Adding 1-tube reverb

[tubenit]

I've had quite a few forum guys post or PM me about the "one tube reverb".  First off, it's NOT my design. I "stole" it from the D'Lite builders who were using it.  I have used other methods for adding reverb that also worked including Hoffman's "add reverb to Western Circuit".  But this one has worked the best for me.

It has worked on every single amp I've tried it on without a problem. I have it on the 3 amps I currently own and play. No oscillation issues at all.

This uses the "Fender" type replacement reverb transformer and tank that Hoffman sells. Same one you'd use for a Princeton Reverb.

I have owned a Princeton Reverb and played numerous AB763 Fenders. Comparing this to those, I like it better because:
1) it uses just one tube, 2) it verbs more mids (for a fuller tone to my ears) and 3) I don't do "surf" stuff even though I like that sound.   I honestly prefer the tone of this reverb more than the Fender but again that's just my preference.

With my PR, I used the reverb on around 2.5-3        With the one tube reverb, I use it on about 3 or maybe 4-5 on a slow blues tune. Originally, the design had a 2.2M reverb pot but I changed that to 1M to reduce the reverb, I also added a dwell pot to reduce the reverb.   I typically have the reverb pot at 3 and dwel pot at 5-7 & that gets me the reverb fullness and tone that I want. It has waaaayyy more reverb than I'll ever use.

If you want to see examples in a circuit. Look at the Blues Amp, 56T reverb or my 5879 Carolina Blues Special ......OR
the Carolina Blues Special that was made for my friend Gene. They are all in the SCH library. It has worked on an 18watt type design (reported to me), and I have had success using this reverb with concertina phase invertor, & long tailed phase invertor type amps.
 
With respect, Tubenit

EDIT:


OK,  I actually looked up voltages on 5 amps that had a one tube reverb where I liked the reverb on it and thought it performed to my expectations.
 

On  pin 1                                                On pin 6

321                                                           179
325                                                           205
299                                                           204
280                                                           185
251                                                             ?          I don't have this measurement but it was 251 B+ with a 100k resistor to plate

[Heinz]

I have used this type of reverb in one of my builds. I got a 4F... reverb tank for free and was looking for a way to drive it with a tube.
These tanks have an input impedance of around 1500 ohms and are usually used with solid state drivers.

The driver circuit is basically just a 'normal' grounded cathode stage but with a beefy tube and a pretty high idle current (and therefore low output impedance) which is needed to drive the tank. The tank is coupled via a coupling cap to prevent DC current from flowing through the driver coil. The main advantage is the absence of a reverb transformer. The disadvantages are higher power consumption, more heat and the need for a bigger tube.

Initially I copied the Traynor circuit but made some changes that improved its performance. Traynor uses a power pentode in triode mode and a high power resistor in the driver stage. This worked for me to some extent but didn't give enough reverb depth. Using the pentode as a pentode improved this somewhat but the most significant improvement was the use of an inductor instead of the power resistor. I used the primary winding of a small power transformer which is cheap and readily available.
I used a PCL86/14GW8 (6GW8 is the 6V heater variant) which is a power pentode and a signal triode similar to a 12AX7 in one bottle. An ECL82/6BM8 will also work but needs a higher input signal level. With these two-in-one tubes you can build a 1-tube reverb without transformer that can be added to any amp just as tubenit's circuit.

I have attached a schematic of my reverb module. A coupling cap may be needed at the input, depending on your circuit.
Sorry, I only have it in JSchem format. You can download JSchem from http://dhost.info/jschem if you don't have it already.

[tubenit]

Here is another idea using a 6BM8 one tube reverb. I have not tried this, so I have no idea how well it works?

Tubenit

Pignose amps used the 12AX7 one tube reverb.  Also look at the Gibson Scout for another factory example.

Here is one from Zendragon using a 6DX8

[tubenit]

I thought this was a very interesting application of the one tube reverb.

Note the low values of the gain pots being used.   Also note the low value resistor to ground  4.7k  after the 3rd gain stage. Unusual values from what I normally see.

And especially where the reverb insertion points are.

How does it sound? Maybe something like this :  Cornford Hurricane - PRS Standard 22 - Noodling

With respect, Tubenit

[tubenit]

OK,  here is another one to consider .......................

I am NOT sure about having two pots for the reverb return?   That doesn't look right to me.  Probably would use just one pot and maybe try a 1MA?

With respect, Tubenit

[chocopower]

Just a quick question.
Will be possible-practical a stand-alone  1-tube reverb?
What changes should be done in power supply, signal chain?

[tubenit]

I don't see why you could not make this into a stand alone unit that plugs into a passive effects loop.

I made a active FX loop & reverb unit that did just that.

http://www.el34world.com/Forum/index.php?topic=10624.0

With respect, Tubenit

[chocopower]

Perfect!  thanks!

[charliem]

I've had quite a few forum guys post or PM me about the "one tube reverb".  First off, it's NOT my design. I "stole" it from the D'Lite builders who were using it.  I have used other methods for adding reverb that also worked including Hoffman's "add reverb to Western Circuit".  But this one has worked the best for me.

It has worked on every single amp I've tried it on without a problem. I have it on the 3 amps I currently own and play. No oscillation issues at all.

This uses the "Fender" type replacement reverb transformer and tank that Hoffman sells. Same one you'd use for a Princeton Reverb.

I have owned a Princeton Reverb and played numerous AB763 Fenders. Comparing this to those, I like it better because:
1) it uses just one tube, 2) it verbs more mids (for a fuller tone to my ears) and 3) I don't do "surf" stuff even though I like that sound.   I honestly prefer the tone of this reverb more than the Fender but again that's just my preference.

With my PR, I used the reverb on around 2.5-3        With the one tube reverb, I use it on about 3 or maybe 4-5 on a slow blues tune. Originally, the design had a 2.2M reverb pot but I changed that to 1M to reduce the reverb, I also added a dwell pot to reduce the reverb.   I typically have the reverb pot at 3 and dwel pot at 5-7 & that gets me the reverb fullness and tone that I want. It has waaaayyy more reverb than I'll ever use.

If you want to see examples in a circuit. Look at the Blues Amp, 56T reverb or my 5879 Carolina Blues Special ......OR
the Carolina Blues Special that was made for my friend Gene. They are all in the SCH library. It has worked on an 18watt type design (reported to me), and I have had success using this reverb with concertina phase invertor, & long tailed phase invertor type amps.
 
With respect, Tubenit

I'd like to use this circuit but I'm a noob and have a few questions I'm sure will be irritating and stupid...

I have an 18w bluesbreaker type amp I built, the amp maker pp18. I have enough in the power transformer to run another 12ax7 so this seems perfect. I find the diagram (first one attached to this post) a little confusing. I'm sure I'll be asking the "wrong" questions here but... What are the specs of the trany here? and there are a couple of points (circled C D and E) that I don't really understand what they're for. R and R2 appear to become Rv and Rv2?



Put simply, I can see how most of this works but there are a few blank spots. I wonder if someone would be so kind as to help me work this out.

In case it helps here's a schematic of what I have...

http://www.ampmaker.com/images/ak03kit/ak03sc2.jpg

I do understand where to insert this, I'm not asking someone to create an entire set of instructions or anything, just a little confused and looking for a start point to work from.

Any help much appreciated.

Thanks

Charlie

[sluckey]

What are the specs of the trany here?

It's a typical Fender reverb transformer. Hoffman has them right here.

and there are a couple of points (circled C D and E) that I don't really understand what they're for.

Those are just B+ nodes in the power supply.

R and R2 appear to become Rv and Rv2?

That's right.

[charliem]

Thanks, OK I do believe I've got it. I get a maximum of 275v from my current power transformer so I either need a new one, a separate one or I need to play with some of these values. What do you think?

I notice the three B+ voltages at D and E are pretty close to each other in the second amp insert example. I guess there is an obvious reason for 3 close, yet different voltages?

[sluckey]

I think the reverb circuit will work with a wide range of B+ voltages.

[charliem]

I think the reverb circuit will work with a wide range of B+ voltages.

Yes, I begun to realise that when looking at the inserted examples. I believe the max plate voltage on a 12ax7 is about 330v, I have a few voltages around that point in my circuit so it'll be OK, I reckon I'll be fine. I think I'll order up one of this reverb tranies soon and get it all in.

Thanks for your help getting me past the mental block. 

[kagliostro]

I've found this link and I think it can be of some interest also if it isn't an only one tube reverb

http://www.channelroadamps.com/articles/reverb_driver/


K

[tubenit]

There was a thread that I started revisiting the one tube reverb using a 6BM8.   There was some thought that a regular Fender reverb trannie might work OK with 300v?   

However, it appears that using a trannie similar to what is used on a VibroKing that uses an EL84 to drive the reverb tank might be more suitable.   http://www.hammondmfg.com/pdf/EDB1750B.pdf

The project was not completed, but I think this would work well.

With respect, Tubenit

[kagliostro]

For those who are familiar with Hammond recovered parts (in this case the A0-24113-0 transformer)

a variation on the theme one tube reverb, see attached schematic

here all the explanations

http://www.tdpri.com/forum/shock-brothers-diy-amps/465389-possible-1-tube-reverb-add.html

K

[Ed_Chambley]

What determines the resistance between Rv and Rv2?  The different values I noticed.  I have only used 100K, but I am seeing 150K and 220K?

[kagliostro]

I'm not able to give you an answer, I can only say that in commercial amp I've seen that resistor with a much more higher value (3.3M) and bypassed with a 10p capacitor


I don't know the exact explanation about the function of the resistor, I consider it acting as a sort of mix resistor between the wet and dry signal


K

[tipetu]

Hi, I have a JTM45 and I`d sure like some reverb. The 6BM8 looks simple and cool. This is the schematic for my fresh-built amp:



Where would it be the best to hook it up? Before or after the tone stack?

Thank you!

[sluckey]

Fender liked to add the reverb after the tone stack. It would be easy to add between the Treble wiper and the Master Volume control in your amp. I'm not sure if the 6BM8 circuit has been actually tested?   

[tipetu]

I`ve seen some videos on youtube and it does sound surprisingly good! I`ll try and add a 150k resistor after the treble and hook it up there!

[tipetu]

I`d call this a success-build for once hehe. I made a simple power supply and mounted everything in a small hammond chassis I had laying around. It is currently hooked up to my small 16W all tube PP Dynaco EL84 amp. It sounds pretty good. I`ll try out the JTM45 tomorrow!
I`ve lowered the cathode resistor of the first triode half to 1k ohm to raise the gain.
Replacing the level-pot (1M) to 2,2M didnt do no good. 250k made it much better.

Any idea how to add even more reverb?

Here is a short clip to give you an idea how it sound!

https://www.youtube.com/watch?v=DCFF671rB9M&feature=youtu.be

[tipetu]

The 12AX7 reverb works pretty well in the JTM45. No hum/hiss or any of that crap. But I`m a bit dissapointed because it is fairly low. I`ll try and swap out some of the components and see if that improves it. As the thread-starter said in the first post of this thread, it was way too powerful. hmm I`ll sort it out.

[sluckey]

I think tubenit used a long spring 4AB3C1B tank with his circuit. I would think that would give you more verb than that short tank. What is the model number on your tank? Looking for something with a 8-10Ω input and 2KΩ output.

I've heard tubnit's reverb circuit and it is capable of more reverb than I heard in your demo. But it will not give that Dick Dale or Ventures level of verb.

If you are really wanting a good full bodied sounding reverb in an outboard unit that's capable of subtle or crazy surf reverb , consider the 6G15 unit with a 3 spring 9AB3C1B tank. You will not be disappointed. You can easily use it with any amp. And if you do consider the 6G15, for a few dollars more you can add on the Fender 6G12 harmonic vibrato which is the best sounding tremolo I've ever heard. The Revibe is probably the most useful project I've built.

[tipetu]

Oh, I almost forgot about that old Fender design! A while back I bought all the tubes and components. I was planning to build it, but got distracted hehe. All I need is a neat little chassis for it. I think I`ll have a go at it as well! This tiny 12AX7 driver will work for now ;)

[tubenit]

I typically have the reverb pot at 3 and dwel pot at 5-7 & that gets me the reverb fullness and tone that I want. It has waaaayyy more reverb than I'll ever use.

I used a typical Fender replacement reverb tank and trannie for the one tube reverb.  And yes, it had quite a bit more reverb then what I am hearing in your demo. Sluckey is right about the 4AB3C1B  tank. 

In a Marshall type build I would  put a 150k-220k resistor AFTER the master volume and prior to the .02 input cap into the LTPI. 

Can you post the exact reverb schematic that you are using?   Are you using a .001 cap into a dwell pot?  What are the cathode resistor and cap values.  What voltages are on the reverb tube plates?

With respect, Tubenit

EDIT:  Discovered this layout on a d-style build.  CHECK for ERRORS!

[tubenit]

6GW8 idea is a proven idea on Marshall JMP 25w Specialist

6BM8 is NOT a proven idea, but I think it would work?  IF someone tries this, PLEASE let us know if it works or not?

Reportedly the 6BM8 with Champ circuit worked.

Timbo reported on a Diason Hybrid amp that uses 6GW8 reverb also  1/2016 edit

with respect, Tubenit

[tubenit]

OK,  I found yet another one.  6CX8 reverb.  Reportedly, this is a proven design.

Tubenit

EDIT 9/15/2015

Stumbled across this draft idea of a Bassman with ECL82  "one tube reverb".   Don't know if it works or not?

[MakerDP]

I finally built this into one of my amps yesterday. Used it for a live show today. Sounds nice, but I'd actually like to get a little more verb out of it. I have the dwell and the level full-on but it still is not very present at all. In fact, backing off on either knob even slightly kills it altogether.

I built it exactly as in the first post here using it's layout.

I put it aound a 100k resistor between the MV and LTPI coupler of a Fender-ish pre-amp.

I am using the #022921 reverb transformer and a 4AB3C1C tank.

Just to be clear I am NOT after surf levels, but I can't help but think there is more to be had out of this. Any ideas?

Thanks,
Darren

Edit: I typically don't run the amp full-tilt - maybe around 60% to 70% on the MV and gain just slightly at breakup. Am I just not driving it hard enough from the MV? Should I have inserted it BEFORE the MV?

[tubenit]

You will have to provide me a schematic showing your reverb insertion point and reverb schematic before I can help you.

I've never NOT had enough reverb.  Dwell 5-7 & reverb pot 3-4.

With respect, Tubenit

[John]

Maker, you might have to increase the 100k resistor up some. I'm using a 220k in that spot.


 I used a 12aU7 for the reverb tube. It seems to actually give me a bit more 'verb, and it's a cleaner sound as well.


Mine is just before the MV. This is only a SE amp, but my buddy wanted a MV anyway since he plays in his basement, and he's used to having one.


The tank I'm using is only a 9". With everything full up I have enough reverb, but not too much. If he wants more I'll try some of the tweaks in Tubenit's first post.


I'm really happy with the way it turned out. I found it actually a lot easier to use real spring reverb than the SS I had used in the last 2 builds, for not much more money at all.

[MakerDP]

Thanks John.

I bumped the resistor to a 180k and moved the transformer supply to a 310v node. That gave me more gain on both the input and recovery sides.

Those two changes now give me more reverb than I'll ever need.

I'm thinking of putting this circuit on a PCB or at least make a good tagboard layoutso I can easily add it to all my builds and take up as little space as possible.

Now... I need to figure out how to mount my reverb tank in my cabinet. I did not design it with a tank in mind.

[John]

Little update: today I finally found the 12AT7 I had squirreled away and tried that for the reverb driver. Wow. Very lush, huge increase. Keeper.

[MakerDP]

Yeah I tried an AT in mine too. It really sounds nice. I figured a lot of my problem with low levels has to do with the fact that I use a 12AT7 as my preamp tube so I am not driving the tank as hard as if I was using a 12AX7.

[tubenit]

Stumbled across yet another "one tube reverb" with the Mesa Boogie Mk iii.  Has a couple of unique features to it but overall is similar to other one tube reverbs.

http://el34world.com/charts/Schematics/files/mesa_boogie/boogie_mkiii.pdf

[markmalin]

Hi gents!

I'm going to add Tubenit's 1-tube reverb to a 5E3 build I'm working on.  I'm adding a Master Volume to the 5E3 (see attached), but was wondering...I would add the reverb before the MV, correct?

BTW - thanks for starting this thread, Tubenit!

Mark


PS - excuse the hacked diagram, and feel free to make suggestions if anything looks wrong.

[tubenit]

Yes, that is how I would do it. 

With respect, Tubenit

[sluckey]

Something to watch out for... You're inserting the reverb into the grid of V2b, a cathodyne phase inverter. The grid is very high impedance due to the bootstrap bias circuit and it also has a high dc voltage on the grid for bias. Even a 10M input impedance DMM will load that grid circuit and upset the bias voltage.

So, both reverb lines must have a coupling cap to insure there is no dc resistance path to ground that would upset the grid bias of V2B. V2-b's grid path must only connect to ground through R17.

Also, be aware that MV will not take the volume all the way down to zero.

[markmalin]

Sluckey, thanks for your input.  For the coupling caps, would something like 0.02 be sufficient?  I'm not sure how to calculate that.


(I'd like to ask more about the MV circuit, too, but don't want to pollute this thread.  I see what you mean - I suspect there is a better way to do this, I just don't want it Post PI.)

Something to watch out for... You're inserting the reverb into the grid of V2b, a cathodyne phase inverter. The grid is very high impedance due to the bootstrap bias circuit and it also has a high dc voltage on the grid for bias. Even a 10M input impedance DMM will load that grid circuit and upset the bias voltage.

So, both reverb lines must have a coupling cap to insure there is no dc resistance path to ground that would upset the grid bias of V2B. V2-b's grid path must only connect to ground through R17.

Also, be aware that MV will not take the volume all the way down to zero.

[sluckey]

You probably already have a 500pF cap on the input to the reverb driver. But the output of the recovery tube has a reverb level pot that can provide a dc resistance path to ground. I'd use a .047 or .022 or whatever I had on hand to block that path.

[markmalin]

Sounds good.  I should have something on hand

You probably already have a 500pF cap on the input to the reverb driver. But the output of the recovery tube has a reverb level pot that can provide a dc resistance path to ground. I'd use a .047 or .022 or whatever I had on hand to block that path.

[jbefumo]

Decided to try a single-tube 6BM8-based reverb in my Tweed ODS project.  I've seen a variety of pentode-driven circuits on the web, some of which use a transformer, and others that direct-drive a higher-impedance tank. Can anyone provide some guidance on the advantages/disadvantages of each approach?  Thanks.


Jo4e

[jbefumo]

While we're at it -- any thoughts about using the 6BM8 versus as 12DW7 (with transformer)?

Decided to try a single-tube 6BM8-based reverb in my Tweed ODS project.  I've seen a variety of pentode-driven circuits on the web, some of which use a transformer, and others that direct-drive a higher-impedance tank. Can anyone provide some guidance on the advantages/disadvantages of each approach?  Thanks.


Jo4e

[sluckey]

Since the reverb driver circuit is really just a small SE power amp, and the 6BM8 contains a power pentode, the 6BM8 will give you a much stronger reverb.

[sluckey]

I've seen a variety of pentode-driven circuits on the web, some of which use a transformer, and others that direct-drive a higher-impedance tank. Can anyone provide some guidance on the advantages/disadvantages of each approach?

Capacitors are much cheaper. Both sound good.

[jbefumo]

Since the reverb driver circuit is really just a small SE power amp, and the 6BM8 contains a power pentode, the 6BM8 will give you a much stronger reverb.

Sorry if I'm being dense here -- am I better off using the 6BM8 with a transformer and a low impedance tank, or buy a high-impedance tank?  (And, while I'm being dense -- what would be the best input impedance for the tank?  I've seen mention of 600Ohms, 800, and 1475... 


Somewhat off topic -- been experimenting with 6BM8s since finding one in a defunct Lafyette signal generator, and really like them.  Am going to try building a Hoffman Stout with a pair of them giving me my power section and phase inverter and just one more tube for the preamp.  Also, just for kicks, threw together a one-tube single-ended circuit and not only did it work, but sounded pretty decent for a low power thing...

[sluckey]

Most transformer driven tube circuits I've seen use an 8Ω input and 2250Ω output tank. I would need to see your specific circuit to give a specific answer.

6GW8 is very similar to 6BM8. You could probably use either in the same circuit with a little rewiring of the tube socket. Look at this very recent thread...

     http://el34world.com/Forum/index.php?topic=19654.msg204625#msg204625

[jbefumo]

Thanks - I'll check out that link.  No circuit yet -- thought I'd be smart this time and ask questions before diving head first into the deep end! Did see some circuits for the 6GW8 (here and elsewhere), and noticed that some use a transformer and some go directly to the tank.  Read Merlin's discussion of reverb circuits, and do understand that, with appropriate tube/circuit, the transformer can be eliminated.  Was mainly wondering whether there would be any discernible difference in tone between a properly designed circuit using either approach.  Will post my circuit as soon as I spruce it up and make it presentable.  (Ripped my computer out of the wall to save it from a (thankfully minor) house fire, and am now writing from my phone while I get my desktop back in service ...)


Joe

Most transformer driven tube circuits I've seen use an 8Ω input and 2250Ω output tank. I would need to see your specific circuit to give a specific answer.

6GW8 is very similar to 6BM8. You could probably use either in the same circuit with a little rewiring of the tube socket. Look at this very recent thread...

     http://el34world.com/Forum/index.php?topic=19654.msg204625#msg204625

[jbefumo]

6BM8 Datasheet specifies a load resistance (pentode section) of 5600R


I've been looking most carefully at examples A and B (see attached), but in the first case, I would have thought  something like a 5k->8Ohm transformerlike this:


https://edcorusa.com/xse10-8-5k


(Though I suspect the 10W is vast overkill)


with an 8-ohm tank,


or, without a transformer, driving the highest primary impedance tank I could find (1475 Ohms).


Clearly, I'm missing a critical piece in this puzzle.

Thanks - I'll check out that link.  No circuit yet -- thought I'd be smart this time and ask questions before diving head first into the deep end! Did see some circuits for the 6GW8 (here and elsewhere), and noticed that some use a transformer and some go directly to the tank.  Read Merlin's discussion of reverb circuits, and do understand that, with appropriate tube/circuit, the transformer can be eliminated.  Was mainly wondering whether there would be any discernible difference in tone between a properly designed circuit using either approach.  Will post my circuit as soon as I spruce it up and make it presentable.  (Ripped my computer out of the wall to save it from a (thankfully minor) house fire, and am now writing from my phone while I get my desktop back in service ...)


Joe

Most transformer driven tube circuits I've seen use an 8Ω input and 2250Ω output tank. I would need to see your specific circuit to give a specific answer.

6GW8 is very similar to 6BM8. You could probably use either in the same circuit with a little rewiring of the tube socket. Look at this very recent thread...

     http://el34world.com/Forum/index.php?topic=19654.msg204625#msg204625

[jbefumo]

YUP -- that was one of the circuits I've been pondering. The way I look at it, I'm either going to have to buy a new tank, or a new transformer -- No real issue with either one -- just wondering which will yield the best results, and want to make sure that either way, I buy the component with the optimal specifications.


Thanks again !


Joe

Thanks - I'll check out that link.  No circuit yet -- thought I'd be smart this time and ask questions before diving head first into the deep end! Did see some circuits for the 6GW8 (here and elsewhere), and noticed that some use a transformer and some go directly to the tank.  Read Merlin's discussion of reverb circuits, and do understand that, with appropriate tube/circuit, the transformer can be eliminated.  Was mainly wondering whether there would be any discernible difference in tone between a properly designed circuit using either approach.  Will post my circuit as soon as I spruce it up and make it presentable.  (Ripped my computer out of the wall to save it from a (thankfully minor) house fire, and am now writing from my phone while I get my desktop back in service ...)


Joe

Most transformer driven tube circuits I've seen use an 8Ω input and 2250Ω output tank. I would need to see your specific circuit to give a specific answer.

6GW8 is very similar to 6BM8. You could probably use either in the same circuit with a little rewiring of the tube socket. Look at this very recent thread...

     http://el34world.com/Forum/index.php?topic=19654.msg204625#msg204625