Cary Audio Design Stereo Amplifier CAD 808 User Manual

CAD 808/Rocket 88 R  
Stereo Vacuum Tube  
Power Amplifier  
INITIAL SET UP  
and  
OWNERS MANUAL  
NOTE: Before installing your new power amplifier, please read this manual carefully as it will inform  
you of the specifications, proper installation procedures and operation procedures. Also included in this  
manual are guidelines on how to properly service and care for your new Rocket 88 R.  
1
 
THEORY OF OPERATION  
For the technically minded, a review of the circuit is in order. Your new Rocket 88 R  
operates in push pull triode Class A mode and in class A/B ultra-linear mode. The  
output stage KT-88 tubes are biased with a negative fixed bias voltage for low distortion  
and maximum output capabilities. In the triode mode, the Rocket 88 R is the most linear  
and yields the most musically satisfying presentation. The output power is 30 watts of  
triode power per channel and 60 watts per channel in ultra-linear mode.  
The output transformers on the Rocket 88 R are the most important component in the  
amplifier. They have been specifically designed by Cary Audio for use in the Rocket 88  
R. We have taken the approach in the output transformer design not too dissimilar to  
the single-ended amplifiers we design and produce. The primary and secondary windings  
on portions of the output transformer are wound in a bifilar process with the two  
inductors interleaving sixteen times. The bifilar wind (two conductors wound at the  
same time) will yield the closest balance and coupling of any design currently utilized in  
vacuum tube output transformers.  
The E/I laminates used are silicone impregnated hipersil steel contributing to the  
extremely low loss of the Rocket 88 R output transformer. The above process is similar  
to the single-ended air-gap design found on the Cary single-ended output transformers.  
A balanced drive signal is applied to the control grids of the KT-88 output tubes from  
the 12BZ7 phase inverter/driver tube. This tube is configured in a dual differential  
network that operates in the following manner: The first section of the dual triode  
12BZ7 tube is direct coupled to the input RCA or XLR jack on the rear apron of the  
amplifier. The drive signal is amplified through this first section in a class A, grid driven  
circuit with the output signal inverted 180 out of phase at the anode and then coupled  
to one half of the push-pull bank of KT-88’s. At the same time the second half of the  
dual triode 12BZ7 is cathode driven in a grounded grid non-inverting class A gain stage  
coupled to the other half of the push-pull bank of KT-88’s. With this network the  
balance is a perfect plus and minus dual drive signal to drive the final KT-88’s in a  
balanced push-pull configuration. The 12BZ7 cathodes are direct coupled to the anode  
(sit on top) of the EL-84 in an infinite current source configuration. The EL-84 stage  
takes the place of the conventional dropping resistor network found in conventional  
gain stages. The power supply transformer is designed to operate at 200% continuous  
commercial service at the full rated 80 watt output level. The high voltage power supply  
section is a full wave center tap configuration (not some cheap voltage doubler as used  
in many competitor’s amps) to a dual PI network with two filter chokes. This high  
voltage section feeds the final output KT-88 tubes. An additional choke, filter network  
serves as the power supply for the 12BZ7 phase inverter tubes. Another supply is the  
negative DC grid bias and current source voltage for the EL-84’s.  
A great deal of attention during design of your new Rocket 88 R was concentrated on  
the “overload recovery” ability of the amplifier. The ability of an amplifier to instantly  
recover from clipping is much more important than is commonly believed. In the output  
power war of some amplifier manufacturers, the mentality is focused on high and then  
 
even higher overall power output levels to try to solve the clipping problem. In reality,  
we believe the most critical aspect is how fast a recovery an amplifier can achieve after  
overload. With the incredible dynamics range of live and recorded music, even 2,000  
watts of power is potentially not enough. Most of the music being listened to in an  
average home listening room is only requiring about 1-3 watts of power. It is on the  
transients of loud low frequency program material that tremendous signal voltages will  
appear at the input of the amplifier. It is in this situation that the overload recovery  
ability of an amplifier is of critical concern.  
The Rocket 88 R extols its merits in the ability to handle transients and instantaneously  
recover from brief or even extended overloads. The Rocket 88 R will overload  
symmetrically at any frequency in the audio bandpass. It will also yield faithful  
reproduction of extremely low frequencies at full output levels. The power transformer,  
the power supply regulation and the output transformer design and careful shaping of  
the overall frequency response curve all play a very important part in the ability of the  
Rocket 88 R to recover quickly when overloaded. If one were to monitor the high  
voltage rail voltage of the Rocket 88 R during soft and also loud music passages it would  
be found there is no more than a volt or so change from soft to loud passages.  
Another technical feature of your new Rocket 88 R amplifier is unconditional circuit  
stability. The Rocket 88 R maybe operated with no load (without speaker) without  
damage to the amplifier, output transformer or tubes.  
Operating the Rocket 88 R stereo amplifier is a simple procedure since each unit is  
designed for long term stability in virtually any home operating situation. Therefore, if  
the unit is operated outside the parameters outlined in this owner’s manual, damage  
may result. Please read this manual carefully before putting your new Rocket 88 R  
amplifier in operation.  
The following definitions are applicable to this manual. These definitions must be  
followed explicitly.  
WARNING!  
HAZARD PRESENTS PERSONAL INJURY OR DEATH  
Caution  
EQUIPMENT DAMAGE MAY OCCUR BUT NOT PERSONAL INJURY  
Note  
Proper performance of the amplifier cannot be ensured if disregarded  
Specifications: Rocket 88 R Stereo Power Amplifier  
 
DIMENSIONS:  
WEIGHT:  
10”W x 18”D x 6”H (25.4 cm x 45.7 cm x 15.2 cm)  
45 Lb.. (20.4 kg)  
CIRCUIT TYPE:  
POWER OUTPUT:  
Push-Pull Triode Class A, Ultra-linear Class A/B  
30 Watts Triode, 60 Watts Ultra-linear  
INPUT SENSITIVITY: 1.2 volt for full output  
INPUT IMPEDANCE: 150,000 ohms  
NOISE AND HUM:  
-87 dB below rated output  
FREQUENCY RESPONSE: 10 Hz to 82,000 Hz + 0, -3.0 dB @ 1 watt  
TUBES:  
2-12BZ7 Dual Triode, Phase inverter, gain stage (12AX7, 12AY7)  
2-EL-84 Current source (or 6BQ5)  
4-KT-88 Output tubes (or EL-34, 6550, KT-66, KT-77, KT-90)  
2-1629 Green ‘Cat Eye’ indicator tubes  
TRANSFORMERS:  
RESISTORS:  
1-EI laminated core power transformer  
2-Special interleaved output transformer  
3-Filter Chokes  
200% duty cycle on all transformers  
1.0 % metal film  
CAPACITORS: Polystyrene and polypropylene (oil filled optional)  
POWER SUPPLY  
CAPACITORS:  
2-560 mFD @ 450 VDC  
3-10 mFD Film and foil @ 600 VDC  
1-47 mFD @ 450 VDC  
AC CORD:  
Detachable 3 conductor 14 gauge  
AC POWER  
REQUIREMENTS:  
117 volts or 240 volts AC 50/60 Hz  
300 watts operate  
WARM-UP TIME:  
BREAK-IN PERIOD:  
FINISH:  
3 minutes  
100 hours of music playing time  
Black Epoxy powder coat, Anodized Aluminum face plate  
Specifications are subject to change or improvement without notice or obligation.  
 
Front Panel Features  
AC-ON ROTARY SWITCH: Turns AC power on in the “on” position.  
GREEN ‘CAT EYES’: Indicate audio power output, fully closed eye at maximum power.  
Rear Apron Features  
INPUT: Signal input connection via either RCA or XLR shielded interconnect cables. Pin  
#1 is the shield, #2 positive phase signal on XLR connector.  
INPUT SWITCH: Push in direction of the type of input to be utilized, RCA or XLR.  
OUTPUT: The 5-way speaker binding posts provide the output to the speaker system.  
Red posts = positive connections, Black posts = negative connections.  
AC: 3 conductor detachable power cord  
AC POWER FUSE: Use only a 3 Amp, 250 V ‘slow blow’ fuse.  
Rocket 88 R Top Panel  
BIAS LED: These indicators will light when there is the proper bias voltage operating for  
the EL-84 current source tubes along with the proper DC grid bias voltage for the final  
output tubes. If these LED’s fail to light, discontinue use and place a call to the Cary  
Audio service advisor.  
TRIODE/UL SWITCH: These switches change the operation of the Rocket 88 R between  
triode, class A, to Ultra-Linear, class A/B. These two switches maybe switched during  
operation. If one channel switch is in the opposite position from the other a channel  
imbalance will occur. There is 1 dB more gain in the Ultra-Linear position.  
BIAS: This screw driver adjustment is used to set the proper DC bias current for the  
KT-88 output tubes. REMEMBER, THIS ADJUSTMENT MUST BE ADJUSTED WITH A  
METER READING DC mA CURRENT!  
TUBE FUSE: This is a ‘fast blow’ _ amp fuse to protect the Rocket 88 R amplifier should  
an output tube fail.  
CAUTION  
USE OF ANY OTHER PROTECTION FUSE CAN DAMAGE UNIT  
BIAS JACK: This _” two conductor jack is used to plug in the supplied meter cable. This  
is a shorting jack. In other words, when the plug is removed the circuit is automatically  
 
connected. You may plug in the test plug while the unit is playing. You may hear a slight  
click in the loudspeakers when inserting or removing the plug. This is normal.  
SPEAKER: These switches change the 4 and 8 ohm output taps from the output  
transformer to the speaker posts on the rear of the amplifier. They maybe operated  
with the amplifier in operation.  
EYE TUBE: There are two of these. They set the green eye tube intensity. You may set  
to any desired level for your listening room. The control does not change any of the  
sonic characteristics of the amplifier.  
INSTALLATION  
This section describes the unpacking and installation procedures for the Rocket 88 R  
amplifier.  
WARNING!  
MAKE NO ATTEMPT TO PUT THE AMPLIFIER IN SERVICE WITHOUT  
THE BOTTOM PLATE ATTACHED-CONTACT WITH VOLTAGE INSIDE  
THE CHASSIS OF THE ROCKET 88 R CAN BE FATAL!  
Unpacking  
All shipping containers have been specifically designed to protect their contents and  
special care has been taken to prevent damage under normal shipping conditions.  
Mishandling should be evident upon inspection of the shipping container. If damage is  
found after visual inspection, take care not to destroy the evidence. If necessary,  
document the damage with photographs and contact the transport carrier immediately.  
Carefully remove your new Rocket 88 R amplifier from its packing carton, and examine  
it closely for signs of shipping damage. It is recommended to save all original packing  
cartons to protect your amplifier from damage should you wish to store it or ship it for  
after sales service.  
Warranty Card  
Fill out the enclosed warranty registration card and return it to Cary Audio Design  
within 10 days of original purchase. Keep your original sales slip with the packing  
cartons should you ever need it for reference. Failure to register warranty will limit the  
warranty to one year.  
 
Amplifier Placement and Set Up  
In general, the location of your new Rocket 88 R amplifier is not critical. The best  
placement in your system is near the speaker system with short lengths of speaker  
cables. Certain precautions must be taken to ensure optimum performance. Avoid hot  
locations near radiators or other heating units. Keep the top of the Rocket 88 R clear of  
books, paper, or other equipment to protect against overheating.  
Power Requirements  
The Rocket 88 R is designed to operate from house current mains. The design voltage is  
117 VAC at 50/60 Hz. (Export models are 117 or 240 VAC at 50/60 Hz, depending on  
destination.)  
Cables  
The speaker cables to the speakers can be any convenient length your setup requires.  
Please choose speaker cables of sufficient size to preserve the outstanding performance  
capabilities of your Rocket 88 R. Heavy gauge #14 AWG wire is suitable for distances up  
to 10 feet; #12 AWG for 25 feet. Our recommendation for best sound is to place the  
Rocket 88 R in between the stereo pair of loudspeakers. Use heavy duty loudspeaker  
cables with a length to reach from the Rocket 88 R to the speakers. Avoid long lengths  
that have excess slack. If your loudspeaker has the facility for bi-wiring, then by all  
means use separate cables or bi-wire speaker cables. Your Authorized Cary Audio Design  
Dealer will have proper speaker cable in stock for this purpose.  
Signal input connection is made via the input jacks on the rear of the amplifier located  
next to the output binding posts. The interconnect cables from the output of the  
preamplifier can be any convenient length your setup requires. Through the years we  
have found that using tube amplifiers like the Rocket 88 R, it is better to have short  
loudspeaker cables and long interconnect cables to the preamplifier. The choice of a  
high quality shielded interconnect cable is important. Once again, your dealer will have  
the proper cables in stock for this purpose.  
The tubes used in your new Rocket 88 R have gone through a 48 hour burn in process  
and testing with your individual Rocket 88 R. They are matched and labeled on the tube  
boxes. Look at the top panel of the Rocket 88 R for the proper placement of the tubes.  
Be careful to insert the tubes in the proper sockets with the key way in order. At the  
end of this manual you will also see a block diagram of the tube layout. Your new  
Rocket 88 R is ready for operation after the speaker, interconnect cables and the  
vacuum tubes have been installed.  
AC Power Switch  
Simply turn the AC power to the ON position (the red bias LED’s will light). After 30 to  
60 seconds observe that all tubes are lit (filaments) and the green eye tubes are  
 
illuminated. Should you not observe the above conditions, turn off the amplifier and  
check the power cord and AC socket.  
Triode/Ultra-Linear Switch  
On the top of the chassis behind the KT-88 output tubes is located a chrome handle  
switch. With the handle pushed to the rear of the amplifier the mode of operation is  
ultra-linear. In the forward position the mode will be in triode class A mode. This set of  
switches maybe switched during listening. A slight click maybe heard in the  
loudspeakers. This is normal. Usually the triode position will provide plenty of power  
and is the most preferred position by most audiophiles and the designer of the Rocket  
88 R.  
Bias Setting  
Your new Rocket 88 R bias adjustment has been factory set prior to shipping. Please  
keep in mind that the bias will vary from location to location depending on the AC line  
voltage. The design of the Rocket 88 R is such that you may start listening with the  
factory set level. DO NOT TURN THE BIAS ADJUSTMENT SCREW WITHOUT  
WATCHING LEVELS ON A DC mA CURRENT METER! The type of meter used must  
be a DC current meter or a volt ohm meter with a DC milliampere current scale. A  
digital multi-meter is very inexpensive and available at a local Radio Shack or ACE  
hardware store.  
Included with your shipment of the Rocket 88 R is a black and orange patch cord with a  
_” male plug and two clips. This is the bias adjustment cable. To check and/or set the  
bias simply place the red clip lead on the positive meter lead. The black clip lead will  
hook up to the black negative lead of the test meter. The meter must be placed in the  
DC current mode. If the meter has a selectable scale use the one that measures 0 to  
300 ma DC current. With the Rocket 88 R turned on and operating for about 10  
minutes you will have the resting current level indicated. This measurement should be  
done without any music playing. A nominal level of 200 milliampere (mA) is standard for  
the Rocket 88 R. If the level is lower, advance the bias adjustment to the clockwise  
direction. Higher readings, turn the bias control to the left, counterclockwise direction.  
After you have established a 200 mA reading simply pull out the plug from the bias jack.  
You may hear a slight click in the speaker. This is normal.  
Bias levels will change with time of day and power usage in your home. In fact during the  
summer months when the air conditioner is running you may have less AC line voltage  
available and in turn the bias will be slightly lower. This is not critical. In fact the Rocket  
88 R is designed to operate in the range of 180 to as high as 240 mA DC current. The  
best sound will generally be produced in the 195 to 225 mA region. You may wish to  
experiment if you desire. NEVER ADJUST THE BIAS SETTING WITH A VOLTMETER  
SET TO THE VOLTAGE POSITION!  
 
Break In Period  
The tubes, capacitors and output transformers take approximately 100 hours of music  
playing to fully settle in for peak performance. The Rocket 88 R will sound good fresh  
out of the box. However, after the first couple of hours you will notice increased depth  
and tighter bass. This break in period is normal for tube based components and with  
high performance audio components.  
SERVICE AND CARE  
WARNING!  
MAKE SURE AMPLIFIER IS UNPLUGGED FROM AC MAINS  
Care and Cleaning  
The chassis of the Rocket 88 R may be cleaned with a soft rag and Windex (or a similar  
window cleaner). A dry feather duster is also good for cleaning the chassis.  
Tube Replacement  
If it becomes necessary to replace the tubes in the Rocket 88 R amplifier, a matched set  
of tubes of the same brand should be used. A new tube kit is available from your Cary  
Audio dealer. You should get 2-5 year’s from the output tubes and even more years of  
use from the 12BZ7 and EL-84 tubes with everyday usage.  
Factory Service  
Careful consideration has been given to the design of your Rocket 88 R amplifier to  
keep maintenance problems to a minimum. However, it is possible that some problems  
may arise which cannot be cured by tube substitution. At this point we suggest that you  
contact our Customer Service Department from 1 to 5 PM East Coast Time, phone  
number 1-919-355-0010, to describe your problem in detail. Do not return the amplifier  
to the factory without a return authorization number from the Customer Service  
Department. Cary Audio Design will assume no responsibility if the transportation  
company refuses to pay a damage claim due to improper packing or lack of insurance  
should the unit be lost in shipment.  
Cary Audio Design  
1020 Goodworth Drive  
Apex, North Carolina 27539  
Tel: 919-355-0010  
Fax: 919-355-0013  
 
WARNINGS!  
MAKE NO ATTEMPT TO PUT THE ROCKET 88 R INTO SERVICE  
OUTSIDE OF THE CABINET. CONTACT WITH THE HIGH  
VOLTAGES FOUND INSIDE THE UNIT CHASSIS CAN BE FATAL!  
COMPLETELY REMOVE THE AC POWER PLUG FROM THE WALL  
AND ALLOW 30 MINUTES FOR THE HIGH VOLTAGE  
CAPACITORS TO DISCHARGE THROUGH THE BLEEDER  
RESISTORS BEFORE YOU ATTEMPT TO CHANGE THE TUBES OR  
TO CLEAN THE INSIDE OF THE AMPLIFIER!  
CAUTIONS  
NEVER REMOVE or INSERT AC PLUG WHEN THE UNIT IS ON OR  
THE AC POWER SWITCH IS IN THE “ON” POSITION.  
OBSTRUCTION OF THE TOP PORTION OF THE ROCKET 88 R  
WILL RESULT IN THE TUBES OVERHEATING.  
*PLEASE OBSERVE ALL THE SAFETY DIRECTIONS IN THIS OWNER’S  
MANUAL TO AVOID RISK OF PHYSICAL HARM!*  
 

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