Tube Practice Amp Adding Reverb

[Wolfman88]

Ok on the Accutronics I think there might be something wrong because on 200 ohms I get 29.1 on the output and 0.1 on the input. My meter don't go below 200 ohms. I'm going to need it explained to me in beginners speak because a schematic is greek to me since I'm a beginner. The Belton is a pretty new tank it doesn't have much use on it. The schematic posted I need explained exactly what's going on there.

[Chuck H]

Ok on the Accutronics I think there might be something wrong because on 200 ohms I get 29.1 on the output and 0.1 on the input. My meter don't go below 200 ohms. I'm going to need it explained to me in beginners speak because a schematic is greek to me since I'm a beginner. The Belton is a pretty new tank it doesn't have much use on it. The schematic posted I need explained exactly what's going on there.

The Belton tank you have isn't a good impedance match for a transformer coupled circuit. I'm not even sure it's a good match for a capacitor coupled circuit. And anyway, I don't think a capacitor coupled circuit would give you enough reverb without adding gain stages to the amp. The Accutronics tank is probably busted. I would have expected something more than a dead short for the input.

A project like converting an existing tremolo to a reverb isn't simple. In fact, reverb circuits are sort of complicated. Even more so when you want to add it to an amp that wasn't designed for it in the first place. There are checks and balances in gain levels at every stage. And I'm sorry, but if you don't understand the schematic we're not going to get very far. Too much lack of understanding will make it prohibitively difficult to step by step the process. Especially since this is a point to point wired amp. Because of this construction method there will be much of the circuit that won't even be modified that has to be removed and redone. This is basically a tear down and rebuild of most of the circuit.

I hope you weren't counting on being able to just sort of plug a reverb tank into the tremolo tube.?. Because this isn't really a "Grape jelly instead of strawberry in your PBJ" kind of thing. More like taking what you can from the PBJ, cleaning it off, adding some stuff and turning it into a bread pudding Some cooking skills are involved.

[Wolfman88]

I'm handy with a soldering iron and doing stuff like this I just never learned how to read schematics. So if I buy a reverb tank what would be best for the amp I'm using?

[Chuck H]

I'm handy with a soldering iron and doing stuff like this I just never learned how to read schematics. So if I buy a reverb tank what would be best for the amp I'm using?

Well if you take a couple of full chassis gut shots I can try to work out a layout, I suppose.

The numbers on this tank should translate to other manufacturers as well, but I have included the MOD part number. The transformer is available at triodelectronics dot com.

[Wolfman88]

Ok I will look up how to read schematics. Now is it best to use this tube amp or install the tank on my main amp that I'm using the tube amp as a preamp for? Also how do I convert the speaker output into a line out? I think I saw somewhere that you put some resistors or something on the speaker leads to lower it to a line out. I'll get the pics of the inside of the inside of the amp when I get a chance.

The schematic for my main amp is here http://www.vintagekustom.com/ in the technical schematics by amp model and go to the piggyback and the 69 K100-1

[Wolfman88]

Here's the pics.

[Wolfman88]

2 and 3

[nickb]

Ok on the Accutronics I think there might be something wrong because on 250 ohms I get 29.1 on the output and 0.1 on the input. My meter don't go below 200 ohms. I'm going to need it explained to me in beginners speak because a schematic is greek to me since I'm a beginner. The Belton is a pretty new tank it doesn't have much use on it. The schematic posted I need explained exactly what's going on there.

Your meter's just not good at reading low resistances. It's probably an 8 ohm input and something like 200 ohms out. That would really need additional gain to make to work so I'd forget about it.

The Belton tank is, as I mentioned, best used with opamps (solid state). It's not much harder to wire than a tube but there are power supply complications. The easiest route, and by the sounds of it easy is the way to go with your experience level, is to go for a tube reverb such as suggested by Chuck. The cost is about the same either way but you would get to keep your tremolo with a solid state approach and there is quite a bit more flexibility as you don't have the gain limitations of tubes.

[Wolfman88]

The Accutronics has a circuit board that plugs up I don't know if its some kind of preamp or what.

[Wolfman88]

Here's the board. Is a preamp that would give the gain? If this board is what I think it is all the work might be done already.

[g1]

Since he wants to use this amp as a preamp, how about driving the tank with the power amp?

[Enzo]

Chuck, refer to Princeton Reverb. I am concerned the sample circuit you made might be shy of drive. Note the PR has two stages before the reverb is taken, while yours has only one. Or are you thinking the lack of tone stack will make it up?

[Wolfman88]

I just asked on the organ forum what the circuit board on top of the tank is. I'm hoping it is what I think it is and that will save me a lot of custom wiring to make it work.

[Chuck H]

Since he wants to use this amp as a preamp, how about driving the tank with the power amp?

That's pretty brilliant. The rig wouldn't find muc application outside of a narrow set of circumstances, but it should work great. Considering what Wolfy has posted about what he's up to I think this could be a great option

[Chuck H]

Chuck, refer to Princeton Reverb. I am concerned the sample circuit you made might be shy of drive. Note the PR has two stages before the reverb is taken, while yours has only one. Or are you thinking the lack of tone stack will make it up?

I actually wasn't concerned about getting full BFish reverb and dry signal drive levels. I only wanted to add reverb to the existing amp and keep it's performance similar to stock. The circuit I posted should do that. I raised the input 6dB (because the stock circuit SUCKS) and then added a bypass cap and a hotter bias to V1A for another 6dB. Then the relocated volume control and reverb mix resistor circuit dumps 11dB off the dry signal. Net should be about the same for the dry.

As to the reverb... Notice the dual ganged pot. I have it arranged so that at full there is very little voltage division because series resistance is eliminated. The reverb is recovered, slightly voltage divided and then sent to the grid of the stage driving the power tube for further amplification. I figure at least eight or ten volts of wet signal with the control set full. That should be plenty!

EDIT: Oh, yes. I am counting on the lack of a tone stack to provide adequate drive from a single triode. Pretty sure there are a bunch of Gibson amps and some others that filch the reverb drive from the first gain stage.