Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Archives of favorite topics => Topic started by: tubenit on October 22, 2009, 10:08:22 am
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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
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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.
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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
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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 (http://www.youtube.com/watch?v=mcDVkB73VKc#ws)
With respect, Tubenit
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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
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Just a quick question.
Will be possible-practical a stand-alone 1-tube reverb?
What changes should be done in power supply, signal chain?
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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 (http://www.el34world.com/Forum/index.php?topic=10624.0)
With respect, Tubenit
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Perfect! thanks!
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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 (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
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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.
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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?
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I think the reverb circuit will work with a wide range of B+ voltages.
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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. :thumbsup:
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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/ (http://www.channelroadamps.com/articles/reverb_driver/)
K
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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 (http://www.hammondmfg.com/pdf/EDB1750B.pdf)
The project was not completed, but I think this would work well.
With respect, Tubenit
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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 (http://www.tdpri.com/forum/shock-brothers-diy-amps/465389-possible-1-tube-reverb-add.html)
K
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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?
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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
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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:
(http://i1286.photobucket.com/albums/a604/frank_bentzen/jtm45plus_schematic_v4_zps26041782.jpg) (http://s1286.photobucket.com/user/frank_bentzen/media/jtm45plus_schematic_v4_zps26041782.jpg.html)
Where would it be the best to hook it up? Before or after the tone stack?
Thank you!
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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? :dontknow:
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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!
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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 (https://www.youtube.com/watch?v=DCFF671rB9M&feature=youtu.be)
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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.
(http://i1286.photobucket.com/albums/a604/frank_bentzen/IMG_2525_zps594b3aae.jpg) (http://s1286.photobucket.com/user/frank_bentzen/media/IMG_2525_zps594b3aae.jpg.html)
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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.
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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 ;)
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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!
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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
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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?
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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?
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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
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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.
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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.
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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.
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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.
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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 (http://el34world.com/charts/Schematics/files/mesa_boogie/boogie_mkiii.pdf)
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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.
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Yes, that is how I would do it.
With respect, Tubenit
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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.
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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.
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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.
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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.
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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
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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
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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.
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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.
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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...
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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 (http://el34world.com/Forum/index.php?topic=19654.msg204625#msg204625)
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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 (http://el34world.com/Forum/index.php?topic=19654.msg204625#msg204625)
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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 (http://el34world.com/Forum/index.php?topic=19654.msg204625#msg204625)
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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 (http://el34world.com/Forum/index.php?topic=19654.msg204625#msg204625)
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Clearly, I'm missing a critical piece in this puzzle.
Maybe you're just overthinking this. A tube plate is usually a high impedance (Z) device. The reverb tank input is whatever you specify it to be. If you want a low Z tank, then a transformer is the best choice of matching the high Z tube plate to the low Z tank. If you want a high Z tank, then a capacitor is the best choice for matching the high Z tube plate to the high Z tank.
Your example circuits A, B, and D are all CAPACITOR coupled drivers and require a high input impedance tank. Don't be confused by circuit A. Circuit A is NOT a transformer coupled driver. Someone is just using the primary of a transformer as a choke inductor for the plate load of the driver tube. A 14Hy choke could be used just as well. Hammond AO-43 is an example of a choke plate loaded driver that is CAPACITOR coupled to the tank.
Your example circuits C, E, F, and G are all TRANSFORMER coupled drivers and will use a low input impedance tank. When using a transformer, the transformer is used to match the input of the tank to the plate of the tube. A small output transformer used to couple a speaker to a tube circuit is cheap and plentiful, so most transformer coupled tanks will have a low Z input, typically about 8Ω. However, 600Ω transformers are used in communications circuits. You could use one of these transformers to couple to a 600Ω tank input. (A 600Ω transformer is not a common component that you would find stocked at most guitar amp supply houses.
So, in summary, for tube circuits, "usually" if you see a transformer coupled reverb driver, the tank input will be 8Ω. A cap coupled reverb driver will connect to a high Z tank input. And all tanks will have a high Z output.
The attached file is all the info you will likely need to be able to chose a tank...
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Got it, and thanks again!
Since I have a few old USA-built tanks on hand, I'm leaning toward the transformer approach on this one -- will tinker with the alternative down the road.
I'm gravitating toward the 'F' circuit in my illustration mainly because the specified transformer (Hammond 1750B), with its 5K:8-Ohm windings most closely jives with what I think I understand about power tubes and their required loads. (Will probably use the Edcor trans mentioned in my previous post.)
The recovery side I'm pretty comfortable with.
My plan for the reverb return is to follow the topology used in the Matchless Chieftain -- feeding it to the second input on the phase inverter. My thought is to avoid sending the reverb through the overdrive circuit when it is engaged. Other than that, I'm pretty much going to follow the Tweed OD circuit ... except that the output will be a pair of KT88s -- simply because I have the tubes and associated iron out of an old Sundown amp. Am also using a Hiwatt tone stack for the main circuit, and a 6G4A bass-treble control for the overdrive. May also experiment with the NFB approach used in the old HiWatts.
Thanks again for all the valuable help.
Joe
Clearly, I'm missing a critical piece in this puzzle.
Maybe you're just overthinking this. A tube plate is usually a high impedance (Z) device. The reverb tank input is whatever you specify it to be. If you want a low Z tank, then a transformer is the best choice of matching the high Z tube plate to the low Z tank. If you want a high Z tank, then a capacitor is the best choice for matching the high Z tube plate to the high Z tank.
Your example circuits A, B, and D are all CAPACITOR coupled drivers and require a high input impedance tank. Don't be confused by circuit A. Circuit A is NOT a transformer coupled driver. Someone is just using the primary of a transformer as a choke inductor for the plate load of the driver tube. A 14Hy choke could be used just as well. Hammond AO-43 is an example of a choke plate loaded driver that is CAPACITOR coupled to the tank.
Your example circuits C, E, F, and G are all TRANSFORMER coupled drivers and will use a low input impedance tank. When using a transformer, the transformer is used to match the input of the tank to the plate of the tube. A small output transformer used to couple a speaker to a tube circuit is cheap and plentiful, so most transformer coupled tanks will have a low Z input, typically about 8Ω. However, 600Ω transformers are used in communications circuits. You could use one of these transformers to couple to a 600Ω tank input. (A 600Ω transformer is not a common component that you would find stocked at most guitar amp supply houses.
So, in summary, for tube circuits, "usually" if you see a transformer coupled reverb driver, the tank input will be 8Ω. A cap coupled reverb driver will connect to a high Z tank input. And all tanks will have a high Z output.
The attached file is all the info you will likely need to be able to chose a tank...
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I don't think you want to use a 10w single ended (SE) output transformer (OT) for a tube reverb.
It's way over kill and that OT is big (taking up chassis space) and heavy compared to a standard Fender reverb(~3w, SE) OT.
Also if you use that OT with a small power pentode, 6GW8 or 6BM8, depending on how you set it up/bias it, you may get to much signal output from it and fry the verb tanks input coil.
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I'd stick with a transformer driven reverb circuit just because I'm more familiar with those. The only cap driven circuits I've ever had were Ampeg Gemini II and Magnatone 10A. Both of those sound great too.
12DW7 twin triode makes a good one tube reverb. Use the lo gain triode for the driver and the hi gain triode for the recovery.
I think a 6BM8 --> 1750C --> 8Ω tank is a good combo. I'm using a 6V6 --> Champ OT --> 9AB3C1B (8Ω tank) in my Revibe (http://sluckeyamps.com/revibe/revibe.htm). The cathode resistor will control the amount of drive to the tank.
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That was precisely my conclusion -- will mess with other stuff later ... in my copious spare time :laugh:
I'd stick with a transformer driven reverb circuit just because I'm more familiar with those. The only cap driven circuits I've ever had were Ampeg Gemini II and Magnatone 10A. Both of those sound great too.
12DW7 twin triode makes a good one tube reverb. Use the lo gain triode for the driver and the hi gain triode for the recovery.
I think a 6BM8 --> 1750C --> 8Ω tank is a good combo. I'm using a 6V6 --> Champ OT --> 9AB3C1B (8Ω tank) in my Revibe (http://sluckeyamps.com/revibe/revibe.htm). The cathode resistor will control the amount of drive to the tank.
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I see, and yes, I will hunt up an appropriate reverb transformer (hadn't even considered chassis space -- which I generally come to regret late in the build process). Did figure the biasing would control the power, regardless of the capacity of the transformer. All this stuff works WAY better than 'Luminicity' in staving off Alzheimer's ;^)
I don't think you want to use a 10w single ended (SE) output transformer (OT) for a tube reverb.
It's way over kill and that OT is big (taking up chassis space) and heavy compared to a standard Fender reverb(~3w, SE) OT.
Also if you use that OT with a small power pentode, 6GW8 or 6BM8, depending on how you set it up/bias it, you may get to much signal output from it and fry the verb tanks input coil.
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6BM8 Datasheet specifies a load resistance (pentode section) of 5600R
5600 ohms is just an example that RCA used to show what happens under those conditions. Svetlana gives you an example with a 7000 ohm load and Sluckey gave you a scenario with a 17,500 ohm load. The standard Fender transformer used in amplifiers is around 25,000 ohms. You don't need to use a 5K primary, nor do you want to.
The primary impedance puts an upper limit on how much power you can deliver to the tank. Reducing the primary impedance raises the upper limit, but you have to feed it more current to achieve this limit. It comes down to how hard you want to drive the tank and how many milliamps you're willing to spend.
There is only so much you're going to get out of a tank no matter what you put in. Putting more power into the tank after reaching this maximum is a waste and possibly even dangerous for the input coil. A 25K primary with a tube that can handle sufficient current is plenty for a guitar amp. A 15K primary with an appropriate tube will make sure that the tank is max'ed out long before the driver would clip. A 5K primary is just totally unnecessary.
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Understood -- and thanks again!
Joe
6BM8 Datasheet specifies a load resistance (pentode section) of 5600R
5600 ohms is just an example that RCA used to show what happens under those conditions. Svetlana gives you an example with a 7000 ohm load and Sluckey gave you a scenario with a 17,500 ohm load. The standard Fender transformer used in amplifiers is around 25,000 ohms. You don't need to use a 5K primary, nor do you want to.
The primary impedance puts an upper limit on how much power you can deliver to the tank. Reducing the primary impedance raises the upper limit, but you have to feed it more current to achieve this limit. It comes down to how hard you want to drive the tank and how many milliamps you're willing to spend.
There is only so much you're going to get out of a tank no matter what you put in. Putting more power into the tank after reaching this maximum is a waste and possibly even dangerous for the input coil. A 25K primary with a tube that can handle sufficient current is plenty for a guitar amp. A 15K primary with an appropriate tube will make sure that the tank is max'ed out long before the driver would clip. A 5K primary is just totally unnecessary.
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I've seen the 6GH8A triode/pentode tube pop-up here and on other forums using the pentode as a reverb driver. This tube is cheap and seems to be readily available. Both sections are rated at 2.5W, but the pentode is capable of way more gain than the triode. Since both sections have the same limit when it comes to driving a transformer, I would rather have the high gain one be the recovery. I don't know if there is a microphonic problem with the pentode at higher volumes, but at bedroom levels this setup is Surf City.
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I could easily be mistaken, but my impression was that the driver side is not looking to produce gain, so much as driving current. This would seem to correspond to Fender's use of parallel 12AT7s (or a 6V6, for the stand-alone unit) on the drive side, and a single 12AX7 for the recovery. That also seems to be the way all of the relevant schematics I've seen have been configured. Being basically lazy, I used my usual approach: built a simulation of a standard (BF Super Reverb) circuit, then modeled my pentode-triode circuit against that until I came up with a similar curve, but with a bit more 'oomph' out the back end. Of course, the final arbiter will be how it sounds -- hope to hear that soon! (Only reason I'm taking this approach is to save the necessity of using an extra triode in the driver, though a 12DW7 was also a possibility. (Here again, the '12AU7' side [higher current capability] seems to be typically used to drive the transformer, while the '12AX7' side is used for recovery.) Of course, one could probably use a pair of pentodes, but that seems like driving thumbtacks with a sledge hammer ....
I've seen the 6GH8A triode/pentode tube pop-up here and on other forums using the pentode as a reverb driver. This tube is cheap and seems to be readily available. Both sections are rated at 2.5W, but the pentode is capable of way more gain than the triode. Since both sections have the same limit when it comes to driving a transformer, I would rather have the high gain one be the recovery. I don't know if there is a microphonic problem with the pentode at higher volumes, but at bedroom levels this setup is Surf City.
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I would, however, like to ask another question on this topic: I was considering taking the reverb drive signal from the second preamp stage, after the volume control, but returning it to the second input of the phase inverter, ala' the Matchless Chieftain. My intent is that a) only the clean signal will appear in the reverb, and b) when I kick in the overdrive channel (this is being integrated into a Tweed OD Spcl circuit), the reverb will be relatively less prominent, which is what I generally want. Anyone foresee any problems with this? (Other than interference with the usual placement of the NFB/Presence control -- I will probably try bringing that back to the upper end of the phase inverter, the way the old HiWatts did ...
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I could easily be mistaken, but my impression was that the driver side is not looking to produce gain, so much as driving current. This would seem to correspond to Fender's use of parallel 12AT7s (or a 6V6, for the stand-alone unit) on the drive side, and a single 12AX7 for the recovery. That also seems to be the way . . .
Quoted me, so I guess this is in response to my 6GH8 driver/recovery.
I didn't mean to suggest that the 6GH8 setup would be something for you - - I had reverted to the original subject of the thread having thought that the 6BM8 discussion had ended.
That 6BM8 can do just about double of anything a 6GH8 can do and, as such, can drive a reverb considerably harder while staying well within the limiting values.
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My mistake -- thought you were suggesting using the triode side for the driver and the pentode side for recovery ...
I could easily be mistaken, but my impression was that the driver side is not looking to produce gain, so much as driving current. This would seem to correspond to Fender's use of parallel 12AT7s (or a 6V6, for the stand-alone unit) on the drive side, and a single 12AX7 for the recovery. That also seems to be the way . . .
Quoted me, so I guess this is in response to my 6GH8 driver/recovery.
I didn't mean to suggest that the 6GH8 setup would be something for you - - I had reverted to the original subject of the thread having thought that the 6BM8 discussion had ended.
That 6BM8 can do just about double of anything a 6GH8 can do and, as such, can drive a reverb considerably harder while staying well within the limiting values.
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Doing the layout for a DeArmond R5T which is very similar to a Princeton 5E2. This one has trem & I am thinking I would like to make accommodations to add the 1-tube reverb while I'm at it.
So a few questions;
I have looked at many threads which confirm my thought of adding it at the second-stage grid, which is fed directly from the volume wiper. I have inserted a 100K between the two & have also added coupling cap on the reverb send, though I'm not sure that is necessary, it is in some drawings & not in others. Any other considerations in this area?
Second, I will have to add a 4th B+ node, it looks like they are typically added using a 1K resistor from B+3. What is the preferred voltage differential for the reverb tube plates?
Third, I am thinking about deleting the dwell control, so do I replace the pot with a 1M resistor to ground?
Last, at this point, is regarding grounding. As a signal circuit the reverb should get grounded with the pre-amp & the trem, as a power circuit get grounded with the B+?
Thanks,
TD
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That 6BM8 can do just about double of anything a 6GH8 can do and, as such, can drive a reverb considerably harder while staying well within the limiting values.
I can confirm this firsthand. I'm the author of two of the 6BM8-based schematics that tubenit posted (the 5F1 Champ with Eric Barbour-inspired one-tube 6BM8 reverb, third schematic in Reply #26 in this thread and the third schematic in Reply #2).
That 5F1 w/ 6BM8 reverb schematic in Reply #26 is a bit old--it is version 1.0j, and the final one is at 1.0l (see attachment). The design does work and has worked well for five years now. It is meant to be a clean/dry reverb and was designed around the 500pF capacitor's trebly tone. To warm it up considerably, change that 500pF to a 0.001uF--BUT, read further before doing so.
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I decided to sign up and post here specifically to confirm that the 6BM8 is more than powerful enough to overdrive an 8F-series (high impedance) reverb tank via direct capacitor-coupling when using the pentode side in pentode-strapped-as-a-triode mode for the reverb driver and the triode side as the reverb recovery. So powerful that when I replace the 500pF cap with a 0.001uF cap--with a 470K resistor right behind it (see schematic version 1.0l) instead of the 220K (in 1.0j)--it introduces a overdrive/distortion that's scary enough that I wonder if I'll break the reverb tank's input coil. You can hear the tank vibrating and the springs rattling.
Easy fix when swapping the 500pF with the 0.001uF is to keep the 220K resistor as it originally was in version 1.0j. Another possible fix that I haven't tried is to replace the 0.470uF coupling cap with a smaller and less-expensive 0.022uF cap. Both of these component choices should reduce the signal/bandwidth being shoved into the reverb tank if you choose to go with a warmer tone.
Anyway, the 6BM8 is a good choice for a one-tube reverb. It can be arranged to send more than enough current into the reverb tank with plenty of room for tweaking and tone-shaping.
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Welcome dchang0! :icon_biggrin:
Thanks for posting that information. We hope we continue to see you posting in this forum. :icon_biggrin:
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I can confirm this firsthand. I'm the author of two of the 6BM8-based schematics that tubenit posted (the 5F1 Champ with Eric Barbour-inspired one-tube 6BM8 reverb, third schematic in Reply #26 in this thread and the third schematic in Reply #2).
Thanks for taking the time to post this.
The additional drive looks good & plus no transformer...(?)
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Thanks for taking the time to post this.
The additional drive looks good & plus no transformer...(?)
Thanks for the warm welcome, everyone!
Yes, the circuit was specifically designed not to use a transformer because the tight quarters inside and under a 5F1 chassis would not allow the attachment of a reverb transformer.
Also, Eric Barbour's original 6BM8 reverb driver example featured a transformer, so I figured that people interested in that approach could simply follow his schematic (see attachment) with some adjustments (he doesn't show a reverb recovery circuit, so you would have to take the triode side of the 6BM8 and move it over to the recovery side).
I ended up mostly ignoring Barbour's schematic because the transformer is so integral to its design and designed my 6BM8 driver by drawing new load lines and picking one that produced more current to drive the tank through the coupling cap.
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Huh -- I just threw something very similar, together on a hunk of 2X4, just to see if a one-tube amp would be feasible, and was really impressed by result. Those 6BM8s open many possibilities - push-pull power amp + LTP in a pair of bottles, gain stage plus cathodyne PI, two preamp gain stages plus two pentodes in SW Parallel .... I've really looked no further than just the gain factor, but that suggests that the triode section of the 6BM8 is similar to a 5751 (or a 6SL7GT), which is just fine by me, and pentode section is similar to an EL82 -- haven't checked that. Just seems like a multiplicity of ways to do the Fender Tweed Champ size/power thing with alternative approaches.
Thanks for taking the time to post this.
The additional drive looks good & plus no transformer...(?)
Thanks for the warm welcome, everyone!
Yes, the circuit was specifically designed not to use a transformer because the tight quarters inside and under a 5F1 chassis would not allow the attachment of a reverb transformer.
Also, Eric Barbour's original 6BM8 reverb driver example featured a transformer, so I figured that people interested in that approach could simply follow his schematic (see attachment) with some adjustments (he doesn't show a reverb recovery circuit, so you would have to take the triode side of the 6BM8 and move it over to the recovery side).
I ended up mostly ignoring Barbour's schematic because the transformer is so integral to its design and designed my 6BM8 driver by drawing new load lines and picking one that produced more current to drive the tank through the coupling cap.
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jbefumo shared this on this thread
http://el34world.com/Forum/index.php?board=13.0 (http://el34world.com/Forum/index.php?board=13.0)
With respect, Tubenit
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KNEW it looked familiar :dontknow: encroaching dementia?
jbefumo shared this on this thread
http://el34world.com/Forum/index.php?board=13.0 (http://el34world.com/Forum/index.php?board=13.0)
With respect, Tubenit
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I've just successfully incorporated the 1-tube reverb (as per tubenit's schematic in the first post) in a 50 watt plexi build, and so far I'm impressed with it. I made a little strip of eyelet board next to the tube socket, so that the rest of the amp layout was unchanged from a stock plexi layout.
It took a little tweaking to get the supply voltage right - at first I connected the reverb transformer to the phase inverter point in the power supply and the plate voltage was too high for my JJ ECC83. Moving it down one node solved that problem. It has less depth available than a blackface fender style reverb, but on those I typically run the reverb knob at no more than 2 on the dial and turning the 1-tube reverb to 7 or 8 gets me to a similar place. It seems a good match for this style of amp - nobody plays surf with a plexi, but it's great for adding a nice wash of 'verb to bluesy leads.
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I would like to add a 1-tube reverb to a Ted Weber amp that I built. It is the smokin joe II amp. Attached is the schematic. I have plenty of room in my chassis and enough power for at least one more 12ax7. I really don't know where to add the reverb circuit but I think it has to be after the Tone and/or Volume. The preamp stage uses an SRPP design. I have never built an amp with this type of tone control before. I really like the sound and simplicity of this amp. It is small, light weight and puts out about 15 watts. Plenty loud enough when mic'd. I have marked up two potential spots in the circuit where I could insert the reverb. Have a look, let me know if it is possible with this amp.
Thanks very much,
Steve
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The one on the right between the volume and LTPI. I'd use a 150k mixing resistor. Look at the 5879 blues amp GIF attached to the first post of this thread on the first page.
With respect, Tubenit
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After a week in Mex, I got the 1-tube reverb installed in the Weber Smoking Joe II using the Blues Amp circuit. Thanks tubenit! I left out the the dwell pot and used a 1M resistor instead. I used a 3 spring 9xxx reverb tank.
Sounds perfect. Exactly what I was hoping for.
Steve
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Hello all,
I'm looking to build my first amp, a Matchless Lightning clone. I'll be using a layout and schematic from the good folks at Trinity amps, but I would like to add reverb to it.
Could someone help me with where the insertion point should be? I believe that it should go after the Tone-stack & before PI tube OR if it should go after the Master Volume?Full disclaimer I am at the beginning of this hobby/addiction and as far as amp expertise and knowledge, I am like a Kindergartener who knows their letters but can't actually read yet. I can look at a schematic and identify just about everything on it, but I'm not understanding everything at 100% right now. I appreciate any help you could provide.
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I am wondering about that schematic that you posted being correct? It might be but I've never seen a resistor in that one spot before?
Here is how I would do it.
With respect, Tubenit
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I am wondering about that schematic that you posted being correct?
It's correct. The preamp is pretty hot in the lightning. That 220K and 100K make a voltage divider to knock the signal down quite a bit before it hits the PI.
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I am wondering about that schematic that you posted being correct? It might be but I've never seen a resistor in that one spot before?
Here is how I would do it.
With respect, Tubenit
Thanks so much Tubenit. I'm new to the forum so I don't see a like/give kudos/thanks button, but I found this to show my appreciation :worthy1:
I know most people are adding these reverbs into the circuit as a separate board to the main board, but would there be any reason to not include it on the main if I plan on having Hoffman make the board anyway?
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but would there be any reason to not include it on the main if I plan on having Hoffman make the board anyway?
That's how I'd do it.
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I agree with Sluckey & would put it on the main board.
Tubenit
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Tubenit, in the schematic you provided are the two 1M resistors the Potentiometers for the reverb controls? If so, are their lugs 1-2-3 from north-middle-south?
Also, what are "E" and "B"?
Assuming that the 1M resistors are the pots, I've done a mock layout. I know the spacing, etc. is wrong, but I've never tried to translate a schematic to a layout before. Could those more knowledgable than me check this layout against the schematic Tubenit provided?
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The 1M "resistors" are indeed 1MA potentiometers.
I don't know what 1,2 & 3 is? You'll have to figure out that one on your own or get help. I don't number the lugs.
E and B are nodes on the B+ rail. I simply cut and pasted from a schematic I had to illustrate the insertion points.
With respect, Tubenit
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Perfect, that's what I was thinking. I just meant pot lug numbers. I've only seen them numbered before, but the way you have it they are implied and clear. Thanks again.
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You need to move the ground wires to the left lug on those pots in your layout.
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You need to move the ground wires to the left lug on those pots in your layout.
Ok, thanks. I have to triple check things when orientations change and I didn't there. We're there any other errors?
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Yes, there are several other errors. Put the schematic and the layout side by side and it should be easy to sort them.
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Well, that's embarrassing. I'll give it another go then.
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That's how we learn. Post your revised layout and I'll have another look. And I'll be more specific next time. Wanted you to try to sort it first.
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Sluckey, here is my second attempt. Did I at least move from an F to a C-?
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If I was grading you I'd give you a B on this drawing. The only thing that I see that's wrong is the 220K and 500pf on the return jack. Look at the schematic again. You'll see it immediately.
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Yeah, they are parallel to ground? Should I just ground them to the closest star ground or run them back onto the board to be grounded?
Also, any tips about ways to improve the layout would be helpful. Like I said this is my first schematic to layout attempt, so I understand it may be functionally right, but not logically correct. I've really searched for a good tutorial on this, and found some, but nothing that has just clicked with me yet.
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Fender didn't use that 500pf. They only used the 220K and it was mounted directly on the return jack.
Hanging out on this forum (and others), looking at what others have done, designing your own layouts based on the schematics, etc. will go a long way toward making good logical board layouts. You'll get better as you go. I feel that my stuff has progressed a lot since my first layouts. Oh, and making mistakes is a good teacher too! :icon_biggrin:
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So, with your help, I got my Epiphone Pacemaker running. While I was going through all my parts, I realized I have everything to install one of these 1 tube 'verbs in my AO43 Hoffman Stout TMB, (except a tank, not sure which one to get)
I have an extra open noval socket in the chassis, plenty of room at that end of the chassis to use the circuit in tubenit's first post, and plenty of heater current.
I am just circuit challenged. I've been through all the posts, all the layouts and schematics, and I can't figger out where to insert the circuit in the the tmb circuit.
Attached is the layout and schematic, although the schematic doesn't include the MV parts.
Any help would be appreciated..
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I'd do it like this...
Refer to the schematic... Remove R12. Disconnect C5 from C8 and install a 100K resistor between C5 and C8. Connect Tubnit's reverb circuit input to the junction of C5 and the 100K. Connect the reverb output to the junction of the 100K and C8.
Or refer to the layout... Replace R12 (470K) with a 100K. Remove the short ground buss jumper from the bottom of R12. Remove the short jumper between the bottom of C5 and C8. Install a jumper between the bottom of C8 and the bottom of R12 (now a 100K). Bottom of C5 connects to reverb input. Bottom of C8 connects to reverb output.
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I'd do it like this...
Refer to the schematic... Remove R12. Disconnect C5 from C8 and install a 100K resistor between C5 and C8. Connect Tubnit's reverb circuit input to the junction of C5 and the 100K. Connect the reverb output to the junction of the 100K and C8.
Or refer to the layout... Replace R12 (470K) with a 100K. Remove the short ground buss jumper from the bottom of R12. Remove the short jumper between the bottom of C5 and C8. Install a jumper between the bottom of C8 and the bottom of R12 (now a 100K). Bottom of C5 connects to reverb input. Bottom of C8 connects to reverb output.
Is that C5 and C8, or C5 and C6?? Thanks!! actually where I thought it should go, (more or less) use an 8 ohm tank, correct?
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C8 should be C6. Sorry, bad eyes.
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C8 should be C6. Sorry, bad eyes.
No worries, that's what I thought. Thanks again!
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How do you think the originally posted 1 tube circuit would work with an EF86?
EF86>LTP>EL84PP
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I would like to add this to a peavey windsor. I was wondering where I would add the in and out signal for the one tube reverb. Thanks
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I would like to add this to a peavey windsor. I was wondering where I would add the in and out signal for the one tube reverb. Thanks
The Valve King is very similar to the Windsor and they put the reverb across a 330K resistor coming off of the Master Vol. wiper.
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A big hearty Thank You to Tubenit for the circuit, and sluckey for the wiring advice!! I added the 1 tube reverb as shown in the 1st photo of this thread, and other than being a little ugly on my part, it works GREAT. It took a little fiddlin' to get it added in around everything else, but I did it.
The circuit can be seen in the accompanying photo in the lower right corner.
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Nicely done! Thanks for sharing! Glad it worked out for you.
With respect, Tubenit
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Hey T, The 6DX8 reverb circuit in the Moody GA-40 was not successful.
I had enough information on the circuit but no matter what I did, it seemed to be unstable, with effects on other parts of the amp that I can not explain due to my lack of tube techness.
Wanting to move this amp along the 6BM8 IS a proven working circuit with plenty of boing without being over the top.
Compared to transformer driven spring reverbs, I find capacitor coupled circuits to be less trebly and hashy.
Using a 8EB2C1B short tank is bright enough with a much richer smoother effect, very different to transformer driven tanks.
I don't think capacitor coupled reverbs will do surf.
(http://i761.photobucket.com/albums/xx254/Timbo-08/001%203_30.jpg) (http://s761.photobucket.com/user/Timbo-08/media/001%203_30.jpg.html)
This is how I inserted it into the main circuit.
I do think adding it after the TS is a good idea, as more treble can be added if needed and a stronger signal is also available at this point.
(http://i761.photobucket.com/albums/xx254/Timbo-08/002_22.jpg) (http://s761.photobucket.com/user/Timbo-08/media/002_22.jpg.html)
Due to the large current draw of the 6BM8 pentode (6GW8 also has a large current draw) some beefing up of the PSU was needed.
As you can see a large wattage resistor (string of 5x1k/5w) was needed to supply the reverb node, I found that tapping off node "B" was the best to use.
Also the plate resistor got quite hot, again I increased the wattage to 10w by paralleling two 5w resistors, this also gets very hot but seems the hold.
(http://i761.photobucket.com/albums/xx254/Timbo-08/003_19.jpg) (http://s761.photobucket.com/user/Timbo-08/media/003_19.jpg.html)
I've tried to tweak the voltages as best I could to what sounds good.
(http://i761.photobucket.com/albums/xx254/Timbo-08/010_18.jpg) (http://s761.photobucket.com/user/Timbo-08/media/010_18.jpg.html)
This how I have mounted the tank as the amp is HEAD cab.
The tank I have used is a 8EB2C1B used for horizontal open side down. The tank should be an 8EB2C1D vertical mounted connectors down, but I don't have one.
Just as a tip, I hard wire my tanks as this prevents problems of the RCA's working loose and a problematic connection.
Thanks Timbo
Overall the 6BM8 is a good reverb driver with a great effect for BLUES style playing.
https://www.youtube.com/watch?v=aXE4vN1nKok (https://www.youtube.com/watch?v=aXE4vN1nKok)
Just found a great demo that is dam close to what I have, maybe not as much when dwell and level are maxed.
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Hello everyone ;)
I’m new at the forum. Tons of information here!
I’m building a rather straightforward EL84 single ended and I’ll insert the 'one tube reverb' in it. Regarding the power supply, I find that my VDC references in those power chain capacitors are lower in value compared to the ones in Blues Amp, Carolina Blues Special ,etc posted here.
This is the layout of the amp
http://i1347.photobucket.com/albums/p715/squarebet/SingleendedEL84_V10_zpsc7mjn8js.jpg (http://i1347.photobucket.com/albums/p715/squarebet/SingleendedEL84_V10_zpsc7mjn8js.jpg)
So, from your experience, can anyone tell me if the reverb layout will ‘work OK’ under those VDC values? Any tips are welcome!
Thank you all in advance ;)
Cheers.
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I think the voltages would probably be OK, but you probably need another gain stage after the reverb insertion to work well.
I have inserted the reverb around a tone/volume topology before and had that work well for me. This allowed another gain stage after the insertion point. Only downside is you may wish to adjust the reverb IF you make significant changes with the volume knob. I did this on a Carolina Blues Special amp (or two) and it worked well for me.
Also the Gibson Scout does something similar. http://el34world.com/charts/Schematics/files/gibson/Gibson_GA-17RVT_SCOUT.pdf (http://el34world.com/charts/Schematics/files/gibson/Gibson_GA-17RVT_SCOUT.pdf)
It probably would have been better to post this on Tweaks as you would have more forum members reading and responding to it.
with respect, Tubenit
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Thanks Tubenit!
The Gibson Scout is a great example. As I wasn't thinking on adding another valve, I think I'll try something like this
http://i1347.photobucket.com/albums/p715/squarebet/SingleendedEL84_V11_zpsxkr9d2ai.jpg (http://i1347.photobucket.com/albums/p715/squarebet/SingleendedEL84_V11_zpsxkr9d2ai.jpg)
Do you think I should put a resistor before RV2?
From now on, I'll post this on Tweaks. :wink:
Thanks again!
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I would try it just as you've drawn it and see if you like it?
With respect, Tubenit
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2Deaf shared this 12DW7 transformerless reverb idea that he implemented in a Princeton Reverb type build. He states he has about 320v on the driver plate. Another option for a "1-tube reverb".
The thread is here: http://el34world.com/Forum/index.php?topic=20975.msg224322#msg224322 (http://el34world.com/Forum/index.php?topic=20975.msg224322#msg224322)
With respect, Tubenit
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Hi guys, This 6BM8 reverb circuit has turned up in another Fi Sonic amp.
I like the 6BM8 circuit very much.
The original circuit has way too much reverb and is not great at all.
I have done this mod to my other amps and found it a much better circuit.
(http://i761.photobucket.com/albums/xx254/Timbo-08/002%206_11.jpg) (http://s761.photobucket.com/user/Timbo-08/media/002%206_11.jpg.html)
I also like the way it has been inserted into the preamp.
When the reverb is dial out it has NO effect on the preamp workings.
Circuit here..........
http://el34world.com/Forum/index.php?topic=21998.msg234757#new (http://el34world.com/Forum/index.php?topic=21998.msg234757#new)
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I've abandoned the one-tube reverb concept. Don't get me wrong, the one's I've tried sound "OK" but that's about it... just "OK." The return on quality vs effort and money for me to do it right is much better just using a quality reverb pedal like a Hall of Fame in the loop or even out front.
Now please excuse me while I put on my asbestos suit as the purists flame away! :icon_biggrin:
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I found another interesting "one tube reverb" in the Cornford amp. It seems to parallel an FX loop. It also uses a .002 smoothing cap between the plate and cathode of the send triode.
http://el34world.com/charts/Schematics/files/cornford/Cornford%20Hellcat.pdf (http://el34world.com/charts/Schematics/files/cornford/Cornford%20Hellcat.pdf)
With respect, Tubenit
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http://www.channelroadamps.com/articles/reverb_driver/ (http://www.channelroadamps.com/articles/reverb_driver/)
Interesting use of a 6GH8 pentode/triode for reverb
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Hi guys, Another one to add to the list.
This is straight out of a Hammond AO-48 organ amp.
I have not tried it WITH a 12DW7 as I don't have one, but the 12AX7 sounds awesome.
Uses a standard reverb transformer and tank.
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Hey Timbo, you show a 150Ω resistor connected to the top of the reverb pot. Are you sure about that resistor value?
Edit... I just looked at the original schematic (page 22 of the pdf you linked on the main board) and that resistor is indeed 150K, not 150Ω as shown on your revised drawings.
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Thanks, Done :thumbsup:
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Someone asked me should the reverb be before or after an overdrive section. My answer is that I think it would sound best after the overdrive as illustrated in this attachment.
With respect, Tubenit
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These are reported proven designs for 6BM8 reverb from TAG (The Amp Garage)
With respect, Tubenit
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Hi T, This is a collection of one tube reverb circuits that I have used and all work very well.
(https://i.imgur.com/fgina7j.jpg)
(https://i.imgur.com/BsQdXaO.jpg)
(https://i.imgur.com/L9eT5V9.jpg)
(https://i.imgur.com/nZY0xwI.jpg)
(https://i.imgur.com/LyyDDmB.jpg)
(https://i.imgur.com/V52TymM.jpg)
(https://i.imgur.com/MraG58I.jpg)
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It looks like there is yet another option for a "one tube reverb" using a Belton Brick. Thanks for John in sharing a proven build using this approach that was successful. Please read his comments carefully especially regarding a separate 6.3v power supply that is not used for heater wiring.
Note Sluckey's comments in this thread Reply #15
https://el34world.com/Forum/index.php?topic=23554.0 (https://el34world.com/Forum/index.php?topic=23554.0)
Anyone ever incorporate an accutronics brick into their builds? (el34world.com) (https://el34world.com/Forum/index.php?topic=28744.0)
Also note Ed's comments comparing the Belton Brick to a spring reverb in reply #9
With respect, Tubenit
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I've started playing a little more jazz and as a result of that, I was looking for a very warm reverb tone that added some fullness but stayed away from a strong "surf music reverb". I am very happy with this. To my ears, it seems to add reverb to more mid tones which gives a fuller sound while staying away from the strong treble reverb tones.
Worth a try if your reverb sounds too bright or too thin, IMO. I am playing with the reverb pot between 5 & 6.
With respect, Tubenit
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Thanks for the info, T
I'm finding I'm getting a smoother deeper boing with the long tank and a sharper "in your face" with the short.
What size tank are you using?
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I'm using a "typical" fender 4AB3C1B. It's the one Doug sells.
Jeff
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2Deaf shared this 12DW7 transformerless reverb idea that he implemented in a Princeton Reverb type build. He states he has about 320v on the driver plate. Another option for a "1-tube reverb".
The thread is here: http://el34world.com/Forum/index.php?topic=20975.msg224322#msg224322 (http://el34world.com/Forum/index.php?topic=20975.msg224322#msg224322)
With respect, Tubenit
I tried to implement this on my 18 watt tmb built but all signal disappear as soon as i connect it to the circuit. I use a 150k instead of the 3.3M
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Hello everyone!
I recently implemented the 1-tube reverb circuit as described in the 1st post of this thread in a clone of a VOX AC10 SRT. I've found that it really sings with a 12AT7!
While measuring voltages, I noticed that the cathode voltage of the triode that drives the tank was a bit above 10 volts. This suggests that approximately 7mA are flowing through the tube.
My B+ isn't particularly high... perhaps 220V?
Is this typical, or am I going to burn out the tube?
Thanks!
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These are reportedly nice sounding reverbs.
With respect, Tubenit
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Adding this one to the 1 tube reverb stash... https://guitar.com/guides/diy-workshop/build-tube-spring-reverb-unit-amplifier/
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Hi all, new to this forum, see a lot of great info here!
Was thinking of incorporating the recently posted 12DW7 reverb driver into a new build and had a quick question. Would the coupling caps C28 and C33 even be necessary in the attached dwg? Are they needed for any tone shaping? The attachment points seen to be free of any DC voltage already...
tia
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The tank drive coil is inductive, I guess that C28 and 30 are sized to drive it evenly over the frequency range we’re interested in.
The tank’s pick up coil will be prone to boomy feedback, especially if used in a combo cab, unless some bottom end is rolled off; C33 is probably sized to achieve that.
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I built a Hoffman 6V6 Plexi and really love that amp. Now I want to build another but with the 1 tube reverb mod. I printed off the layout for the board and did some cut and paste. almost everything to the left of where the master volume comes in is untouched, as is everything to the right of the NFB input. the plan is to stretch the length of the board to make room for the reverb components rather than have a second board. I think what I have hacked together here will work. I have stuff to build the board but want opinions before I drill. I have a kinda crappy scanner/printer so this is what I got, it's life size (hard for me to write the numbers that small) and ready to be a pattern.
I drew in all the changes, but not all the connections... the preamp and tone stack will be unchanged etc. one other mod I wanted was to remove the presence pot and replace it with a fixed resister. thanks....
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I think I saw that on Ancient Aliens recently! :icon_biggrin:
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yep.... scratched on the wall of my cave with a flint hatchet.
should I try it?
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I guess. The only thing I recognize is the tall man pointing to a star cluster.
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... The only thing I recognize is the tall man pointing to a star cluster.
THIS changes EVERYTHING
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I've used the one tube reverb from the first post of this thread a few times. It has worked well in Marshall 18 watt style circuits, but I have oscillation issues with it in a Vox AC30. Perhaps layout or lead dress issues, but I've tried messing with those, and I've managed to reduce but not eliminate it.
Anyway, my question is, would it be beneficial to add, say, a 15K grid stopper to the driver and/or recovery triodes?
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would it be beneficial to add, say, a 15K grid stopper to the driver and/or recovery triodes
I have NO idea if that would be beneficial or not. Try it and let us know.
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...I have oscillation issues with it in a Vox AC30. Perhaps layout or lead dress issues, but I've tried messing with those, and I've managed to reduce but not eliminate it...
It would be a good idea to try and identify what stages are involved in the feedback loop or loops that are oscillating, eg add a small plate to cathode snubber cap to a stage and see what effect that has on the issue. Document and move the snubber on to the next stage.
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...I have oscillation issues with it in a Vox AC30. Perhaps layout or lead dress issues, but I've tried messing with those, and I've managed to reduce but not eliminate it...
It would be a good idea to try and identify what stages are involved in the feedback loop or loops that are oscillating, eg add a small plate to cathode snubber cap to a stage and see what effect that has on the issue. Document and move the snubber on to the next stage.
It appears to be the reverb recovery stage oscillating. It will still oscillate with the tank return unplugged. Grounding the grid stops it of course. I have a couple more things to try with lead dress and layout, as the AC30 build was the first time I've tried reverb switching using relays, instead of the Fender style foot switch.
This question came about though as my laptop got stolen with all my layouts and schematics, so I am having to redraw them all. I'm doing another 18 watt build, and was curious whether to try the grid stoppers here, and also in the next revision of the AC30.
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so.... did the 1 tube. it works, but only makes reverb when controls are at "8" or better. it's OK, but not that great. circuit is Hoffman 18 w Plexi
thoughts?
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Show us your schematic with values and voltages and how you implemented it (insertion point), please & we can give you a comment.
Without knowing what you've done, it's almost pointless trying to resolve your problem? There are a variety of "one tube reverbs" and a variety of "18watt" amps and a variety of places people have chosen as the insertion point.
Typically, I have all the reverb I need with the reverb pot dialed between 3-4.
In this attached example, you might use a 2.2M reverb pot. You might need another resistor (maybe 100k) between the master volume and the 150k insertion point resistor.
With respect, Tubenit
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sluckey
I've built an Ampeg Jet J12b from your schematic and layout for the RCA radio conversion. It is an awesome amp and thanks for the layout and tremolo revisions. Would tubenit's 1 tube reverb work well for this amp and would the insertion points be the same?
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sluckey
I've built an Ampeg Jet J12b from your schematic and layout for the RCA radio conversion. It is an awesome amp and thanks for the layout and tremolo revisions. Would tubenit's 1 tube reverb work well for this amp and would the insertion points be the same?
Don't know but probably. Just build it and see. May have to experiment a bit with insertion points but a good starting place would be between the Volume pot wiper and V2-1.
If you decide to try this post a new thread in the Tube Amp Building forum. Lots of people would be interested. Pics are highly desirable too.
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sluckey
I've built an Ampeg Jet J12b from your schematic and layout for the RCA radio conversion. It is an awesome amp and thanks for the layout and tremolo revisions. Would tubenit's 1 tube reverb work well for this amp and would the insertion points be the same?
Don't know but probably. Just build it and see. May have to experiment a bit with insertion points but a good starting place would be between the Volume pot wiper and V2-1.
If you decide to try this post a new thread in the Tube Amp Building forum. Lots of people would be interested. Pics are highly desirable too.
Thanks, I believe I will give it a try! Also I really appreciate the layout for this amp. It's the only layout I have found for an Ampeg amp. Would love to find one for a Reverberocket II and Gemini II.
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What tanks are people using with this circuit? I am wanting to add this to my amp, and was originally thinking of a 9AB2C1B for the tank. Now Im wondering if the circuit would have an easier time driving a 8AB2C1B instead? The 9AB2C1B is 3 delay lines comprised of 6 springs (Each set of 2 springs tied together). The 8AB2C1B is 3 delays lines with 3 springs. So with the 8AB2C1B there would be less mass to vibrate. I'd assume the 9AB2C1B would have a slightly more complex/deep sound though, so if there isn't a major difference driving the tanks it prefer to use it.
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Have a look at this page:
https://www.amplifiedparts.com/tech-articles/accutronics-products-and-specifications (https://www.amplifiedparts.com/tech-articles/accutronics-products-and-specifications)
It's a description of Accutronics' naming conventions and contains a lot of basic tank info. That'll get you started. Also have a look at Merlin's pentode reverb and a good discussion of basic reverb theory at:
http://www.valvewizard.co.uk/reverbdriver.html (http://www.valvewizard.co.uk/reverbdriver.html)
Rich
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Thanks for the links.
Interesting that "Accutronics quote the saturation current of their cores as 3.5Amps per turn (rms)" So, do I understand correctly then that longer/more spings = more turns = lower current requirement (and therefore lower voltage)? If so, then I guess my original logic was backwards and 9AB2C1B would actually be easier to drive than the 8AB2C1B, since the 9AB2C1B should have approximately twice as many turns. Sometimes electronics is counter intuitive lol.
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The formula refers to the number of turns on the bobbin at the input transducer. The saturation current is much higher than what you need, so you don't need the calculation anyway.
Just look at how different tubes drive different tanks and you will notice, you won't need more than a 6V6 and can go as low as you like.
I think the mixer is the more tricky part.
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I found 2 more amps using transformerless 1 tube reverb.
The schematic does not specify the tube type but after researching, it appears to be a 12AX7
Have never heard either of them
EDIT: I learned that Carvin used an unusual tank, the 8GB2C1B. Not a typo-- 8G.... Spec is 8333 ohm/735 ohm input, 2575 ohm/200 ohm. It does not seem to be available from sources in the US. TAD in Germany sells it.
Possibly this unusual tank is needed with a 12AX7 as the reverb driver (capacitor driven off the plate)
Also, Carvin went to digital reverb quite a while ago, and currently, does not seem to offer guitar amps any more.
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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
Wouldn’t a 12AT7 shake the tank harder? 10mA vs. 1 mA? Would have to lower the cathode resistor. Also why such a big cathode bypass resistor? 10uf across 1.5k has a corner freq. 106Hz. You’re already reducing bass with a .001 input coupling cap. 22uf would lower the corner freq. further to 48 Hz. {1 / 1500 x 6.28 x 22 = .0000048}.
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General question about retrofitting these reverbs into existing amps (or amp designs).
The reverbs add several extra parallel loads/resistive paths to ground:
1- The reverb input has either a dwell pot or voltage divider or at least grid leak to the reverb driver
2- The reverb output, usually a reverb level pot, which also forms a grid leak for the following stage
3- The reverb recovery stage itself as the reverb level is turned up
4-not a fourth load, but a voltage divider formed by mixing resistor and the reverb level/reverb recovery stage
In grand summation these can change what was a simple 1M load resistor or Volume pot for the preceding stage to well under a few hundred, even just tens of ohms.
So in real world implementation, how does the overall character of the amp's sound and volume change with the dry signal having the life sucked out of it? I can't conceive of how this translates into decibels, and change in character by reducing gain so drastically.
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So in real world implementation, how does the overall character of the amp's sound and volume change with the dry signal having the life sucked out of it?
Where are you getting the idea the dry signal has "the life sucked out of it"? Not why you're presuming that? :dontknow:
I'm not sure I'm understanding your question as you may be intending? And I'm not sure you're understanding the schematics I've posted in the first post on this thread.
My experience is the amp sounds pretty much the same except with reverb added.
The dwell pot is rarely turned down low. The mixing resistors I use are reasonably small 220k or less because the 1M reverb pot (which is not in the dry signal path) plays a factor in the mixing vs. standard 100k Fender reverb pot with 3.3M mixing resistor (which is in the signal path).
Respectfully, Tubenit
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Thanks Tubenit.
I am confused how the parallel loads added do not suck down the signal.
Am i misunderstanding? An example, 5F1, if you insert a reverb after the first gain stage, it has not only the 1M load of the volume pot, but also the parallel loads of the input divider or dwell pot to ground, plus the reverb recovery/level pot to ground. If those three are 1M each, the parallel load is 330K, which means the resulting signal is 1/3 the AC voltage when it reaches the second gain stage in the original circuit. Some of these schematics show voltage dividers, pot values and pot orientations that create even lower impedances plus attenuation, and as far as I can tell, will send a lot of signal to ground.
If they still sound the same, same gain, same volume, that is wonderful, but I am perplexed.
respect to you too!
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I've installed one tube reverb on quite a few amp builds. I have never lacked volume in any of the amps whether 6L6,5881,6V6 or 6BM8's. The reverb doesn't "dull" the amp or kill tone. Quite the opposite.
It is rare that I'd have the volume pot above 4 or 5. Most of the amps I've built for myself have master volumes (usually a PPIMV) on them also.
So far, it's never been a negative experience for me or for others where I've added a one tube reverb for them.
Take one of the schematics in the first post of this thread and follow the signal chain thru to the speaker. Try using a highlighter pen. Then ask yourself where in the reverb section is the signal being killed in the signal chain?
With respect, Tubenit
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I am confused how the parallel loads added do not suck down the signal.
There are tens on thousands of Fender amps that have a parallel (||) reverb circuit and they don't sound like the dry signal had the life sucked out of it.
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I've installed one tube reverb on quite a few amp builds. I have never lacked volume in any of the amps whether 6L6,5881,6V6 or 6BM8's. The reverb doesn't "dull" the amp or kill tone. Quite the opposite.
It is rare that I'd have the volume pot above 4 or 5. Most of the amps I've built for myself have master volumes (usually a PPIMV) on them also.
So far, it's never been a negative experience for me or for others where I've added a one tube reverb for them.
With respect, Tubenit
That is reassuring to hear, and I guess that if you are not diming your amp that you have more room to move. i.e. you were never going to use the maximum range of your preamp to start with.
Take one of the schematics in the first post of this thread and follow the signal chain thru to the speaker. Try using a highlighter pen. Then ask yourself where in the reverb section is the signal being killed in the signal chain?
With respect, Tubenit
Respectfully, you are missing the point. The added parallel loads when adding the reverb circuit draw down the signal AC voltage at the preceding tube stage. It is the load on that tube's output I am talking about.
There are also losses through the subsequent path due to the voltage divider of mixing resistor over reverb output impedance, whether that is the reverb level pot or when the reverb is turned up full, back though the reverb recovery triode.
I will draw and post some pics and load lines when I have the chance.
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I am confused how the parallel loads added do not suck down the signal.
There are tens on thousands of Fender amps that have a parallel (||) reverb circuit and they don't sound like the dry signal had the life sucked out of it.
And respectfully to you, I am not arguing to the contrary, but the Fender design adds a post reverb gain stage to make up for these load losses. Look at the typical blackface on through silver etc... There is a gain stage post tone stack to make up for the loading losses from the stack. Then the reverb mix and parallel reverb, then another post reverb gain stage. These single tube reverbs do not add that extra gain stage to make up for the load and voltage divider losses inherent in the addition of the reverb.
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I am not arguing to the contrary, but the Fender design adds a post reverb gain stage to make up for these load losses.
No, that gain stage is for boosting the verb, not the dry signal. (And you are arguing to the contrary.)
Your leaving out that Fender knocks down the dry signal with a 3M3 R before the final verb mix gain stage. If the || verb kills the dry signal by loading it down, why does Fender have to put the 3M3 R in series with the dry signal? Because there's too much dry signal compared to the verb signal.
Look at the typical blackface on through silver etc...
Yeah, I know what a Fender verb circuit looks like. :laugh:
....Then the reverb mix and parallel reverb, then another post reverb gain stage. These single tube reverbs do not add that extra gain stage to make up for the load and voltage divider losses inherent in the addition of the reverb.
They don't need to. Different animal.
Your leaving out that 3M3 series R in the dry signal.
The 1 tube reverb's don't use a 3M3 R, they use a MUCH smaller R there. Like 100K to 330K. That's a huge difference.
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Bottom line is tubenit has built and when building these 1 tube verbs he has tried different things/values while tweaking them.
I know tubenit well for many years now. I know how much time he will invest in getting an amp, a circuit to sound and work not just well, but as best as can be.
Say what you want, but he's done the work and what he is telling you and what he has gone to the trouble of posting here for the benefit of others, after all his experiments, I'm sure is correct.
Most, if not all of these 1 tube verb's won't get the surf verb that a stand alone verb or a the standard 2 tube verb of a Fender combo amp, but they will get plenty of verb for most purposes.
And they will still have plenty of dry signal on tap. Even when dimed.
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That is reassuring to hear, and I guess that if you are not diming your amp that you have more room to move. i.e. you were never going to use the maximum range of your preamp to start with.
This is wrong in real world use and in assumption.
We've seen many guys build a small combo amp with 1 tube verb or add a 1 tube verb to their existing amp build and no one has ever complained that the amp lakes enough dry signal, at any setting, including full up.
Respectfully, you are missing the point. The added parallel loads when adding the reverb circuit draw down the signal AC voltage at the preceding tube stage. It is the load on that tube's output I am talking about.
There are also losses through the subsequent path due to the voltage divider of mixing resistor over reverb output impedance, whether that is the reverb level pot or when the reverb is turned up full, back though the reverb recovery triode.
Hummm, and yet there is plenty of dry signal available and plenty of reverb short of surf verb.
You must be missing something? :think1:
I will draw and post some pics and load lines when I have the chance.
You might be better off spending that time building a 1 tube verb amp and seeing how it sounds? :think1:
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I will draw and post some pics and load lines when I have the chance.
If that's useful to you, please feel free to do so. You seem to be concerned there is something about this circuit that impacts the tone of an amp in a negative way?
Do you have any real life experience with the one tube reverb being added to an amp?
Respectfully, Tubenit
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You seem to be concerned there is something about this circuit that impacts the tone of an amp in a negative way?
Yes.
Do you have any real life experience with the one tube reverb being added to an amp?
Yes, two, and more to come.
Thanks for you input Tubenit.
Wilabe, I am sorry it seems I have raised your hackles, wasn't any such intent.
I apologize for posting.
Best to you both.
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Please feel free to share what was negatively impacted in the tone or volume with your experiences adding one tube reverb.
What did you hear differently after the reverb circuit was built in?
My experience has been that it has always worked well for me, given me a tone I liked and I still had plenty of volume. The one tube reverb is not a good choice for Dick Dale surf stuff, but works well for what I am looking for.
And if you could post an exact schematic of how you added the reverb that would be helpful. It may help inform someone on the forum considering trying this as to whether or not they want to experiment with it.
If it didn't work well for you, give some details of what your experience was along with the schematic please. Your sharing that could be useful to others.
With respect, Tubenit
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Again, sorry I posted. Seems like misunderstanding all around. I am not complaining about your circuits, and no question, I do believe that what you have built suits your needs.
And I am not reporting problems with the one tube reverbs I have built, but they are not in a similar context as retrofit to already existing design.
I am trying to reconcile an electronic puzzle that occurs when these are inserted into already established circuits.
The two I have built are not relevant to that context.
I'll figure it out with my next build which inserts a reverb in an altered Fender deluxe type circuit where it is a retrofit to essentially already established design.
I posted my question here wanting to go into the build with better fore-knowledge, but will proceed anyway to find out through my own experimentation.
Carry on.
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You brought up a reasonable question. It may prove to be a useful insight and/or question for others. Solid information may help others to make a decision whether to consider this approach or not.
I'm limited in my understanding of electronics and just sorta grasp some of the basics needed to design and build amps. So you may be on to something that I've totally missed. You're welcome to post any thoughtful information that you may see useful to others.
Most of my values/taste/preferences regarding tone are based on many hrs of simply experimenting til I find what works well for me. Given limited knowledge of electronics, I have to rely on what I'm hearing instead of the math/science to guide me.
Best regards and respect, Tubenit
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Here is one example of what happens EDIT can happen when inserting a reverb circuit into an existing amp. This is not a conventional way of analyzing or evaluating, but you might be interested in the results
I’ve got an amp build on the breadboard, very similar to a Blackface Champ. The preamp follows the Tone King Imperial 20th Anniversary schematic, with V1A unbypassed and a slightly tweaked tone stack. I also have the V1B cathode bypass cap down at 5 uF. So not quite as high gain as the Champ.
Running a .1V 1000hz signal into the amp , and out through an attenuator to a Canabis Rex speaker, I get a sound level of 83 dBC. This test would be intolerably loud without the attenuator.
After adding the 1-tube reverb with 2meg reverb isolation resistor as shown in the attached schematics, sound level dropped to 67 dBC. Amp settings, mic position, etc. were the same for both tests.
So there is a big volume drop. But other than that, there is no loss of tone. Still sounds great, plenty of “life,” just not as loud.
There are any number of schematics out on the web for adding reverb to a Champ. Most if not all add a recovery gain stage after the reverb isolation resistor and before the 6V6. From this test I can see why. It sounds good at low volume practice levels, but that’s all you get.
I don’t have room for another tube. 2deaf/Ten Over designed a LND150 recovery stage that shows promise.
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I am wondering if it would have a volume drop like that simply with the 2.2M isolation resistor in the circuit? Perhaps it has little or nothing to do with the reverb circuit itself.
Again, as previously mentioned, the isolation resistors I use are of a much smaller value. Often 150-330k with a 1M reverb pot vs. 3.3M with a 100k reverb pot.
And to date, IIRC, I have not ever added reverb to a single ended amp.
With respect, Tubenit
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On the 6V6 grid 1, spec sheet says only 100K for total grid resistance, = grid stopper and grid return R's. Fender got away with 250K grid return and 1K5 grid stopper.
That 1M pot and 5K2 grid stopper is too much. It will kill the 6V6.
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On the 6V6 grid 1, spec sheet says only 100K for total grid resistance, = grid stopper and grid return R's. Fender got away with 250K grid return and 1K5 grid stopper.
That 1M pot and 5K2 grid stopper is too much. It will kill the 6V6.
Thanks for that info Willabe. It must be a slow death. I have been using it that way for over 20 years.
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I am wondering if it would have a volume drop like that simply with the 2.2M isolation resistor in the circuit? Perhaps it has little or nothing to do with the reverb circuit itself.
Again, as previously mentioned, the isolation resistors I use are of a much smaller value. Often 150-330k with a 1M reverb pot vs. 3.3M with a 100k reverb pot.
And to date, IIRC, I have not ever added reverb to a single ended amp.
With respect, Tubenit
Yes, I agree the volume drop depends on the reverb isolation resistor. I quickly popped in a 330K and the SPL difference between reverb and reverb bypass was only about 10 dBC. But there is still a volume drop, and I think even a 150 k would still show some volume drop, though maybe not noticeable with a push/pull amp. If your amps sound good with the 150K, I would say your transformer-driven setup is more efficient. The capacitor-driven circuit I am working with sounds a lot better with 1-2 meg for the isolation resistors, which lead to considerable signal loss, as shown by these sound level readings. I've got to say, this is a good sounding reverb, and I'm determined to make it work, signal loss and all. Ampeg must have found the signal loss acceptable, since they used 2 meg in many of their amps with capacitor driven reverb.
In the end I don't know if I added anything to the discussion of whether 1 tube reverb sucks the life out of an amp.
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It must be a slow death. I have been using it that way for over 20 years.
:laugh:
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I quickly popped in a 330K and the SPL difference between reverb and reverb bypass was only about 10 dBC.
Do you mean between the reverb and dry signal?
If your amps sound good with the 150K, I would say your transformer-driven setup is more efficient. The capacitor-driven circuit I am working with sounds a lot better with 1-2 meg for the isolation resistors, which lead to considerable signal loss, as shown by these sound level readings.
So, even with the 330K series R the verb signal was not loud enough compered to the dry signal?
Notice that Tubenit also upped the verb pot to 1M, that will increase the verb signal a lot.
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Yes. Reverb bypassed-85 dBC. Reverb in circuit- 75 dBC
I did not change the reverb pot for that quick&dirty test. I know the pairing of resistor and reverb pot makes a difference. Last summer, I started out with 150K and 1 Meg and evolved from there, as covered in my earlier thread " 1-tube transformerless reverb breadboard-fest (https://el34world.com/Forum/index.php?topic=31634.msg348366#msg348366) " I've beeen fortunate to get a lot of help from 2Deaf / Ten Over. He recommends 1M resistor w/1M reverb pot or 2M resistor w/ 100k pot.
At that time, I had the reverb in a loud LTP + push/pull amp, and did not notice the signal loss effect.
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Yes. Reverb bypassed-85 dBC. Reverb in circuit- 75 dBC
Do you mean verb bypassed as in dry signal?
This is a confusing way to put it. You 2 signals, 1. un-effected by the reverb = dry signal and 2. a wet signal = reverb signal.
So it's either dry or reverb.
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I did not change the reverb pot for that quick&dirty test. I know the pairing of resistor and reverb pot makes a difference. Last summer, I started out with 150K and 1 Meg and evolved from there, as covered in my earlier thread " 1-tube transformerless reverb breadboard-fest (https://el34world.com/Forum/index.php?topic=31634.msg348366#msg348366) "
In your 1-tube transformerless reverb breadboard-fest, the Swart/Ampeg 1 tube verb has 100K/1M pot. There's a reason Swart ended up with those 2 values.
I think he uses the same verb circuit for all his amps, SE and PP.
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Swart gets a lot of good comments on their reverb. I’ve never heard one live. You own one, right?
I have never seen a bona fide Swart schematic. The Guitar.com reverb was supposedly copied from Swart. That’s as close as I’ve ever been able to get.
That article shows the reverb between the preamp stages. Evidently the 100k resistor and 1meg pot work well in that implementation. As far as I can tell (by trial and error) it does not work equally well with the reverb after the preamp. I never tried 100k but the verb was pretty weak with 150k isolation resistor and 1 Meg reverb pot.
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Yes, I bought a used Swart Antares. I swapped out the type 4 short 2 spring tank medium delay and put in a type 9 long 3 spring tank with long delay. Much better now.
The verb is not as strong/deep as a Fender BF 2 tube verb, but it's pretty strong/deep. Most guys would probably be fine with it. It's just a hair or 2 shy of what I set the verb to on a BF verb amp, which is ~ 2.5 to 3. But it's pretty close, just not quite as deep.
I play pretty clean and I like a bit more verb than most guys, this amp's pretty good for that. The verb helps the guitar sing/sustain a little bit more and gives the sound more depth.
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That article shows the reverb between the preamp stages. Evidently the 100k resistor and 1meg pot work well in that implementation. As far as I can tell (by trial and error) it does not work equally well with the reverb after the preamp. I never tried 100k but the verb was pretty weak with 150k isolation resistor and 1 Meg reverb pot.
Yes, this is all about balancing the dry and wet/verb signals.
Tapping the dry signal to send to the verb tank driver stage after 2 gain stages, there's more signal there than if it's tapped after only 1 gain stage.
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This post has impressive legs, and so much great info!
The one thing I don't quite get from the most-shared "18 Watt Minimalist Reverb" schematic is why the Reverb pot is using the center lug as the input and the side lug as the output to the mixing resistors instead of the reverse/a typical voltage divider orientation, like in the Fender reverb. How is the pot functioning in this configuration and what is the purpose of doing it this way instead of as a voltage divider?