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Electro Research Corp. Model A 75 Iverson power amplifier.
Electro Research Corp. Model A 75 Iverson power amplifier.
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Old 21st October 2019, 06:39 PM   #1
as_audio is offline as_audio
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Default Electro Research Corp. Model A 75 Iverson power amplifier.

Last week in my workshop : the "legendary" Iverson Power Amplifier.

Pictures of front and backside. The original time counter has been replaced
by one made in Germany and has already counted more than 8000 hours.

Speaker posts and RCA sockets are not original.
Attached Images
File Type: jpg IMGP5124.JPG (129.6 KB, 143 views)
File Type: jpg IMGP5127.JPG (125.9 KB, 145 views)

Last edited by as_audio; 21st October 2019 at 08:34 PM.
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Old 21st October 2019, 06:42 PM   #2
ubergeeknz is offline ubergeeknz  New Zealand
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That is one industrial looking piece of gear
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Old 21st October 2019, 06:47 PM   #3
as_audio is offline as_audio
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Default More pictures

Top and bottom cover can be removed for full access to the self supporting chassis.

The main caps are not original. Somebody added a supply and regulator for the fan.

Mains transformer has a primitive EI core. Driver board in front is separated from the
current amps on the heatsinks. The big caps seem to be assigned l and r, but share
the same rectifier.
Attached Images
File Type: jpg IMGP5125.JPG (139.0 KB, 147 views)
File Type: jpg IMGP5126.JPG (132.1 KB, 141 views)
File Type: jpg IMGP5128.JPG (135.5 KB, 135 views)
File Type: jpg IMGP5129.JPG (132.3 KB, 67 views)
File Type: jpg IMGP5130.JPG (132.1 KB, 60 views)
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Old 21st October 2019, 06:49 PM   #4
as_audio is offline as_audio
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Default manual

This attachment was called a manual. Simple version is : to start the amp push "Power" and then "Reset".
Attached Files
File Type: pdf A-75-manual.pdf (368.9 KB, 46 views)
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Old 21st October 2019, 06:52 PM   #5
as_audio is offline as_audio
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Default schematic diagram

This bad copy is supposed to be an original schematic.
I do not have a better version and can not tell it is complete or correct.
Attached Files
File Type: pdf A75-6.pdf (718.6 KB, 55 views)
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Old 21st October 2019, 06:55 PM   #6
as_audio is offline as_audio
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Default schematic with mods

Here the diagram of a single channel with changes and modifications made by
Russ Sherwood of EKSC Eagle, eagle audio .

The amplifier in question apparently has these modifications.
Attached Files
File Type: pdf A75-newest.pdf (392.0 KB, 63 views)
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Old 21st October 2019, 06:57 PM   #7
as_audio is offline as_audio
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Default Conversion to European Mains Voltage

The transformer has two primaries which can be wired in parallel for 120 and series for 240 volts ac.
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File Type: jpg A75-220V.jpg (107.8 KB, 51 views)
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Old 22nd October 2019, 01:23 AM   #8
dexter is offline dexter
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Quote:
Originally Posted by as_audio View Post

Mains transformer has a primitive EI core.

PSU transformers: EI vs. toroidal, and more – Audial
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Old 22nd October 2019, 01:53 PM   #9
tubesguy is offline tubesguy  United States
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Location: Madison, WI
Quote:
Originally Posted by ubergeeknz View Post
That is one industrial looking piece of gear
That's one reason that I really, really wanted one back in the day.
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Old 22nd October 2019, 02:27 PM   #10
Mark Tillotson is offline Mark Tillotson
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I would suggest adding a SpeakON jack if there's room.
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