Early Fender Non-Opto Vibrato/Tremelo Circuit - diyAudio
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Old 5th January 2014, 12:55 AM   #1
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Default Early Fender Non-Opto Vibrato/Tremelo Circuit

Want to add a simple fender tremelo (it's not really vibrato) to my Deluxe breadboard, having a free 1/2 12AX7 available. Built the Princeton AA964 circuit, wired it to the 6V6 bias point (ala Princeton), see the tremelo signal on my scope, but it's not working.... Need a detailed description of how this circuit works. No luck in Internet (lots on opto ckt). Thanks!
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File Type: pdf VIBRATO-Princeton-AA964-schematic.pdf (344.4 KB, 39 views)
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Old 5th January 2014, 03:57 AM   #2
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OOps! Just realized my power tubes are cathode biased, Princeton is fixed (no cathode resitor, negative voltage supplied to grids). Will ground my cathodes, and try the -34VDC tremelo signal again.... AND found on other forum posts that proper bias is critical to this tremelo functioning. Will keep them mellow.
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Old 5th January 2014, 04:01 AM   #3
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Circuitos Para Guitarra Eléctrica (Incluyen diagramas de pedales Boss)
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Old 6th January 2014, 02:19 AM   #4
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Finally got it working, after changing the 6V6s to fixed bias, finding a missing connection on my circuit (funny how one missed connection can ruin a whole day), AND figuring out that shorting the vibrato switch turns it OFF.... Had to reduce the bias a lot to get good tremelo, down to 10mA on the plate (liked it better at 20). Need to boost the tremelo signal. Maybe that's why they added another half an AX7....
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Old 26th February 2014, 11:04 PM   #5
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I'm reviving this thread because I've built another tremelo for another amp, and can't get it to oscillate. Or at least know what it looks like on my scope.... Is not connected to any amp yet, just the circuit. The pics show two similar circuits, look more like Hartley than Colpitts (with caps off the plate, and resistance off the grid). Why does one (a Fender design) need 5 Meg for speed, and the other (a Gregory low-plate voltage amp) only 300K? What determines the oscillation frequency? I'm using 1/2 a 12AX7 with 300 VDC B+. Is the plate load resistor value critical? Thanks
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File Type: jpg GREGORY TREMELO.jpg (126.7 KB, 36 views)
File Type: jpg scan0001.jpg (237.4 KB, 36 views)
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File Type: doc PRINCETON TREMELO.doc (182.0 KB, 1 views)
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Old 27th February 2014, 12:21 AM   #6
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A Phase-shift oscillator! Thanks to Valve Wizard. Now to dig into the design....
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Old 27th February 2014, 03:23 AM   #7
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Got it working! Adhered to the attached pic, 390K plate load, used an LED instead of cathode R & cap (per the Wizard a well), and presto!. I guess I've answered my own question, but may help someone else...

The Valve Wizard- Tremolo Oscillator
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File Type: jpg VLV WZD SCHEM.jpg (28.7 KB, 30 views)
File Type: jpg WIZ LED SCHEM.jpg (26.1 KB, 30 views)
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Old 27th February 2014, 11:48 PM   #8
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Cool. Love the LED biased tremolo. I always bring the LED to the control panel so I can see what's happening
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Old 28th February 2014, 01:05 AM   #9
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dj - You're right about the LED! Been playing with the circuit (now that I got it working), trying to get a 12AU7 to oscillate - is pretty low mu. Vox uses 4 RC stages, supposedly gives more gain (an impedance thing I think). Also thought about running the LED to the front! Trying different RC combinations (using the 1/15*R*C formula).
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