PL-700 OTW

Fixin to find out. Just finished replacing all four fuse holders. Don't worry, NOS Bakeliite. Will check DC offset then see about bias on both C. as well.
 
OK, here is where it stands. DC offset will just about zero completely out on both channels so no problem there. The left C. bias pot has less range. I don't think this is good because I have to turn the pot all the way down to get .438 mV on that side. The right C. bias pot has much more range. I have them both dialed in at .440 mV and both DVM are holding steady at .440 after a long warm up. Drawing normal current of 0.05 A at 120VAC
 
IIRC, you can change the value of R19 to get that down. Should be a 1K I think...
 
OK, got crazy. Hooked it up to my C1 and my best set of speakers, Bose 901 Series 1. Listened to Beach Boys California Dreaming. Left channel I must do something with still The bias is too high.
 
R19 for all the world is a diode on my board...:scratch: I know that does not make sense but its so. Yes, just made 100% sure. Where the drawing shows a resistor there are diodes on both channels on my amp.
 
On a parts list that Ed made up and sent to me in order to help it shows this " R19 5.6 1W or 5.6K 10% ? - (may see some with a 1N4752 33V zener diode)" Leave it to me to find and buy the Friday model...OH shit man,,,(inhales strongly and gulps beer) look ! We can put these two diodes in and see what happens !!!
 
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20180228_135106.jpg The picture there has both bias pots out at the time . Disregard please. They are both back in
 
Oh and I forgot to tell Perry that I got the "farngulator" put back in place. You can see its on the left side of the board kind of in the middle there. Blue silver cap with long blue and black leads.
 
VSAT88 said:
On a parts list that Ed made up and sent to me in order to help it shows this " R19 5.6 1W or 5.6K 10% ? - (may see some with a 1N4752 33V zener diode)" Leave it to me to find and buy the Friday model...OH shit man,,,(inhales strongly and gulps beer) look ! We can put these two diodes in and see what happens !!!
Click to expand...

Jim,

Yeppers! You have one of the newer model 700's.

If you hadn't come to me, you probably still be scratching your head over the R19 1N4752 33V zener diode as it isn't documented anywhere in any Phase Linear service manual.
This modification was also performed on the 700HF (High Frequency) amps built for Bell Labs. R28 was also replaced in the Bell Labs 700HF's with a IN4752 33V zener diode .

In the PL0171 pc boards I have been rebuilding, I replace both R19 and R28 with 1N4752's by suggestion of Dean N. (the Phase Linear Lynnwood, WA last factory service manager).

Ed
 
Jim,

Here is a photo of a PL0171 pc board I restored a few years ago.

NOTE: All parts were extensively tested before installing on the pc board.

Notice the MPS5172's are missing since I eventually install 2N3403 p-strapped bias transistors mounted to the heat-sinks.

All of the carbon composition resistors have been replaced with carbon film. Horizontally all resistors color code can be read from left to right. Vertically the color codes can be read from bottom up. (You may find it interesting to compare the values to what you have on your board.)

R19 and R28 have been replaced with the 33V zener diodes.

The trim-pots have all been replace with new.

The original electrolytic capacitors have all been replaced with Nichicon. Notice that I clock the lettering so it is face up and easier to read.

The original tantalum capacitors have been replaced with new old stock Kemet tantalums

The 40327 transistors have been replaced with 2N3440's.
The 2N1304's have been replaced with new.
The 2N1305's have been replaced with new old stock.
The MM4003's are re-used/tested MM4003's. I could have used either 2N5415's or 2N5416's.
The 40412V1's are re-used/tested 40412V1's

All of the TO-92 transistors have been replaced with new transistors.
NOTE: The 2N5401's have been replaced with MPSA93's as recommended in a later Phase Linear service bulletin
(NOTE: This service bulletin does not appear in some Phase Linear 700/700B service manuals. However it does appear in some later 400 series 1 service manuals.)

All of the ceramic disc capacitors are original Mallory RMC (Radio Material Corporation) brand capacitors.

Essentially, I tried to keep the board as close to original as possible. Generally, using only parts that Phase Linear would have used.

Ed
 

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oldphaser said:
Jim,

Here is a photo of a PL0171 pc board I restored a few years ago.

NOTE: All parts were extensively tested before installing on the pc board.

Notice the MPS5172's are missing since I eventually install 2N3403 p-strapped bias transistors mounted to the heat-sinks.

All of the carbon composition resistors have been replaced with carbon film. Horizontally all resistors color code can be read from left to right. Vertically the color codes can be read from bottom up. (You may find it interesting to compare the values to what you have on your board.)

R19 and R28 have been replaced with the 33V zener diodes.

The trim-pots have all been replace with new.

The original electrolytic capacitors have all been replaced with Nichicon. Notice that I clock the lettering so it is face up and easier to read.

The original tantalum capacitors have been replaced with new old stock Kemet tantalums

The 40327 transistors have been replaced with 2N3440's.
The 2N1304's have been replaced with new.
The 2N1305's have been replaced with new old stock.
The MM4003's are re-used/tested MM4003's. I could have used either 2N5415's or 2N5416's.
The 40412V1's are re-used/tested 40412V1's

All of the TO-92 transistors have been replaced with new transistors.
NOTE: The 2N5401's have been replaced with MPSA93's as recommended in a later Phase Linear service bulletin
(NOTE: This service bulletin does not appear in some Phase Linear 700/700B service manuals. However it does appear in some later 400 series 1 service manuals.)

All of the ceramic disc capacitors are original Mallory RMC (Radio Material Corporation) brand capacitors.

Essentially, I tried to keep the board as close to original as possible. Generally, using only parts that Phase Linear would have used.

Ed
Click to expand...
God bless you Ed. You are right. Asking for help really pays. My thanks !
 
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Nice stuffed board Ed. I normally swap out ceramics for silver mica, especially in the input filter and any feedback compensation areas.

If I restore an amp, I too like to keep things original, but the ceramic caps (most of them) and carbon comp resistors have to go.
 
I would not mind my CV A-2200 amp redone Ed, bet it would be a piece of cake for you. Has two separate preamp boards, it's a dual mono
 
What amp and volt bridge rectifier should be used on this one ? 50A 400V ? 60A 600V ? Thanks.
 
R19 and R28 have been replaced with the 33V zener diodes. Still high bias on the LC. Bias resistors otw as well as new caps, new diodes, new trim pots. Other stuff I cant remember what all right now.
 
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