Rickresource Rickenbacker Forum

Charlie: Some articles I have read have claimed that the Fender Tremolo is less than adequate and that others such as Marshall's 18W tremolo is superior. Do you have an opinion on this? Are the tremolo circuits designed differently for Fender and Marshall or are they basically the same?

Further to my original question I have done some more reading with regard to the vintage Fender Vibrato, which is of course really a tremolo.

There are curmudgeons out there who have noted this discrepancy and I am with them all the way. Try doing a search for vibrato and tremolo and you will eventually become confused if you are looking for a proper definition and usage of the terms.

There are critics of the Fender tremolo who suggest that the the only decent circuit was in the 6G16 Vibroverb Vibrato system. I cannot speak to the technical reasons why this is best in their view. Having a vibrato associated with a preamp is one complaint some amp tech have made suggesting it should be part of the output stage.

What I do know is that I am taken by the tremolo effect in the recently manufactured Marshall 1974X 18 Watt amplifier. The wave form is pleasant and smoother to what I have heard in the Fender Twin Reverb.

Should there be anyone who shares this view or can at least describe why these effects, Fender versus Marshall, appear to be so different I would be most interested in hearing from you.

The tube tremelo and vibrato circuits in vintage amps are all similar to a certain extent in that they all have an oscillator and a modulator circuit in the amp. The tremelo modulates the volume of the note, and the vibrato modulates the phase of the note. Fender had several circuits and variations, but as you mentioned, all of them were tremelo and not vibrato, despite how Fender labelled the amps. All the blackface Fenders except the Princeton Reverb and maybe another one (can't recall right now) used an optoisolator (or commonly called a roach or bug) to produce the oscillation and the circuit shorts the signal to ground intermittantly. Most of the earlier amps used a tube oscillator and modulated the bias of preamp tubes, or power tubes. One of the Fender circuits, and the one that people commonly mistake for vibrato, is the one that uses the most tubes. It was on some of the brown amps in the early 60's (6G16 Vibroverb style) and is a pitch changing tremelo....it makes the volume of the highs and lows go up and down and work off each other, and sounds REALLY nice. Its an expensive circuit though because of all the tubes and the labor to build it, so except for enthusiasts today who build kits (Webervst, Hoffman, etc) no one uses that circuit anymore.

Marshall and Vox all had tremelo too. Vox likes to say their AC30 has vibrato, but it isn't...it is just a complicated tremelo. The only real true vibrato was in Magnatone amps like the 260 model. These use similar parts to a trem circuit, but also use varistors. The Magnatone vibrato is like nothing else and sounds REALLY cool! I agree with you also that the trem in the new Marshalls is really cool too.

I don't really understand trem and vibrato circuits much beyond that except for how to make them do what I want. You can change verious resistors and caps to speed up or slow down the trem, and to vary the intensity. You can also inject the trem at different points to make it have more or less effect. Some people don't like the ones that modulate the bias (called bias wigglers) because they are playing with something (the bias) that should be completely stable, and it is hard on the tubes that are having their bias moved around. Other people say to hell with it because the bias wigglers sound good. Most people are used to the blackface Fender style roach trem, and it probably is one of the worst sounding of the types. A roach trem CAN sound quite good though...case in point, the trem on the Silvertone 1484 Twin Twelve head. It is a roach trem also, but the main difference between this trem and Fenders blackface style is that Silvertone has it injecting earlier in the amp circuit, so it has a deeper effect. The roach itself is probably different too, but I have no info on that besides just the appearance of the roaches in both amps.

Greg: Thanks so much for this. It has given me a deeper understanding of tremolo in terms that I am able to comprehend.

I am having my 1970 Fender Reverb repaired and I am going to have the Marshall tremolo circuit installed. I will keep you posted.

While original specs are appealing, there is little point when the period sound can be improved upon.

Peter, I hope they are going to add the same exact circuit setup as in the Marshall, or it will sound different. Things like tube type used for the oscillator, or a roach for the oscillator, cap and resistor values and locations in the circuit, voltages, where in the amp they inject the oscillation...all this stuff matters and changes the sound significantly.

People don't use the 6G16 Vibroverb trem setup nowadays mainly because of price. It is one of the coolest sounding trem circuits ever in my opinion. It is very labor intensive to build and uses twice the tubes, resistors, and caps as a normal trem circuit. Ted Weber at Webervst has a Revibe kit, which comes with that trem circuit, and an outboard reverb circuit like the old Fender reverb units, and I plan to build myself one at some point because they sound soooo cool. It would be really hard to improve on this trem setup, or on the Magnatone vibrato setup.

If you're trying to improve on the roach style trem in the Fenders, the easiest way is to install a switch to have it work on one channel or the other, and install 2 caps and 2 resistors to isolate each channel from each other, and just move the point where the trem injects into the circuit. Right now it happens after the channels are mixed after the reverb recovery/mixer stage. If you move it to after 1 stage in each channel, and have the roach oscillator ouput go to the middle of the switch, and each side of the switch goes to one channel or the other, you get trem on both channels, one at a time. You can also get a slight gain boost on whichever channel doesn't have the trem selected because the trem effect doesn't load down that channel. It may require some voltage changes and value changes of caps and resistors to make it work right, but the end effect will be a much richer and deeper sounding trem. I did this on my brother's Silvertone I spent the last 8 months modifying and while the stock trem sounded pretty good, it sounds VERY nice now, and is very flexible too. Food for thought anyway.

Greg: Unless I am mistaken the 6G16 circuit uses only one 12AX7. Am I reading this wrong? This looks like it may be a viable circuit to use in my Twin Reverb.

Hey Peter...I confused that circuit with the other one I was thinking about...sorry about that. Thats what I get for not looking it up before I post and trying to go from memory! Yes, that one would be a viable solution in your twin reverb. It modulates the bias up and down. In order for it to work correctly, the amp should be biased a little colder than usual, which makes the amp sound a little stiff. If you don't do this, you can get beating with the trem on, and the power tubes can go into cutoff at max depth on the trem, which is to be avoided at all costs...hence the cold biasing.

The one I was thinking of was the multi tube trem in the brown amps and a couple others where it modulates the lows against the highs. An example of this one would be the 6G4 Super. Its the best sounding trem I've ever heard, but uses 3 complete dual triodes.

If it was my amp, I would probably move the trem injection point to after the first stage and set it up like I suggested in the other post. Its a little easier to accomplish and would sound better than it does now, but the 6G16 would work fine too.

I have what I believe to be a 1972 Fender Twin reverb amp. It has a master volume control, casters and the tilt back stands on the sides.
My tremelo seems to be working, but the effect is not being amplified. I can hear it pulsing. It seems to change with a speed adjustment, but the intensity control seems to have no affect.
Other than this, the amp plays fine.

It sounds like a resistor or cap is bad in the trem circuit, the intensity pot is bad, or the ground reference for the intensity pot is missing. It requires some troubleshooting to figure it out for sure.