PL700 Rebuild

Overundr1

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Sep 12, 2024
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#1
The new to me PL700 arrived safely today. Yes I know its the first generation and a little more effort to rebuild however those early 70's VU meters get me every time.
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Peeking at the back I note that almost all the transistors are original xpl909's with hand written hfe values along with one rca 2n3773. The pnp drivers are half motorola 7439 and half 7311's. Need to pull them all and test before even thinking of applying power to establish a baseline to work from. Also need to find one transistor cover or figure out a way to protect myself from an inadvertent high voltage mishap.

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This amp must have been n a band PA system, there are 1/4" output jacks mounted to the right side along with the standard rear panel stuff. They are there, poor camera operator at the controls :)

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Not too much rust, dents or dings, here is the serial number and transformer.

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Will be a week or two before I get started, need to clear the bench of a couple of client repairs first :)

At the minimum without even applying power believe I will need the WOPL control board, main caps, outputs, snubber and speaker relay. Many thanks to Joe at WOPL for the reply to my email and the suggested upgrade path. This forum rocks.

Since I am the 700 newbie in the room feel free to fire away with comments, suggestions and any other cool off topic thoughts to help the thread along :)
 

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laatsch55

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#4
Past build threads are a treasure trove of information. And if you go back far enough, ypu can see the evolution of White Oak and one man's idea of customer service and building the best product he can ....and then making it better.....and better....and better...
 

Overundr1

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#6
Ugh, what a rats nest to unwind.
Main caps esr values both less than 4000uf and esr values close to 5ohms, toasted.
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They drilled out the side panel for dual 1/4" speaker jacks, wires everywhere.

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Control board looks ok at first blush other than rusted adjustment pots. At this point recognise the need for the WOPL Control board.

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Also worth mentioning is the volume pots even after cleaning have several dead spots and need to be replaced (need to source those)

Unit arrived with a Watts Abundant bare relay board, will order the parts/rca jacks/binding posts along with the other goodies and start there once I get a Clients amp repaired. Also need to order a bunch of different nuts/bolts/sheet metal screws to replace all the rusty ones.
 

mlucitt

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#8
Also need to order a bunch of different nuts/bolts/sheet metal screws to replace all the rusty ones.
Post a list of what you need, members here likely have them. You may not find exact replacements are available commercially.

Your PL700 was assembled in November, 1972 and was the 25th unit assembled that month. The production of the PL700 began in February, 1971.
 

Overundr1

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#10
Figures I would miss that detail when I placed my Mouser order. Anyways have an email in to WOPL for Joe to check and respond with any additions before I order the goodies from him :)
 

mlucitt

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#12
Figures I would miss that detail when I placed my Mouser order. Anyways have an email in to WOPL for Joe to check and respond with any additions before I order the goodies from him :)
Joe is a busy guy. He is the designer/engineer of the circuit boards and kits and he builds and sends the orders for the boards and component kits himself. Try to limit your requests for merchandise that can be found on his eStore website. All your technical answers and most parts can be found here, usually for free.
 

Gepetto

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#15
And tht board has the bias trannie ON THE BOARD , not on the chassis backwall.. You need a coupl 2N5088's stuffed in a P strap and bolted to the chassis..
Or better yet, replace the chassis as put in the backplanes to get full comp operation.
 

Overundr1

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#17
Well, I was hoping that the output transistors were savable however not the case, they have outlived their useful life with many having hfe values of 5 or less :(
Along with the twenty mj21196g's what are the preferred transistors for the bottom row, had motorola sj2741's in each of the right bank and spc7311's in each of the left.
Backplate cleaned up nicely as did the fins, still need to dig out the last of the thermal grese.
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Overundr1

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Sep 12, 2024
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#19
Hoping to save original chassis and backplane for first build. Having said that along with the 21196’s what are the four recommended transistors to replace the Motorola’s?
 

Overundr1

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Sep 12, 2024
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#20
Just for fun, here are four driver cards I helped finalize through beta testing I ordered ENIG/black assembled and tested this spring.
1729375195157.png 1729375195157.png Not afraid to dig into this build, just have a roadblock when WAF saw the price of the backplane and chassis price add in lol.
 
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