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Ancient Civilization Artifact - Rotel RB-990bx

Wombat

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#21
Since I'm new to the game of using practically antique gear (I know...stop yelling....some of you are older than me!), and I'm not an electronics engineer, I needed to educate myself on some of the terms that get thrown around so loosely in forums. I understood the rough idea of bias and offset (as it pertains to amps), but lacked background. I found this article which does an excellent job of explaining why bias is important, why high wattage AB amps have some advantages over smaller ones, and what issues are common with VR pots used for bias adjustment. Good stuff.

http://www.tnt-audio.com/clinica/bias_e.html
You have started from scratch and seem to be progressing well. An excellent forum for learning is http://www.diyaudio.com/forums/index.php

Good wishes. :)
 

RayDunzl

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#22
My Variac showed up.

Even though it's that cheap Chinese Red, it works well.

Just tried small loads so far. It doesn't warm up or spark or do anything else untoward.

The big knob and the voltage markings are accurate to a volt or two.

Nice smooth turn, no smoke, no smell.

Dims an LED 60W equivalent nicely, and takes the roar out of my air moving fan.

Now I want another one...
 
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#23
Don Hill or Jorj,
I recently bought a Rotel RB-990BX. It will power up, but has no output. It stays in "Protection" mode even without having a load (speakers connected) to it. It has not blown any of the fuses either. I have gotten to the PCB that has the Rotel part # DE7150F472M Spark Killer (snubber, suppressor cap) It seems Murata might be the company that makes this part. I'm going to de-solder it and see what i can find out. Any words of wisdom PLEASE ???
 

Jorj

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#24
Don Hill or Jorj,
I recently bought a Rotel RB-990BX. It will power up, but has no output. It stays in "Protection" mode even without having a load (speakers connected) to it.
Scott, I'm definitely not the guy to ask about this one. I'm not clear on what logic the protection relay uses to trigger, despite being told that it's not a sophisticated system check. The only advice I could offer would be to head to any of the excellent DIY forums and post there, or take it in to a local shop that specializes in older gear. I found a shop in my area that knows the Rotel line very well and they answered a few of my technical questions. Sorry I could not be more help. Welcome to ASR!
 

NorthSky

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#25
Don Hill or Jorj,
I recently bought a Rotel RB-990BX. It will power up, but has no output. It stays in "Protection" mode even without having a load (speakers connected) to it. It has not blown any of the fuses either. I have gotten to the PCB that has the Rotel part # DE7150F472M Spark Killer (snubber, suppressor cap) It seems Murata might be the company that makes this part. I'm going to de-solder it and see what i can find out. Any words of wisdom PLEASE ???
You suspect that it is the defective part? Something looks out of the ordinary, like a bad connection, a smoked part, ... you did test the fuses with a fuse tester right? And your preamp has the speaker selector on?
 

amirm

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#28
Scott, I'm definitely not the guy to ask about this one. I'm not clear on what logic the protection relay uses to trigger, despite being told that it's not a sophisticated system check.
They usually perform DC offset check on the output of the amp and sometimes temperature overruns. I suspect the former is at play here meaning something seriously shorted out in one of the channels.
 
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#29
God I hope your wrong on the shorted channel idea. This is the second used 990BX that's gone bad on me in one month.
 

NorthSky

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#30
I've read few threads over @ diyaudio forum on this Rotel amp, and also @ Audiogon. Get something else much better, like from Canada for example...a Bryston amp. ...Scott?

By the way you look a bit like Denis Villeneuve, the French Canadian filmmaker...The Arrival, Sicario, Blade Runner 2049.


 
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