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Old 16th April 2015, 10:48 AM   #1
DefQon is offline DefQon  Australia
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Default Unison Research SR-1 Hybrid Tube amp troubleshooting/help

Hello

Have one of these amps that needs some troubleshooting as it passed onto me. There seems to an array of fuses missing once the top cover is popped off for different supply rails from the secondary windings to the output stage/preamp boards.

Anybody here have a schematic or service manual or complete internal shots would be great (the pictures on google are not sufficient for troubleshooting).

Regards,
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Last edited by DefQon; 3rd February 2016 at 07:46 AM.
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Old 3rd February 2016, 07:44 AM   #2
DefQon is offline DefQon  Australia
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Ok saving the trouble with starting a new thread and continuing on from this one, I managed to troubleshoot and fix most of the amp which worked for an hour whilst playing music.

The amplifier has 9240 and 240 complimentary pair of mosfets for output and a pair of 12AU7 triodes for the input stage.

There is a protection circuit for the output stage and a warmup circuit with LED indication for the input tubes, overheating (amp gets shut down) and overloading when output clips greater then 1% of THD.

The original quad Itelcond 10000uf 63v 85'C filter capacitors was swapped out to 12000uf CDE 380LX 63v 105'C capacitors as the original ones had ESR measuring into 0.8ohms and the CDE's were the only ones I had on hand (0.04ohm ESR).

There is a KBPC 25Amp rectifier bridge for the main supply and then 3 W10M 1.5amp 1000v rectifier bridges that splice the supply to the 12AU7 heater and B+ voltage.

Now the problem is after repairing the amplifier (nightmare) without a schematic powering on the amplifier there is an LED that will glow red or orange and then green.

If the LED glows red then it means the AC mains supply is too low or too high.

The LED glows orange on powerup to warmup the tubes, about a minute it will be green and the protection circuit LED's for the output will go green as well and engage the output.

I had the amplifier hooked up to some standard 6ohm bookshelfs for testing, every powerup will glow green until I rolled in some RCA 12AU7 that I've had sitting in my drawer for a long time, the amp would go orange LED to green then go back to orange a few times before it would finally stay green and allow me to play music. So I took the tubes out and put in some used (for testing) Sylvania 12AU7's and powered on the amp, it was all fine and playing music till the amplifier stopped and went back to orange LED (warmup tubes) and it would stay like that till now. (If I turned the volume too loud it would go to orange LED, forgot to mention the amplifier is 120v and I only had a 100v step down at hand).

I did a diode test on the main rectifier bridge and it was fine but 2 of the W10M rectifiers are shorted. Now my question is could the increased capacitance in the filter supply have caused the short with transient spikes to the W10M's whenever the amplifier restarts (tube warmup mode) and powering on/off. I obviously need to replace them, if so what value should I increase it to and do I need to have snubber caps parallel on each leg?

Thanks
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Old 3rd February 2016, 10:27 AM   #3
DefQon is offline DefQon  Australia
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Some older pictures I preserved before the rebuild/repair.

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Protection circuit for output

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Output devices

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Old 5th February 2016, 07:43 PM   #4
DefQon is offline DefQon  Australia
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No one can help?
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