PL700 Rebuild

After studying @Hexis22 thread on the original 700 build It seems that is an original copper plate. Now any reason why not to replace all four rca jacks along with the switch or should i convert it to a two jack assembly?
 
Overundr1 said:
Thought I would get the input/output jacks sorted out, keeping the relay instructions cloase at hand (and yes have those 8 fiber washers safely stored away). Cannot believe this is factory, they are all 1/4" jacks soldered to a copper substrate that floated above the fiber washers.
View attachment 83918
And another view
View attachment 83919

Now with them separated for a close up.

View attachment 83920

And finally the output jacks. Worth noting there were a pair of 1N4004's paralleled nose to tail between the copper ground plane of the input jacks to the ground buss on the output jacks that you can see at the top of the picture above.

View attachment 83921

If anyone has a image to share of a clean installation after rework that would be awsome.
The potentiometers cleaned up nicely and now track well so that is done.
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That is not factory Lee...some prior owner kludged that in there...
 
Overundr1 said:
After studying @Hexis22 thread on the original 700 build It seems that is an original copper plate. Now any reason why not to replace all four rca jacks along with the switch or should i convert it to a two jack assembly?
Click to expand...
Convert to two RCA input and bypass the switch altogether. Run the inputs directly to the control board with high quality RG316 coax.
 
And the diodes? Leave them in or remove them ? Also trim and use the copper shield or just a tied ground wire?
So tight in there only want to do this once :)
 
I haven't seen a 700 in ages (90's I think). After studying the photos and reviewing the manual, the 700 used 2 sets of input jacks (direct and capacitor coupled). The 700B?700II used one set of input jacks and a micro switch to short out the cap for direct coupled.

If I was doing this I would go with 700II config (see attached, page 11) with capacitor coupled and eliminate the switch and 2nd set of jacks. Plan B would use the microswitch to short out the input coupling cap. My logic? Direct coupled amplifies any DC offset of the preamp.
 

Attachments

Like this without the switch (snipped from the schematic)?
1729823167127.jpeg


Have not yet received the boards etc from Joe so cannot study them to see if there are coupling caps on the input lines. My usual go to for coupling caps is a 1uf MUSE with a paralleled 0.47 ecq which would be easy enough to either direct wire to the input jacks or at the board input connection point. Interesting side note, a friend is finishing up a very lengthy and thorough restoration and upgrade of a Dynaco ST-400 and we are in a discussion at the moment on how to quell the Frankenstein light dimming that occurs when those twin 15,000uf caps first charge up. Sort of settling on a SL32 inrush limiter thus using him as a test subject for the PL-700 with the same size caps.
 
Overundr1 said:
Like this without the switch (snipped from the schematic)?
View attachment 83925


Have not yet received the boards etc from Joe so cannot study them to see if there are coupling caps on the input lines. My usual go to for coupling caps is a 1uf MUSE with a paralleled 0.47 ecq which would be easy enough to either direct wire to the input jacks or at the board input connection point. Interesting side note, a friend is finishing up a very lengthy and thorough restoration and upgrade of a Dynaco ST-400 and we are in a discussion at the moment on how to quell the Frankenstein light dimming that occurs when those twin 15,000uf caps first charge up. Sort of settling on a SL32 inrush limiter thus using him as a test subject for the PL-700 with the same size caps.
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Lee the input on the control board is direct coupled. It is recommended that you direct couple the RCAs into the input of the control board. Any decent preamp has a large coupling cap on the output. For reference, every PL400 ever built was direct coupled and came from the PL factory that way.
 
The 700 Pro came direct coupled with no switch.
The resistors were those big gold heat sinked Dales attached to the chassis with screws.
I don't remember any caps or else. Usual standard copper plate and fiber washers.
They came with 1/4" input jacks easily replaced with a RCA.
 
If I understand the forum consensus - - - Direct wire the rca jacks (one set), eliminate the volume potentiometers (leave them in the front panel for show), trim the copper plate to fit and block off the bottom two and round switch hole with plugs for appearance. Correct?
The new pats including MJ21196G's arrived yesterday, other goodies inbound as well. Project starting to come together.
 
Overundr1 said:
If I understand the forum consensus - - - Direct wire the rca jacks (one set), eliminate the volume potentiometers (leave them in the front panel for show), trim the copper plate to fit and block off the bottom two and round switch hole with plugs for appearance. Correct?
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Correct.

Post lots of pictures so we can follow along and provide feedback along the way
 
Wish I could make my solder points as nice as yours sir. Anyways mounted the new rca jacks to the copper board this morning and verified integrity and proper grounding. After deliberation also mounted the bottom two jacks as well. they are 'dummies' at the moment however don't bother anything and keep the back panel looking nos.
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Pulled the pre driver caps off the backplane board, they were well beyond their useful life. Supposed to be 4uf.

1729873776214.jpeg

And installed the new Panasonic 4.7uf 250v ecq's, a snug fit but still clears the control board.

1729873875022.jpeg
 
I use SwitchCraft RCA's and solder the ground tabs shoulder directly to the copper plate with a Heavy Duty Weller soldering gun.
No attenuators or anything else between the RCA and control board other then Belden 83284 mil-spec coax.
I've replaced the volume attenuators with red LED lamps.
 
Yes, ground tabs directly soldered to copper plane, attenuators removed. Like the LED idea, do you remember what size led you ordered?

New binding posts installed.
1729887049815.jpeg

And Don's most superior speaker relay board mounted. White wires just floating above board not hooked up.

1729887090766.jpeg

And thats about all I can accomplish until the WOPL order arrives.
Also have black silicone plugs en route for those extra holes drilled in the side panel.
 
If clearance is a issue, maybe a nice rubber grommet to hold a LED.
It'll be interesting to see what you do with the internal lighting.
Not sure if there's a WOAD LED light board for that early model.
 
I have a large assortment of both filament and led fuse lamps used in the restoration of all the major Japanese gear. Once running will measure voltages and see what looks best.
 
Busy reading threads as I wait for parts. Seems to be different thoughts on the predrivers. This amp had rca410's on each of the left channel output bank and motorola 7439's on the right channel banks. Question then becomes use one rca in position 2 and 4 counting from the transformer or use the rca in each of the 4 bottom positions as I found it?
Since not much else to do started playing with various led ideas blatantly copying where other members have gone before :)
Plus it lets me fool around with my bench top power supply, various banana leads of destruction and multiple sizes of rubbers.
After all I am sure I read somewheres in the forum rules we must practice safe mounting of any LED's.

1729974543654.jpeg
 
Overundr1 said:
Busy reading threads as I wait for parts. Seems to be different thoughts on the predrivers. This amp had rca410's on each of the left channel output bank and motorola 7439's on the right channel banks. Question then becomes use one rca in position 2 and 4 counting from the transformer or use the rca in each of the 4 bottom positions as I found it?
Since not much else to do started playing with various led ideas blatantly copying where other members have gone before :)
Plus it lets me fool around with my bench top power supply, various banana leads of destruction and multiple sizes of rubbers.
After all I am sure I read somewheres in the forum rules we must practice safe mounting of any LED's.

View attachment 83952
Click to expand...
Does no harm either way, they are only essential in columns 2 and 4 as you correctly note.
 
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