Optimation PA-250AC Lab-Grade Audio Amplifier - diyAudio
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Old 21st May 2012, 10:35 AM   #1
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Default Optimation PA-250AC Lab-Grade Audio Amplifier

Hello everybody!

I was recently given this amplifier, an Optimation PA-250AC, and I would like to know if any of you all know anything about it. As far as I can tell, it is NOS, or near NOS. It even came in its original shipping box! I also have all the tubes for it and the manual. First of all, this thing is a monster and weighs in somewhere around 90 pounds. According to the manual, it is a lab-grade audio amplifier, capable of delivering 250 watts at 0.01% THD! At reduced power, the frequency response is 5 to 100,000 Hz. It takes 8 EL34/6CA7s on the output stage. It also has 3 impedance outputs, 3.75, 15, and 60 ohms. It's also capable of delivering a constant-current or constant-voltage output, and the meter can measure the output voltage, output current, or the plate current of each individual output tube. It uses both negative and positive feedback to keep distortion to a minimum, and even has overload protection. Overall, it sounds like a pretty amazing amp. Also, the front panel is hinged so you can easily access the circuitry. I know tube amplifiers pretty well, but this thing is far more advanced than anything I'm familiar with.

I've included a few pictures of this beast that I took before I installed the power tubes and played with it. First of all, it sounds incredible! It goes down to 5 Hz with ease, and it has power to spare.

If any of you know anything about this monster, or have had any experience with one or something like it, please let me know! Apparently it's pretty rare, since I couldn't really find anything about it on ol' Google, but just because something is rare doesn't mean it's worth anything.
Attached Images
File Type: jpg Optimation Front.jpg (484.2 KB, 155 views)
File Type: jpg Optimation Rear.jpg (483.5 KB, 145 views)
File Type: jpg Optimation Inside.jpg (481.6 KB, 143 views)
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Old 21st May 2012, 05:41 PM   #2
kevinkr is offline kevinkr  United States
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Rather cool, probably would make a great subwoofer amplifier..
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Old 21st May 2012, 07:04 PM   #3
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It sure does! The only speaker that I really had to test it with was a subwoofer, and it was fun to take the amp down to 5 Hz and just watch that cone move in and out! As for music, it sounded incredibly good on anything from jazz to hard rock and techno. In fact, it was probably the best sounding subwoofer amplifier that I had ever heard!
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Old 21st May 2012, 08:15 PM   #4
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I know this amplifier. They were used for AC calibration to supply wideband high voltage from an oscillator. The full system was an AC104A consisting of RCD1062 sinewave oscillator. RT1003 ratio transformer. T103 matching transformer. And PA1015 power amp. I have several of these amps in storage and gave away,as scrap, several others when I was forced to relocate. PA250 was also a valid designation for the HV model.

Some versions did not have 100% interleaved laminations in the OPT, while the other ones did. They were supplied in several configurations depending on how the output was trapped for voltage. The meter scales were accordingly different. Some of the amplifiers I had used 8417s while others had EL34s like yours. Optimation was taken over by Julie Research Labs in NY. (Lobe Julie)

Of the amps I do still have (3 or 4?) I had planned on rebuilding with the transformers and 6550s, but it's been quite a while and I may never get to it. One person I know actually listened to music through them and thought they were pretty good. Most all of mine came from Government surplus like yours. I recognize the sticker on the front panel.
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Old 21st May 2012, 08:18 PM   #5
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Julie Labs was my first thought when i saw these. Yes, they are very good when set up right. No one knows what they are so they get junked despite their huge build cost.
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