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Vintage Luxman showdown: MQ60, MQ70, MQ80, SQ38FD, ?

smurfer77

smurfer77

Super Member
I'm rebuilding the above mentioned amps at the moment in between other projects. I've done the MQ60, parts for the MQ80 are here, I've made a parts list for the SQ38FD, and MQ70 is yet to be inspected. All of this could be finished within either 2 weeks, or 6 weeks (I have some travel 2 weeks from now for a couple of weeks).

What I'm wonder is, is there much interest in my posting my thoughts and opinions after doing blind A/B/C/D?

I have a amp selector box for such purposes, and so far haven't compared the amps directly, or listened to the unrestored ones extensively (because I don't trust those output coupling caps to protect the precious output transformers). I've had the MQ60 for a while (actually I have 3 of them) but the others are all new acquisitions so I will anyway be doing some comparisons. What I'm especially interest in is how does the MQ70 stack u pto the MQ60 which looks very similar but has common EL34 output tubes instead of the rare 50CA10. The MQ80 is a completely different beast. The SQ38FD has the 50CA10 outputs but also a preamp, since it's an integrated amp.
 
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Yes, we or at least I would enjoy reading your findings. I've always been a Luxman fan. Never did collect a lot of their gear but the little I did have I liked a lot. It was the 90's a gear was flying in and out so fast I never stopped to enjoy and hold onto the good ones. Ah foolish youth and early ebay dazes!
 
I'm interested in the what the relay does in the MQ-80. I've stared at the schematic for hours and hours and still can't figure out what it does. I see three sets of switch contacts but no relay contacts. There 's the normal line power switch, S1 and another two sets, S2a,b in the HV circuit that I heard one was a safety switch. Is there a mistake or something left off the schematic, please fill me in.

Craig

I currently have a Luxkit A3700II with the KT-88 option, it's stripped and ready for a rebuild, trying to decide what to do with it.
 
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llwhtt said:
I'm interested in the what the relay does in the MQ-80. I've stared at the schematic for hours and hours and still can't figure out what it does. I see three sets of switch contacts but no relay contacts. There 's the normal line power switch, S1 and another two sets, S2a,b in the HV circuit that I heard one was a safety switch. Is there a mistake or something left off the schematic, please fill me in.

Craig

I currently have a Luxkit A3700II with the KT-88 option, it's stripped and ready for a rebuild, trying to decide what to do with it.
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The MQ-80 was the last of those 4 amps I expected questions on! :). I'm new to the MQ-80, but let me have a quick look at the schematic; ok, at turn on the high voltage to the output and driver tubes are disconnected. Once the relay charges up after some time (see capacitor) it switches (note: both S2a and S2b must be interconnected; when 2a switches, 2b must switch with it) and high voltage is connected. Maybe this delay is to avoid any problems, when high voltage is present across the tube, in the brief time before grid is established during warm up and bias correctly. It might also be to simply avoid having any output until the heaters warm up so you don't have to listen to that warm-up phase.

Note the neon lamp in that part of the circuit right next to s2b? (it looks like a capacitor symbol, but with a little dot on one side). You can see it is turned off when the high voltage is in the connected state. That is the 'standby' lamp. Perhaps I could give more details/insight, after I work on this amp in the coming weeks but hope that helps.
 
S2a is in the relay energizing path so it can't be part of the relay as the relay can't do anything if S2a is open. S2 must be a manual switch. The power supply is very involved, you don't see many SCRs and PUTs in amplifiers. Where are those relay contacts??????? Very curious.

Craig
 
llwhtt said:
S2a is in the relay energizing path so it can't be part of the relay as the relay can't do anything if S2a is open. S2 must be a manual switch. The power supply is very involved, you don't see many SCRs and PUTs in amplifiers. Where are those relay contacts??????? Very curious.

Craig
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I see what you are saying. I think the next stage, before we lose our minds analyzing the schematic, is for me to check if the schematic is accurate, since I will have the amp open for it's recap soon. Then if all is good, we can get back to the schematic. Give a bit though, it may be a couple of weeks before I get the recap done.
 
Well, I just cracked open the MQ70 to make a parts list and it appears to already have film caps in the critical positions (they even look quite stock, NKT brand, without evidence of post-factory soldering. Can anyone comment on if this is likely to be the case?
 
Are these the amps you are working on:

MQ60, 1969 release (per audio database) using 4 50CA10 tubes for 30 wpc
MQ70, 1982-83 available per web infor using 4 6CA7 tubes for 45 wpc
MQ80, 1974 release (per audio database) using 4 6446a tubes for 40 wpc
SQ38FD, 1976-77 using 4 50CA10 tubes for 30 wpc

Definitely interested in what you are doing to refurbish these amps and put them in shape for many years to come. I have a pair of MB3045 (1976-80, 2 8045G tubes for 50 wpc modified to use KT88/6550 with the lack of availability of the 8045G). Sure wouldn't mind seeing what you have going on. Looking forward to the evaluation.
 
Blue Shadow said:
Are these the amps you are working on:

MQ60, 1969 release (per audio database) using 4 50CA10 tubes for 30 wpc
MQ70, 1982-83 available per web infor using 4 6CA7 tubes for 45 wpc
MQ80, 1974 release (per audio database) using 4 6446a tubes for 40 wpc
SQ38FD, 1976-77 using 4 50CA10 tubes for 30 wpc

Definitely interested in what you are doing to refurbish these amps and put them in shape for many years to come. I have a pair of MB3045 (1976-80, 2 8045G tubes for 50 wpc modified to use KT88/6550 with the lack of availability of the 8045G). Sure wouldn't mind seeing what you have going on. Looking forward to the evaluation.
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100% correct. Here is a thread on my previous MQ60 (I sold it, but since replaced it and did similar recap). MQ 70/80 and SQ38FD I haven't touched yet beyond ordering parts. Will post some pics here as I work on them. I want to get them all into spec before comparing. If anyone is on instagram you can see some of the progress as I go along on there - "california_audiophool".

The MQ60 and SQ38FD have related main amp sections it seems and same output tubes but the MQ70 is a bit of a different beast in terms of circuit and the MQ80 uses unusual output tubes. Should be interesting!
 
Just a quick update here... I haven't done the big showdown, or the chinese tube testing, but I am getting close... the SQ38FD (well three of them now actually) are half restored and I hope to get around to this soon! But I need to clear a couple of other amps first....

Luxman, I have not forgotten thee.
 
smurfer77 said:
Just a quick update here... I haven't done the big showdown, or the chinese tube testing, but I am getting close... the SQ38FD (well three of them now actually) are half restored and I hope to get around to this soon! But I need to clear a couple of other amps first....

Luxman, I have not forgotten thee.
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Maybe I can send you my pair of Ma-88's to compare also. :p
 
I've finally gotten around to servicing the Luxman power amps. Still haven't finished off the integrated amps. But for the power amps I have done some comparisons and they do sound quite different. More on that soon.

I've also compared my Luxman MQ60 head to head with original NEC output tubes vs Shuguang tubes. These are the rare 50CA10. The chinese tubes have irregular glass height, and also logo position, and a few other little quirks but otherwise appear to be of very high construction quality.

I had no problem biasing any of my 20 Chinese tubes I have; all behave nicely electronically. I also saw good channel match and all other specs such as power output and distortion appear unchanged when using the chinese tubes.

So I moved onto audio comparisons and I can not tell the difference between the Japanese tubes and the Chinese tubes. That's not to say there is no difference, just that I personally do not hear or measure it.

As for long term reliability, I can not say as I've only used these for a short time. If I have any problems I will report back here, but for now I'm fairly confident these tubes are the 'real deal' :). A good option to keep these amps running well past my lifetime.

Sadly, in the years it's taken me to do this comparison, the Chinese tubes are now also rare too! (They haven't been made for a long time as far as I know).
 
June 2017
smurfer77 said:
I'm rebuilding the above mentioned amps at the moment in between other projects. I've done the MQ60, parts for the MQ80 are here, I've made a parts list for the SQ38FD, and MQ70 is yet to be inspected. All of this could be finished within either 2 weeks, or 6 weeks
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Sept 2019
smurfer77 said:
I am getting close... the SQ38FD (well three of them now actually) are half restored
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Feb 2022
smurfer77 said:
I've finally gotten around to servicing the Luxman power amps.
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This is lightning speed compared to some of my personal projects. Well done. I might have threads with questions on gear I'm working on that were started before you joined and the unit isn't finished, yet. But heck, that is how we have collections!

I was going to say it is nice to see a 50CA10 tube available for these amps but the Chinese variant is as you say no longer easy to find. Unfortunately, it doesn't seem to be a tube that will allow easy conversion of the amp to use a common tube as is the case with the 8045G allowing amp mods to use KT88/6550.

Yup, hanging on every post in this thread. Thanks for the latest addition.
 
Blue Shadow said:
June 2017

Sept 2019

Feb 2022


This is lightning speed compared to some of my personal projects. Well done. I might have threads with questions on gear I'm working on that were started before you joined and the unit isn't finished, yet. But heck, that is how we have collections!

I was going to say it is nice to see a 50CA10 tube available for these amps but the Chinese variant is as you say no longer easy to find. Unfortunately, it doesn't seem to be a tube that will allow easy conversion of the amp to use a common tube as is the case with the 8045G allowing amp mods to use KT88/6550.

Yup, hanging on every post in this thread. Thanks for the latest addition.
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I bought 20 of the Chinese tubes nearly a decade ago. I guess I'm set for life :). It's actually easy to by used NEC 50CA10, but at a price that is about the same as the new Chinese tubes it's hard to say what to go for. You could get lucky with those NEC tubes but they could also be on their last legs... tricky.

Yeah, it's really not easy to convert, due to those 50V heater filaments on the 50CA10. You really need an additional transformers to get a lower heater voltage as far as I can see. I've seen some ugly mods, with transformers handing off of the back of the MQ60... perhaps you could fit one inside if ordering carefully....
 
Luxman? is their stuff any good?:D

In all seriousness, if you don't mind me asking, where did you find and acquire all this Luxman goodness? I'd be stoked if I found just one of those units.
 
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Dswankey said:
Luxman? is there stuff any good?:D

In all seriousness, if you don't mind me asking, where did you find and acquire all this Luxman goodness? I'd be stoked if I found just one of those units.
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:) Luxman is amazing quality. I can only speak for the vintage stuff though to be fair.

My units were purchased from Japan; I use to live there and have connections. I have 3 MQ60 (sold one a couple of years back so used to have 4), MQ70, MQ80, 3x SQ38FD, SQ301 and SQ505. I think that's about it, but it's hard to know what's in the boxes these days.

The chinese tubes I bought directly from china years ago.

Sadly, I will be letting go of 99% of my collection over the next 3 months, due to an international house move :(. I'm gutted but the shipping container costs have gone through the roof.
 
^ My initial post was meant as a joke as I'm big fan of vintage Luxman gear.

Sorry to hear about the downsizing hopefully whatever you let go will find a good home.
 
Dswankey said:
^ My initial post was meant as a joke as I'm big fan of vintage Luxman gear.

Sorry to hear about the downsizing hopefully whatever you let go will find a good home.
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I got it, otherwise there wouldn't have been a smiley face in my comment.

Yeah, it's heartbreaking. Perhaps one or two units will make the trip with me.... :)
 
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