Author Topic: LUXMAN MQ70 tube amplifier (new issue)  (Read 2298 times)

Offline hope

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #30 on: January 12, 2020, 06:27:12 PM »
Aha!

Offline Agaton Sax

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #31 on: January 12, 2020, 06:42:47 PM »
Charles

The MQ 70,ARC D 90, possibly Acoustat TNP pre amp, Tannoy Golds,Quad ESL and Linn Ekos Shure Ultra 500 were in storage in Gauteng for more than 15 years before ending up with the gardener.

 This is all I have left  of the documentation and I think is the block diagram you are referring to? Curiously the  pencilled ECC 85 bit seems to have disappeared. Maybe it was on the actual circuit diagram.



The elusive 6240G. I get cold just thinking of those anxiety filled times. The orange labelled bastids.





deja dingus

« Last Edit: January 12, 2020, 07:04:00 PM by Agaton Sax »

Offline charles

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #32 on: January 12, 2020, 11:21:48 PM »
Agaton Sax

My documentation is the same.

Mine is complete except for the original correct circuit diagram.

All I can say this amplifier sounds very good.
 
 

Offline charles

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #33 on: January 13, 2020, 07:37:30 AM »
 Just a correction please:

"There is a neat block diagram (description) of the set in the documentation that indicates:   The Driver Differential Amplifier use 6GC7 (6240G)
So this set use 6GC7/6240G valves and not ECC85 ones."

it should read 6CG7 and not 6GC7



Offline Ampdog

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #34 on: January 14, 2020, 12:06:24 AM »
Before we get too bogged down in minutiae:

One reads in various places that "the 6CG7/6FQ7 is a direct plug-in replacement for the 6240G . . ." - -
(direct plug-in replacement for me means exactly that only: The pin-puts are the same, plus the characteristics possibly similar . . .)

but then the schematic posted earlier shows the driver as 6AQ8 - which is the exact equivalent of the ECC85, not 6CG7  (American vs. Continental numbering system). Only, the 6AQ8/ECC85 has about 2,3 times the Gm of the 6CG7 at the same Ia; enough to make a noticeable difference to NFB stability, depending (apart from the former having a higher 'Vao  max.' rating.)

(Bottom line: Not simply a direct replacement-and-switch-on).

. . . and one is still hunting for confirmation of what exactly the elusive 6240G is supposed to be - and caring less by the minute.  (If of any earthly interest: for beefy high Va driver triodes I still prefer using E182CCs, despite some difficulty to get both triodes of a pair within narrow tolerance.)

[Hope, I am unfortunately unable to read the interesting information posted by you; cannot seem to get the brightness up.)

As said the MQ70s which came my way were happy with the ECC85 drivers with which they came (though I can no longer recall whether I affected minor NFB compensation capacitor changes).

If not mentioned: There was some interesting discussion of this amplifier on the internet several years ago.
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Ampdog

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #35 on: January 14, 2020, 12:54:17 AM »
and Charles and I Affected by the same spelling Effect . . .

Previous post: Should read "I cannot recall whether I effected minor adjustments  :blah:  I did not  make the time limit for modifications  :-[
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline hope

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #36 on: January 14, 2020, 06:20:43 AM »

[Hope, I am unfortunately unable to read the interesting information posted by you; cannot seem to get the brightness up.)

Any better?karthik jayaram

Offline Nidri

Whilst Nidri takes reasonable care to ensure that the information in this message is correct and up to date, this might not always be the case. Nidri does not give any warranties as to the accuracy and safety of any information appearing in this message.

Offline Ampdog

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #38 on: January 24, 2020, 05:36:46 AM »
The reissue one probably looks much better than the original one.
It has newly designed output transformers and a new circuit design. The physical layout of the amplifier differs from the old one. 

Charles,
Here you mentioned two different amplifiers (newly designed output transformers and a new circuit design.) Can you explain or please give a source, since I do not seem to find anybody else globe-wise who knows about this?

Not to belabour so once again I will leave it there unless others are interested. (It requires no  more than 2nd year valve knowledge plus a set of proper Va/Ia graphs to show that the schematic shown earlier cannot be practically balanced with 'ordinary-spread' valves and zener voltages.)
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Ampdog

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #39 on: January 27, 2020, 05:01:34 AM »
This subject never seems to stop, does it :(

I am still receiving conflicting messages/questions - trying my best to keep peace. E.g. I have several times asked for elucidation on what the mysterious diodes are, particularly those which I found to be zeners, contrary to the symbols given - no information seems to be forthcoming.

But Charles:
In Post #27 you seem to be rather convinced that the MQ70 does not use ECC85 driver valves;



You then seem to dispute this schematic, indicating 6AQ8 (ECC85), as authentic?  Did you get any other schematic with your acquisitions or valves listed in your parts list?

(Other indications that this schematic is not issued by Luxman are the several question marks with the relevant diodes. Does Luxman not know what they are using? Such designations are most uncharacteristic for any official document.)   Further the vague designation "semiconductor" or similar description found in parts lists (under correction) confuses.

Thus one seems to be no closer to reality, judging from what is evident from several different models doing the rounds, and I would be rather careful to make categorical statements on what the MQ-70 actually was or should be  - if any one model did in fact exist.  (Again: claims to "this is the 'new' MQ70" . .  which is then which??) I have at least given diode numbers I found (1N4760), but nobody confirms/disagrees . . . .?)

A singular situation in my long years of amplifier experience; all this tends to make one wonder: What is actually 'official', if anything?
 :headbanger:   :popcorn:

(I am awaiting final replies from a few internationally known friends. I am not holding my breath - -  The sooner this can end the better; I think there are better amplifiers on the market.)

Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline charles

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #40 on: January 27, 2020, 12:23:25 PM »
Refer to an earlier post:

I had a good look at the MQ70 documents I have, call it a "service manual" .

There are no ECC 85 valves in the set according to this documentation.

There is a neat block diagram (description) of the set in the documentation that indicates:   The Driver Differential Amplifier use 6CG7 (6240G)
So this set use 6CG7/6240G valves and not ECC85 ones.

In this set of original MQ70 documentation:

Complete alignment procedure and adjustment location diagram

Part List (with Luxman stock number) and description and a part layout diagram

Also the following valve list:

V1L & V1R = 12AX7
V2L & V2R = 6CG7
V3L & V3R = EL34
V4L & V4R = EL34 

This is a very good sounding amplifier
« Last Edit: January 27, 2020, 12:25:53 PM by charles »

Offline Ampdog

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #41 on: January 31, 2020, 02:26:09 AM »
Time to conclude my contribution here:

I had little to no informative reaction to queries PM'd to other notable members of earlier contributions. Nobody offers any particular clarity regarding the 'mystery' diodes; in fact, surprise was expressed re further interest. I could also not retrace the previous thread (some 5-6 years ago).

Thus I  must suffice with own experience and memory. As said, all hail to whoever is happy with their MQ70s at present.  The amplifier iron at least is/was very good.

[Footnote: Regarding the driver valves, because of the design of the stage a number of medium- triodes will actually serve. Main requirement is a low Va(sat) value because of the extra signal amplitude required by the EL34 cathode feedback feature. In this respect the 6SG7  (equivalent of the old workhorse 6SN7)  is slightly better suited than the ECC85; the 12BH7 would be better still.  (Again the choice of a 'long' tail in the form of a cathode resistor of all of 10K in this stage , 'robbing' it of some sorely needed h.t., mystifies   . . . but enough.)]
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Ampdog

Re: LUXMAN MQ70 tube amplifier (new issue)
« Reply #42 on: January 31, 2020, 06:31:56 AM »
" In this respect the 6SG7  (equivalent of the old workhorse 6SN7) "

What is it with this thread and valve numbers!!

This time I mistyped. The '6SG7' above should of course have been '6CG7' !
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)