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Thread: Ampex AG440 C , help

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    Ampex AG440 C , help

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    Hello everyone, first to congratulate you for all the information you share in this great forum.
    This is my first post, I tell you, it turns out that I got my hands on an Ampex AG440C, I had no idea what state it was in, if it worked properly or not. On the back it indicates (I will attach images) volts 117, amps 2.7 and hertz 50. In my country (Chile), we use 220v, so I got a transformer from 220 to 110, the plug and it turns out that their motors worked at their speeds, But after a couple of minutes, a burning smell started coming out, I unplugged it and I realized it was from the reproduce card. It turns out that a 24ohm resistor burned out as I could see in the manual. This is where I need your help, I do not know what could be the reason that it has burned, maybe the 220 to 110 transformer does not work for me? The ampex cable is missing the ground leg, it could be that time, well I hope you can help me please. Best regards
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    Greetings.

    The 24R resistor that burned, R30, is one of the two output resistors on the reproduce card (R31 is the other one...each one connects to the respective emitters of the differential pair of output transistors, Q7 & Q8). I’m not sure why that resistor would fry like that, but if the machine was already in use in your country is it possible it was already internally modified to operate on your country’s power?

    There is supposed to be a 39VDC power differential across Q8, R31, R30 & Q7. +39VDC should be present at pins 7 & 8 of the card, ground at pins 1 & 2, and the signal output is on pins 5 & 6. The first thing I would do is verify your step-down transformer produces clean power as specified, then if it does I would unplug the electronics modules from the electronics power supply located underneath the transport and measure the output of the power supply. It should be at or close to +39VDC.

    Please be careful. I don’t know what you’re skill level is with electronics. Millivolts can kill. I cannot be responsible for your safety or any damage that may occur to your equipment as a result of your troubleshooting efforts. I’m only sharing what I would do if it was my machine. Proceed at your own risk.

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    Quote Originally Posted by sweetbeats View Post
    Greetings.

    The 24R resistor that burned, R30, is one of the two output resistors on the reproduce card (R31 is the other one...each one connects to the respective emitters of the differential pair of output transistors, Q7 & Q8). I’m not sure why that resistor would fry like that, but if the machine was already in use in your country is it possible it was already internally modified to operate on your country’s power?

    There is supposed to be a 39VDC power differential across Q8, R31, R30 & Q7. +39VDC should be present at pins 7 & 8 of the card, ground at pins 1 & 2, and the signal output is on pins 5 & 6. The first thing I would do is verify your step-down transformer produces clean power as specified, then if it does I would unplug the electronics modules from the electronics power supply located underneath the transport and measure the output of the power supply. It should be at or close to +39VDC.

    Please be careful. I don’t know what you’re skill level is with electronics. Millivolts can kill. I cannot be responsible for your safety or any damage that may occur to your equipment as a result of your troubleshooting efforts. I’m only sharing what I would do if it was my machine. Proceed at your own risk.
    It is an honor that you help me, I follow you on your youtube channel, I tell you that I had a tascam m308b (I sold it to buy some monitors), and I saw your video of the tascam m312, it helped me understand my m308b, I currently have a soundtracs mrx 24, your post of the soundtracs was my guide to clean and disassemble mine, we have similar toys.
    Returning to Ampex, I will show your help to a professional friend, since my knowledge in electronics is quite basic, I will be informing how I am doing, and once again thank you very much for your help. Greetings

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    I’m glad to help. Do keep us posted.

    Yeah the Soundtracs was a nice sounding console and pretty well-built. My main issue with it was the design of the grounding. But that’s neat you have the MRX, with the bank of 8 “return” strips on the right. I like the “split” console layout, so much that I obviously went wild and converted my MX into one!

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