• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Project: SX-7730 (SX-737)

Super Noob

Super Noob

Super Member
As the saga continues, I had an opportunity to pick up a couple of vintage Pioneers locally. As you know my flavor is Pioneer, and here is what landed in the garage.

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A euro 737 and SA-8800. The 7730 had two noticeable issues.... glass was replaced with Lexan & tuning needle was not moving. I really enjoy early 70s pioneers including the early direct coupled units. I have a 1010 and have built a 727 for a friend. These early units never disappoint.

7730 or 737
Power output: 35 watts per channel into 8Ω (stereo)
Frequency response: 15Hz to 40kHz
Total harmonic distortion: 0.5%
Damping factor: 40

The following posts will highlight my build in the hopes that you will enjoy the journey and maybe be inspired to revive this rig if it ends up at your stable. Pretty much have solid stock of parts here... UKL, UPW, UKA, and films. It should be noted that many of the parts are likely on back-order; however, if you look hard enough I am sure you find some acceptable alternates. Many have documented builds of the 737, and there are good foundation lists floating around from the likes of MTF and Larry'D.

Let's Begin ;)
 
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Lets see what the deal is with that tuning needle... Never have had to work on one.

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The magnet is glued on a mounting post at the bottom... this had broken free and shifted. With some time, 2-part 5 minute epoxy, some four letter words, and she is working again.
 
Power Supply Assembly (AWM-057-0)
Elected to just go with caps and diodes on this board.
Capacitors:
C7 1000 uF 50v Electro (CEA) UPW1J102MHD 1000 uF 63v
C8 330 uF 50v Electro (CEA) UPW1H331MPD 330 uF 50v
C9 330 uF 50v Electro (CEA) UPW1H331MPD 330 uF 50v
C10 330 uF 50v Electro (CEA) UPW1H331MPD 330 uF 50v
C11 220 uF 16v Electro (CEA) UPW1E221MPD 220 uF 16v
C12 220 uF 50v Electro (CEA) UPW1H221MPD 220 uF 50v
C13 100 uF 50v Electro (CEA) UHE1H101MPD 100 uF 50v
C16 220 uF 16v Electro (CEA) UPW1E221MPD 220 uF 16v
C17 22 uF 25v Electro (CEA) UPW1V220MDD 22 uF 25v
C18 100 uF 16v Electro (CEA) UPW1E101MED 100 uF 25v
C19 100 uF 35v Electro (CEA) UPW1V101MPD 100 uF 35v
Diodes
D1 SR3AM-4 3A / 400V STH5L06RL 5A / 600V
D2 SR3AM-4 3A / 400V STH5L06RL 5A / 600V
D3 SR3AM-4 3A / 400V STH5L06RL 5A / 600V
D4 SR3AM-4 3A / 400V STH5L06RL 5A / 600V
D5 SIB01-02 1A / 200V 1N5059TR 2A / 200V
D6 SIB01-02 1A / 200V 1N5059TR 2A / 200V
D7 SIB01-02 1A / 200V 1N5059TR 2A / 200V
D8 WZ-130 13V, 1/2 Watt 1N5243B
D9 WZ-140 14V, 1/2 Watt 1N5244B

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Protection Assembly (AWH-025-C)
Capacitors:
C1 0.22 uF 10v Electro (CSSA) 0.22 uF 100v MKS2D032201B00KI00
C2 0.22 uF 10v Electro (CSSA) 0.22 uF 100v MKS2D032201B00KI00
C3 330 uF 6.3v Electro (CEA) 330 uF 16v UPW1C331MPD
C4 330 uF 6.3v Electro (CEA) 330 uF 16v UPW1C331MPD
C5 4.7 uF 25v Electro (CEA) 4.7 uF 50v UPW1H4R7MDD
C6 100 uF 16v Electro (CEA) 100 uF 25v UPW1E101MED

Transistors:
Q1 2SC869 KSC1845
Q2 2SC869 KSC1845
Q3 2SC945 KSD1616A
Q4 2SC945 KSD1616A
Q5 2SC733 KSA733CLTA
Q6 2SC945 KSC2383YTA
Q7 2SC1384 KSC2690AYS

D8 1S2473 New 1N4004
1N4004 fly-back diode is added between pins 9 (anode +) and 10 (cathode -)

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Equalizer Amp (AWF-011-0)
Capacitors:
C1 1 uF 25v Electro (CSSA) 1 uF 63v MKS2C041001F00JC00
C2 1 uF 25v Electro (CSSA) 1 uF 63v MKS2C041001F00JC00
C7 330 uF 6.3v Electro (CEA) 330 uF 25v UKA1E331MPD
C8 330 uF 6.3v Electro (CEA) 330 uF 25v UKA1E331MPD
C11 3.3 uF 25v Electro (CEANL) 3.3 uF 16v UKL1H3R3MDD
C12 3.3 uF 25v Electro (CEANL) 3.3 uF 16v UKL1H3R3MDD
C17 100 uF 25v Electro (CEA) 100 uF 35v UKA1V101MED
C18 220 uF 16v Electro (CEA) 220 uF 25v UKA1E221MPD

Transistors Schematic:
Q1 2SA725 KSA992FBU
Q2 2SA725 KSA992FBU
Q3 2SC1313 KSC1845FTA
Q4 2SC1313 KSC1845FTA
Q5 2SC1313 KSC1845FTA
Q6 2SC1313 KSC1845FTA

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Control Amp (AWG-030-0)
Capacitors:
C1 1 uF 25v Electro (CZZA) 1 uF 25v MKS2C041001F00JC00
C2 1 uF 25v Electro (CZZA) 1 uF 25v MKS2C041001F00JC00
C5 100 uF 16v Electro (CEA) 100 uF 25v UKA1E101MED
C6 100 uF 16v Electro (CEA) 100 uF 25v UKA1E101MED
C9 4.7 uF 25v Electro (CEANL) 4.7 uF 50v UKL1H4R7MDD
C10 4.7 uF 25v Electro (CEANL) 4.7 uF 50v UKL1H4R7MDD
C17 4.7 uF 25v Electro (CEANL) 4.7 uF 50v UKL1H4R7MDD
C18 4.7 uF 25v Electro (CEANL) 4.7 uF 50v UKL1H4R7MDD
C19 4.7 uF 25v Electro (CEANL) 4.7 uF 50v UKL1H4R7MDD
C20 4.7 uF 25v Electro (CEANL) 4.7 uF 50v UKL1H4R7MDD
C21 47 uF 10v Electro (CEA) 47 uF 10v UKA1E470MDD
C22 47 uF 10v Electro (CEA) 47 uF 10v UKA1E470MDD
C23 2.2 uF 25v Electro (CZZA) 2.2 uF 25v MKS2C042201K00JO00
C24 2.2 uF 25v Electro (CZZA) 2.2 uF 25v MKS2C042201K00JO00
C29 100 uF 35v Electro (CEA) 100 uF 35v UKA1V101MED
Transistors:
Q1 2SA726 KSA992FBU
Q2 2SA726 KSA992FBU
Q3 2SC1344 KSC1845FTA
Q4 2SC1344 KSC1845FTA
Q5 2SC1344 KSC1845FTA
Q6 2SC1344 KSC1845FTA

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MIC Amp (AWG-066-0)
Capacitors:
C2 220 uF 35v Electro (CEA) 220 uF 35v UKA1V221MPD
C3 0.47 uF 16v Electro (CSSA) 0.47 uF 63v MKS2C034701C00MSSD
C6 220 uF 6v Electro (CEA) 220 uF 16v UKA1C221MED
C7 0.47 uF 50v Electro (LL) 0.47 uF 63v MKS2C034701C00MSSD

Switch Volume (AWG-071-0)
C5 220 uF 6v Electro (CEA) 220 uF 16v UKA1C221MED

Transistors:
Q1 2SC1344 KSC1845FTA
Q2 2SC1344 KSC1845FTA

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AMP Assembly (AWH-033)
(note that bias and offset instructions have VRs indicated incorrectly)
Capacitors:
C1 0.33 (found 4.7) uF 25v Electro (CSSA) UKL1H4R7KDDANA 4.7 uF 50V
C2 0.33 (found 4.7) uF 25v Electro (CSSA) UKL1H4R7KDDANA 4.7 uF 50V
C7 220 uF 6v Electro (CEA) UPW1C221MPD 220 uF 16V
C8 220 uF 6v Electro (CEA) UPW1C221MPD 220 uF 16V
C9 47 uF 35v (found 50) Electro (CEA) UPW1H470MED 47 uF 50v
C10 47 uF 35v (found 50) Electro (CEA) UPW1H470MED 47 uF 50v
C19 22 uF 10v Electro (CEA) UKA1C220MDD 22 uF 16V
C20 22 uF 10v Electro (CEA) UKA1C220MDD 22 uF 16V
VR1 100
VR2 100
VR3 10K
VR4 10K

Transistors:
Q1 2SA726 (matched Q1-Q3) KSA992FB
Q2 2SA726 (matched Q2-Q4) KSA992FB
Q3 2SA726 (matched Q1-Q3) KSA992FB
Q4 2SA726 (matched Q2-Q4) KSA992FB
Q5 2SC1451 KSC3503ESTU
Q6 2SC1451 KSC3503ESTU

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Main Filter Caps...
One thing I should have noted early on... is this rig does not have bleed resistors.
Reminder to myself to check this every time before starting work.

Qty 2 (each below)
6800 uf 50v ESMH800VSN822MA45S 8200 uF 80v
Bleed Resistors PRO3000206201JAC00 6.8K Ohm (3W) = (used different ones / but recommend these)
Bypass Caps ECW-FD2W105Q1 1uF 450v
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Tuner (AWE-040-0)
Capacitors:
C25 4.7 uF 25v Electro (CEA) 4.7 uF 50v UPW1H4R7MDD
C27 10 uF 16v Electro (CEA) 10 uF 25v UKT1E100MDD
C28 0.47 uF 50v Electro (CEA) 0.47 uF 63v MKS2C034701C00MSSD
C33 1 uF 10v Electro (CSSA) 1 uF 63v R82DC4100DQ60J
C38 0.33 uF 10v Electro (CSSA) 0.33 uF 63v MKS2D033301E00KSSD
C39 1 uF 10v Electro (CSSA) 1 uF 63v R82DC4100DQ60J
C40 0.47 uF 50v Electro (CSSA) 0.47 uF 63v MKS2C034701C00MSSD
C49 0.47 uF 50v Electro (CEA) 0.47 uF 63v MKS2C034701C00MSSD
C50 0.47 uF 50v Electro (CEA) 0.47 uF 63v MKS2C034701C00MSSD
C58 4.7 uF 25v Electro (CEA) 4.7 uF 50v UPW1H4R7MDD
C59 47 uF 6V Electro (CEA) 47 uF 16v UPW1C470MDD
C64 10 uF 16v Electro (CEA) 10 uF 25v UKT1E100MDD
C66 0.1 uF 25v Electro (CSSA) 0.1 uF 25v MKP2C031001F00JSSD
C67 220 uF 16v Electro (CEA) 220 uF 16v UKA1C221MED
C68 100 uF 16v Electro (CEA) 100 uF 25v UKA1E101MED

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I like the idea with the Bleed Resistors and Bypass Caps, even if there are none recommended in the original Schematic.

Would like to hear some comments from the experts about this extra modification.
Is it more for safety and/or protection like the fly back diode on the Protection Board, or will it give some improvement to the sound quality?
 
Bleed resistors are for safety…. They discharge the main capacitors once the unit is turned off so you don’t get shocked (while working on the unit). Bypass capacitors are to for sound quality but many here like to debate this…. what I can tell you is they are used by some well thought of manufacturers & amplifier designers. Here is one non-debatable fact = they can’t hurt performance.

https://audiokarma.org/forums/index.php?threads/filter-caps-bypassed.336048/
 
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Super Noob said:
Bleed resistors are for safety…. They discharge the main capacitors once the unit is turned off so you don’t get shocked (while working on the unit). ...............
Click to expand...

That’s definitely a good point and could have helped me a lot and timesaving during my actual SX-737 project.

For the Bypass Caps, is it necessary to go to 450v, if you have only 80v caps? And there should by around +/-36 dcv coming from the transformer.
 
I like to use polypropylene for bypass and most of these are 250v or higher…. As long as you are higher than the rails you would be fine.
 
I only couldn't find here what are the best replacements for power amp output transistors?
Thanks
 
MJ21193G & MJ21194G. Or the 95G and 96G. Essentially the same transistors AFAIC. A bit of overkill, But they're the GO TO transistors for Mid to High wattage units that use TO-3 transistors as Finals.
 
A bit of a thread resurrection here, also pertaining to the output transistors Q11-14: I have a stash of 1194G which have the same values and look identical. Are these OK to use? What would be the difference if I used them? A shame to have 10 of these unused from a previous project, but to go and spend $9/ea on the ones in the 737 BOM, IF the ones I have are good to go. Thanks for any input!
DOH: I just reread larryderouins comment. So, yes, the 1194's work fine. Can I use all 1194s, or do I have to use two of each?
 
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