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1、RadioFans.CN 收音机爱 好者资料库 1 GIBSON GOLD TONE GA-15 CIRCUIT DISCRIPTION Please refer to circuit diagram for DC voltages and other information INPUT SECTION AND PREAMP SK1 is the guitar input to the preamp. C3 is to block any DC from the input that may unintentionally be present, this would otherwise ch
2、ange the bias point of the first valve stage. V1a is the first gain stage and is configured as a cathode bias, common cathode, voltage amplifier with bypassed cathode resistor for increased gain. R6 and C6 give a slight presence lift and the frequency of the Bright effect is set by C7, which, when s
3、witched in, is across pins 2 and 3 of RV1 (Volume). Obviously connected like this the amount of brightness added will decrease as RV1 is turned up. V1b is the second gain stage configured similar to before, C9 is added across the anode resistor R8 to smooth out the top end. The Tone network is passi
4、ve and controlled by RV2. This is a dual ganged potentiometer, one part of which effectively controls the mids (RV2B) while the other part inversely controls the treble (RV2A). R34 and R35 act as a potential divider to lower the signal sent into the phase splitter. POWER STAGE The phase splitter (V2
5、A and V2B) is a differential input splitter which produces the two anti- phase signals necessary to drive the push pull output stage. V3 and V4 are the two EL84 output valves connected as a push pull, cathode biased class A power amplifier. The quiescent current is set by R24, which is bypassed by C
6、19 for extra gain. OUTPUT TRANSFORMER AND SPEAKER CONNECTIONS The output transformer has secondary taps for 16 and 8. The 16 tap is used to drive the External Speaker Output, SK2. When a jack plug is inserted into SK2 the internal speaker is disconnected. RadioFans.CN 收音机爱 好者资料库 2 The two LINK posit
7、ions are provided on the PCB so that different impedance internal speakers can be used in production. Depending on whether the internal speaker is 16 or 8 the correct LINK should be fitted. This has been done purely so that different impedance speakers can be used if there are any problems with supp
8、ly. POWER SUPPLIES The HT supply is a very simple bridge rectifier diode network, with 4n7 1KV capacitors across each diode for EMC reasons, which is then smoothed by C22, to supply the centre tap of the output transformer. This is then further smoothed by R32/C23, R30/C25 and R31/C26 to supply the
9、screen grids, phase splitter and preamp respectively. R28 and R29 are to discharge the high voltage capacitors when then unit is turned off. The ac heater supply is simply connected via a twisted pair connecting lead to V1, V2, V3 and V4. Paul Stevens 30 June 1999 RadioFans.CN 收音机爱 好者资料库 VELOCETTE A
10、LL VALVE GUITAR AMPLIFIER Introduction The Velocette is no nonsense, compact, purists valve guitar amplifier. It has the minimum controls necessary to produce a good range of sounds, from clean to overdriven, into its single speaker. The circuit topology has been based on traditional guitar amplifie
11、r designs, with new ideas incorporated where beneficial. The preamp and power stage sections are 100% valve. The valves used are two ECC83/12AX7s and two EL84/6BQ5s. REAR PANEL CONTROLS INPUT A single jack socket is provided for connection to your instrument. This is a high impedance input which all
12、ows for perfect matching to both passive and active guitars. BRIGHT SWITCH The BRIGHT switch adds more high frequencies when selected. It works in the traditional way, therefore as the volume control is increased the effect becomes less apparent. VOLUME This sets the overall volume level of the ampl
13、ifier as well as the tone and the amount of overdrive. From low to about halfway, depending on the output level of the guitar used, the sound should remain reasonably clean. Increasing the control further will progressively increase the level of distortion in the sound, obviously being a valve amp i
14、t will respond to the players dynamics and use of the instruments volume. TONE Unlike other single tone controls on other amplifiers, which act merely as a treble roll off, this control works in a different way. In the fully anti-clockwise position the midrange is dominant in the sound, turning the
15、control clockwise decreases the mids while at the same time increasing the higher frequencies. EXTERNAL SPEAKER OUTPUT This is provided so that the user can connect the Velocette to an external 16 speaker cabinet, such as a 4x12, for a different sound. This is useful for both live and studio use. Wh
16、en a jack is inserted into this socket the internal speaker is disconnected. Always ensure that the amplifier is correctly loaded when in use. POWER SWITCH (OFF/STANDBY/ON) As the name implies, this switches the amplifier from OFF to STANDBY mode, where only the valve heaters are on, to ON for actua
17、l use. This should be used correctly every time the unit is used to prevent problems with valves and increase their life. Before mains is applied to the unit, check that it is the correct voltage and make sure the POWER switch is in the OFF position. Connect power lead to mains outlet then switch to
18、 STANDBY and wait at least 30 seconds before switching to ON. This will ensure that the valves have time to warm up before large voltages are applied to the plates. During short breaks the amplifier can be switched to standby and will therefore be ready to play when next needed. MAINS FUSE In the ev
19、ent of having to replace the mains fuse always use the same rating and type as marked on the units rear panel. Using one of higher rating will invalidate the guarantee. If after replacement the mains fuse should blow a second time, immediately refer the unit to a TRACE ELLIOT approved service engine
20、er for checking. ORIENTATION OF VALVES Looking at the VELOCETTE from the rear with the vinyl covered rear paneI removed you will see four valves, the two on the left should be ECC83/12AX7s and the two on the right should be EL84/6BQ5s. For improved performance and reliability the EL84/6BQ5s should b
21、e a matched pair. TECHNICAL SPECIFICATIONS INPUT IMPEDANCE1 M TONE CONTROLSINGLE DUAL FUNCTION PASSIVE CONTROL CIRCUIT TOPOLOGYPREAMP AND POWER STAGE 100% VALVE SPEAKER SINGLE 10” CELESTION POWER RATING 15W Paul Stevens 1996 VELOCETTE SPECIFICATIONS Velocette Facilities Rear Panel Input Impedance 1M
22、eg Ohms. ControlsVolume & Tone controls, plus Bright switch. OutputClass A,15 watts RMS into either internal speaker connected inside chassis or external 16Ohm External Speaker Output on rear panel. Valves 2 x ECC83/12AX7, 2 x EL84/ Speaker Configuration 1 x 10” (Celestion Vintage 10) Dimensions W45
23、5mm/H3375m/D182mm Weight 10Kg 1 C32-PC00042x3. GIBSON GA15 ISSUE 3 2/6/98 PS DescriptionPart CodeQtyWhere Used PCBPC00042 issue 21 RESISTORS 0 ohm link72-RCZERO14R9 R10 R27 SW1 8 ohms (and links as shown on PCB) 1K0 6W72-RWW1K-6W1R32 1K2 1/4W72-RM1K21R14 1K5 1/4W72-RM1K54R2R7R22 R23 4K7 4W72-RWW4K7-
24、4W1R30 10K 1/4W72-RM10K2R33 R36 10K 1W72-RM10K-1WATT1R31 27K 1/4W72-RM27K1R13 33K 1/4W72-RM33K1R5 47K 1/4W72-RM47K1R19 68K 1/4W72-RM68K1R35 100K 1/4W72-RM100K1R11 100K 1W72-RM100K-1WATT3R8R15 R16 220K 1/4W72-RM220K2R20 R21 220K 1W72-RM220K-1WATT2R1R29 470K 1/4W72-RM470K2R6R12 1M0 1/4W72-RM1M5R3R4R17
25、 R18 R34 120R 6W72-RWW120R-6W3R24 R25 R26 SEMICONDUCTORS 1N400772-D-IN40074D1D2D3D4 CAPACITORS 47p 500V ceramic72-C47P-500VCD1C29 220p 1KV ceramic72-C220P-1KVCD2C7C12 470p 1KV ceramic72-C470P-1KVCD1C6 1n0 1KV ceramic72-C1000P-1KVCD1C9 2n2 1KV ceramic72-C2200P-1KVCD4C30 C31 C32 C33 1u5 35V tant72-C1.
26、5-35VT1C1 2u2 35V tant72-C2.2-35VT1C8 22u 450V elect axl72-C22-450VA2C25 C26 100u 400V elect rad73-CAP-100400V2C22 C23 220u 25V elect rad72-C220-25VER1C19 2 22n 400V poly box72-C22N-400VPR3C5C16 C17 47n 400V poly box72-C47N-400VP1C14 100n 100V poly box72-C100N-100VP4C3C21 C27 C28 100n 250V poly box7
27、2-C100N-250VB3C13 C15 C18 CONNECTORS 3way 0.1”72-HEAD-3W-25HTR1 - 5 2way 0.2”72-HEAD-2W-21TX3 3way 0.2”72-HEAD-3W-33TX1 TX2 TX4 SOCKETS 1/4” MONO JACK SKT73-SKT-JCKBNBG2SK1 SK2 SWITCHES Mini Toggle SPDT vert73-SWT-M-TGL-PCB1SW2 POTENTIOMETERS 1M073-POT-A1M1RV1 250K LIN DUAL GANG73-POT-B250K-DG1RV2 VALVE BASES B9A PCB valve base73-VAL-SOCKET4V1V2V3V4 FLYING LEADS Cathode heater leadC00-LEAD-VEL-HTR1HTR1 - 5 Speaker leadLOOM-000501LS1
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