Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Toxophilite on November 11, 2017, 03:03:23 pm
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I'm looking for a decent tube tremelo circuit with the lowest component count that I can shoehorn into and AO-44 conversion
I'm using this schematic as it's very simple as well
It's basically going to be a small distortion box for amp switching but it would be cool if it had tremelo too
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Are you settled on what the existing tubes will be used for? In other words, do you know what tubes are available to be used in the tremolo circuit?
A real schematic would be more useful than the layout diagram you included. That picture is missing info like which tubes those are, and a regular schematic would show what parts of each tube (cathode, grid, plate) are connected to each point. Layouts are great for building, not as good for modifying.
There are ways to do a tremolo with solid-state parts, which could allow the signal to be carried by vacuum tubes but control their behavior with solid-state. Likely a good compromise if you want "real tube sound" but don't have tubes to spare.
See this vibro-champ schematic: http://i.imgur.com/SRvehme.jpg
That bottom section, using both halves of one 12AX7, produces a changing voltage over time. The 1/2 of a 12AX7 above it actually carries signal, and is adjusted by what the bottom circuit is doing. You could potentially replace that bottom section with something solid-state.
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If you want a SS tremolo
(https://i.imgur.com/Wu6mYAP.jpg)
BTW, your layout looks near this
(https://i.imgur.com/2R9AmVa.gif)
Franco
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The layout last given to me by an amp building fellow on a guitar forum
It's a A0-44 power amp with a particular marshall type simple preamp in front of it
Anything involving a tremelo would require adding a tube socket and components.
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Look on page 2 of this pdf...
http://sluckeyamps.com/lil_maggie/Magnatone_M2.pdf
The trem circuit only needs 1/2 of a 12AX7. It feeds into the power tube grids. This is a Magnatone M2 amp that I built using an AO-44 as a donor.
Your preamp circuit is using parallel triodes. You could remove the parallel jumpers and use the now free triode to build the tremolo circuit. It works fine with the ECL86 tubes.
I originally had an AB763 preamp shoehorned into the original AO-44 chassis. Here are some pics of how I added the tube socket...
http://sluckeyamps.com/PeeWee/peewee.htm
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If using a spare triode for trem in an amp where there is an odd number of triodes used in the signal path, then combining the LFO stage in the same dual triode envelope as a cathodyne splitter is a good idea (i.e. the way a BFPR combines the two stages in the same envelope). The opposing phase outputs from the cathodyne plate and cathode are useful for dealing with trem-ticking cross-talk that otherwise emanates from the LFO stage.
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But his phase inverter is in the glass with his ECL86 output tubes.
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Well then, feel free to use whatever triode is at hand
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Try this one.
This is my all time favorite .
Preamp tube bias trem 1/2 tube.
Www.robrobinette.com/Compact_Reverb.htm
Check that link also
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Thanks all!
Hey S Luckey
Is that Fm 'vibrato you have in the magnatone an actual pitch shifting vibrato? and do you need the magnatone preamp to use it?
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I don't think any of these circuits can do pitch shifting. It was often called "vibrato" in older designs but is similar to what we now call "tremolo".
EDIT: slucky did give a better answer, apparently it does do pitch shifting...
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Is that Fm 'vibrato you have in the magnatone an actual pitch shifting vibrato? and do you need the magnatone preamp to use it?
Yes, it's true pitch shifting vibrato. You need the V2 modulator circuit and the two varistors (odd circuit symbol) to do the pitch shift.
But I wanted you to look at the oscillator and follow it's output through the switch (in the shaded area) to the output tube grids. That's the simple tremolo circuit. That phase shift oscillator can be used to produce tremolo or vibrato.
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Yes, it's true pitch shifting vibrato. You need the V2 modulator circuit and the two varistors (odd circuit symbol) to do the pitch shift.
But I wanted you to look at the oscillator and follow it's output through the switch (in the shaded area) to the output tube grids. That's the simple tremolo circuit. That phase shift oscillator can be used to produce tremolo or vibrato.
Huh, is there anywhere I can read more about this? I don't understand how this accomplishes pitch shifting. Is it a frequency mixer, which uses a relatively high frequency to add/subtract from the signal?
I was under the impression the vibrato oscillator was only changing a couple times per second (or maybe like 10) and I don't imagine this being fast enough to practically do anything but change amplitude, but maybe I'm mistaken about the speed of oscillation or something else.
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http://sluckeyamps.com/magnatone/NON_LINEAR_IMPEDANCE_ELEMENTS.pdf