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Tube Amp recomedations for AR 2ax


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I am wanting/desiring/lusting to get my first Tube amp, Probably an integrated but i will consider all options. From what i have read on the "always accurate interewebs"  the nature of an acoustic suspension speaker design dictates  power requirements that may not be the same as a ported system.  What are those requirements  or any and all  considerations to be aware of,  specifically for my AR 2ax speakers.  I am interested in the basic theory of amp power output and how it relates  to acoustic suspension  in general  but for my budget, 1200.00 ish, suggestions of options in that price range  for my speakers would be helpful.  I know tube types can affect sound, how does that relate to acoustic suspension speakers.

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In its time, the AR-2ax was very commonly used with kit & factory-assembled tube amplifiers from Dynaco, Eico, and Heathkit, who were direct competition for each other in the American market; and it wasn't unusual to find the AR-2ax connected to a pricier McIntosh or Harman-Kardon Citation amplifier, although certainly not to the same extent as the less expensive types.

When higher-powered solid state amplifiers became available, the market for popularly-priced tube amplifiers declined dramatically, and then pretty much disappeared.

Many people who run vintage-based audio systems are looking for a certain era-authentic sound from their tube amplification, which isn't at odds with extracting maximum performance from their old speakers, but is not necessarily conducive to it.

A fully-restored AR-2ax connected to say, a Dynaco Stereo 70 (35 nominal watts/channel) vacuum tube power amplifier will sound just fine, but probably not as fine as it would if connected to a modern high-wattage solid state power amplifier. In the $1200 price range, you could have either.

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Thanks for taking the time to reply.  I have   many solid state units such as a Sansui QR6500.  I am specifically interested in the power requirements for the acoustic suspension design of these speakers. i have read that a lower powered amp might not take advantage of full potential from the woofers of this type of acoustic suspension speaker. I.E. under powering will not give optimal bass.  I want to make sure i purchase a tube amp that has the optimal power, not under powered,  for my speakers. Conversely i do not want to repeat the mistake i made of blowing a woofer by running them on an amp with more power than they can handle, the woofer gods smiled on my once and it may not happen again.

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Take a look at the AR-3 instructions here: http://www.classicspeakerpages.net/library/acoustic_research/original_models_1954-1974/original_models_manuals/ar-3_instructions/ar-3_instructions.html

"At least 30 watts per channel" and 60 wpc is "not unreasonable". The AR amp was, not coincidentally, 60 wpc. Many people have been happy with the 35wpc Stereo 70 and the Bob Latino 60wpc gets rave reviews.

btw, an underpowered amp, driven too hard, will do more damage than an overpowered one. For solid state amps many of us use 100, 200, 300 or more wpc with our 12" AR speakers.

Kent

PS: The 12" ARs are 4 0hm speakers that like power. I would think the 8 ohm 2ax would do fine with 30wpc, maybe less. My first stereo had AR-4x speakers driven by a dynaco ST-35 tube amp (17wpc) and that sounded great in a smallish living room.

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Reminds me of a question that I have had for years and have posted in several places but have never received a definitive answer for.

When loudspeakers are oriented horizontally, which way do most of you think is best to have the tweeters facing and why...to the inside or outside?

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I've driven my AR90 with my 60wpc tube amp and am thinking of using it with a pair of my AR9.

I will tell you the sound of the bass using a tube amp is quiet different from a solid state amp with high damping factor.

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Interesting question! 

I purchased my first pair of AR speakers last week, coincidentally a pair of AR-2Ax speakers. I've re-foamed the woofers and ordered new capacitors and L-caps. They should arrive this week so I'm hoping to to have everything assembled and ready for use by the weekend.

So, here's my question, which should be right on-topic and help with the discussion by adding some specific choices. Which of my receivers/amps will pair best with a pair of AR-2ax's?

Fisher 500C

Fisher 500B

Fisher 400

Sherwood S8000IV

Monobloc Heathkit W5M's w/Advent 300 used as preamp 

Sansui 8010 receiver (Solid State 40 WPC)

Harman Kardon HK3490 (SS 120 WPC)

BTW, in answer to the Jim Pierce question, I've always assumed that the tweeters should be positioned on the inside, closer together, and woofers on the outside, further apart. My rationale has always been that the lower frequencies need more separation to give a stereo effect, while less distance/separation is needed for stereo with higher frequencies. 

 

 

 

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On 10/11/2020 at 6:07 PM, JKent said:

Take a look at the AR-3 instructions here: http://www.classicspeakerpages.net/library/acoustic_research/original_models_1954-1974/original_models_manuals/ar-3_instructions/ar-3_instructions.html

"At least 30 watts per channel" and 60 wpc is "not unreasonable". The AR amp was, not coincidentally, 60 wpc. Many people have been happy with the 35wpc Tereo 70 and the Bob Latino 60wpc gets rave reviews.

 

Just curious if the AR power recommendations could have been IHF ratings and not RMS? Prior to 1974 when the FTC intervened, most HiFi manufacturers rated their their amps using IHF guidelines which were not nearly as demanding as the RMS ratings. Once the FTC guidelines took effect, everyone's power ratings dropped around 40%. The dates above are 1954-1974. Do you think the AR instructions could refer to IHF power ratings? If so, 30 WPC might actually be closer to 20 WPC. 

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5 hours ago, Norman Nicolai said:

Just curious if the AR power recommendations could have been IHF ratings and not RMS? Prior to 1974 when the FTC intervened

I think AR was referring to "McIntosh" level watts and possibly " Fisher" watts and later AR watts in the case of the AR receiver and integrated amp which were 45watts at 8 ohms and 60 at 4 ohms IIRC.  More available power is better.

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My guess is they were talking about pre-1974 RMS, measured with a 1kHz test tone. An amplifier measured with that method would have a rating 15-20% higher than one measured with the 1974 standard.

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2 hours ago, Aadams said:

.............................  More available power is better.

Why?

Are you worried about clipping a signal? Tube amps roll off the signal and solid state will try to push that signal and clip.

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30 minutes ago, DavidR said:

Why?

Headroom for modern audiophile recordings, vinyl or digital.

1 hour ago, genek said:

measured with a 1kHz test tone.

I thought I remembered this from somewhere.  It is from a 1971 brochure.

image.thumb.png.adfd5a96bc5e3c560d5ccfbc376d7f4e.png

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2 hours ago, genek said:

Yes, but that's the AR amplifier, not the recommended power for AR speakers.

Of course you are correct. The speculation was whether the AR wattage recommendation for speakers was based on IHF or RMS.     I was pointing out, that well before 1974,  AR's preference for continous power was same as used by McIntosh for its tube amps in the 1960s.

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Yes, as far back as the late 50s-early 60s, most higher-end audio specified RMS watts, though they often provided IHF and "music power" as well.

There was a fair bit of wiggle room in RMS power as well.

McIntosh manual for the MA-230 (1963) specifies continuous power (RMS), but power, distortion and frequency response are separate values, that is, power and distortion are not specified at any frequencies.

The 1968 AR amplifier manual doesn't seem to have any specs in it at all. The separate spec sheet for it specifies RMS power and frequency response, and gives distortion across a frequency range but states full rated power at 60 and 7,000 Hz, not across the entire frequency range. Which, IMO tells us a bit more than the McIntosh specs, but still not as much as the 1974 FTC specs.

 

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Yes and no. If you're only looking at modern stereo tube amps, then all you need to do is look at the specs. But if you are throwing vintage amps into the mix, then understanding the differences between all the ratings methods that have been used over the decades is important when looking at something that says it delivers "60 watts." 

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12 hours ago, genek said:

Yes and no. If you're only looking at modern stereo tube amps, then all you need to do is look at the specs. But if you are throwing vintage amps into the mix, then understanding the differences between all the ratings methods that have been used over the decades is important when looking at something that says it delivers "60 watts." 

Feb 1968 Stereo Review test of the AR amplifier. Page 35

https://worldradiohistory.com/Archive-All-Audio/Archive-HiFI-Stereo/60s/HiFi-Stereo-Review-1968-03.pdf

Gives AR stated published rating of Continous power over  4 8 and 16 ohms over 20- 20k with distortion plus lab tests against AR stated specs .   

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What it says is that the distortion is rated from 20-20k at any power output up to the rated max, not that it's going to actually deliver that max power over the entire frequency range. It outperformed the specs, but in those days most AR stuff did.

Original spec sheet attached.

AR AU spec sheet.pdf

Pre-1974, amplifier power specs were often smoke and mirrors with a lot of weaselly language. You can't compare vintage watts without deciphering the code.

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Fisher 500c would be adequate, as would a 500b.

Dynaco ST70, Eico HF87, Heathkit AA121 all would be sufficient.

Just about any of the Cayin/Prima Luna/Jolida EL34 integrated amps would be good matches.

Higher power is better, but not as necessary with the 2ax due to an easier load.

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On 10/16/2020 at 9:09 AM, rl1856 said:

Higher power is better, but not as necessary with the 2ax due to an easier load.

  rl1856 can you expand on that? "better but not necessary"  -   "easier load" 

 

The tangential conversation was interesting.

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