One triode tremolo

[Swampertech]

Hey Tubenit, I've been researching a one triode tremolo, and downloaded Rob Robinette's one tube tremolo add on .diy file last night. Your circuit looks like the values Rob uses. I found, though, that Rob had a jumper between pins 2 & 3, or at least appeared that way. I know that has to be wrong. Any thoughts, or did I miss a correction on the layout? Thanks for all your input!!

[DummyLoad]

Hey Tubenit, I've been researching a one triode tremolo, and downloaded Rob Robinette's one tube tremolo add on .diy file last night. Your circuit looks like the values Rob uses. I found, though, that Rob had a jumper between pins 2 & 3, or at least appeared that way. I know that has to be wrong. Any thoughts, or did I miss a correction on the layout? Thanks for all your input!!

that would be a wiring error - the 1MΩ connects to the cathode + fixed the grid connection,.


--pete

[tubenit]

I am not able to open your file.

Look at some of these schematics:

https://el34world.com/charts/Schematics/files/Vox/Vox_cambridge_reverb_v_3.pdf

https://el34world.com/charts/Schematics/files/Epiphone/Epiphone_ea_33rvt.pdf

https://el34world.com/charts/Schematics/files/Gibson/Gibson_hawk_2.pdf

[Swampertech]

Thanks Tubenit, looks like Pete has a corrected layout. Thanks guys!!

[Swampertech]

Is there a preferred procedure for setting the bias on a tube tremolo power tube circuit? Also, can this tremolo drive 6L6's?

[sluckey]

Hey guys. Would y'all consider posting a pdf or image file rather than those *.diy files. Very few of us are using DIY Layout Creator so we have no way to comment on those. THX

[Swampertech]

Hey Steve, this is the schematic Rob has posted. Wondering about this pushing 6L6's. Also, the setup procedure to set bias.

[sluckey]

Hey Steve, this is the schematic Rob has posted.

That circuit can't possibly work. Big errors!

[Swampertech]

Is that not the standard tremolo circuit for an AA1164 Princeton? Can you explain the errors? Thanks Steve!

[DummyLoad]

Hey guys. Would y'all consider posting a pdf or image file rather than those *.diy files. Very few of us are using DIY Layout Creator so we have no way to comment on those. THX

please see attached.


--pete

[sluckey]

I'll just fix the schematic and let you compare the two to find the two errors. This is not the first time this same trem schematic has passed through the forum. Maybe Rob will fix it.

This circuit "may" have enough trem signal to wiggle 6L6s a tiny bit but it would be a weak tremolo effect. There are a couple things that will boost the trem signal quite a bit that may work OK with 6L6s, but even the 2 tube trem circuits have trouble reliably wiggling 6L6s for a strong effect. I suspect that's a major reason that Fender switched to the roach circuit and never looked back.

[Swampertech]

OK Steve, I see it. R32 is NOT connected to the grid, but to the cathode. The R31/C20 junction goes to the grid. Rob must have used the bad schematic to build that .diy file where the grid and cathode are tied together. Knew that was wrong. Any other error? Do you recommend the roach circuit for a one triode tremolo?

[sluckey]

I don't see any other errors. I don't recommend a one tube roach although I have a very good idea for one, but I'll save that for another thread. Why are we discussing driving 6L6s in tubenit's 6BM8 minimalist PR thread?

[DummyLoad]

I don't see any other errors. I don't recommend a one tube roach although I have a very good idea for one, but I'll save that for another thread. Why are we discussing driving 6L6s in tubenit's 6BM8 minimalist PR thread?

typical... thread spawned to another question on same topic.


use a MOSFET source follower if you don't want to add another tube.


--pete

[Swampertech]

I was discussing 6L6's just because I had my first 5E3 build designed for lo/hi power (6V6's and 6L6's). I guess this circuit WILL push 6V6's OK, just want to know my options. I do know there's an option to use a MOSFET. I'm also trying to fit all this in a PR chassis, and so far I'm using 1 12AX7 for the Fender/Marshall preamps (part of your Dual 50 design), 1 12AX7 for the TMB circuit and 1/2 12AX7 summing before PI, 1 12AX7 for the PI, and 1 6GH8A for the Reverb driver/recovery. That would leave me 1/2 12AX7 for the tremolo. I believe a PR chassis would accept one more 9 pin socket. So, if you DO design a 1 triode roach tremolo that will push 6L6's, please share.

[Willabe]

Why are we discussing driving 6L6s in tubenit's 6BM8 minimalist PR thread?

I was discussing 6L6's just because I had my first 5E3 build designed for lo/hi power (6V6's and 6L6's).

That's nice but, really doesn't have anything to do with Tubenits OP.

Why not start your own thread on it?

[vampwizzard]

I was discussing 6L6's just because I had my first 5E3 build designed for lo/hi power (6V6's and 6L6's). I guess this circuit WILL push 6V6's OK, just want to know my options. I do know there's an option to use a MOSFET. I'm also trying to fit all this in a PR chassis, and so far I'm using 1 12AX7 for the Fender/Marshall preamps (part of your Dual 50 design), 1 12AX7 for the TMB circuit and 1/2 12AX7 summing before PI, 1 12AX7 for the PI, and 1 6GH8A for the Reverb driver/recovery. That would leave me 1/2 12AX7 for the tremolo. I believe a PR chassis would accept one more 9 pin socket. So, if you DO design a 1 triode roach tremolo that will push 6L6's, please share.

I know youre trying to use one triode, but tying a full tube trem circuit into the PI is how fender did it with the 5e9a. Pretty sure the 1/2 tube version could tie in the same way? just some food for thought.

[Swampertech]

Thanks Vamp. Looks like the 5E9A uses two triodes. How about the G12 Ampeg trem? It has a one triode phase shift oscillator with the plate variations driving the light in a roach. The roach light varies the roach resistor which is in series with the signal in a preamp stage. The intensity pot is in parallel with the roach resistor. Your thoughts?

[vampwizzard]

brad the guitologist has a video demoing one of those on YT.. id give it a listen. Sounded kind of weak but honestly probably more to do with how much reverb he was using. If you like that sound, you should be good to go. It may be a bit more powerful without a reverb circuit following it as well.

If I were in your shoes though, id 100% hit up Sluckey's Tremor-lator circuit he posted a couple days ago. If he found it worth imaging up, annotating, and sharing with us its probably DAMN good. You would place it in the same location, in the pre phase inverter signal path, if im reading that correctly.

https://el34world.com/Forum/index.php?topic=24334.0

[Swampertech]

Vamp, I was going to ask Sluckey to comment on the Ampeg G-12 tremolo design. He has many more years experience with tube amps than I do. My desire was to have a one triode non-bias varying tremolo. The reason for this is that I want to be able to use 6V6's or 6L6's, and not have to worry about the re-biasing procedures involved in having bias modulating tremolo. But since he put so much work into his one triode Tremor-lator, I assume he came up with a better design. I am looking at using his basic Dual 50 design, but without the Marshall 800 cold clipper one tube circuit. I have added the one tube 6GH8A reverb circuit, and plan on using a one triode tremolo. Sluckey has already said his circuit could be inserted before the PI. I'll get my schematic modded with the Tremor-lator and submit it to the forum. Thanks for your comments.

[tubeswell]

... My desire was to have a one triode non-bias varying tremolo. The reason for this is that I want to be able to use 6V6's or 6L6's, and not have to worry about the re-biasing procedures involved in having bias modulating tremolo. ...

There are lots designs that wiggle pre-amp tube bias (thus avoiding your concern about re-biasing output tubes)


And you can do this with one oscillator stage. However, an impedance buffer (of some sort) helps to preserve the strength of the Trem by saving the LFO stage's output from being loaded down, but it needn't be a tube buffer if you haven't got enough tube stages to spare. You could use a FET buffer. Plenty of examples on this site searching on 'IRF820'

[Swampertech]

Thanks for the reply tubeswell. Have you had an occasion to implement the Ampeg G-12 tremolo, where the photoresistors' R is in series with the preamp output that feeds the tone stack? The intensity control parallels the R, and this is a one triode phase shift oscillator. I'm not sure of the placement of the tremolo before the tone stack though. Sluckey has just posted his Tremor-lator, and it will absolutely fit my needs, and even has a frequency lowering switch mod for the oscillator. He calls it "Swamp".

I had previously studied some of the MOSFET driver diagrams you mentioned, but I would like to keep this amp as void of solid state as I can. The variable resistance of a photoresistor seems to be a logical way to implement tremolo of the signal path.

Again, thanks for your input.

[sluckey]

I owned a Gemini II G-15 in the '60s and '70s. It had the exact same tremolo circuit. Sounded great. I didn't use tremolo much back then. I have a Sunn Sceptre that lost it's extinct optocoupler. I used a VTL5C1 instead and modified the insertion point to look just like the Ampeg G12. Works great. Here's the schematic for that...

     http://sluckeyamps.com/sunn/sunn_sceptre_1971.pdf

One thing to know about the G12 tremolo... That series attenuation idea requires the bulb to be lit when the trem is off, otherwise you have a very attenuated guitar signal. My Tremor-Lator is meant to be used in a shunt circuit just like the AB763 circuits.

[2deaf]

My Tremor-Lator is meant to be used in a shunt circuit just like the AB763 circuits.

You know how the AB763 used the negative bias voltage to shut down the bias.  They needed to put those tubes firmly into cut-off so that no current went through the optocoupler.  If they just grounded-out the positive feedback loop, there would be enough idle current going through the optocoupler to lower the resistance of the photocell.

Your Tremor-Lator will also have a low optocoupler output resistance when in the "off" condition.  You might want to consider using the bias to put your tube into cut-off if you want an output resistance of more than 50K or so.   

[sluckey]

That could be. It didn't occur to me to check operation in the "OFF" mode.   

[Swampertech]

Steve, isn't that what Rx is for, to provide a load for the insertion point?

[sluckey]

R_x is just to tame the intensity if desired. I played with several different values in my mockup but liked it best without any R_x

[2deaf]

I fooled with the Tremor-Lator a little on the bench and I would say that this is a significant improvement over the AB763 roach tremolo.  Much nicer signal.

The LDR I tried had a 33K resistance in the "off" condition.  My Twin has a 28K output resistance when using ground instead of bias to turn it off.  It only took -9V on the grid of the Tremor-Lator to make the output resistance too high to measure.  Attached is a suggested modification.

[sluckey]

Thanks 2deaf

[Toxophilite]

So you just take a feed from your bias circuit and the 2.2m resistor knocks it down to acceptable levels?

[Swampertech]

Doesn't the LED in the roach on the Tremor-Later provide cathode bias to keep the tube on?

[sluckey]

So you just take a feed from your bias circuit and the 2.2m resistor knocks it down to acceptable levels?

No. The negative bias is used to insure the oscillator is off when you turn it off. It also insures that the oscillator will start quickly when you turn it on. Like a kick start.

[sluckey]

Doesn't the LED in the roach on the Tremor-Later provide cathode bias to keep the tube on?

The LED provides fixed bias to the tube.

[Swampertech]

Correct that, and the negative bias between the grid and cathode is the breakdown voltage of the diode.

[Toxophilite]

Where does the bias voltage come from?

[sluckey]

From the bias store.

[Toxophilite]

right, smartypants    You mean from the bias supply for the power amp yes?

[sluckey]

Crap. That's what I meant to say.

[Toxophilite]

That's what I was asking a few posts ago! Hilarious!

I think you might've quoted me by accident when you were responding to the post prior to you a few back.

At least I had the right idea initially.


I'm going to have to buy a couple of those vactrol thingies and try this out. It's a cool idea.

[sluckey]

Your reply #29 makes more sense to me now. But a couple points... The 2.2M doesn't knock down the bias voltage at all. The full bias voltage will appear at the grid of the oscillator tube since there is no current flow. In this condition the tube is in hard cutoff and there is no trem effect. Now when you turn the trem on by closing the footswitch contacts you ground the downstream side of that 2.2M. This removes the negative bias from the tube and it snaps back into conduction, quickly bringing up the trem signal. The 2.2M isolates the bias supply from being shorted to ground and actually becomes a very light load on the bias supply.

The main advantage of using the bias voltage is to provide a "snap into action" response from the oscillator. Without this circuit the oscillator would slowly start up but you probably would not have tremolo for a couple seconds after stepping on the footswitch. That's no fun.

Vactrol is extinct except for the few that are in the dusty bins of suppliers. However, there are other companies making the VTL5C1 which is the part number to get. They run about 7 bucks.

[Toxophilite]

Just ordered some for fun.
Thanks!