Can you drive a reverb circuit with 1/2 a tube?

[CitizenCain]

I'm doing an amp project and I'd like to include reverb in it, but I only have three preamp tubes, one of which is the PI.

Can I use 1/2 a tube to drive the reverb and the other 1/2 as the recover? The schematic I have for a reverb circuit calls for using both sides of the tube as the driver. It uses a common resistor/cap off both cathodes. If I did split it down to one side driving, would I have to alter the resistor/cap values if I used the same tube type and voltages?

Thanks!

PS - I don't care if I get a dripping wet reverb, I just like a little spacious effect.

[Old Tele man]

...yes, if you feed the reverb tank "output" signal back around as ONE input to the first preamp tube.

[CitizenCain]

Come again?!

http://img116.exs.cx/img116/934/z0tdntknw.gif

[Old Tele man]

...use the AVAILABLE one-half as driver, and (visualize 4-holer Fender Tweed) feed the reverb tank output signal back around into one of the 4-jack inputs, ie: co-use the FIRST preamp tube as REVERB-recovery preamp too.

...also, it *IS* possible to use the speaker output to drive the REVERB unit, then connect the REVERB-output directly into one of the 4-input jacks...so, effectively, you wouldn't need ANY extra tubes...or even portions of unused tubes.

[hasserl]

Carvin builds all their amps to use one tube for reverb, one triode as a driver, the other as recovery. 12AX7 too.

Check this schematic for an example: http://www.carvinmuseum.com/pdf/amps/V16.pdf

[CitizenCain]

...use the AVAILABLE one-half as driver, and (visualize 4-holer Fender Tweed) feed the reverb tank output signal back around into one of the 4-jack inputs, ie: co-use the FIRST preamp tube as REVERB-recovery preamp too.

...also, it *IS* possible to use the speaker output to drive the REVERB unit, then connect the REVERB-output directly into one of the 4-input jacks...so, effectively, you wouldn't need ANY extra tubes...or even portions of unused tubes.

Bizarre! Do you just wire the reverb output to the jack connections inside the amp? Can the jack still be used as an instrument input?

[CitizenCain]

Carvin builds all their amps to use one tube for reverb, one triode as a driver, the other as recovery. 12AX7 too.

Check this schematic for an example: http://www.carvinmuseum.com/pdf/amps/V16.pdf

Thanks, hasserl! That's exactly what I had in mind :D

[tele_player]

I'd love to hear a reverb done that way, it saves 1/2 a tube AND a transformer.

What's not clear from the schematic is exactly what reverb tank to use, the one used in typical Fender combos expects to be driven by a transformer, to which it presents an 8 ohm load.

If it really works well with a single tube, this is a very good trick to know.

[CitizenCain]

I'll let you know :D My donor amp has a transformer so I'm just gonna try the 1/2 tube thing and see how it works. Old Tele man blew my mind, I gotta stick with what I can grasp at this point!

[Old Tele man]

Old Tele man blew my mind, I gotta stick with what I can grasp at this point!...look at how Fender did it: http://www.ampwares.com/ffg/schem/champ_12_schem.gif

[John Phillips]

It does work, but it's very difficult to arrange it so the reverb sounds good and deep, but doesn't feed back. The Champ 12 has a trimmer to set it 'just so', but it still isn't the best reverb Fender ever put in an amp...

[teleman1]

I have Mullard & Telfunken tubes that either triode one or two is bad,but the other side is working and working well. Can these tubes be used????

[hasserl]

I'd love to hear a reverb done that way, it saves 1/2 a tube AND a transformer.

What's not clear from the schematic is exactly what reverb tank to use, the one used in typical Fender combos expects to be driven by a transformer, to which it presents an 8 ohm load.

If it really works well with a single tube, this is a very good trick to know.

It uses an Accutronics reverb tank, which may have an internal transformer. I"m not sure about that. But, the result is not a Fender type reverb, but a reverb that is still deeper and lusher than I need or care to use. I'm just not much for reverb and really don't miss it on amps without.

[WaltC]

I added reverb to an early amp I built just by using 1/2 a 12AX7 to drive and the other half to recover, using the standard Fender circuit, transformer and tank. It is not nearly as strong or "boingy" as a Fender, but sounds good and gives a decent, though relatively weak, ambiance to the notes.

Since most folks keep Fender Reverb knobs down around 2-3 on the dial I figured "what the heck" and went for it. It has received favorable comments and I've ended up putting a similar circuit in a couple of old PA amp/guitar amp conversions with good results.

[HarryB]

I'm glad someone posted this topic. I have a Silvertone Twin Twelve 1474 that I just got running this past weekend. It was a freebee and came without a reverb tank. A Fender style tank seems more realistic then trying to track down a Silvertone tank. Besides the Silvertone has a rep for sounding like crap. The Silvertone uses 1 triode for feeding the tank and 1 triode for recovery. I'd like to keep that configuration.

I contacted Carvin to try and find out the reverb tank information. They said it was made by Accutronics, but didn't give a model number. Their selling price is around $35...eeekkkk!!! I may buckle down if I go the route of the Carvin circuit and pay the extra in the name of "engineering fees". This option seems to be the best for me because I won't have to drill any holes in the chassis. Just my preference. If anyone has access to one of these amps and has a model number for the tank, it would be appreciated.

It's good to hear also that someone used the Fender style circuit and it worked. Fender originally used two triodes for driving the tank so I wonder if an impedance mismatch is creating some part of the volume drop. I would think that using a single ended transformer, but the 16 ohm secondary tap instead of 8 ohm would correct the mismatch. Does that make sense to anyone else?

[CitizenCain]

...look at how Fender did it: http://www.ampwares.com/ffg/schem/champ_12_schem.gif

Wild! So you tap the signal off the speaker output and route that into the reverb tank then inject it back into the signal path? Sort of like how the negative feedback loop works?

As you can tell, I'm pretty new to all this, learning everyday! There's some guys who know some stuff around here :D

Walt, glad to hear the basic idea I had works in real life. Harry, interesting observation about the impedance mismatch into the reverb tranny. Could I address it somehow with my existing transformer? It's a Schumacher trans like Fender uses.

BTW, I'm working with a Sundown amp as my donor.

[HarryB]

...Harry, interesting observation about the impedance mismatch into the reverb tranny. Could I address it somehow with my existing transformer? It's a Schumacher trans like Fender uses.

BTW, I'm working with a Sundown amp as my donor.


No, I don't think so.

I assumed that the Fender Reverb Unit used the same transformer as was used to drive the tank in the Reverb amps (Twin Reverb, Deluxe Reverb, Princeton Reverb, etc.). If that was the case then a single ended output transformer with various taps could be substituted to adjust the impedance reflected back to the single tube. But a little research shows me that the reverb transformer in the amps seems to have a 25Kohm primary to 8 ohm secondary. I'm fairly sure the Reverb Unit would have around a 5k-10k ohm primary to 8 ohm secondary. So these transformers are not the same and my proposal wouldn't be practical.

[WaltC]

The Silvertone's I've worked on (those with reverb) had a really strange reverb "tank" that consisted of a single or double spring suspended from the ends of the transducers hung above the surface of the chassis on the front right (as you face the rear of the amp) and wired directly into the chassis with no plugs to speak of. Sounded weak most times and with short dwell all the time. Adding an external tank should help the sound, but do you have the real estate in the cab to fit the tank? A short tank might work on some and will sound better than the stock one <G>.

[teleman1]

So no one can answer my question????????

[BLC]

I have seen a Gretsch amp that took the full signal from the speaker jack and ran it thru a resistor to the reverb tank and then back into the preamp thru a twin triode tube....I dont think it was a 12 A?7..... I think it was a 6eu? or something similiar. I believe Sano made the amp for Gretsch. My friend in CA has a Sano that was exactly like the Gretsch I was working on.

Also I=in one of the TUT books, O'Conner explains several different reverb circuits and 1 of them is similiar to this using just 1 twin triode.

[Old Tele man]

I have Mullard & Telfunken tubes that either triode one or two is bad,but the other side is working and working well. Can these tubes be used????...only a circuit that needs the "good" side of the respective 'half-working' tube(s)...50-50% chance of "good" side coinciding with the circuit...unless you (1) test tube to know which half is OK, (2) match said tube with circuit, or (3) design circuit to work with that half-OK tube.

[HarryB]

The Silvertone's I've worked on (those with reverb) had a really strange reverb "tank" that consisted of a single or double spring suspended from the ends of the transducers hung above the surface of the chassis on the front right (as you face the rear of the amp) and wired directly into the chassis with no plugs to speak of. Sounded weak most times and with short dwell all the time. Adding an external tank should help the sound, but do you have the real estate in the cab to fit the tank? A short tank might work on some and will sound better than the stock one <G>.

I'm pretty sure I have the room Walt. I'm not at home or I'd check. The only problem may be speaker clearance. My amp had the tank in the bottom of the cabinet held in the air by two pieces of foam. I've seen the type you are talking about (on the Silvertone model 1484) where the reverb is right on the chassis. My amp is a big combo with 2-12" speakers. I did try using a short (8-series Accutronics) reverb tank with the amp by driving it as someone suggested with the speaker output. The stock recovery circuit worked well with this tank. Feedback was a problem.

[teleman1]

Old Teleman!

If one side is messed up and the amp needs the other triode of the tube,(the working one). Can it be used and the 1/2 that is messed up or not working,(not affect the amp in any way)?

[Old Tele man]

Old Teleman!

If one side is messed up and the amp needs the other triode of the tube,(the working one). Can it be used and the 1/2 that is messed up or not working,(not affect the amp in any way)?...the ONLY way to use the "good" part is to NOT CONNECT the bad part, which (usually) means disconnecting that portion of the tube socket...a major/minor modification.

..."minor" cause it's simple to do, but likewise "major" because often you have to also 'disconnect' other components along the signal chain for safety or signal preservation.