Adding 1-tube reverb

[2deaf]

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.

[rlh5599]

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.

[tubenit]

Nicely done!  Thanks for sharing!  Glad it worked out for you.

With respect, Tubenit

[TIMBO]

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.

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.

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.

I've tried to tweak the voltages as best I could to what sounds good.

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
Just found a great demo that is dam close to what I have, maybe not as much when dwell and level are maxed.

[Squarebet]

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

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.

[tubenit]

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

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

[Squarebet]

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
Do you think I should put a resistor before RV2?
From now on, I'll post this on Tweaks. 

Thanks again!

[tubenit]

I would try it just as you've drawn it and see if you like it?

With respect, Tubenit

[tubenit]

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

With respect,  Tubenit

[TIMBO]

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.

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

[MakerDP]

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! 

[tubenit]

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

With respect, Tubenit

[tubenit]

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

Interesting use of a 6GH8 pentode/triode for reverb

[TIMBO]

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.

[sluckey]

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.

[TIMBO]

Thanks, Done

[tubenit]

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

[tubenit]

These are reported proven designs for 6BM8 reverb from TAG  (The Amp Garage)

With respect, Tubenit

[TIMBO]

Hi T, This is a collection of one tube reverb circuits that I have used and all work very well.

[tubenit]

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


Anyone ever incorporate an accutronics brick into their builds? (el34world.com)

Also note Ed's comments comparing the Belton Brick to a spring reverb in reply #9

With respect, Tubenit

[tubenit]

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 

[TIMBO]

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?

[tubenit]

I'm using a "typical" fender 4AB3C1B.  It's the one Doug sells.

Jeff

[Skilpadda]

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

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

[Mwaller]

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!   

[tubenit]

These are reportedly nice sounding reverbs. 

With respect, Tubenit

[echuta13]

Adding this one to the 1 tube reverb stash... https://guitar.com/guides/diy-workshop/build-tube-spring-reverb-unit-amplifier/

[knebiter]

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

[pdf64]

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.

[Beezerboy]

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....

[sluckey]

I think I saw that on Ancient Aliens recently! 

[Beezerboy]

yep.... scratched on the wall of my cave with a flint hatchet.

should I try it?

[sluckey]

I guess. The only thing I recognize is the tall man pointing to a star cluster.

[2deaf]

... The only thing I recognize is the tall man pointing to a star cluster.

THIS changes EVERYTHING

[Fiat_cc]

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?

[tubenit]

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.

[pdf64]

...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.

[Fiat_cc]

...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.

[Beezerboy]

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?

[tubenit]

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

[jdlan55]

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?

[sluckey]

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.

[jdlan55]

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.

[clbraddock]

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.

[Lectroid]

Have a look at this page:

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

 Rich

[clbraddock]

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.

[Williamblake]

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.

[pullshocks]

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.

[marshallguy]

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}.

[mountainhick]

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.