Ceriatone 50W and 100W amplifiers
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1. Yes this does pose someone of a problem While it is not recommended and highly dangerous most individuals adjust these trimmers while the amplifier is on so they can more easily monitor changes and find their preferred endpoint If you find yourself in this position and unwilling to follow recommended safety guidelines please follow these warnings and recommendations O o00o000 O Use only non conductive screwdrivers Do not adjust trimmers with your guitar strapped on Do not wear loose clothing or jewelry Adjust only in proper lighting Have a clear idea what trimmer you are going to adjust and how you are going to adjust it Take your time If you need to measure values with your DMM keep the black probe plugged into the black bias probe when measuring with the red probe keep your opposite arm bent behind your back measure from above holding the probe at an angle can cause arcing and shorts KEEP PROBE CLEAR OF ALL POINTS YOU DO NOT WANT TO MEASURE Again Ceriatone is not responsible for any damages or injuries resulting from user adjustments Do need to use matched power tubes Although not necessary matched power tube sets are recommended for best results Do I need to use a matched and balanced phase inverter tis not necessary Feel free to experiment with different tubes of the same type in your OTS though i ESF lve read that the components used in this type of amplifier are really important2. 6 7 8 Turn POWER AMP MASTER control to about 9 00 clock face f a j 9 Set front panel BRIGHT and MID BOOST switches in the down position 10 Set front panel ROCK JAZZ switch in the up position ROCK 11 Set rear panel MAINS switch in the ON position with adjacent switch to STANDBY for 30 seconds to allow tube filaments to warm up 12 Set rear panel OPERATE STANDBY switch to OPERATE 13 ROCK 3 FRONT PANEL CONTROLS On the front panel of the Overtone Special you can see thirteen items of interest From left to right 1 INPUT instrument jacks FET and NOR 2 VOLUME control 3 BRIGHT two way toggle switch 4 MID BOOST two way toggle switch 5 ROCK JAZZ two way toggle switch 6 TREBLE control 4 MIDDLE control BASS control LEVEL OVERDRIVE control RATIO OVERDRIVE control MASTER POWER AMP control PRESENCE POWER AMP control T 8 9 1 1 1 13 INDICATOR LED 0 1 2 3 INPUT jacks provide two tonal options First FET routes your signal through a high input impedance low output impedance JFET gain stage before hitting the first triode tube stage Originally the FET input was designed for piezo pickups without an onboard preamplifier Since then it has provided players a unique option for fine tuning their tone Second NOR is a typical 1megaohm input impedance as seen on most guitar amplifiers In most circumstances NOR will provide the best results in cle
3. What is inside my OTS We use a combination of parts custom made for us to our specifications power transformer output transformer choke high temperature low ESR electrolytic capacitors and those used in the original amplifiers Vishay Dale RN65 precision metal film resistors 1W carbon film resistors SBE 6PS polyester film capacitors high quality ceramic disc capacitors Belton tube sockets and Alpha potentiometers We prefer high quality enclosed Cliff built in the UK jacks to the open style Switchcraft jacks used in the originals and many clones Finally we occasionally use NOS components from our vast surplus parts collection in locations they work well and complement the voicing or enhance the performance of the amplifier l like to use rack mounted multieffects units What is the output level straight from the EFFECTS LOOP SEND jack 10dB or 4qB While not exact 10dB is a better approximation than 4dB The actual output level will depend on your settings particularly the volume controls 4dB is usually reserved for recording P A equipment with balanced connections This all seems kind of complicated can you tell me where all of these controls are in the preamp so have a better idea how to set up my amplifier Clean and OD Stage 1 Tonestack Input Vol Clean and OD Stage 2 ROCK JAZZ BRIGHT MID BOOST PAB
4. 6GC 100W version only n 1c In this diagram we have color coded three features for simplicity 1 Green arrows red probe jacks 2 Yellow arrow black probe jack 3 Blue arrow bias adjustment potentiometer shaft To measure your power tube bias carefully follow these steps with the amplifier in OPERATE and connected to a speaker load not doing so may damage your ampilifier 1 Turn on a digital multimeter DMM and set it to read millivolts mV in the 100mV range this will vary from DMM to DMM 2 Plug a black probe into the color coded jack on your DMM and do the same for a red probe 3 Insert the black probe tip into the black probe jack blue arrow This is GROUND in the OTS amplifier 4 Insert the red probe tip into the red probe jack green arrow on the far left This measures bias for V4 Right down the value your DMM reads You might expect a value between 35mV and 45mV 5 Repeat for the next red probe jack to the right V5 again one more to the right V6 and finally that on the far right V7 NOTE 50W heads will have two red probe jacks From this view the probe jack on the left is for V4 and on the right for V5 ee E a Okay now I ve measured my bias Now what To calculate bias there are two pieces of information you need to know your amplifier s power tube plate voltage and the published value for maximum plate dissipation for the power tubes used in your amplifier To save you some time and
5. Ceriatone Overtone Special JOW and UUW amplitiers 4 E User s Manual Thank you for the purchase of your Ceriatone Overtone Special guitar amplifier Here we hope to explain how best to use your new amp Table of Contents 1 About ING Overt ne SCC lal ses sepspsnceeceaceacaaanscaacaasdessssssssssssesssesutyevasvis yeni EEEE EEEE eaaet niti page 2 2 QUICK SEL o O E EES ARRARATS page 3 IN PEOML Panel COMO S scree alee sae A EET page 4 4 Rear Panel CONN fasts ras5 sana teananadevanseene aoe aeccne taneeeten aaa eennaaaeeaaaaaeee arent coe oa vance aanber page 7 5 Tube compliment and external bias jacks and adjustment ccccccccccceeeeeeeeeeeeeeeeeeeeeeeeseeeeeeeeeees page 10 6 Freguently Asked QUESTIONS 4c 6 6 voce E esse easel lal lll ll iis else page 14 1 About the Overtone Special 100W and 50W amplifiers The release of our Overtone series of amplifiers has been overwhelmingly popular and the support of customers such as you has instigated the release of currently 8 different versions within the series In addition we have released the Klein ulator and C lator effects loop interfaces specifically for use with our Overtone amplifiers We have been pleased to provide many players access to our unique take on these legendary amplifiers In particular we have a special place in our heart for our first foray into this type of amplifier the original Overtone Special aka OTS The OTS is our unique t
6. IMPEDANCE three way rotary selector Set this selector to the position that matches the impedance of your speaker cabinet NOTE if you are using two speaker cabinets in parallel ex two 16 Ohm cabinets set the impedance selector to half that of a single cabinet in this case 8 Ohms EFFECTS LOOP RETURN instrument jack can be used to directly interface the power amp of the OTS thereby bypassing the preamp and using the amplifier as a power amplifier Conversely this is usually used as the RETURN of the effects loop Plug the output of your effects unit or interface device ex C lator Klein ulator into this jack using 4 instrument cable The effects loop in the OTS amplifiers are all passive like the originals i ESS EFFECTS LOOP SEND instrument jack can be used to directly interface the preamp of the OTS thereby bypassing the power amplifier and using the OTS as a preamp Conversely this is usually used as the SEND of the effects loop Plug the input of your effects unit or interface device ex C lator Klein ulator into this jack using instrument cable The effects loop in the OTS amplifiers are all passive like the originals OVERDRIVE two way toggle switch manually switches between clean and overdrive channels If you are using the foot pedal set this in the PEDAL position If you are not using the included foot pedal the toggle switch in the PEDAL position switches the OTS to OVERDRIVE mode In the
7. MANUAL position the OTS is in CLEAN mode PREAMP BOOST aka PAB two way toggle switch manually switches between boosted and normal configurations In this series of OTS amplifiers the PAB accentuates midrange frequencies and attenuates low frequencies making it great for cutting through during a solo Engaged you will also notice an increase in gain and distortion characteristics If you are using the foot pedal set this in the PEDAL position If you are not using the included foot pedal the toggle switch in the MANUAL position switches the OTS to PREAMP BOOST mode In the PEDAL position the OTS is in normal mode NOTE if the FOOT PEDAL is plugged in but the PAB and or OVERDRIVE toggles are in MANUAL the foot pedal LED indicators will still light up but functions will not be switched For the FOOT PEDAL to function PAB and OVERDRIVE rear panel toggles MUST be in PEDAL FOOT PEDAL 5 pin DIN female jack is used to connect the foot pedal to the amplifier Use the foot pedal to control the OVERDRIVE and PREAMP BOOST modes Red LED indicates OVERDRIVE and Green LED indicates PREAMP BOOST 5 TUBE COMPLIMENT AND EXTERNAL BIAS JACKS AND ADJUSTMENT 50W Overtone Special 100W Overtone Special From left to right V1 12AX7 ECC83 clean and overdrive stages 1 and 2 V2 12AX7 ECC83 overdrive stages 3 and 4 V3 12AX7 ECC83 phase inverter for power amplifier V4 6L6GC V5 6L6GC V6 6L6GC 100W version only V7 6L
8. ake on the 80s style of a certain Californian amp Many refer to this model as a high plate non HRM model with the Skyline tone stack This design is known for its fat and harmonically rich clean tone and a complex fluid overdrive tone with a unique push in the midrange frequencies Some players feel this is the most playable version of the OTS amplifier possibly due to a pleasing compression and forgiving touch on the overdrive channel f y e o ao While our work could not have been possible without the gracious information shared over the last decade in the public domain we hope you appreciate our modifications component selection and construction techniques Most of all we hope the OTS becomes an integral part of your tone equation to exhilarate your playing and music Rock on Nik Azam 2 QUICK SETUP for instant gratification Plug your guitar using a 1 4 instrument cable into the NOR input on the lower left of the front panel Plug a suitable power cable from the OTS s rear panel MAINS cable inlet to your wall power receptacle Plug the OTS into your speaker cabinet using 1 4 speaker cable Set the IMPEDENCE selector to the match the impedance of your speaker cabinet Set the OD and PAB switches on the rear panel in the PEDAL position Set all rotary controls on the front panel to 12 00 clock face 1 2 3 4 5 Plug the footswitch cable into the FOOT PEDAL jack on the rear panel of the amplifier
9. an and overdrive modes VOLUME adjusts the signal strength coming out of the tonestack and going into the second tube stage Think of this as a gain control primarily for your clean channel but note it will impact the overdrive mode as well BRIGHT is a high frequency boost that can be used to add sparkle to your tone in both clean and overdrive modes This high frequency boost is more prominent as VOLUME is turned down With the toggle switch in the UP position BRIGHT is on In the DOWN position BRIGHT is off MID BOOST is a midrange frequency boost You can use this to add fatness to your clean or overdrive tones or even make single coil guitars sound thicker and less scooped We particularly like MID BOOST with the overdrive mode With the toggle switch in the UP position MID BOOST is on In the DOWN position MID BOOST is off ROCK JAZZ adjusts the overall frequency response and voicing of the amplifier ROCK has a fatter midrange and a deeper spongier bottom end You might find ROCK more familiar territory JAZZ tightens up the bottom end and adjusts the contour of eS the midrange giving the amplifier more of a hi fi response Experiment with both as great sounds rest in each With the toggle switch in the UP position ROCK is on In the DOWN position JAZZ is on TREBLE adjusts the high frequency response for both clean and overdrive modes At near maximum settings you may also notice an increase in gain MIDRANGE adjust
10. energy here are those two values 440 450VDC 30W Approximate plate voltage for OTS series amplifiers Maximum plate dissipation for 6L6GCs and now some math The formula for calculating bias is as follows maximum plate dissipation oo __ _ x percent of maximum dissipation x 1000 bias current mA amplifier plate voltage In most cases amplifiers are biased between 50 and 75 dissipation We bias the OTS to approximately 35mV 40mV reading on a DMM An example is as follows 30W x 55 x ZA0VDC 55 x 1000 about 35 40mA You might wonder why your DMM is set to millivolts and not milliamps simply we have a 1 Ohm resistor placed between your probe jacks and ground to convert a current reading to a voltage reading That way a bias current of 35mA measures as 35mV on your DMM NOTE Only set your DMM to mV for measuring bias on the OTS amplifiers Not doing so may damage your DMM e j Now that you know how to calculate bias all you need to do is 1 Follow steps 1 5 on page 11 2 Calculate what bias voltage reading you will set your tubes to in this case we will use 35mV 3 Insert your red probe in the probe jack of the power tube reading somewhere in the middle bias measurement of your power tubes variation in bias measurements from tube to tube is to be expected so selecting one measuring in the middle will approximate bias for all tubes Turn the bias potentiometer shaf
11. his is part of the original design that controls the amount of signal sent into the first stage of the overdrive circuit Different settings on this control can yield dramatically different results to the tone amount of gain and feel of the overdrive channel The OD trim sounds like fun to play with Can adjust it myself Well yes it can be fun to play with However adjusting it requires you to remove the chassis and adjust a small trimpot that is near high voltages We highly recommend the use of a non conductive rubber screwdriver and only adjust the trimpot when the amplifier is not powered and disconnected from the wall outlet DO NOT ADJUST THE OD TRIMMER WHILE THE AMPLIFIER IS ON Note that the power supply capacitors in the amplifier can will still store charge and you can still be bitten by 450VDC even though the amp isn t connected to the wall Adjust the OD TRIMMER only at your own risk The picture on the following page shows a few of the inside of the chassis facing the input jack side The OD trim is indicated by the green arrow Insert the non conductive screwdriver into the trimmer make a small adjustment and relisten We set the trimpot at about 10 00 to 11 00 o clock viewing the trimmer from the input jack side down to the indicator LED side You can also measure this by setting your DMM to the resistance measurement about 100K and plug the black probe into the black bias probe jack Place the red probe on the ce
12. metimes function fine without a buffer before them In addition some of these rack mounted effects can pad the volume they receive preventing it from overloading Pedals do not have proper input impedance or padding ability and therefore do not play nicely For best results an effects loop interface like the C lator or Klein ulator should be used with the OTS amplifiers These units prevent impedance mismatching as well as provide the ability to pad down the volume sent to the effects units hence preventing any overloading Can I substitute different tube types for the 12AX7 ECC83s or 6L6GCs Although you can try 12AT7s 12AU7s 5751s without any harm the design is optimized for 12AX7s and are therefore the only recommended tube in the preamp positions Usage of other power tubes ex modern 6V6s like Electro Harmonix JJ may be possible but please first consult Ceriatone Amplification or your local competent amplifier technician What settings do you recommend Try setting all controls at 12 00 and adjust MASTER to a suitable volume n 1 have the foot pedal plugged in but it s not switching functions The LEDs on the foot pedal still light up though Make certain the rear toggles for OVERDRIVE and PREAMP BOOST are in the PEDAL positions lve read about something called an OD trimmer inside of the amp Does the OTS have it and what does it do Yes the OTS amplifier has an OD short for overdrive trimmer T
13. nter lug wiper of the trimmer Less resistance less gain More resistance more gain ff i revit yY i Inside chassis view of OTS 100W Green arrow indicates OD trimmer lve read about something called a PI trimmer inside of the amp Does the OTS have it and what does it do Yes the OTS amplifier has a PI short for phase inverter trimmer This is part of the original design that controls the balance of plate voltage between the two triodes of the phase inverter Different settings on this control are very subtle and are typically monitored with an oscilloscope and not ears e _ Hmm the PI trimmer doesn t sound as fun Oh well still want to play with it Is that okay Again before we continue realize that you are adjusting PLATE VOLTAGE In this case your screwdriver is about a millimeter away from about 300VDC DO NOT adjust this trimmer with the amplifier on Furthermore measurement of the progress of the adjustment is tricky because you are measuring near 300VDC We highly recommend the use of a non conductive rubber screwdriver and only adjust the trimpot when the amplifier is not powered and disconnected from the wall outlet DO NOT ADJUST THE PI TRIMMER WHILE THE AMPLIFIER IS ON Note that the power supply capacitors in the amplifier can will still store charge and you can still be bitten by 450VDC even though the amp isn t connected to the wall Adjust the PI TRIMMER only at your own
14. o way toggle switch 10 PREAMP BOOST two way toggle switch 11 FOOT PEDAL 5 pin DIN female jack ee E a MAINS IEC cable inlet plug a suitable IEC power cable into this inlet to power your amplifier 3 AMP 2 AMP slow blow fuse used to protect your amplifier from voltage spikes or excessive current draw Replace only when necessary 3A is used for amplifiers used with a 120VAC country supply and 2A is used with 240VAC MAINS two way toggle switch powers the OTS on and off With the toggle switch in the UP position the OTS is ON In the DOWN position the OTS is OFF OPERATE STANDBY applies high voltage to the vacuum tube anodes and screen grids during use of the OTS To ensure long tube life first power the unit on with the toggle switch in STANDBY position for approximately 30 seconds Then switch to OPERATE to use the OTS With the toggle switch in the UP position the OTS is in OPERATE mode In the DOWN position the OTS is in STANDBY mode SPEAKER OUTPUT speaker cable jacks Use a 1 4 speaker cable to connect your speaker cabinet to the amplifier using these jacks If you use one speaker cabinet use the jack labeled MAIN If you want to run two cabinets in parallel connect the second cabinet to the amplifier using the jack labeled EXTENSION NOTE never turn your amplifier to OPERATE mode without connecting the amplifier to a speaker cabinet or suitable dummy load Failing to do so may damage your amplifier
15. risk On the next page there are three arrows The ORANGE arrow is the PI trimmer The GREEN arrow is the test point for measuring the plate voltage at V3A The BLUE arrow is the test point for measuring the plate voltage at V3B To measure the plate voltage at V3 your amplifier must be in OPERATE mode and connected to a dummy preferable or a speaker load Turn the MASTER down to minimum Set your DMM to the VDC measurement between 200VDC and 1000VDC and plug the black probe into the black bias probe jack Place the red probe on the bare wire at the tip of the GREEN arrow Write this value down this is your V3A plate voltage Now plate the red probe on the bare wire at the tip of the blue arrow Write this value down this is your V3B plate voltage Best results are typically with V3A being about 6VDC higher than V3B To increase the voltage to V3A or V3B turn the trimmer with a non conducting screwdriver toward the test point you want more voltage on ONLY ADJUST WHEN THE AMPLIFIER IS OFF AND DISCONNECTED FROM THE WALL n 1 Blue arrow indicates V3B test point Green arrow indicates V3A test point Adjusting those trimmers sounds intimidating Am missing anything if don t experiment with them Absolutely not We adjust each trimmer to ensure the best results for each amplifier leaving our shop r 1 How am supposed to monitor changes in tone after adjusting internal trimmers while the amplifier is off
16. s the mid frequency response for both clean and overdrive modes BASS adjusts low frequencies in your amplifier for both clean and overdrive modes LEVEL OVERDRIVE adjusts the amount of gain and in turn distortion in the overdrive mode RATIO OVERDRIVE serves a sort of volume control for the overdrive channel However just like this version of the original amplifier there are not individual master volume controls for the clean and overdrive channels Instead the RATIO control serves to balance out the volume of the overdrive channel with the clean channel MASTER POWER AMP sets the overall volume of your amplifier PRESENCE POWER AMP adjusts the high frequency response of the power amplifier using negative feedback Use this control to add sparkle and clarity to your tone INDICATOR will illuminate when the OTS is powered by turning the rear panel MAINS toggle switch to the ON position If INDICATOR does not turn on check your power cable connections and then the 2A slow blow fuse on the rear of the unit 4 REAR PANEL CONTROLS On the rear panel of the Overtone Special you can see eleven items of interest 1 MAINS IEC cable inlet 2 3 AMP 2 AMP slow blow fuse 3 MAINS power two way toggle switch 4 OPERATE STANDBY two way toggle switch 5 SPEAKER OUTPUT speaker jacks 6 IMPEDANCE three way rotary selector 7 EFFECTS LOOP RETURN instrument jack 8 EFFECTS LOOP SEND instrument jack 9 OVERDRIVE tw
17. t SLOWLY until your DMM reads 35mV Wait 1 minute Recheck all power tube bias measurements Readjust bias potentiometer shaft if necessary A FEW COMMENTS ON BIASING Due to the nature of vacuum tube amplification there are inherent risks when biasing your amplifier Extremely high voltages are present and vacuum tubes reach high temperatures during use The risk of electrical shock and or skin burns should ALWAYS be kept in mind Therefore bias at your own risk and only while paying attention and taking all precautionary measures Biasing should only be done on a clean workbench with no distractions Do not wear loose clothing or any jewelry Take your time and think carefully before each step Even though the bias test points and adjustment is external to reduce risk of electrical shock all precautions must be taken while biasing Again bias at your own risk Ceriatone Amplification is not responsible for any damages or injuries resulting from user biasing 8 6 FREQUENTLY ASKED QUESTIONS How do I hook up this thing See Section 2 beginning on page 3 When plug effects into the effects loop my tone noticeably changes Sometimes the effects don t sound quite right What s the deal Generally what you re hearing is a significant mismatching of impedances and or an overloading of the effect unit itself Most rack mount units have different input impedance than pedals and thus can so
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