listen, without added brightness.
3) The last thing I noticed, so far, is that the midrange is nicely more prominent. Not a lot, but enough that I really appreciate the difference. In tracks where I would turn up the volume to hear (usually) the lead singer with more volume, there's no need with these 12B4A's rolled in. The mids are sufficiently more prominent that when all of the other voices are just where my ear prefers them, the mids are as much there as I prefer as well.
Overall, with these 12B4A's (relative to NOS RCA), I would say that I get the fluidity of sound that I've come to associate with a tube amp, coupled with more of the clarity and level of fine detail that I've heard from my all-discrete solid state amp (the Purity Audio KICAS Caliente). And what's really nice about this is that: I usually pay $9 per 12B4A (including shipping) when I buy them in a batch of four. For this pair, I paid $13 per 12B4A (including shipping). So, I'd say that it's a very nice amount of sonic benefit for a modest number of dollars. It's almost a 50% increase, but for a modestly-priced piece of gear. I did not hear these kinds of differences in the past, when switching between NOS Sylvania, GE (non-red-labeled) and RCA 12B4A's in the past.