G-9000 diy evaluation/restoration - Advice needed

[djbono]

Hi folks,
first of all - just want to tell you right away that I did my homework and spent lots of time these last days reading your excellent posts/replies to similar thread - and let me say Thank you in advance!

Preambule:
Got the G-9000 10 years ago, for 200$. I was 16 or 17 at the time,and I sorta "knew" or "felt" like I could not let this baby go even though I had no real constant use for it...until now. It was owned by my friend's dad who keeps real care of his belongings... and I'm quite thankful for it.
And so I've been using it on/off since then, with different speakers - either for huge parties where its 160wpc came into help - or with more delicate speakers alongside my turntable; and the sound astounds me. I'm currently looking for high-end speakers, and was going to consider buy a cheap tube amp (if such a thing exists) but the present forum convinced me to invest time and effort on my G-9000 and use it for good.

Symptoms:
Since I got it - (and I was warned) - it always exhibited what I now know are common/known issues:
> Lower volume from right channel: I suspect the difference is highly non-linear and haven't found if the delta between left/right depends on overall volume and/or frequency played.

> Right channel dropping out: More common when volume is low, right channel drops (same thing on VU meters) - I had already diagnosed it was part either of the power amp or relays - but now, reading other posts, am pretty sure it's only the speaker relays.

I plan to restore my G9000, but first, I'd like to evaluate it's present condition (to compare against "brand new" specs and foremost, to compare with the results i get when done restoring)

So for this I need your help, I just picked up a scope, and plan on using a cheap USB sound card as a signal source (don't laugh!)

Tests:
1) Amp curve: I plan on measuring the output levels (for a given volume position) at different frequencies (will try to follow logarithmic scale)
Need help!: For this test, I was planning to use a passive load (like a 4/8ohmz,10W resistor) instead of a speaker. Do you advise against ? Have other suggestion ?

2) Phase shift

3) THD ?: How would you test that? (I will need to pull out my school papers!)

Any good resource/websites/ideas for tests to perform to evaluate an amp ?
Of course - I will share those results with the community.


Restoration
Ok this is the big one; I don't mind spending for high quality replacement parts - but is it all needed?

1) Cleaning I've read about deoxit and other products - which ones do you suggest ? Also, what procedure/method to follow for cleaning ?
Do you recommend using compressed air to dust off first ?

2) Connectors: Not sure if needed, but I was thinking of changing each and every RCA connectors.
They don't show any sign of oxydation or anything - would that be a complete waste of money and time ?

3) Components (caps, relays): Now this is really keeping me from sleeping. The unit already plays beautifully well (aside from the issues described above). I understand I need to change the speaker relays ASAP...but the caps... I'm afraid to alter the sound in a bad way. I mean, aren't caps critical components of amplifiers ? So changing them... wouldn't that be like playing God's role ?...altering the sansui sound ?
It's been five years since I first opened it (just to dust off) so I don't remember if I saw any obvious signs of cap damage; but if you guys suggest I should change them I won't hesitate a second and change them all.
For this - is digikey a good source of good enough quality caps ? I saw a few names in different posts - which brand/series do you recommend for which section (I know it's an impossible question to answer) ?
Also - what about the transistors ? I'd say "if it ain't broke don't fix it..." ?

4) Casing I'm not too fond of the plasticky-fake-woody cover... what do you guys suggest? I saw many times the word "Veneer" ... sorry to ask, but what is that ? (I'm French-speaking and this doesn't mean anything obvious to me) I googled abit and found it's a process of "covering" the cover with a wood finish ? Where does one have this made ? How much to expect ? Any alternative to wood finish ?


As you may deduct from my incredibly long first post - I will spam this thread with my progress/findings/pictures.... and probably some more questions!

I will be doing this over the next three weeks - starting with the initial tests next week then the overhaul will begin the week after next.

I thank you guys for all the info you've already provided in different threads I've read - and thank you also for your answers/ideas/comments/encouragement!

Regards,

Pierre

 

[larryderouin]

From what I can figure, you have a "DIRTY UNIT".

UNLESS you have the equipment, are familiar with it, and have the knowledge to test the amp PLEASE DON'T! USE THE SERVICE MANUAL and make Bias, DC OFFSET, and such tests and adjustments PER THE MANUAL. If you need more or want it to make max possible with least amount of THD, take it to a shop and have them set up the amp. 10W resistor is WAY TOO SMALL. I don't know how big the 9000 is but I imagine 100W or more?


CLEAN, CLEAN AGAIN, AND KEEP CLEANING switches, pots, etc. until the disparity is minimal. THEN CHECK! Clean again if needed. Some of the switches, and pots are a gold plated bastard to get to on some receivers so keep at it. You WILL NOT GET GOOD READINGS if anything is dirty. Make Doubly sure everything is clean FIRST! If the switches are OPEN Rotary switches, you can use a small toothbrush with the de-oxit.

Use a small paint brush and a q-tips dipped in alcohol to clean the boards.

The caps are the components that will MOST LIKELY need to be replaced. Start with the SMALLER values on the POWER SUPPLY, PRE-AMP, and POWER AMP boards. Don't worry about the big filter caps right yet. They won't dry out as fast as the smaller ones. Electrolytics, Tantalums need to come out. Replace the Tantalums with Poly's or Mica's. That's MHO and the more knowedgeable guys will chime in. Nichicon
UPW or Panasonic FC are good. Mouser, Digikey, NEWARK, Parts Express. Mouser usually has better shipping tho IME.

Transistors. If it ain't broke............ HOWEVER. If the Unit has TO-3 Power outputs get some Mica spacers, and Heat sink Grease and renew them on the OPT's. The old stuff has gotten hard, and dry and doesn't transfer heat as well.

Resistors. Any burnt or out of spec REPLACE. Higher Wattage ones,(2W & more) keep 3/8" or more from board if possible and space permits for cooling. Wrap the leads in heat shrink tubing or spaghetti tube if you do this.

connectors (RCA). again if it ain't broke.........Just clean them with D5 De-Oxit and a pipecleaner.

Veneer: Wood or Vinyl sheet that is finished. It's either self stick or Glued down. Wood Veneer is ALWAYS Better looking but harder to work with. Parts Express, or just google Wood Veneer. About $50. for a 24"x 96" sheet on average.


CLEAN FIRST!
Test.
Then figure out what you want to do as far as restoration. It may be less than you originally thought.


GO FOR IT! It's gonna take you longer than 3 weeks.
GO SLOW, TAKE TONS OF PICTURES, work on ONE CIRCUIT BOARD AT A TIME!
Don't stop in the middle of a component and comeback tomorrow, YOU WILL FORGET!!!
Keep one hand in pocket while working inside.
NO JEWELRY! If the wife has gas about not wearing a wedding ring, hang it around your neck on a small chain/string INSIDE YOUR SHIRT!!!
INSULATE ALL BUT THE last 1/16" of your DVM LEADS!
Use a DBT when powering up a newly built section the First time.

Hope this helps, although I got this feeling I just repeated most everything everyone else said.

Larry

 

[MAXZ28]

Here's a thread if you're interested in veneering your cabinet. If I can do it - anyone can. :yes:

http://www.audiokarma.org/forums/showthread.php?t=183816

 

[hatman]

Hi, plenty of specific advice via AK searches. My abbreviated advice is get the Service Manual, take its pulse by recording offset and bias readings, take pictures/ notes on dis assembly for cleaning access. Build a Dim Bulb Tester and get used to the bright to dim sequence, weak performance, relay delay time, and low voltage readings.

Per cleaning thread, clean the controls with DeOxit. May need a few cleanings. Then with luck your channel drop will be cured and you can follow up with DeOxit Gold and/ or Fader Lube. The left side switch and Tone Defeat seems especially troublesome and can cause channel problems.


DeOxit/clean connectors, fuse holders, and confirm that correct fuses are installed while you are at it. Replacing RCA's and Speaker connectors seems something for later. Get it working with a cleaning is the first step, then the experts will help once the usual problem stuff is done. This G9000 sold for about $1000 and in today's money that is $4000 ~ $5000.

To get this far takes time and patience, and repeated cleanings. Once you start testing, hope you will not smoke something when your test probe slips. Better yet, shut down when you are changing test positions and get good test hooks and clips.

 

[corbin]

I bet if you clean it all your problems will be gone...

 

[LBPete]

Hi folks,
first of all - just want to tell you right away that I did my homework and spent lots of time these last days reading your excellent posts/replies to similar thread - and let me say Thank you in advance!

Preambule:
Got the G-9000 10 years ago, for 200$. I was 16 or 17 at the time,and I sorta "knew" or "felt" like I could not let this baby go even though I had no real constant use for it...until now. It was owned by my friend's dad who keeps real care of his belongings... and I'm quite thankful for it.
And so I've been using it on/off since then, with different speakers - either for huge parties where its 160wpc came into help - or with more delicate speakers alongside my turntable; and the sound astounds me. I'm currently looking for high-end speakers, and was going to consider buy a cheap tube amp (if such a thing exists) but the present forum convinced me to invest time and effort on my G-9000 and use it for good.

djbono, welcome to AudioKarma exclusively Sansui Forum. As you have found, you have one of the best receivers ever made by anyone. Your instincts were good for a teenager. It is well worth the effort to restore.

Symptoms:
Since I got it - (and I was warned) - it always exhibited what I now know are common/known issues:
> Lower volume from right channel: I suspect the difference is highly non-linear and haven't found if the delta between left/right depends on overall volume and/or frequency played.

> Right channel dropping out: More common when volume is low, right channel drops (same thing on VU meters) - I had already diagnosed it was part either of the power amp or relays - but now, reading other posts, am pretty sure it's only the speaker relays.

These are typical symptoms of dirty controls. It is likely that cleaning will bring it back to life. Get these Caig Deoxit products, Deoxit D5, ProGold and Faderlube. Clean everything first with the D5. Then use the ProGold on the switches and the Faderlube on the pots. To do this effectively you must get the cleaners inside the switches and pots. It takes a good deal of disassembly to get sufficient access. Take pictures and make notes first.

I plan to restore my G9000, but first, I'd like to evaluate it's present condition (to compare against "brand new" specs and foremost, to compare with the results i get when done restoring)

So for this I need your help, I just picked up a scope, and plan on using a cheap USB sound card as a signal source (don't laugh!)

Tests:
1) Amp curve: I plan on measuring the output levels (for a given volume position) at different frequencies (will try to follow logarithmic scale)
Need help!: For this test, I was planning to use a passive load (like a 4/8ohmz,10W resistor) instead of a speaker. Do you advise against ? Have other suggestion ?

If by output levels you mean power output, the big G will turn a 10w resistor into flaming rubble before you get 3 on the volume scale. You need a minimum 150w and preferably a 200w resistor to do this measurement.

2) Phase shift

3) THD ?: How would you test that? (I will need to pull out my school papers!)

Sorry I don't know what this is. Get a service manual. It lists every conceivable specification.

Any good resource/websites/ideas for tests to perform to evaluate an amp ?

Of course - I will share those results with the community.[/QUOTE]This site has a lot of information and links. Be sure to look in the DIY and Vintage Audio forums.

Restoration
Ok this is the big one; I don't mind spending for high quality replacement parts - but is it all needed?

1) Cleaning I've read about deoxit and other products - which ones do you suggest ? Also, what procedure/method to follow for cleaning ?
Do you recommend using compressed air to dust off first ?

See my post above. Start with a vacuum. Compressed air can blow dirt into places you don't want it so it needs to be used carefully. Get a little natural bristle paint brush and some isopropyl alcohol and wash everything down. I also use Windex.

2) Connectors: Not sure if needed, but I was thinking of changing each and every RCA connectors.
They don't show any sign of oxidation or anything - would that be a complete waste of money and time ?

Skip this one. There are more important places to spend time and money. If the original RCA jacks are not oxidized or corroded, there is no sonic benifit.

Components (caps, relays): Now this is really keeping me from sleeping. The unit already plays beautifully well (aside from the issues described above). I understand I need to change the speaker relays ASAP...but the caps... I'm afraid to alter the sound in a bad way. I mean, aren't caps critical components of amplifiers ? So changing them... wouldn't that be like playing God's role ?...altering the sansui sound ?
It's been five years since I first opened it (just to dust off) so I don't remember if I saw any obvious signs of cap damage; but if you guys suggest I should change them I won't hesitate a second and change them all.
For this - is digikey a good source of good enough quality caps ? I saw a few names in different posts - which brand/series do you recommend for which section (I know it's an impossible question to answer) ?
Also - what about the transistors ? I'd say "if it ain't broke don't fix it..." ?

Aaah, grasshopper, the eternal question, the great debate. Caps rarely fail outright unless they are overheated due to design shortcomings or other electrical failure. Your 30 year old receiver may sound great but in my opinion, replacing the electrolytic capacitors is the single best service to improve the sound of your vintage electronics.

Electrolytic capacitors loose performance over time. They simply dry out and as they do, sound quality degrades. This happens slowly over time and unless you have a fresh new example of the same model amp to compare it to, you won't notice a difference. My self and other AK members have made direct comparisons between original old and newly recapped gear and the differences is noticeable. Notes are fuller and more detailed.

I like to keep as many of the original semiconductors as possible. There are good modern replacements for most of them. The output transistors in your G-9000 are truly special. Take very good care of them.

4) Casing I'm not too fond of the plasticky-fake-woody cover... what do you guys suggest? I saw many times the word "Veneer" ... sorry to ask, but what is that ? (I'm French-speaking and this doesn't mean anything obvious to me) I googled abit and found it's a process of "covering" the cover with a wood finish ? Where does one have this made ? How much to expect ? Any alternative to wood finish ?

Wood veneer is a thin slice of real wood typically applied over a plywood substrate. Sansui and the other audio manufacturers used it extensively on their cases up through the mid 1970s but by the time the G series was introduced, it was too expensive.

There are many threads here describing the process. To do it right is very time consuming but it is also very rewarding. The case on the G-9000 is one of the easiest designs to veneer. It's a good starter project.

As you may deduct from my incredibly long first post - I will spam this thread with my progress/findings/pictures.... and probably some more questions!

I will be doing this over the next three weeks - starting with the initial tests next week then the overhaul will begin the week after next.

I thank you guys for all the info you've already provided in different threads I've read - and thank you also for your answers/ideas/comments/encouragement!

Regards,

Pierre

I hope this information is helpful. We look forward to your project. Please post pictures and keep us informed.

- Pete

 

[djbono]

Hi guys;

first of all - thank you very much for your comments/precious info ! Really appreciated.
Forgot to mention - I already bought the service manual years ago when I first planned to clean it. Also - the "balance" problem is not that bad - I mean, I'd say there could be up to 3-5% differnece between the two channels at the worst. It's not really noticeable if you don't pay attention / watch the VU meters like crazy.

@Larry - When you say clean first (before testing) is it because of concerns that I'll damage the unit or get faulty results ? I want to test before touching anything so between each steps (cleaning, cap replacement, and so on) I can re-test and be able to "quantify" the changes. I'm afraid my audio-memory won't be good enough to tell the before/after differences.

Also thanks very much for the great information - I will take lots of pictures, put stickers on parts to remmeber where they go; also good advice on "don't stop in the middle.. I'll forget" I'm quite prone to this!


@Larry/Hatley
I've seen many threads on how to build a diy variac/Dim Bulb Tester - but haven't seen any that explains why you would do that. Why would you want to lower the power supply input voltage ? I'm truly missing something here.

@MaxZ28
Wow thanks for the great info - but foremost, Kudos for the Impressively clean work! Wow! I wish mine looked like that!
Also - besides wood veneer... have you ever considered Aluminum sheets, then finished with a black chrome coating ? I wonder how that would look. I guess keeping a vintage wood look is a better/more conservative idea.

@LBPete
Thanks for the very detailed information; The "output transistors are truly special" ... what do you mean ? Are there replacement available

Also, for the dummy load, when I meant 10W... was not to test at full blast. I reckon I should get a 200W load instead just to be safe. I found one on parts exchange; but that would cost around 70$ shipped and customs cleared to my house... I guess it's worth it but still, considering what it is, I find kinda steep. I guess I'll first go to a electronics store and buy some higher resistance/Lower wattage res to put in a nice series/parallalel design to acheive 200W, 8Ohms.

Again I haven't started my project yet - but I'm all excited and confident, thanks to you guys!


Pierre

 

[flyingtm88]

@Larry - When you say clean first (before testing) is it because of concerns that I'll damage the unit or get faulty results ? I want to test before touching anything so between each steps (cleaning, cap replacement, and so on) I can re-test and be able to "quantify" the changes. I'm afraid my audio-memory won't be good enough to tell the before/after differences.

Not having the clean controls will result in poor testing performance. The dirty controls can't send the signal to the driver section of the amp, which causes the faulty readings on the output area. If you recapped it before cleaning, you'd experience the same crackles, pops, and fuzzy noise that you hear now.

I treat all of the amps that I get carefully when I first get them. Clean them well with DeOxit, then (since I don't have a DBT) I let mine idle with no speaker load. Then I slowly bring them back to playing. Take your time, you have a nice gem from Sansui!

 

[larryderouin]

@Larry/Hatley
I've seen many threads on how to build a diy variac/Dim Bulb Tester - but haven't seen any that explains why you would do that. Why would you want to lower the power supply input voltage ? I'm truly missing something here.

Pierre

Dim Bulb tester(DBT) is a poor mans variac. Resistance in the bulb limits voltage to the unit. And you get a visual indication if something is wrong immediately. When you 1st turn one on with a DBT and a 60W bulb you get a glow from the bulb for a second or two, then the bulb should dim down. This is from the caps charging. Once they charge, the load SHOULD go down if nothing is shorted or problematic. If the load stays high, the bulb continues to glow (big problem). If the bulb is dim and a short occurs the light glows and tells you to turn it off NOW! Good way to minimize damage to the unit. If testing shows no faults (light stays dim), use a 100 watt bulb then to bring the voltage up higher. This will put increasing strain on the system in steps instead of shocking it all at once with straight line voltage. Again if no faults, then bring it up on line voltage. you actually do less damage by this method and end up fixing less problems, than to just plug it in the wall and go for it.


Larry

 

[LBPete]

Before you dive off the cliff, just clean the unit. It will likely fix all your current issues. It will also give you the opportunity to "get acquainted" with the interior of the unit. To do a proper cleaning, you will have to disassemble it. Take notes.

Forget about the load resistor and power testing. It's not really a priority. Build and learn how to use the dim bulb tester. It is a lifesaver.

If you want to get more involved and spend some money, get a more common, simpler receiver or amp and start rebuilding it. Get some experience on something other than this unit. That way if you fark something up, you haven't killed your beloved G-9000. Besides, you can listen to the big G while you rebuild the other one.

- Pete

 

[ccheath]

3) THD ?: How would you test that? (I will need to pull out my school papers!)

You'll need a distortion analyzer to test that. They are very pricey. You might be able to find some old decent ones on ebay for less than $100, however they may/may not need work. But since getting older equipments, always assume they need work unless warrantied. I just got myself a HP 332a for low price but it does need work. While it is nice to have, you can actually get away without a distortion analyzer while restoring. Unless you want to go absolutely 100%, you do not absolutely need the distortion analyzer.

 

[djbono]

Resistor

Hi guys,

I went to my electronics shop and found a 10Ohms (variable) 150W resistor.
I paste the picture here before trying it because I don't know if its "non inductive" or whatnot and would like your advice on this.

I set it at a clean 8.0Ω; I hope this doesn't do weird stuff like imaginary (in maths terms) inductance (or do we say complex ?) that would make the power stage go bizzerk

So before trying it out I'll wait for your input.

I also bought some DeoxIT D5 and FaderLube (only very small tube though) - they didn't have any brush, would one from a crafts shop do ?