ISO PL 700B advice

Schmurpy

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Apr 9, 2021
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79
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La Center Wa
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If it isn't broke, fix it until it is.
#1
Hello people!

Looking at a PL 700B that needs some work, and was hoping some of your great folk could give an opinion.

Here is what I know about it:

Phase Linear 700B Stereo Power Amplifier acquired from the family of the original owner. I gave this unit a quick test using a tuner/preamplifier and a pair of JBL speakers. I believe this amplifier was conservatively rated at 350 watts per channel. The front of the amplifier states "700 watts RMS". Unfortunately, this power amplifier does Not work. It produces a loud hum, and that's it. As can be seen in the photos, it powers up and that's as good as it get. No output other than a hum. I removed the top cover and took a picture so that you can see what your getting. Cosmetically a few small marks here and there but nothing that would even show up in the photos. I tested this unit for approximately two seconds and pulled the plug when I heard the loud hum. Plugged it in for another two or three seconds to take pictures
 

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Gepetto

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#2
Hello people!

Looking at a PL 700B that needs some work, and was hoping some of your great folk could give an opinion.

Here is what I know about it:

Phase Linear 700B Stereo Power Amplifier acquired from the family of the original owner. I gave this unit a quick test using a tuner/preamplifier and a pair of JBL speakers. I believe this amplifier was conservatively rated at 350 watts per channel. The front of the amplifier states "700 watts RMS". Unfortunately, this power amplifier does Not work. It produces a loud hum, and that's it. As can be seen in the photos, it powers up and that's as good as it get. No output other than a hum. I removed the top cover and took a picture so that you can see what your getting. Cosmetically a few small marks here and there but nothing that would even show up in the photos. I tested this unit for approximately two seconds and pulled the plug when I heard the loud hum. Plugged it in for another two or three seconds to take pictures
For a 700B, all you need to know is:

Is the transformer good?
Are the meters good?
Are you getting a good price on it?

Everything else has a replacement part.
 

Gepetto

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#6
Cosmetically looks pretty good. Meters obviously work as does the transformer. That is what counts.

Will the seller take $300 for it?
 

Gepetto

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#10
Others can give you offer advice. I haven't purchased one in a long time, they have climbed in price significantly since I purchased my last one.
 

mlucitt

Veteran and General Yakker
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Jun 24, 2011
Messages
3,339
Location
Jacksonville, FL
#13
Never plug speakers (especially nice ones like JBL) into a vintage Phase Linear amplifier. The loud hum is due to a failed capacitor allowing stray voltage to get to the speakers.
Always use a dim bulb tester (DBT) when powering on a vintage amp and then measure voltage at the speaker terminals with a meter when no inputs are connected. If any voltage AC or DC is present or the bulb stays bright (indicating a short circuit), the amp needs service.
You (and the seller) have been warned.
 
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