OESTEX
© Tube Amplifier Pages
THE McINTOSH
MC-3500 MKII
350W rms HI-FIDELITY TUBE AUDIO
MONO AMPLIFIER
FOR THOSE
INTERESTED IN THE WORLD'S BEST VACUUM TUBE AMPLIFIER - CONSIDER THE EXTREMELY
EXCELLENT McINTOSH HI-FIDELITY AMPLIFIER - GRAB ONE IF YOU CAN!!
Introduction:
(click on links to connect)
In the December 1949 issue of US
"AUDIO" magazine, Frank H. McIntosh and Gordon J. Gow, of
the McIntosh Engineering Laboratory Inc. published a paper detailing their new
concept in audio amplifier engineering.
The design shown had just been granted
US Patent
2,477,074 on July 26 1949 in the name of Frank McIntosh.
Thus the conditions were right to
reveal to the world their new and very advanced concepts for electronic
circuitry and transformer engineering design.
Since 1949 this unique amplifier
design has undergone numerous upgrades and variants, culminating in the MI350
and MC-3500 350W rms models produced in 1968-1971.
A wide range of McIntosh variants have
been manufactured since but none in the 350W power class of tube amplifiers.
Details are readily available on the net.
The story of McIntosh amplifiers is
told in my web page https://www.oestex.com/tubes/Mac/MC-3500.html
Further information is available at https://www.mcintoshlabs.com/brand/mcintosh-heritage
and Roger Russel’s website
THE MC-3500 MKII
In 2019, after a two year development process,
McIntosh announced production of a new revised and upgraded version in keeping
with its current style, design standards and modern aesthetics. The two year
development process building on the MKI experience suggests a very carefully
re-engineered product from a fresh and more experienced design team who
intended the new model should be superior to the original MC-3500 MKI model.
The EL509S is a heavier duty tube than
the original 6LQ6/6JE6 and the guaranteed +2.4db dynamic headroom specification
indicates the amplifier is conservatively rated at 350W rms.
An important difference is that the
EL509S does not have a top Plate connection cap, thereby making tube
replacement safer. This is not an issue for the home user who relies on
specialist services to change tubes.
Two MC-3500 MKII mono amplifier units
are required for a two channel stereo system and up to five units are required
for a surround sound cinema system with sub-woofer.
One important change is that of
“style” or “look”. The style of the MC-3500 MKI was based upon the versatile
MI-350 that was created for rack mounted Industrial/Commercial applications. It
has an obvious “broadcast” equipment appearance typical of the era. In
contrast, the MC-3500 MKII is specifically intended for the hi-fi audiophile
market and is styled to suit its purpose.
For the audiophile, two units side by
side on a benchtop or cabinet would be an ideal configuration for both
appearance and cooling.
MC-3500 MKI and MC-3500 MKII –
Physical Comparison
McIntosh tells it this way:
The
following is a press release issued by McIntosh.
“Binghamton, NY – November 4, 2021 – McIntosh, the global leader in
prestigious home entertainment and ultimate-quality audio for over 70 years, is
proud to announce the MC-3500 Vacuum Tube Amplifier Mk II.
Originally
used to power the sound system for Woodstock* ’69 amongst other formative music
events, the iconic monoblock amp was recreated by McIntosh’s expert team of
engineers and designers to include modern upgrades that celebrate the brand’s
rich history of powering pivotal moments in music, while showcasing its
commitment to technological innovations and acoustic advancements. The
reimagined version can be used with a variety of preamplifiers, turntables, CD
players, media streamers, speakers, etc. to form a complete home audio system.
The
MC-3500 Mk II boasts 350 Watts of power and is upgraded with modern components
that deliver an audio performance worthy of its predecessor. As in the
original, the MC-3500 Mk II uses McIntosh’s Unity Coupled Circuit™ output
transformer, allowing the full 350 Watts to be safely delivered to virtually
any speaker. The MC-3500 Mk II has a fully balanced driver section that
utilizes three 12AX7A and one 12AT7 vacuum tube, while the output is powered by
eight EL509S high-power output vacuum tubes specifically chosen due to the
similarity to the 6LQ6 “sweep tubes” found in the original MC-3500. All the
vacuum tubes are located behind the power and output transformers and are
covered by a 12-gauge stainless steel wire cage.
“At
the 50th anniversary of Woodstock in 2019, there was a lot of buzz resurfacing
about the McIntosh sound system,” said McIntosh President, Charlie Randall.
“This enthusiasm was infectious and inspired me to get our engineering team
together to redesign the amp that has obviously resonated with music fans as
being a historically significant piece of audio gear. After over two years, we
are really proud of the result. The MC-3500 Mk II takes its inspiration from
the original 1968-71 MC-3500 and incorporates all the knowledge we have gained
surrounding vacuum tube amplifier design since the 1960’s.”
MC-3500
VACUUM TUBE AMPLIFIER MK II FEATURES INCLUDE:
·
McIntosh’s
Power Guard Screen Grid Sensor™ (SGS) technology that prevents premature
vacuum tube failure
·
Sentry
Monitor™
technology to actively observe the output current to ensure operation within
safe limits
·
Balanced
and unbalanced input(s)
to connect with home audio system and multi-amp configurations
·
McIntosh’s
patented, gold-plated Solid Cinch™ speaker binding posts that easily but
securely attach the speaker cables to prevent them from coming loose
The
MC-3500 Mk II is both modern and retro in its design. As an homage to the
original, the Mk II includes U-shaped siderails, a unique feature that provided
strength and durability when the original amps were used on the road. The Mk II
also has replicated the black rubber bumpers found in the original amps that
allowed them to be temporarily set upright for shows and were big enough to
prevent the model from being damaged during setup at concerts. The front panel
is machined aluminum with a bead blast finish and gold anodizing that emulates
the original MC-3500. Just as in the original MC-3500, the Mk II version
includes an output meter, though this version is larger and centered on the
front panel rather than offset to the left side as in the previous version. The
meter uses a variation of McIntosh’s DualView™ Power Output Meter design, with
the top scale showing the power output in both Watts and decibels, while the
bottom scale shows the amplifier warmup time.
*Woodstock
is a registered trademark of Woodstock Ventures LC.
Pricing
and Availability
Orders
for the MC-3500 can now be placed with Authorized McIntosh Dealers with
shipping expected to begin in December 2021 to the United States and Canada,
and to the rest of the world shortly thereafter. Suggested retail price (VAT,
shipping and any customs duties related to current standards of individual
countries are excluded): $15,000 USD.”
(End
quote)
Quote
from the McIntosh Website:
“It
was at a 2019 event to celebrate the 50th Anniversary of Woodstock where
McIntosh President Charlie Randall, realizing the historical importance of the
MC-3500, first dreamed of bringing it back into production. That proved no easy
task considering it was first designed over 50 years ago. But after more than
two years of development, that dream has become reality as McIntosh is proud to
announce the MC-3500 Vacuum Tube Amplifier Mk II.
The
MC-3500 Vacuum Tube Amplifier Mk II is a conservatively rated 350 Watt
monoblock that takes its inspiration from the original 1968-71 MC-3500 and
incorporates everything we have learned about vacuum tube amplifier design
since the 1960s.
It
has been upgraded to modern standards and with modern components to deliver an
audio performance worthy of its predecessor and the legacy of their shared
model number – all while adhering to the original design as much as possible.
Like the original MC-3500, the MC-3500 Mk II uses our Unity Coupled Circuit
output transformer, which allows the full 350 Watts to be safely delivered to
virtually any speaker regardless if it has 2, 4 or 8-Ohm impedance.
The
MC-3500 Mk II is powered by eight EL509S high-power output vacuum tubes. The
EL509S tube was chosen specifically due to it having many similar qualities and
characteristics of the 6LQ6 "sweep tubes" used on the original
MC-3500. Like the 6LQ6, the EL509S is very rugged thanks to its robust cathode
and associated heating element which produces a high peak plate current
capability in excess of 1 Amp.
Sweep
tubes like the original 6LQ6 were primarily designed for 1950-60s era TVs where
they would sweep the cathode ray gun in the picture tube across the phosphor
screen. This was a very power-hungry process that required these high-powered
sweep tubes. The use of sweep tubes by McIntosh engineers in the original
MC-3500 amplifier was a very cool and innovative application. By using the
high-power EL509S vacuum tubes, the MC-3500 Mk II amplifier remains as faithful
as possible to original MC-3500 output design. In addition, just like in the
original MC-3500, the MC-3500 Mk II uses an additional feedback loop to enhance
the linearity of the output tubes.
Like the original MC-3500, the MC-3500 Mk II has a fully balanced driver
section that utilizes three 12AX7A and one 12AT7 vacuum tubes. The first 12AX7A
is the differential input amp; the second is the buffer/driver for the voltage
amp; the third is the voltage amp. The 12AT7 is the buffer/driver for the
EL509S output tubes. All the vacuum tubes are located behind the power and
output transformers, and are covered by a 12-gauge stainless steel wire cage
with a black powder coated finish. The cage is shaped so that our patented,
gold-plated Solid Cinch™ speaker binding posts are easily accessible even when
the cage is installed.
Our
exclusive Power Guard Screen Grid Sensor™ (SGS) technology is included in the
MC-3500 Mk II. Power Guard SGS is designed specifically for our vacuum tube
amplifiers and similar in nature to our patented Power Guard® technology found
in our solid-state amplifiers. Power Guard SGS helps prevent premature vacuum
tube failure by monitoring the screen grid current in the output vacuum tubes.
If the current becomes too high, a circuit in Power Guard SGS is activated
which dynamically attenuates the input signal in real time to keep the vacuum
tubes operating at safe levels. The fully balanced driver section of the
MC-3500 MK II is an ideal match to use with Power Guard SGS. Sentry Monitor™,
which observes the output current and shuts the amplifier off if it ever
exceeds safe limits, is also included.
Both
a balanced and unbalanced input are included for connecting to your
preamplifier and the rest of your home audio system. A balanced and unbalanced
output are also included for multi-amp configurations, such as bi-amping or
tri-amping.
Just as the original MC-3500 did, the Mk II version has an output meter, though
it's larger and centered on the front panel instead of offset to the left side.
This makes the meter easier to read and presents a symmetrical look in a
typical two-channel stereo system layout. The meter uses a variation of our
DualView™ Power Output Meter design, with the top scale showing the power
output in both Watts and decibels, while the bottom scale shows the amplifier
warmup time. When powered on, the meter starts to slowly rise; once it reaches
100%, it drops back down to zero and the amplifier is ready to play music.
The
MC-3500 Mk II has handles just like the original, but they have more ergonomic
design that are friendlier on your hands when moving this 121 lb. (54.9 kg)
heavyweight. The base of the chassis is stainless steel polished to a mirror
finish. The front panel is machined aluminum with a bead blast finish and gold
anodizing that emulates the look and finish of the original MC-3500. A clear
glass insert covers the meter; a black glass insert at the bottom houses the
knobs and illuminated lettering.
As
an homage to the look of the original MC-3500, the Mk II features two U-shaped
siderails that wrap around the top, back, and bottom of each side. Many of
original MC-3500s were used on the road a lot and these siderails provided a
lot of strength and durability. It is a very unique design element that we
wanted to duplicate in the MC-3500 Mk II. There were also four black rubber
bumpers on the back of the rails that allowed the amp to be temporarily stood
upright while setting up for shows; the bumpers were big enough to prevent any
parts sticking off the back of the amplifier from scraping against the floor
and being damaged. These bumpers have also been replicated on the MC-3500 Mk
II.”
(End
quote)
SPECIFICATIONS:
ELECTRONIC
SPECIFICATIONS
Power Output per Channel: 350W @ 2,
4 or 8 Ohms
Number of Channels: 1
Total Harmonic Distortion: 0.3%
maximum harmonic distortion at any power level from 250 milliwatts to rated
power, 20Hz to 20,000Hz
S/N below rated output: 120dB
Dynamic Headroom: 2.4dB
Damping Factor: >25
Wideband
Rated Power Band: 20Hz
to 20kHz
Frequency Response: +0,
-0.5dB from 20Hz to 20,000Hz
+0,
-3.0dB from 10Hz to 70,000Hz
CONTROL
Remote Power Control: Yes
Multi-Channel DB25 Cable: N/A
TUBES: EL509S – 8 pieces EL509S (EL509 SQ) Svetlana Data Sheet
12AX7
– 3 pieces
12AT7
– I piece
GENERAL SPECIFICATIONS
Circuit Configuration: Unity
Coupled
Circuit Design: Vacuum
Tube
Mono Bridge: No
Mono Parallel: No
Output Type
Unity Coupled Output Transformer
Meters: Yes
Meter Light Switch: Yes
Balanced Input: Yes
Front Panel: Machined
aluminum with handles
Illumination: Direct
LED
Chassis Style: Polished
stainless steel
CONNECTIVITY
Speaker Binding Post Type: Patented
Solid Cinch™ Speaker Binding Posts
WEIGHTS & DIMENSIONS
Unit Dimensions: 18"
(45.7cm) x 11-13/16" (30cm) x 21-5/8" (54.9cm) - (W x H x D):
Unit Weight: 121
lbs (54.9 kg)
Shipping Weight: 147
lbs (66.7 kg)
McINTOSH MCX3500 MKII
BROCHURE:
McINTOSH MC-3500 MKII OWNER MANUAL (Read Carefully)
TUBE DATA SHEET EL509/6KG6 SVETLANA (MC-3500 MKII)
TUBE DATA SHEET JJ EL509S (MC-3500 MKII)
TUBE DATA SHEET 6JS6C/6LQ6 (MC-3500 MKI)
MC-3500
MKII SCHEMATIC (Not available)
A
COMPARISON MKII to MKI:
My
MC-3500 page proclaims the McIntosh MC-3500 to be
“the worlds’ best tube amplifier”.
If
so how can the MKII be better?
Q1:
Is the MKII version superior to the original?
A1:
That question must be broken down into its elements of “sound”, dynamic
response, frequency response, aesthetics, fashion, performance, reliability,
maintainability, tube life, engineering design standards, component and
construction quality.
Laboratory
performance tests with resistive loads produce results to industry standards
and are published with the manufacturer’s specifications.
Subjective
results can only be determined by the listener using specific speakers in a
specific listening room, because speakers are the real world load on the
amplifier.
What
can be said with certainty is that MC-3500 MKI amplifiers from the original
production runs between 1968 and 1971 are still performing with excellence more
than 50 years later. It is reasonable to expect the MKII to be at least as
good.
The
MC-3500 MKII is a superb example of engineering excellence, designed and built
with modern electronic engineering knowledge and modern quality components.
It
also benefits from modern solid state control systems that protect critical
components and ensure high reliability.
Q2:
Does it sound “different”?
A2:
Conceptually the answer is likely to be “yes” because the MKII has a different
electronic design that uses just four pre-amp twin-triode driver tubes compared
to five twin-triode driver tubes in the MKI .
Also,
the EL509S tube has different characteristics to the 6JS6G and is likely to use
different metals in its electrode construction.
Fewer
tubes means a shorter signal path with fewer sound modifying circuits – i.e. a
“simpler” audio design
“Difference”
– if any - is a subjective assessment.
Note
also that if different non-McIntosh OEM tubes are installed as replacements –
i.e. substitute brands and versions –
then the sound may change. Hum, microphonics, hiss, rattle and other detractors
may be experienced.
Q3:
Does it sound “better” ?
A3:
That question can only be subjectively decided by each listener, personally and
objectively by using the MKI and MKII side by side in the same room at the same
time with the same signal source and the same speakers – i.e. by switching from
one amplifier to the other. (A/B test)
Note
that if a MKI is in one stereo channel and a MKII in the other, they will sound
different because of the listener’s hearing (left and right ear), different
system dynamic gain and room acoustics.
Q4:
Is it suitable for Rack Mounting?
The chassis width of 17 ½” facilitates
19 inch rack shelf or drawer mounting. The current design offers potential for
a purpose-built industrial model MI-350 equivalent later on incorporating a
full 19 Inch rack mounting front panel and hopefully cooling fans. Note the MC 3500 MKII cooling is via natural
convection.
Minimum ventilation requirements are
specified in the MC-3500 User Manual.
MC-3500 MKII Power Transformer and
Unity Coupled Output Transformer
MC-3500
MKII Front
MC-3500 MKII Rear
MC-3500
MKII Top
MC-3500
MKII Top
MC-3500
MKII Rear Angle
MC-3500
MKII Rear Angle Right
IMPORTANT COPYRIGHT
NOTICE:
Copyright
and intellectual property in these audio amplifier designs and circuits remains
with their original owner.
Their
inclusion in this page as reference materiel is not a license to reproduce or
use them for any purpose contrary to the terms of any original copyright notice
or license.
These
reproductions are presented for historical information and education purposes only
and are not intended for construction.
No
warranty is given of any kind as to fitness for purpose or performance or
rating.
Their
source is not acknowledged here because I am unable to determine their origin.
This
page was last modified 13 December 2022
This
page is located at http://www.oestex.com/tubes/Mac/MC-3500
MKII.html