Need help to restore Sansui 500A

fastvideo · 11th December 2010, 12:56 AM

I am restoring a Sansui 500A amp sections.
Use a cd player to play a 1Khz sinewave.
Measure waveform from output transformer with 8ohm load, distortion found.

Installed 2 6aq8, measure waveform at C707, C716, waveform looks good.

Installed 2 6bl8, measure waveform at C804, C805, C809, C810, the waveform looks different between R&L channels. The voltage I got is quite some different from reference voltage from the schematic.

Voltage after the rectifier measure good according to schematic.
If I want to replace C804, C805, C809 and C810, what type of capacitor to use?

Sansui 500A Service Manual

Eli Duttman · 11th December 2010, 01:18 AM

Sansui used oil caps., which are known to become leaky. Replace the interstage coupling parts with Soviet surplus 0.33 μF. K40s, which are paper in oil (PIO). The Russian stuff is modestly priced and WELL made.

fastvideo · 11th December 2010, 02:52 PM

Is Polypropylene Capacitor ok to use?

Eli Duttman · 11th December 2010, 03:53 PM

Assuming the value and WVDC rating are correct, it is electrically fine. The unit may be bright sounding, with polypropylene dielectric in those positions.

BTW, don't use metalized film construction. Use film and foil parts.

fastvideo · 11th December 2010, 11:43 PM

Are C804, C805, C809 and C810 can cause distortion?
VR001 - VR004 pots are these use to adjust bias? and how to adjust.
I got -17v at test point C1,C2,C3,C4.

fastvideo · 13th December 2010, 09:31 PM

How to adjust bias?

fastvideo · 19th December 2010, 02:20 PM

Quote:

Originally Posted by fastvideo

Are C804, C805, C809 and C810 can cause distortion?
VR001 - VR004 pots are these use to adjust bias? and how to adjust.
I got -17v at test point C1,C2,C3,C4.

any help?

LinuksGuru · 19th December 2010, 06:30 PM

Hi, fastvideo,

Although I don't have Sansui 500A, but rather Sansui AU-70 (waiting for restoration), and AU-111 (to be completely rebuilt), advices you are asking for are common for vintage equipment restorers.

I would advise you to learn tube schematic a little bit to avoid common problems and mistakes.

I have comprehensive walk-through in my blog, for Pioneer SM-83 and Fisher 400. Sansui 500A is very close to these two.

Pioneer SM-83 Vacuum Tube Amplifier Restoration | MacGuru HQ
Fisher 400 Vacuum Tube/Valve Tuner/Amplifier Restoration | MacGuru HQ

fastvideo · 5th January 2011, 12:34 AM

Quote:

Originally Posted by LinuksGuru

Hi, fastvideo,

Although I don't have Sansui 500A, but rather Sansui AU-70 (waiting for restoration), and AU-111 (to be completely rebuilt), advices you are asking for are common for vintage equipment restorers.

I would advise you to learn tube schematic a little bit to avoid common problems and mistakes.

I have comprehensive walk-through in my blog, for Pioneer SM-83 and Fisher 400. Sansui 500A is very close to these two.

Pioneer SM-83 Vacuum Tube Amplifier Restoration | MacGuru HQ
Fisher 400 Vacuum Tube/Valve Tuner/Amplifier Restoration | MacGuru HQ

Thank you, it is very useful.
On the Pioneer Amp, you replaced 7189A with 6P14P-EV.
I just got 4 6P14P-EV, but it did not work with my unit.
Is this pin to pin replacement tube?

Eli Duttman · 5th January 2011, 12:41 AM

The Russian 6П14П-ЕВ (6p14p-ev), AKA EL84M, is a genuine 7189 (no "A") equivalent. There are socket wiring differences between the 2.

In any event, your Sansui unit uses 6BM8s, not 7189s.

11th December 2010, 12:56 AM	#1
fastvideo diyAudio Member Join Date: Jan 2005 Location: montreal	Need help to restore Sansui 500A I am restoring a Sansui 500A amp sections. Use a cd player to play a 1Khz sinewave. Measure waveform from output transformer with 8ohm load, distortion found. Installed 2 6aq8, measure waveform at C707, C716, waveform looks good. Installed 2 6bl8, measure waveform at C804, C805, C809, C810, the waveform looks different between R&L channels. The voltage I got is quite some different from reference voltage from the schematic. Voltage after the rectifier measure good according to schematic. If I want to replace C804, C805, C809 and C810, what type of capacitor to use? Sansui 500A Service Manual

11th December 2010, 01:18 AM	#2
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Sansui used oil caps., which are known to become leaky. Replace the interstage coupling parts with Soviet surplus 0.33 μF. K40s, which are paper in oil (PIO). The Russian stuff is modestly priced and WELL made. __________________ Eli D.

11th December 2010, 03:53 PM	#4
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Assuming the value and WVDC rating are correct, it is electrically fine. The unit may be bright sounding, with polypropylene dielectric in those positions. BTW, don't use metalized film construction. Use film and foil parts. __________________ Eli D.

5th January 2011, 12:41 AM	#10
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	The Russian 6П14П-ЕВ (6p14p-ev), AKA EL84M, is a genuine 7189 (no "A") equivalent. There are socket wiring differences between the 2. In any event, your Sansui unit uses 6BM8s, not 7189s. __________________ Eli D.

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11th December 2010, 02:52 PM	#3
fastvideo diyAudio Member Join Date: Jan 2005 Location: montreal	Is Polypropylene Capacitor ok to use?

11th December 2010, 11:43 PM	#5
fastvideo diyAudio Member Join Date: Jan 2005 Location: montreal	Are C804, C805, C809 and C810 can cause distortion? VR001 - VR004 pots are these use to adjust bias? and how to adjust. I got -17v at test point C1,C2,C3,C4.

13th December 2010, 09:31 PM	#6
fastvideo diyAudio Member Join Date: Jan 2005 Location: montreal	How to adjust bias?

19th December 2010, 06:30 PM	#8
LinuksGuru diyAudio Member Join Date: Aug 2008	Hi, fastvideo, Although I don't have Sansui 500A, but rather Sansui AU-70 (waiting for restoration), and AU-111 (to be completely rebuilt), advices you are asking for are common for vintage equipment restorers. I would advise you to learn tube schematic a little bit to avoid common problems and mistakes. I have comprehensive walk-through in my blog, for Pioneer SM-83 and Fisher 400. Sansui 500A is very close to these two. Pioneer SM-83 Vacuum Tube Amplifier Restoration \| MacGuru HQ Fisher 400 Vacuum Tube/Valve Tuner/Amplifier Restoration \| MacGuru HQ

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