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Old 14th June 2011, 08:55 PM   #11
milosz is offline milosz  United States
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Yes it's true that the tube's power capability is fixed, based on the tube design / construction. However, a lower feedback design will have more distortion as you ask the tube for more power- while a higher feedback design will let you push the tube harder. If you arbitrarily set 1% THD as the maximum allowable distortion level, the low NFB design will produce less power at that limit.

Here you can see that you can get about 3 watts at 8 ohms at 1% THD with high negative feedback, and less than 2 watts at 1% THD without NFB.

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Cayin A-300B, 4 ohm tap, high negative feedback, distortion (%)vs 1kHz continuous output power into (from bottom to top at 1W): 16, 8, 4, 2 ohms, one channel driven.

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Fig.7 Cayin A-300B, 4 ohm tap, zero negative feedback, distortion (%)vs 1kHz continuous output power into (from bottom to top at 1W): 16, 8, 4, 2 ohms, one channel driven.
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Old 14th June 2011, 09:59 PM   #12
Jeb-D. is offline Jeb-D.  United States
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Ok, you are correct if using the 1%THD rating for output power. I was reffering to maximum output (clipping).
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Old 30th January 2013, 06:10 PM   #13
milosz is offline milosz  United States
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Default Long term reliability Audioromy FU-29 amplifier

This amp has been in daily use for about 2 years now, filament on one 6N1 failed (opened) so replaced that tube.

Good reliability.
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Old 14th February 2014, 12:45 AM   #14
milosz is offline milosz  United States
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Default Further notes- Audioromy FU-29 amp

Another year of daily use. Another 6N1 input tube failed- filament not open but tube has no gain. Replaced it, these are cheap tubes, easily gotten.

The plate caps for the FU-29 (829) tube have turned brown and brittle, I replaced them with some ceramic ones.

Amp still working fine.

Note that mine is the original SILVER version. The Audioromy FU-29 being sold now has a gold color top plate on the chassis, and different driver tubes; is supposed to sound better.

Daily use for more than 4 years and it only needed 2 cheap 6N1 tubes, that is pretty good IMHO. Many people claim that all Chinese-made audio is cheap unreliable junk, but here we have an amp with very nice sound you can get for under $500 and that is quite reliable. Cheap junk would never run day in and day out for 4 years. I've had expensive tube amps die in 6 months. Higher price does not guaranty higher quality.

That said, this is not a perfect amp- not as transparent as many other good amps. But pair it with the right speaker and you get a little magic. This amp with the little Polk RT25i gave me very satisfying and musical sound for under $700. I liked this amp with the RT25i better than any other amp I tried with the little Polks. I am arranging to try the amp with some other little 2-way speakers, which are upmarket from the Polks. I'll report on that in a later post.

I tried the FU-29 on my Quad ESL-57's and the sound was OK, but the Quads want more power. I usually use a Citation II on the Quads, that sounds much better to me. The Audioromy with the ESL-57's had a kind of bloated bass. Likely too much interaction with the weird impedance of the ESL-57's.
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