![]() ![]() ![]() There's also a 41% increase when comparing a 2 and 4 The NFB voltage from an 8 ohm speaker output gives 41% The 820 / 47 "light" NFB circuit cuts the signal by 95%. "heavy" NFB circuit attenuates the output transformer secondary signal voltageīy 89%. The "heavy" NFB circuit uses an 820 / 100 ohm divider while the others use a "light" 820 / The feedback circuit is made up of two NFB resistors that form a voltage "heavy" NFB circuit compensated for the lower secondary voltages. These multi-speaker amps used 2 and 4 ohm output transformer secondaries so the Reverb, Dual Showman and Twin Reverb use a "heavy" negativeįeedback (NFB) circuit compared to the other AB763 amps' "light" circuit. The multi-speaker amps, the Tremolux, Band-Master, Concert, Super The smaller cap also tends to tighten up the overdrive tone. Reduce bass frequencies into the Fender closed back extension cabs which exhibitĮxtended bass response compared to open back combo cabs. Inverter compared to the other amps' 1000pF (.001uF). The head cab AB763's, the Tremolux, Band-MasterĪnd Showman, use 50% smaller 500pF coupling caps leading to the phase With three preamp gain stages can send both channels through the third preamp Won't damage them but the tone will be thin and funky. Their channels because the Normal channel only uses the first two preamp stages and the VibratoĬhannel uses all three so the two channels are out of phase (each gain stageįlips the signal voltage). Amps with three gain stages cannot jumper The amps with two preamp gain stages can jumper theirĬhannels together for a fatter tone. Signal loss from the reverb circuit but the extra stage more than makes up for the lossĪnd gives earlier dirt and more total distortion. The primary purpose of the extra gain stage is to make up for The Deluxe Reverb, Super Reverb, Vibroverb and Twin ReverbĪmps. The blackface amps without reverb, the Deluxe, Vibrolux, Tremolux, Pro,īand-Master, have only two preamp gain stages compared to three stages in The other AB763 amps fall between these two extremes.Īll the AB763's with reverb have "verb" or "reverb" in their Preamp gain stages, a no-sag solid state rectifier, four big power tubes andĭual 12 inch speakers assaulted by 85 watts. Mighty Twin Reverb has high output power and output transformers, three Two preamp stages, two small power tubes and a single 12 inch speaker driven by Lowly AB763 blackface Deluxe has anemic power and output transformers, Power tube type and number, output transformer and speaker configuration. Model differentiation comes from the power supply, the number of preamp stages, Inverter driving two or four power tubes in a push-pull Class AB configuration.Īll of the AB763 amps have tremolo and some Input, two or three preamp gain stages, a high output long tail pair (LTP) phase ![]() The basic AB763 circuit has two channels, both with a Hi and Low Graph is from the excellent and free Duncan The Mid control is set to 6.8k to simulate the standard 6.8k With the Treble and Bass tone controls set to maximum the tone curve clearly AB763 Mid Scoop With Treble and Bass Set to Maximum (Treble, Mid, Bass) tone stack sets this mid frequency scoop. The blackface tone is known for its "mid scoop." The AB763 TMB Layout below have been annotated with component functions so use them for AB763 The AB763 circuit is considered by most to be Tail pair phase inverter and so carried a different circuit designator. ![]() Princeton or Harvard because these little amps did not use a long "Blackface" refers to the panel color and 763 means July 1963.ĭeluxe, Deluxe Reverb, Twin Reverb, Super Reverb, Band-Master, Showman, Pro, Vibrolux, 'AB763' was Fender's internal model designation for the 1963īlackface circuit. Have comments or corrections? Email rob at: robinette at from Harvey Radio Labs.AB763 Blackface Amp Model Differences What's the difference between a blackface In French: TSF for Télégraphie sans fil.Īll listed radios etc. Here you find 35 models, 26 with images and 7 with schematics for wireless sets etc. See "Data change" for further contributors. Improved version of TBS-50 with crystal control / external VFO-connectors. 3 tubes microphone preamplifier for use with crystal microphone already installed. Optional APS-50 mains power supply, DPS-50 dynamotor or VPS-50 vibrator pack supply, optional external VFO. Transmitter, AM / CW, covers 80 - 2 m ham bands.Tablemodel, high profile (upright - NOT Cathedral nor decorative).Model: Bandmaster Deluxe TBS-50D - Harvey Radio Labs., Harvey.Powered by external power supply or a main unit. ![]()
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