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In Reply to: RE: Stereomour w/45s questions posted by Jim_R on September 22, 2009 at 14:46:57
No, the primary impedance design target is 4K for the new Bottlehead transformers. (Actually it looks like about 3947 ohms into 8 ohms on the 8 ohm tap, 3538 at 16 ohms with the new design). At the standard maximum operating point for the 45 (275v, 36mA) my nominal load design target is 3809 ohms. The RCA standard of 4600 ohms is a bit conservative relative to my nominal. But I will say, the best sounding 45 amp I've ever heard used a TFA-2004Ni at 3000 ohms so I am pretty confident that this load is going to sound good.An interesting third option is to set the amp up for 45 operation but plug in a 2A3. The voltage and current will be very close to the 45 design point, the output power will be in between the 45 and 2A3 levels, and the 2A3 will last longer at the more conservative operating point.
I have a shunt-regged 45 option in mind as well, using Zeners - not as good as a tube or hybrid regulator, but might be a modest improvement. No work on that until we get the basic product done though!
Edits: 09/22/09Follow Ups:
Wow so how many people will be running these with 45s then over the 2A3s?
Fascinating. The best tube amp I've heard so far for my classical music tastes has been a 45. Switching to rock you'd pop in your 2A3s, right?
I dont know JT, I love rocking out on my SR45!
Nice! I love to hear that.
It's cool when pieces break stereotypes (no pun meant).
Well, as I have 3 pairs of 45s here and no 2a3s, I'll probably build it as a 45 and then plug in the 2a3 to see how it goes, seeing as Paul says this will be ok. If the 2a3 sounds better whith my speakers and space, then I'll go back and convert it to the full 2a3 operating point.
I'm not sure which tube I'll ultimately pursue for an all-out amp, but the stereomour will give me a relatively low cost way to explore both possibilities, and if it happens to hit the sweet spot with the rest of the system, then all the better.
Thanks again Paul, for your thorough and detailed responses. Very much looking forward to this kit.
-- Jim
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