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08-02-2021, 06:49 PM
(This post was last modified: 08-02-2021, 06:50 PM by Sherlok Ohms.)
Hello Mr Makinrose
May I kindly suggest that the oscillator itself can be interfaced with whatever you wish, as far as I understand. Yes, Vox likes to apply this signal to the EL-84 grids, which tells you the magnitude of the oscillation assuming the tubes can be driven to cutoff (10-15V peak).
Depending on the circuit point you wish to tie the tremolo to, you might consider using direct modulation, say to the the grid-leak of a triode gain stage. This would eliminate the need to have a 10mA or higher current available for the LED side of your preferred LDR interface. The B+ can certainly supply this but there will be a lot of heat in the dropping resistor.
I believe KOC suggested a nifty "current steering" interface where the LED in the LDR is always tied to the dropping resitor, and a modulation element is tied in parallel with it. The current is constant and goes through the LED or the element or is shared by both depending on the point of tremolo signal. The element could be a transistor, mosfet or jfet. The voltage is limited by the LED itself in the LDR. if you drove this from the Vox oscillator, then no specific voltages have to be derived from the plate supply - just have appropriate decoupling. The current steering is a method used to reduce "thumping" through the supply and into the amplifier. You can place a pot between the oscillator and the element.
I may be "talking out of my posterior", as they say, but I believe the above to be correct
Cheerio
May I kindly suggest that the oscillator itself can be interfaced with whatever you wish, as far as I understand. Yes, Vox likes to apply this signal to the EL-84 grids, which tells you the magnitude of the oscillation assuming the tubes can be driven to cutoff (10-15V peak).
Depending on the circuit point you wish to tie the tremolo to, you might consider using direct modulation, say to the the grid-leak of a triode gain stage. This would eliminate the need to have a 10mA or higher current available for the LED side of your preferred LDR interface. The B+ can certainly supply this but there will be a lot of heat in the dropping resistor.
I believe KOC suggested a nifty "current steering" interface where the LED in the LDR is always tied to the dropping resitor, and a modulation element is tied in parallel with it. The current is constant and goes through the LED or the element or is shared by both depending on the point of tremolo signal. The element could be a transistor, mosfet or jfet. The voltage is limited by the LED itself in the LDR. if you drove this from the Vox oscillator, then no specific voltages have to be derived from the plate supply - just have appropriate decoupling. The current steering is a method used to reduce "thumping" through the supply and into the amplifier. You can place a pot between the oscillator and the element.
I may be "talking out of my posterior", as they say, but I believe the above to be correct
Cheerio
