Phase Linear 700B
- Thread starter King bleu
- Start date
I emailed white oak. They have the output drivers availale on their website but I don't see the pre drivers on the website. Hopefully they will have one for me.
After testing the XPL909 outputs I have determined that two of them are shorted. If I can find 2 original XPL909 that would be the best case. If I can't find 2 original I will replace all 10 with MJ21196G.
After testing the XPL909 outputs I have determined that two of them are shorted. If I can find 2 original XPL909 that would be the best case. If I can't find 2 original I will replace all 10 with MJ21196G.
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Everything in the amp is suspect due to age.
All caps need replaced, all other components need tested. Many resistors are probably drifted and small signal transistors are noisy.
Many of us don't even plug these in when we buy them.
We gut them and rebuild with White Oak Audio components.
Nothing wrong with bringing them back to life as original, a good learning experience. Just make sure you've installed the WattsAbundant speaker protection relay to protect your speakers from the next failure.
All caps need replaced, all other components need tested. Many resistors are probably drifted and small signal transistors are noisy.
Many of us don't even plug these in when we buy them.
We gut them and rebuild with White Oak Audio components.
Nothing wrong with bringing them back to life as original, a good learning experience. Just make sure you've installed the WattsAbundant speaker protection relay to protect your speakers from the next failure.
If this was mine I would give it the royal treatment. This is for someone else who doesn't want to put money into it. The goal is to get it running safe and operational. However I understand this may not be possible without a total restore of the driver board and a speaker protect relay. I will have to inform the customer that a fire extinguisher would be a good investment.
So far so good. I installed the output drivers and predrivers. Replaced the few electrolytics on the driver board. Tested all transistors on the driver board. The amp is operational. DC offset on one channel is in the milivolts and about 7.0v on the other channel. One problem I need to solve is the idle current. Idle current on the left is fine and is adjusted to 350mv The idle current for the right channel will only go as low as 406mv. I did replace the trimmer resistor but that had no effect.
After rechecking DC offset Im getting Left 20mv Right 15mv. I probbably didn't have a good connection on the speaker terminal the first time I checked. I took out Q1 and Q2 from both channels and measured HFE. I took the best match and installed them on the Left channel. Now I get DC offset Left 21.4mv Right 17.6mv. Go figure!
I also tried to get the idle current down on the Right channel. I tried a couple different values at R19 with little or no effect. I put the original 1K resistor at R19 and the idle current has stabilized to 392mv.
Both the DC offset and the idle current are within the parameters of the service manual so I will leave it for now. I think to get better I would need to replace at minimum Q1-Q4
Next up is to hook up a load and test at different frequency to insure there is no oscillation.
I also tried to get the idle current down on the Right channel. I tried a couple different values at R19 with little or no effect. I put the original 1K resistor at R19 and the idle current has stabilized to 392mv.
Both the DC offset and the idle current are within the parameters of the service manual so I will leave it for now. I think to get better I would need to replace at minimum Q1-Q4
Next up is to hook up a load and test at different frequency to insure there is no oscillation.
Yup. Seems what your experiencing is a very common occurrence with the old parts.
PL went through many revisions trying to get it right.
Some revisions were to make it better, some were cost cutting.
Gene, a long time member here, has brought many 400 Series 1 amps back to working status using the original configurations.
He's shown that it's a battle, and sometimes a mystery why a amp has issues.
PL went through many revisions trying to get it right.
Some revisions were to make it better, some were cost cutting.
Gene, a long time member here, has brought many 400 Series 1 amps back to working status using the original configurations.
He's shown that it's a battle, and sometimes a mystery why a amp has issues.
I have successfully got the amp stable. I went through a few output transistors in the process. Five in total. DC offset left 18mv Right 17mv. Idle current left 390mv right 402mv. Right trim pot is fully CCW. On start up right idle current is around 450mv then stabilizes after 10 minutes or so. No oscillation from 20hz-20k. This is my first experience with a phase linear 700b. I dare not hook it up to my main speakers without protection but I have been listening to it on the garage speakers B&W DM17 they have fuse protect built into the speaker. The amp sounds great lots of punch. Low end is very nice. Mids and highs blend great. Sound stage is there not too wide but full enough. I would really like to listen to this on a worthy pair of speakers.
