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Author Topic: Valve Tremolo - Help Wanted Please  (Read 871 times)

nodz

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Valve Tremolo - Help Wanted Please
« on: December 24, 2020, 03:30:47 PM »
Hi All,
Was wondering if anyboy could help - attached is a schematic that was drawn up by me to add a valve tremolo to an amp.  I obviously used certain reference data, schematics etc but for the life of me, I cannot find the original schematic and what I have drawn up doesn't appear quite right.  The only diagram I've managed to find is that of the Symphonic MA50 amp (?) att.
My original schematic uses 6AT6 as trem with F/S, Speed intensity controls driving a second section that was between the tone stack of the first stage and the phase inverter.  What is strange is that the O/P of the trem unit is fed to plate of second stage and not the grid.
So question, is the schematic correct? WIll it work? What have I messed up etc.
Cheers,
Nodz
« Last Edit: December 24, 2020, 03:40:56 PM by nodz »

Jazz P Bass

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Re: Valve Tremolo - Help Wanted Please
« Reply #1 on: December 25, 2020, 12:11:16 AM »
It does not look as if the Tremolo is connected properly.
It "normally" feeds the bias of the output tubes.

nodz

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Re: Valve Tremolo - Help Wanted Please
« Reply #2 on: December 25, 2020, 01:49:00 PM »
Understood that it normally feeds the bias of say the phase inverter of output.  Perhaps I should have included the full circuit, in that the tremelo is connected to the plate of the next stage 1/2 12AX7 which in turn connects to to the 12AX7 phase inverter.  So very similar to say the Fender concert schematic attached, I've labelled the 'similar' sections of the two diagrams for comparison.  The tremelo on the Fender concert uses 4 x 1/2 7025 but the O/P is connected to plate of Section C, which both in turn connect to grid and bias of Section D the PI.
So
Section A tremelo unit
Section B tone stack
Section C Intermediate amp (I've used it as a mid drive/master volume section on my amp)
Section D PI
Section E PA


Jazz P Bass

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Re: Valve Tremolo - Help Wanted Please
« Reply #3 on: December 26, 2020, 11:13:05 AM »
Why not simply copy the one circuit and place it in yours.
At the junction of R23/ R24. (remove the Ground connection)
The Fender circuit is slightly different as it is a fixed bias amp.
Yours is cathode biased.
« Last Edit: December 26, 2020, 11:16:10 AM by Jazz P Bass »

g1

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Re: Valve Tremolo - Help Wanted Please
« Reply #4 on: December 26, 2020, 04:43:48 PM »
You are not understanding the 6G12 circuit.  The normal channel (blocks B and C) are not affected by the trem.
You can just ignore them.  The reason the trem has no effect on the normal channel is because the plate signal is so big.  That is why your circuit will not work.
Trem will only work if it is introduced into grid or cathode circuits.

nodz

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Re: Valve Tremolo - Help Wanted Please
« Reply #5 on: December 26, 2020, 05:00:20 PM »
That is why your circuit will not work.  Trem will only work if it is introduced into grid or cathode circuits.

With respect to my amp
So if I took the O/P from the trem unit (section A) after the 0.056uF coupling cap and introduced it at the junction 0.022uF (C14)  and 1M (R16) of the grid of the PI (Section D) - all well and good?

So basically free running LFO mixed with the signal from Sections A & B, without having to actually have seperate trem channels as per
http://www.valvewizard.co.uk/trem1.html


Jazz P Bass

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Re: Valve Tremolo - Help Wanted Please
« Reply #6 on: December 27, 2020, 12:11:51 AM »
I don't think that you have it right as of yet.
The output is cathode biased not fixed as in the Fender.
Why not hook it up as I stated in my last post.

nodz

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Re: Valve Tremolo - Help Wanted Please
« Reply #7 on: December 28, 2020, 08:30:26 PM »
Rightho, finally found the original doco.  Phase shift oscillator where O/P is capacitively coupled to the plate of the first stage audio amplifier.  I coupled it to the intermediate mid drive amp rather than the first stage.