Ming Da push pull monoblocs with 845, 300B and 6SN7.

[Patrick Turner]

For those wondering what model Ming Da amps I modified, it was those
shown at

http://www.mei-xing.com/English/cp/2_300845-AB.html

But the tubes shown above were not the same as I found in my sample of
these amps which may be a few years older. The 845 were Shuguang type
845A, 300B were non balloon bottle and 6SN7 were all CBS made in USA.

The data on the Meixing site says they make 75W and have 4 and 6 ohm
load match outlets.

I found PO at clipping at about 85W on the original amps, but found
the matches for loads to be ideal when you use 8 ohms on the "4 ohm"
outlet, 23ohms on the "8 ohm" outlet. Using 6 ohms on the "8 ohm"
outlet woud destroy output tubes.

The only way 4 ohms can safely be used is when plugged between 4 and 8
terminals.

Much better performance can be attained by improving the absurd driver
amp for the 845 which uses 300B with only 5mA for Ia and in SE mode.

I have a set of schematics in neat .gif form for anyone interested.

The work of improving each monbloc involved removing about 30 R&C
parts, and replacing with 25 but with better and simpler circuit.

The Ming Da uses point to point with some strip circuit boards with
brass terminals. These are actually brass stand off spacers but used
as solder points. They all have a nut on a thread to hold them in the
strip boards and many have a lug under the nut to which wires around
the circuit are soldered. Therefore many connections are via solder
lug and bolted connections which of course may one day come loose or
corrode. So I removed all the lugged and bolted connections and made
sure ALL connections are soldered only. Ming Da should know better
than to create amps which have such appalling defects. I found that
adjusting the bias on the 4 bias pots meant you must have the amp
sitting upside down on a block of wood under the power transformers to
stop the weight pressing on the tubes. Then one has to probe around he
ciircuit while twiddling bias pots. The 300B have a shared cathode
heating supply so adjusting bias for the 300B is impossible, and just
total ****ing bull****. So bias adjustment is a completely difficult
and bamboozling process likely to lead owners to breaking tubes or
electrocution. I have never seen worse. Soldering quality is poor with
many parts hanging around in mid air. Nowhere near enough thought was
ever put into parts placement within the chassis. There is no choke
filtering in the anode supply for 845 tubes, just CRC with 117uF, 50
ohms, 117uF. However, there is enough class A power and it is
adequate. Fanatics will find there is plenty of room to place a 5H
choke to replace the R in the CRC filter. Another major improvement is
to arrange the 300B as an LTP and have a CT choke to get dc to the
300B anodes and so there is at least 20mA for Ia which would then have
the 300B working better to make a more detailed accurate sound.

When one looks at the underchassis area of a Ming Da, one is impressed
by the neat tidy wirig but frankly, looks are deceiving because what
they have there is a ****ing big mess.

Its the same with so many Chinese made amps. I rewired a pair of
Quad-40 also recently.
They never quite go the full distance to real quality.


Patrick Turner.

[[email protected]]

On Feb 26, 8:54*pm, Patrick Turner > wrote:
> For those wondering what model Ming Da amps I modified, it was those
> shown at
>
> http://www.mei-xing.com/English/cp/2_300845-AB.html
>
> But the tubes shown above were not the same as I found in my sample of
> these amps which may be a few years older. The 845 were Shuguang type
> 845A, 300B were non balloon bottle and 6SN7 were all CBS made in USA.
>
> The data on the Meixing site says they make 75W and have 4 and 6 ohm
> load match outlets.
>
> I found PO at clipping at about 85W on the original amps, but found
> the matches for loads to be ideal when you use 8 ohms on the "4 ohm"
> outlet, 23ohms on the "8 ohm" outlet. Using 6 ohms on the "8 ohm"
> outlet woud destroy output tubes.
>
> The only way 4 ohms can safely be used is when plugged between 4 and 8
> terminals.
>
> Much better performance can be attained by improving the absurd driver
> amp for the 845 which uses 300B with only 5mA for Ia and in SE mode.
>
> I have a set of schematics in neat .gif form for anyone interested.
>
> The work of improving each monbloc involved removing about 30 R&C
> parts, and replacing with 25 but with better and simpler circuit.
>
> The Ming Da uses point to point with some strip circuit boards with
> brass terminals. These are actually brass stand off spacers but used
> as solder points. They all have a nut on a thread to hold them in the
> strip boards and many have a lug under the nut to which wires around
> the circuit are soldered. Therefore many connections are via solder
> lug and bolted connections which of course may one day come loose or
> corrode. So I removed all the lugged and bolted connections and made
> sure ALL connections are soldered only. Ming Da should know better
> than to create amps which have such appalling defects. I found that
> adjusting the bias on the 4 bias pots meant you must have the amp
> sitting upside down on a block of wood under the power transformers to
> stop the weight pressing on the tubes. Then one has to probe around he
> ciircuit while twiddling bias pots. The 300B have a shared cathode
> heating supply so adjusting bias for the 300B is impossible, and just
> total ****ing bull****. So bias adjustment is a completely difficult
> and bamboozling process likely to lead owners to breaking tubes or
> electrocution. I have never seen worse. Soldering quality is poor with
> many parts hanging around in mid air. Nowhere near enough thought was
> ever put into parts placement within the chassis. There is no choke
> filtering in the anode supply for 845 tubes, just CRC with 117uF, 50
> ohms, 117uF. However, there is enough class A power and it is
> adequate. Fanatics will find there is plenty of room to place a 5H
> choke to replace the R in the CRC filter. Another major improvement is
> to arrange the 300B as an LTP and have a CT choke to get dc to the
> 300B anodes and so there is at least 20mA for Ia which would then have
> the 300B working better to make a more detailed accurate sound.
>
> When one looks at the underchassis area of a Ming Da, one is impressed
> by the neat tidy wirig but frankly, looks are deceiving because what
> they have there is a ****ing big mess.
>
> Its the same with so many Chinese made amps. I rewired a pair of
> Quad-40 also recently.
> They never quite go the full distance to real quality.
>
> Patrick Turner.

China did produce high quality products years ago. They
were not available outside of the communist countries block,though.
Once again,it was many years ago during Mao period. The junk with
which it has flooded the entire world certainly doesn't create a
positive image for China as an advanced modern civilization...

[Patrick Turner]

On Feb 27, 3:29*pm, wrote:
> On Feb 26, 8:54*pm, Patrick Turner > wrote:
>
>
>
>
>
> > For those wondering what model Ming Da amps I modified, it was those
> > shown at
>
> >http://www.mei-xing.com/English/cp/2_300845-AB.html
>
> > But the tubes shown above were not the same as I found in my sample of
> > these amps which may be a few years older. The 845 were Shuguang type
> > 845A, 300B were non balloon bottle and 6SN7 were all CBS made in USA.
>
> > The data on the Meixing site says they make 75W and have 4 and 6 ohm
> > load match outlets.
>
> > I found PO at clipping at about 85W on the original amps, but found
> > the matches for loads to be ideal when you use 8 ohms on the "4 ohm"
> > outlet, 23ohms on the "8 ohm" outlet. Using 6 ohms on the "8 ohm"
> > outlet woud destroy output tubes.
>
> > The only way 4 ohms can safely be used is when plugged between 4 and 8
> > terminals.
>
> > Much better performance can be attained by improving the absurd driver
> > amp for the 845 which uses 300B with only 5mA for Ia and in SE mode.
>
> > I have a set of schematics in neat .gif form for anyone interested.
>
> > The work of improving each monbloc involved removing about 30 R&C
> > parts, and replacing with 25 but with better and simpler circuit.
>
> > The Ming Da uses point to point with some strip circuit boards with
> > brass terminals. These are actually brass stand off spacers but used
> > as solder points. They all have a nut on a thread to hold them in the
> > strip boards and many have a lug under the nut to which wires around
> > the circuit are soldered. Therefore many connections are via solder
> > lug and bolted connections which of course may one day come loose or
> > corrode. So I removed all the lugged and bolted connections and made
> > sure ALL connections are soldered only. Ming Da should know better
> > than to create amps which have such appalling defects. I found that
> > adjusting the bias on the 4 bias pots meant you must have the amp
> > sitting upside down on a block of wood under the power transformers to
> > stop the weight pressing on the tubes. Then one has to probe around he
> > ciircuit while twiddling bias pots. The 300B have a shared cathode
> > heating supply so adjusting bias for the 300B is impossible, and just
> > total ****ing bull****. So bias adjustment is a completely difficult
> > and bamboozling process likely to lead owners to breaking tubes or
> > electrocution. I have never seen worse. Soldering quality is poor with
> > many parts hanging around in mid air. Nowhere near enough thought was
> > ever put into parts placement within the chassis. There is no choke
> > filtering in the anode supply for 845 tubes, just CRC with 117uF, 50
> > ohms, 117uF. However, there is enough class A power and it is
> > adequate. Fanatics will find there is plenty of room to place a 5H
> > choke to replace the R in the CRC filter. Another major improvement is
> > to arrange the 300B as an LTP and have a CT choke to get dc to the
> > 300B anodes and so there is at least 20mA for Ia which would then have
> > the 300B working better to make a more detailed accurate sound.
>
> > When one looks at the underchassis area of a Ming Da, one is impressed
> > by the neat tidy wirig but frankly, looks are deceiving because what
> > they have there is a ****ing big mess.
>
> > Its the same with so many Chinese made amps. I rewired a pair of
> > Quad-40 also recently.
> > They never quite go the full distance to real quality.
>
> > Patrick Turner.
>
> * * * * * * *China did produce high quality products years ago. They
> were not available outside of the communist countries block,though.

Er, could you tell me when that was?
If you go back to 1960, in the middle of Mao's rule where everyone in
China was not allowed to get rich and wherever anyone tried to
criticize the CCP regime's centralist was hammered flat, you would
have found all products made were inferior to their western nation
equivalent.

Go back maybe 1,200 years ago and sure, China thougt its products were
way ahead of the West, and they sort of shut the door on outsiders and
stopped innovating. Well now they are gathering pace and they show
that they are capable of almost anything. Just look at how their
Olympic sports teams are performing.

While so many Chinese are willing to work hard to better themselves
and the world, many get their wires all crossed up in their enthusiasm
and arrogance. China generates cyber war against Google, and many
drugs made in china are fake and being sold cleverly to western
nations and oh how the money rolls in. So there is a certain
percentage of chinese dliberately making stuff which is second rate
and they still laugh all the way to the bank.

Better to go to a bank laughting with profits generated by selling
good looking junk to western fools than be poorer than you neighbour.

China does well because thw GSM, (Great Stoopid Majority) in the West
has forgotten how to tell the difference between **** and clay.


> Once again,it was many years ago during Mao period. The junk with
> which it has flooded the entire world certainly doesn't create a
> positive image for China as an advanced modern civilization...

Huh? quality on Mao's time? Do mean their bicycles? everyone had to
have one.
It was heavy. A damn clunker. But lucky many roads in China are flat.

Just what did the average man have in possessions in 1960? a bike,
( not really his, maybe the party's ) and maybe a radio, and
ramshackle junk hardly worth two bob, Povety was enforced by glorious
socialism until Deng said in effect, " To get rich is glorious".

Well, Chinese ppl are hell bent on parking their bike behind a shed
and buying cars and building roads and buildings and constructing a
whole new middle class society. To ensure there are enough goods they
can buy methods of production used for slow evolution of quality have
been ignored in favour of a desperate lunge to vast quantities of
production where real quality don't matter. Look what happened when
that last big earthquake happened. Many schools collapsed because of
shoddy building quality and many children were killed. There is a
scorching hatred within the majority of the Chinese for the endemic
corruption and lack of ethical behaviour.

I would guess that in 20 years much of the efforts to build
infrastructure now will need vast amounts of repair and maintenance. I
expect none of the cars made now will be still on the road then.

But here I still see cars 40 years old being driven around.

I would hazard a guess that the CEOs of companies like ARC, CJ, Manley
Labs and other venerable old amp making companies will be raising
their hats to chinese productions knowing that what they make is cheap
and poorly designed even though it is spectacularly good looking.

I would say that in 20 years this trend might be quite different as
the next generation of one child per family brats mature and become
very bad tempered with the sea of mediocrity in which they feel they
are drowning. No problem, by then all the old western nation makers
will have died out and China may be making every damn thing.

In time China may well surpass Japanese enthusiasm for quality which
exceeds all other nations. There will be mistakes along the way. Just
look at the stew over Toyota accelorators and the needless deaths.
Brilliance can all to easily lead to too much complexity and
simulation so a driver cannot TURN OFF THE ****ING ENGINE WHEN AUTO
SYSTEMS FAIL.
Once companies forget basic human needs, they become top heavy. So it
is the same for nations full of ppl.

Anyway, Ming Da would do well to read all I have said here and do well
to read my website.

They need to simply settle down and learn to criticize their own work
and do things better.

More glorious audio quality will be the result, and they can get a
better price.


Patrick Turner.


- Hide quoted text -
>
> - Show quoted text -

[Andre Jute[_2_]]

On Feb 27, 1:54*am, Patrick Turner > wrote:
> For those wondering what model Ming Da amps I modified, it was those
> shown at
>
> http://www.mei-xing.com/English/cp/2_300845-AB.html
>
> But the tubes shown above were not the same as I found in my sample of
> these amps which may be a few years older. The 845 were Shuguang type
> 845A, 300B were non balloon bottle and 6SN7 were all CBS made in USA.
>
> The data on the Meixing site says they make 75W and have 4 and 6 ohm
> load match outlets.

Aw, sheet, Patrick, I made 75W of blissful *single-ended* sound In my
Type 99 Millennium End with only five tubes per side, including in the
power supply: 417A/300B/2x SV572-3/6D22S. Admittedly, the transformers
were enormously expensive and heavy custom designs by Menno van der
Veen (those designs are now for sale from Amplimo and Plitron) but so
would the Ming Da trx have been if they did the job right.

Man, all I can say is that the owner of the Ming Da made the right
decision when he got you to rework it!

Andre Jute
Visit Jute on Amps at
http://www.audio-talk.co.uk/fiultra/
"wonderfully well written and reasoned information for the tube audio
constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site containing vital gems of
wisdom"
Stuart Perry Hi-Fi News & Record Review


> I found PO at clipping at about 85W on the original amps, but found
> the matches for loads to be ideal when you use 8 ohms on the "4 ohm"
> outlet, 23ohms on the "8 ohm" outlet. Using 6 ohms on the "8 ohm"
> outlet woud destroy output tubes.
>
> The only way 4 ohms can safely be used is when plugged between 4 and 8
> terminals.
>
> Much better performance can be attained by improving the absurd driver
> amp for the 845 which uses 300B with only 5mA for Ia and in SE mode.
>
> I have a set of schematics in neat .gif form for anyone interested.
>
> The work of improving each monbloc involved removing about 30 R&C
> parts, and replacing with 25 but with better and simpler circuit.
>
> The Ming Da uses point to point with some strip circuit boards with
> brass terminals. These are actually brass stand off spacers but used
> as solder points. They all have a nut on a thread to hold them in the
> strip boards and many have a lug under the nut to which wires around
> the circuit are soldered. Therefore many connections are via solder
> lug and bolted connections which of course may one day come loose or
> corrode. So I removed all the lugged and bolted connections and made
> sure ALL connections are soldered only. Ming Da should know better
> than to create amps which have such appalling defects. I found that
> adjusting the bias on the 4 bias pots meant you must have the amp
> sitting upside down on a block of wood under the power transformers to
> stop the weight pressing on the tubes. Then one has to probe around he
> ciircuit while twiddling bias pots. The 300B have a shared cathode
> heating supply so adjusting bias for the 300B is impossible, and just
> total ****ing bull****. So bias adjustment is a completely difficult
> and bamboozling process likely to lead owners to breaking tubes or
> electrocution. I have never seen worse. Soldering quality is poor with
> many parts hanging around in mid air. Nowhere near enough thought was
> ever put into parts placement within the chassis. There is no choke
> filtering in the anode supply for 845 tubes, just CRC with 117uF, 50
> ohms, 117uF. However, there is enough class A power and it is
> adequate. Fanatics will find there is plenty of room to place a 5H
> choke to replace the R in the CRC filter. Another major improvement is
> to arrange the 300B as an LTP and have a CT choke to get dc to the
> 300B anodes and so there is at least 20mA for Ia which would then have
> the 300B working better to make a more detailed accurate sound.
>
> When one looks at the underchassis area of a Ming Da, one is impressed
> by the neat tidy wirig but frankly, looks are deceiving because what
> they have there is a ****ing big mess.
>
> Its the same with so many Chinese made amps. I rewired a pair of
> Quad-40 also recently.
> They never quite go the full distance to real quality.
>
> Patrick Turner.

[stam]

Hi Patrick,

I am interested in acquiring copies of the schematics. Are they still
available? I have a Ming-da 300B-45A that needs repair work.

Thanks,

Steve