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Old 31st May 2011, 06:45 PM   #121
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Quote:
Originally Posted by stellavox View Post
Hello,

I am trying to get some basic info on the OTL amp Acoustat made.

What were the output tubes they used (V1 thru V4)?

And is any other web-based info available?

THANKS

CHarles
Go to www.audiocircuit.com, Acoustat section, and you will find more information on Acoustat's direct-drive tube amplifier, called the Servocharge Amplifier, as used on Acoustat's original Model X and some of the Monitor Series. You should be able to locate schematics there. If I remember correctly (which I might not) the tubes used were 6HB5's.
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Old 31st May 2011, 06:57 PM   #122
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Quote:
Originally Posted by speedracer5 View Post
Thanks Andy!
What I need to do now is find two identical examples. That is to do what I'm planning.
If you are looking for two identical amplifiers with the intention of bridging them, I would strongly recommend against that. Each half of a bridged amp 'sees' only half the load impedance. Since the Acoustat is low impedance to begin with, presenting the amplifier with only half of that impedance is asking for trouble. A 250-watt amplifier of sufficient current output should be all that you need to get the most out of your Acoustats.
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Old 31st May 2011, 06:59 PM   #123
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Quote:
Originally Posted by AcoustatAnswerMan View Post
If you are looking for two identical amplifiers with the intention of bridging them, I would strongly recommend against that. Each half of a bridged amp 'sees' only half the load impedance. Since the Acoustat is low impedance to begin with, presenting the amplifier with only half of that impedance is asking for trouble. A 250-watt amplifier of sufficient current output should be all that you need to get the most out of your Acoustats.
Oh yeah - I remember we talked bfore about your idea, which was NOT bridging amps. Ignore my previous comment (still good advice, but not applicable to your situation).
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Old 31st May 2011, 07:14 PM   #124
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Yes i'm positive the tubes in the servo amps are

4 = 6HB5 MrAcoustat

If you have ANY problem with the amps the man to contact is Mike Savuto
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Life without Acoustat is possible BUT senseless.

Last edited by MrAcoustat; 31st May 2011 at 07:17 PM.
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Old 1st June 2011, 07:21 PM   #125
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How is the Acoustat a "low impedance"??

The impedance curves published for the mk-121 interface on model 3s (iirc) showed a minima of ~6 ohms. The idea that they do not have super low Z dips like some (ML for example) is because of the Strickland double transformer/dual match design.

If you've got other information, I'm interested.

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Old 1st June 2011, 08:03 PM   #126
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All Acoustat model, are 4ohms you realy have to push them hard to dip to three ohms i own the most difficult model the 1+1s 81db but with the mods that have been done to them i think they are not that difficult now, but have no idea of there efficiency.
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Old 1st June 2011, 10:04 PM   #127
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I think one has to actually measure the impedance.

I don't see how "pushing them" changes the impedance.

The published curves, from Acoustat showed an impedance above 6 ohms, iirc.
It's easy enough to do an impedance measurement vs. freq, I'd do it myself but my Acoustats and myself are separated by some miles and my time is limited in audio to making a few posts - that is expected to change in a few months.

Any volunteers?

_-_-bear
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Old 1st June 2011, 10:41 PM   #128
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Quote:
Originally Posted by bear View Post
I think one has to actually measure the impedance.

I don't see how "pushing them" changes the impedance.


_-_-bear
You have to push them @ 35mph to get them below 3 ohms ....
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Old 2nd June 2011, 12:07 AM   #129
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Quote:
Originally Posted by bear View Post
I think one has to actually measure the impedance.

I don't see how "pushing them" changes the impedance.

The published curves, from Acoustat showed an impedance above 6 ohms, iirc.
It's easy enough to do an impedance measurement vs. freq, I'd do it myself but my Acoustats and myself are separated by some miles and my time is limited in audio to making a few posts - that is expected to change in a few months.

Any volunteers?

_-_-bear
Technilly i'm a big 0 i tought that you ad to drive your speakers pretty hard for the impedance to go lower so i'm wrong guess i'll do what i do best KEEP LISTENING and leave the technical stuff to the savy people.
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Old 9th October 2011, 06:58 PM   #130
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I've had a McIntosh MC-2500 that was no match for my Acoustats 2 + 2.
The meters were always on the right edge and the lights dimming.
Restek Exponent mono's no succes either, burned them up.
Cute Tube amps....
Anything with a low impedence switch on the back like these Resteks or Accuphase are suspects to fail.
Good matches electrically from that era:
1. Big Thresholds (not the bridged versions);
2. Krells in general of course;
3. Levinson ML-3, No.23, No.20
4. Jeff Rowland model 5, 7, 8 and 9

A few weeks ago I have been driven a Sumo Nine Plus that did a pretty credible job against a Krell FPB-600. Really amazing how powerful and musical that tiny amp sounded.

Btw Andy is really a great asset to have on this forum.
He always gave me great advice on Acoustat.

Best I heard on mine:
Threshold SA/1 optical bias, Jeff Rowland model 7 Transimpedance version and Levinson ML-2 (sadly these amps do not have enough max. outputvoltage (17 Volts) do drive them at loud levels but I found them magical sounding on my Acoustats.
Friend drives his with a ML 20.6 and they do sound wonderful also.
These speakers, I have them now for 20 years, need a really high quality frontend to drive them to their full potential.

Last edited by RobertS61; 9th October 2011 at 07:01 PM.
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