Sick Clair 700 Series II

jimcomly said:
Would the bias settings be the same between Full and Quasi Complementary? I'm getting 543/514mV
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Sounds high... 350-360 on anything I’ve worked on but I’m a relative n00b. Lee or another expert will confirm.
 
If the bias gets much higher (600 mv), all outputs will turn full on and go to war with each other with mass casualties. Once the bias is reset, wave a hair dryer from a foot away or so, on low heat, at the bottom of the heat sinks while watching the bias. Bias should decrease slightly as chassis warms up. Several minutes after the hair dryer is turned off the bias should be close to the adjusted value
 
Thanks so much! BTW, I found the thread from 2020 that discussed another 700 II Full Comp from Saudi Arabia. I was able to get the schematics, etc. from there. I really love reading about the history of these amps from the experts. I assume from the posts that there are many former employees on this forum which is really cool.

I'm not young, but I won't say how old I was when these amps were new ;)
 
Thanks very much! I've pretty much read through the SM. Understanding it is a whole new challenge for me, especially the theory of operation. Going through these tests, etc. have been very helpful in filling in the gaps in understanding. I appreciate everyone's input!
 
wattsabundant said:
If the bias gets much higher (600 mv), all outputs will turn full on and go to war with each other with mass casualties. Once the bias is reset, wave a hair dryer from a foot away or so, on low heat, at the bottom of the heat sinks while watching the bias. Bias should decrease slightly as chassis warms up. Several minutes after the hair dryer is turned off the bias should be close to the adjusted value
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Genuinely appreciate you sharing this no-kidding tip to verify the proper dynamic behavior of the bias circuit. I have a certain level of confidence if I can adjust something to a correct value while the output stage is idling. But testing this adjustment via external heat & watching it (hopefully) react correctly to protect the output stage gives me much more confidence that the amp will stay fixed, long term...

Stuff like this is what you hear from those who have years of hard-won experience. Pure maintenance gold. (!)

Thanks again!
 
Adjusted bias to 375mV and did the hair dryer thing. Adjustment pots were at full adjustment before adjustment. Maybe someone in it's past figured it's best to "turn it up to 11" :)

All behaving very well now. I'll use it as is for now, and develop some critical listening skills before doing some WOPL upgrades.

Thanks to all for the information and help!

Jim
 
I've seen R101 (7.5K/2W) fail (open) several times. When that happens it shows no sign of heat stress. That channel goes full DC on the output. If one or both channels lacks low end, C101 (100uf/6.3V) has drifted.
 
Thanks for the tips. Would you recommend replacing R101 as a precaution? Can C101 be checked in place?
 
Clarification, C111 is the critical cap for low end response. However all electrolytics should be replaced. The display boards have a pile of electrolytics too.
 
jimcomly said:
I'm not young, but I won't say how old I was when these amps were new ;)
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All you've told us so far leads me to believe you have a big birthday coming in the next year or two. Glad you'll have the main rig ready for that blowout bash. You were very young when PL was getting underway. But I don't know their time line well enough to know if you were even around to enjoy the first models.
 
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