Luxman SQ77T - II

afroaudio

afroaudio

Active Member
Am trying to track down some info on this one. Picked one up this week from a local radio repair shop (i'm in Cape Town, South Africa) I powered up on dim bulb and had a little smoke from one driver board when audio was passed through and vol went past 9o'clock. I think I will start by recapping and then send her over to my tech to check what else needs doing.
pics later on.. :)
 
Oh, it's that one. It's a tube amp that they shoe-horned transistors into, for some reason (maybe they just wanted to try them out real quick). Probably not very good, then. But cool looking!
 
Yeah exactly, SQ77 was a valve amp with 12Watts per channel I think. This one should be close to a valve sound maybe? Will be interesting to put this on a scope and see how the 50yr old transistors are doing. These must be very rare considering I can hardly find any info on the net from an actual owner. Anyway interesting piece and easy on the eyes.
 
Bump ****
Must be some other owners on this site? My unit was taken back to the repair shop that I bought her from and is now running rather nicely after having some electrolytics replaced :)
 
Managed to track down a schematic for SQ77T (not version II) if anyone ever needs do get in touch. I have had some success recapping this amp with all new Nichicons (KZ, FG, KG) sound is now quite impressive.. I am just not totally happy with the noise floor and hoping to find a way to lower it still.

image by bregtje_lush, on Flickr

image by bregtje_lush, on Flickr

image by bregtje_lush, on Flickr
 
Those round barrel transistors... man they are weird-looking. What are their part numbers?

Noise is usually caused by small transistors. Maybe even those.
 
Yeah the big round ones are 2SB421 germanium, was hoping to do a silicon replacement and did find a diagram somewhere on the web - below- that showed BC640 replacing this and BC639 replacing the NPN (2SC826) then one resistor changed value from 10 to 22ohms to sort the bias out (?)This substitution did not work out however and I decided to go back to the original transistors at least until the recap was done. The other ones in the preamp and main amp were 2SC369 which I have switched out for low noise 2SC2240.

I did find some ST Micro 2N3773 and may try those out and see if things improve at all with the noise.
 

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To sort out the bias when using silicon transistors, maybe it is a good idea take away the NTC/resistor/diodes stuff between the driver transistors and replace it with a transistor/trimming resistor combination.
Example this idea:
Look at R10 / Q1 in figure 3 on this page: http://www.sentex.ca/~mec1995/tutorial/xtor/xtor6/xtor6.html
Be aware with the taper of R10 up (towards the collector of Q1) there is a safe condition, the lower you get at some point you'll get the output transistors start conducting and it is easy to get too much current when adjusting....
 
Thanks gslikker. I will look into doing this. I have a friend who is a very competent tech and will run this by him and report back wen I get something done.
 
Hi, I know that I am seriously late coming in to this discussion and I really hope you still have the "77" but here goes anyway:
The Mk.II is the one to have. It was usually sold with the nice timber case. The earlier ones had a rather industrial looking metal case.The SQ77T was supposed to be Luxman's solid state equivalent of the original tube SQ77. It used germanium transistors throughout and if any need replacing try and get germanium types/equivalents, as in my opinion they sound sweeter, plus there is also no need to revise the circuit to accommodate silicon types.
Up until recently I owned a Mk.I and a couple of Mk.II's. I sold the Mk.I to a friend and he is in the process of trying to establish what the electrical/circuit differences are with one of my Mk.II's. One of them is what you might call "mint" as I have owned it since new. It was purchased in the late 1960's. The other is in perfect working order but the case is in need of refurbishment which I'm working on now.
The SQ77T/II is a great little amplifier with more grunt than you would expect as most people think that the 30 watt rating means 15 watts per channel when in fact it is 30 watts per channel RMS into 8 ohms. It also has a half reasonable phono stage.
Finally, I still have the original owners manual for the Mk.II which includes the circuit. I have scanned and converted it to PDF so if you need this just let me know your email address and I'll pass it on to you.
Cheers, Andre.
P.S. Baron is correct about the small germanium transistors causing the noise. Lets face it, they are around 45 years old! If you are replacing them, try and do as I suggested above and search for germanium replacements. They are about if you look hard enough.
 
Also coming very late to this one. I just got a SQ77T/ii and am listening to it right now through my Rogers monitors for the first time. Very nice. Very warm and open sound I'm really impressed. I don't have much experience with little vintage integrated amps but I'd definitely rank it quite a bit above the several Sansui 555a's I've had. I'm probably repeating others when I say there is a guess what you'd call a lushness to it's sound that is a bit tube like. Also it's such a beautifully looking little amp in that wooden case with its silver face and knobs and warm little orange light....neat as a pin. A beauty, highly recommend grabbing one if you get the chance.
 
I have recently refurbished one of the 77's that I have and am using it now. They are great little amp's and definitely don't need to be messed around with by doing silicon upgrades. Germanium devices sound much closer to valve amp's anyway.
By the way, I recently purchased a pair of original Wharfedale "Column 8" speakers with some old Pioneer drivers in them. I've restored the cabinets and fitted Wharfedale Super 8's as the original "8/145" drivers are impossible to find. How many are there in Australia? It's anybody's guess but I'd guess at less than a dozen. I would love to hear from anyone that owns a pair and get their views on them. I am now using the 77 with them and this combo sounds great. Not parting with these, ever! The column type speaker siting behind the Column 8 is a mid 1960's version of the same cabinet but running Magnavox 8WR's which surprisingly also sound pretty good. Have to part with those soon to fund another Wharfedale project!
 

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Back again. Speaking of Luxman products, today I became the proud owner of a Luxman K-250 Cassette Deck. Yes, that's right, CASSETTE DECK. I have a few old (mainly Marantz) decks but they all have one or more issues. I recently salvaged about 300 home recorded and pre-recorded cassettes and wanted to play them, although it was mainly the persistence of my wife and 2 daughters that spurred me on. I had a Marantz SD820dbx which had significant cosmetic issues but was fine electrically and sold it fairly quickly and so purchased this one. It looks almost "mint" and plays beautifully. I'm absolutely amazed at how good it sounds (and looks).

My problem is that it came with no owner manual. Does anyone out there help me with a PDF of the manual? I would be extremely grateful.
Cheers.
 
Hi, I joined this forum as I also own an SQ77T/II which I've had for about 20 years and enjoyed many hours of listening to vinyl on.
Although not a valve amp (I love my 50+yo kenwood valve amp) it is a very warm sounding little unit, and powerful as stated by others.

I picked this amp up second hand in Melbourne somewhere also, but I now live in southern TAS.

Almost all my vinyl was damaged in transport (heat affected) a few years ago, so my analogue equipment was put away, but this christmas my children bought me a new vinyl LP of Dark Side of the Moon, so I've dusted off the old equipment.

Unfortunately moving things the other day, I was careless and managed to lose the 77 amp off the trailer (onto the grass) and backed over it with the car!
It's actually largely unscathed, however the box is slightly damaged, and the front facia is a little scored and bent :(
Typical, I was about to give it some love.

Good to see others are enjoying this old amp, I doubt there are any left in Japan!

I have just had one of my turntables serviced, the other (nicer one) a Hitachi direct drive, has electronic issues I am going to try and get to the bottom of myself.
I am hoping I can get some advice on the turntable and the SQ77T, as I have nothing else decent that takes a phono level input.

I will need to purchase some workshop / lab equipment as I no longer own much else but a selection of soldering irons and a basic multimeter, and I have a few electronics that need maintenence / restoration so I'm also looking at advice for best bang for buck equipment, either new or second hand. I want to be able to deal with digital data too, as I own quite a few 70s and 80s era computer relics that also need servicing and repairing.

In a past life I have an advanced diploma in electronics 25 years ago, but very little worked experience, I would like to learn more about the analogue world.
I have way too much equipment to pay someone else by the hour, I have over 20 years of repairs ahead of me to keep me busy.

Also thanks for the schematics, look forward to geeking out over audio.
 
vivvvi said:
Hi, I joined this forum as I also own an SQ77T/II which I've had for about 20 years and enjoyed many hours of listening to vinyl on.
Although not a valve amp (I love my 50+yo kenwood valve amp) it is a very warm sounding little unit, and powerful as stated by others.

I picked this amp up second hand in Melbourne somewhere also, but I now live in southern TAS.

Almost all my vinyl was damaged in transport (heat affected) a few years ago, so my analogue equipment was put away, but this christmas my children bought me a new vinyl LP of Dark Side of the Moon, so I've dusted off the old equipment.

Unfortunately moving things the other day, I was careless and managed to lose the 77 amp off the trailer (onto the grass) and backed over it with the car!
It's actually largely unscathed, however the box is slightly damaged, and the front facia is a little scored and bent :(
Typical, I was about to give it some love.

Good to see others are enjoying this old amp, I doubt there are any left in Japan!

I have just had one of my turntables serviced, the other (nicer one) a Hitachi direct drive, has electronic issues I am going to try and get to the bottom of myself.
I am hoping I can get some advice on the turntable and the SQ77T, as I have nothing else decent that takes a phono level input.

I will need to purchase some workshop / lab equipment as I no longer own much else but a selection of soldering irons and a basic multimeter, and I have a few electronics that need maintenence / restoration so I'm also looking at advice for best bang for buck equipment, either new or second hand. I want to be able to deal with digital data too, as I own quite a few 70s and 80s era computer relics that also need servicing and repairing.

In a past life I have an advanced diploma in electronics 25 years ago, but very little worked experience, I would like to learn more about the analogue world.
I have way too much equipment to pay someone else by the hour, I have over 20 years of repairs ahead of me to keep me busy.

Also thanks for the schematics, look forward to geeking out over audio.
Click to expand...

Hope you get it sorted out. Seems we got a lot of the Luxman amps in Australia for some reason. Great little amp.
 
Hi Vivvvi.
With regard to your SQ77T/II woes, I can only say, persevere and fix it. Give it the love it deserves!
As for wanting to get into the nitty gritty of working on your own gear (especially tube gear), the first thing I'd purchase is a Variac. Jaycar has a suburban Hobart store and sells them for $199.00.
I would also look at a decent multimeter that also measures L & C plus extra low range R.
Also have a look at WES (in Sydney) on line and then try opening an account with them. They have an unbelievable range of …… everything!
Cheers.
 
Reviving this thread AGAIN! :)

Nice to see others with some love for this obscure and forgotten Luxman.. I just went through mine again and hooked up to my Fostex full range test speakers.. I unfortunately have very bad distortion on my left channel using all inputs. I carefully pulled the Germanium transistors on the driver boards (2SB421) and they test ok but one has hFe 30 (L channel) and the other hFe 60 (R channel) My driver pair are original 2sc826/2sc827 on both boards. All small BJTs were replaced with KSC1845. And again my outputs are 2N3773.
 
Took another look this morning and found I have a snapped off collector leg on one of the Germanium 2SB421 :(

Taking a look at old Japanese cross reference sheets I see that ACY17 or 2N1188 are subs. These are at least available NOS from Eastern Europe so should be worth a go. Havnt found a source for 2SB421 or any other easily available Germanium match.
 
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