Sansui AU-777A xmas break rebuild

Output transistors
Sir, i am looking for equivalents for ALL the transistors for 777a. Kindly post the list here.

Regards

Thanks Vig! Quite a compliment coming from you.



Tom, regarding the output transistors two of the 2SD218 had been replaced at some point by Motorola 32-070 (another obsolete device). I replaced all four 2SD218 (well, two 2SD218 and two M 32-070) with a set of MJ15024G.
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I used MJ15024G instead of the popular MJ15003G, or MJ21194G, because the voltage specs are not quite as high at the original part. (Edit: I don't know where I got the V_EB = 7 V for the MJ15024. It's 5 V on the OnSemi datasheet. V_CB, V_CE of the MJ15024 are upgraded from the MJ15022, but I can't now find anywhere that V_EB is upgraded too).
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I left the other (two 2SD154 and two 2SD143) transistors as they tested good, but I have worked out nice substitutes in the correct packaging so someone give a yell if they want this info.
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Here is a pic of the transistors installed with new insulators and thermal compound.
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Sir
Still waiting for your guidance on transistor equivalents including output for 777a

I didn't reply before because the question you ask is already answered in the previous posts, except for the TO-66 package transistors which I did not replace (I have an idea for good substitutes but will not share that because I haven't tested for myself). There are no big mysteries for substitutes here (maybe except the TO-66 which I don't recommend replacing), just personal preferences like ksc versus ztx. Personally I went for the KSC1845 throughout the amp for almost all small transistors, although I do note that of late I'm becoming a fan of the KSC1815 for the additional current handling capability (but on the other hand the 1845 is listed with better robustness to voltages). The TO3s are listed in a previous post; I'm a big fan of the robust version of the MJs I used and I now use them all of the time even when it's way overspec.
 
I didn't reply before because the question you ask is already answered in the previous posts, except for the TO-66 package transistors which I did not replace (I have an idea for good substitutes but will not share that because I haven't tested for myself). There are no big mysteries for substitutes here (maybe except the TO-66 which I don't recommend replacing), just personal preferences like ksc versus ztx. Personally I went for the KSC1845 throughout the amp for almost all small transistors, although I do note that of late I'm becoming a fan of the KSC1815 for the additional current handling capability (but on the other hand the 1845 is listed with better robustness to voltages). The TO3s are listed in a previous post; I'm a big fan of the robust version of the MJs I used and I now use them all of the time even when it's way overspec.

Highly appreciated. I have taken a lot of notes from your thread.
 
Answering some questions from @slimecity here as some info may be of interest to others.

I think your 2kW transformer is a great idea.... 1kW would be fine (perhaps even 500 or 600W), but 2kW leaves no doubt that the power supply is unaffected by the step-down unit.

1. Yes there was a few errors in the service manual and a few differences between it and what i found in my amp. I definitely didn't catch all of them, but here is what I noted:

  • R611/R612 (phono): 280kOhm in amp (390 kOhm in schematic). Either value is okay ( see my thread for graphs and effect on RIAA)
  • C725/C726 (preamp): manual says 47 uF, 6.3 V but 47 uF, 10 V found in amp
  • C823, C824 (main): 500 pF ceramic (measure voltage and update here), not listed in manual
  • C813/C814 (main): 100 pF, 50 V ceramic not listed in manual
  • R841 (driver): 3.3k Ohm in parts list. 2.7k Ohm installed and service schematic. Not a big deal.
  • R861 (driver): 3.3 (!) Ohm in parts list. 2.7k Ohm installed and on service schematic. A big deal.
  • Note there is a service bulletin on the bias resistors R851/R853 and some nearby caps. Not mandatory unless "the trouble is found" with TR811-TR814
Also note
  • R005/R006 (protect.): 220 Ohm 5W resistors on protector block PCB hit a temperature of over 100 C.

There was definitely some other differences but that should be the main ones. Sorry I didn't note everything. I think you can order based on SM, and then you may have to make a small second order later. This will still be faster than measuring/reading all resistors.

Note that this is for the AU-777A. I haven't actually compared the AU-777D manual closely, although many have said only the power transformer is different.

2. If I recall correctly, the little yellow film caps are nichicon brand. Sorry, I don't remember which series. I just used them because the WIMA were too big. I'm happy with the film cap replacements! Even if not sonically better (they definitely aren't worse IMO), they will last longer than electrolytics. Basically you will find that polypro are large and you may need to go to polyester for larger values, but I personally don't really think polypro is so superior. That said, for some of those smaller values I might try harder next time to replace with C0G ceramics; this is what I did for the smallest values (the little blue caps you can see in my build) but in later rebuilds I tried a lot harder with this.

3. Yes, I used the 1845 for the C458s and a couple of others in this amp. I would not do this now since the 1845 has too small current handling specs; it is not a problem in many applications but unless a tech calculates the current being used, KSC1815 should be used and recommended as the sub. I've later used 1815 a lot and it sounds great too.

A FEW OTHER COMMENTS:
This was perhaps my 2nd or 3rd rebuild when I was getting into this hobby. I would do several things differently now, so I wouldn't take this thread as a bible.

Also, a lot of the magic is in choosing which signal path film caps to leave alone and which to upgrade (and you need to be able to read schematics, at least to the point of recognizing signal paths and feedback, to decide what to do. Sorry I didn't list them as I went along in the thread but if you have questions as you go along please do ask. (even worse, I've seen several threads lately with 'upgrades' where electrolytics where changes to film caps of same (ok), or lesser (not ok) value). Majority of the small signal path caps should go up on capacitance but not all.

Also, many caps are effectively in signal path even if they don't look like they are (for example, a cap that shunts high frequency to ground, might look tangential to signal path, but of course does effect the signal). They fact that so few people recognize all caps in signal path is a good argument for just recommending replacing all electrolytics with film caps to make things simple.

Same goes for resistors and signal path recognition. You could replace just specific resistors and save yourself some trouble, and just stick to audio path. I enjoy the idea of knowing all of my resistors are within 1% :). I think it was worth it too. My 777A is definitely up there with some amps in my collection that it probably shouldn't be and perhaps this is one of the reasons (?).

Something I get asked in PM is what did I use for the TO66 transistors mounted on the chassis near the driver boards. Those are the only two original transistors and I didn't replace them, partly because subs are not ideal. There are some modern options in TO-66 package, but I would be tempted to use a more modern package for better specs, and that just wouldn't look quite right. Anyway those TO-66 rarely fail in the AU-777 series.

And again, looking at my photos, I can definitely see a quite a few little things I would do differently, from power supply to signal path to transistors, now that I have more knowledge and experience so just use this thread as a rough guide. Also, I wrote a few incorrect things in my statements... I was very new to the hobby at that stage.

Looking forward to seeing your amp... I've yet to see another one with films caps and ceramics done AND all resistors.

Okay, back to listening to music.... now, to use my AU-777A. or the Sony TA-N902 I just finished fixing.
 
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Thanks smurfer.

Heres my restore pics so far. I have just done the F1194 and tone control boards so far. Loving the sound. Unfortunately I assumed that the 1W Xicons would be a bit smaller than they actually are. They have made a sonic difference, to my ear anyway.

I have also changed the bridge with my favourite 4 x MUR diodes and snubbers.

IMG_20200521_120625 7.49.50 PM.jpg IMG_20200522_083050.jpg IMG_20200522_083109.jpg IMG_20200522_083143.jpg IMG_20200522_083207.jpg IMG_20200521_171145.jpg

I also found this pretty funny. In amongst a whole lot of the blue Nichicon caps (on board F1183) I pulled two caps which seemed to be the wrong way around.....they turned out to actually be a pair of Matsushita caps - with the POSITIVE helpfully marked with a stripe!:

IMG_20200521_171145.jpg

So far things are going well and the mods are turning out well with no issues. I replaced some of the trannies pictured with KSC1815's (ie: all the 458's), but will probably leave some of the original 631's in place as they sound fine.
 

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'upgrading' the resistor power handling is one of the things I actually wouldn't do if doing this over. It may improve sound (although i couldn't say if it does so audibly), with the idea being that higher wattage resistors will run cooler and generate less thermal noise, as well as present a resistance closer to their nominal value due to running cooler (RE: temperature dependence of resistance) etc etc

But, resistors can act handily as fuses, protecting a device from widespread damage in the event of a fault. So i would stick to original wattage except one or two positions where i believe they used under rated resistor without good reason.
 
But, resistors can act handily as fuses

Yes I agree, this is something I will need to review. Definitely there are many of the larger resistors in the power supply and vertical output boards that arent changed, and I would thought the risk would be highest there - however there may also be risk elsewhere with some of the other boards.
 
BIASING ISSUE:

I've decided to replace the resistors in the F11831 and F1170 boards with metal film replacements of the correct wattages. So Im waiting on those new resistors to come from Mouser.

Im having a funny issue tho - trying to set the bias - on both channels (off the DBT), I have removed fuses 01 and 02, have the meter set to mA. On both sides I am getting the bias at 25mA. It will go up and down for a little bit either side when adjusting the pot, but always settles back to 25mA. This can occur over 15 minutes or so. The correct range is 28-30mA.

I have replaced the 50kohm pots both side - same result. I have a 2SC1815 in at TR801 & 802, and the 2SC283 is in at TR803 & 804 - I have pulled these to test, and they test OK (I then replaced them in the same place). As soon as the new pots were in, the bias read 25mA - its as if the pots are having no real effect on the biasing.

As stated above, Ive only replaced all electro's, ceramics on this board - however I have upped the R819-822 to 5W ohmites (they are 100ohm).

Any ideas on if this is an issue (or not) and where to look? Its a bit unusual to have this occur in both channels I think.
 
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BIASING ISSUE:

I've decided to replace the resistors in the F11831 and F1170 boards with the correct wattages. So Im waiting on those new resistors to come from Mouser.

Im having a funny issue tho - trying to set the bias - on both channels (off the DBT), I have removed fuses 01 and 02, have the meter set to mA. On both sides I am getting the bias at 25mA. It will go up and down for a little bit either side when adjusting the pot, but always settles back to 25mA. This can occur over 15 minutes or so. The correct range is 28-30mA.

I have replaced the 50kohm pots both side - same result. I have a 2SC1815 in at TR801 & 802, and the 2SC283 is in at TR803 & 804 - I have pulled these and they test OK.

As stated above, Ive only replaced all electro's, ceramics on this board - however I have upped the R819-822 to 5W ohmites (they are 100ohm).

Any ideas on if this is an issue (or not) and where to look? Its a bit unusual to have this occur in both channels I think.

Heading to sleep now so not full of ideas, but definitely an issue if you can't adjust bias. It should be wildly adjustable and if not is an indication something is wrong with either amp or procedure. Yes think of things that affect both channels. Maybe also try checking the idle current via emitter resistor voltage as an alternative procedure too.
 
Hmm, this is tricky. Especially as the issue is identical in both channels - which points to a power supply issue.

I've checked all caps in the power supply board and their values are higher than specced by the manual, so I wouldnt have thought any issues there.

Diodes 1 and 2 and the original 10D1 types. All new caps are the correct values - except 821/822 & 805/806 have been made bipolar types. All transistors on the F1183 board are testing fine.

I am getting 70V coming into the F1183 board underneath the fuse holders.

I do wonder how much of an issue this is, if I am getting close the specced mA on the outputs. Altho some adjustability would be good.

I wonder if a resistor may be open somewhere, in which case, replacing them all could sort that out.

To double check the bias - checking that R851/852 (0.5 ohm) are the emitter resistor?

cheers
 
Over the last year I've had a few messages about the AU-777A case. Those who want the vector format template in .eps format (which any CNC router shop will be able to use), just PM me with your email address and I'm happy to share. The template was based on the metal lid for the AU-777A (AU-777 is the same size, I assume other 777 variants are the same).

Also, some (e.g. see this thread) want the dimension of the wood case to replicate that. So here are the dimensions and some pics.

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There are some differences between the metal and wood cover. The metal cover attaches to the chassis four screws, two on either side panel. The metal cover has no base

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There are some differences between the metal and wood cover. The metal cover attaches to the chassis four screws, two on either side panel. The metal cover has no bottom. There is a metal panel on the bottom and four screw in feet.
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On the other hand the wood case skips the bottom feet, and the wood case has a bottom and is shaped such that it doesn't need additional feet. Four wingnut bolts screw into where the feet would screw into if you have the metal case.
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Here are a few more pics, that might be useful for someone making their own wood case.
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For the wood case:
- The wingnut bolts are 26 mm long and 3.88 mm wide including thread.
- outer width is 17-1/16"
- inner width is 16-1/8"
- outer height is 6-1/16"
- inner height is 5-3/16"
- depth is 12-1/8"
- the case is about 1/2" thick at the base, but the sides and top are about 7/16"
- the 'feet' are about 1/2" tall at the tallest parts
- I would drill the holes using your screw holes as templates but as a general reference they are separated by 10-10/16" and 8-10/16"
- the two large cut-outs underneath the wood case are at the rear. exact size/placement is not important... the just allow air to rise up through the slots on the back section of the top panel, i.e. chimney effect.
If you are ever selling one of these wood cases Id love to buy one!! Beautiful
 
I took the wood bonnet off of my 777A today. I screwed in 4 rubber feet on the chassis and popped the plexiglass lid on. Fits nicely. Here are a couple of pics I took this afternoon. It think using a thicker plexiglass has made it look a bit nicer too.

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Do you happen to have the dimensions used for this plexiglass cover?
 
If you are ever selling one of these wood cases Id love to buy one!! Beautiful

I have only the one wood case and it's and original but others have fabricated new wood cases.

Do you happen to have the dimensions used for this plexiglass cover?

I do, but they are not quite correct... I need to modify my design slightly. I've had many requests for me to make a few extra clear cases but time has been limited :(
 
Hello
I am going to replace the power transistors in my AU-777A. I would like to know if there are any checks to be done before installing the new ones.
 
I have only the one wood case and it's and original but others have fabricated new wood cases.



I do, but they are not quite correct... I need to modify my design slightly. I've had many requests for me to make a few extra clear cases but time has been limited :(
Love that plexiglass cover @smurfer77 ...:hug:
 
Hello
on the F11-831 board there are four capacitors of 1000uF. Is it necessary to parallel Wima to improve the treble?
 
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