1962 R12R low volume

[journeyman]

Just got a 1962 R12R; sounds nice and warm, but it has very low volume. I changed the speaker (original was pretty much finished) tubes are all good so I am assuming there is voltage leaking somewhere in the circuit. Its going off to the hospital tomorrow for an assessment and I'll be ordering new capicitors; thinking of replacing the coupling caps as well.

My tech will probably find the problem, but if there is something common to this model of this age that causes the lack of volume, I'm all ears.
   

[jjmt]

Nice amp! I have one just like it, although mine is a '61 and has the blue sparkle covering. The R-12-R is not super complicated, and I'm unaware of any issues special to this model. Once the electrolytics are refreshed, it shouldn't take much effort to identify any remaining issues.

One thing you should probably be aware of is that the power filter circuit uses 6 20uf capacitors. You're never going to find a replacement can with more than 4 20uf sections (don't really know how Ampeg wired these originally), so there will be a couple extra 20uf caps sort of shoved off to the side once the recap is done. Different techs seems to find different ways of attaching them to something solid. But anyway, this is normal.

[journeyman]

One thing you should probably be aware of is that the power filter circuit uses 6 20uf capacitors. You're never going to find a replacement can with more than 4 20uf sections (don't really know how Ampeg wired these originally), so there will be a couple extra 20uf caps sort of shoved off to the side once the recap is done. Different techs seems to find different ways of attaching them to something solid. But anyway, this is normal.

I believe that is what appears on the schematic on the inside of the back panel. The cap can that is actually in the amp corresponds to the later B circuit. My tech will see what caps are actually in it when he removes it. I am assuming this is version 1, but I see on the Fliptops site that they sell cap kits for two versions, 1 & 2, both with 6V6 power tubes. It uses 6sn7 preamp tubes (6sl7 for trem and PI with a 5Y3 rectifier.

I'm hoping that this one will break up a bit when cranked up; unlike my M-12 which stays clean all the way up. So far I'm very impressed by its warmth as a quiet jazz amp.

[journeyman]

I picked up the 1962 R12R from my amp tech today and the volume issue seems to have been solved. All filter caps were replaced and a couple of smaller coupling caps that had drifted. He did open up the front end slightly by changing one cap value. I'll have to write down what he did so I can remember. It sounds very close to my Mercury M-12; maybe a tad brighter. Of course the on-board reverb is nice to have but I'm finding it a bit weak. If I could get more out of it and somehow darken it up a little, I'd be very happy. There was a lot of dirt, dust and nicotine inside the amp and I'm wondering if I should take the reverb tank out and open it up. It seems unlikely that that could be the problem as it is almost a closed environment.

Does anyone have suggestions for reverb tweaks or troubleshooting on this R12?

[jjmt]

IIRC, a properly functioning reverb should lean more towards "overwhelming" than "weak". So, if it's not doing it for you, then it probably deserves some attention. Since it just came back from the shop, is it fair to assume that the tech took the time to check all the resistor values? If he was just doing a cap job, I suppose it's possible that there are components that have drifted in the reverb part of the circuit.

But where I would start is evaluating the tubes. The reverb driver and recovery are the two triodes of V3, and the signal is blended with the dry signal in V2. A weak or imbalanced tube in either spot could result in what you are describing. I would just try different tubes. But if you are like most people and don't have a bunch of 6SN7s laying around, you might just try swapping the two 6SN7s and seeing what the result is? It might give some insight.

I don't know how likely it is that the issue could be the tank. It's not that hard to remove, and I suppose there could be some dust bunnies or something in there that would mute the reverb. Easy enough check. (Well, in my R12R the tank is on the floor of the cab. But if yours is on the side, then that's a bit more work as I would assume you would need to pull the chassis....)

[journeyman]

IIRC, a properly functioning reverb should lean more towards "overwhelming" than "weak". So, if it's not doing it for you, then it probably deserves some attention. Since it just came back from the shop, is it fair to assume that the tech took the time to check all the resistor values? If he was just doing a cap job, I suppose it's possible that there are components that have drifted in the reverb part of the circuit.

But where I would start is evaluating the tubes. The reverb driver and recovery are the two triodes of V3, and the signal is blended with the dry signal in V2. A weak or imbalanced tube in either spot could result in what you are describing. I would just try different tubes. But if you are like most people and don't have a bunch of 6SN7s laying around, you might just try swapping the two 6SN7s and seeing what the result is? It might give some insight.

I don't know how likely it is that the issue could be the tank. It's not that hard to remove, and I suppose there could be some dust bunnies or something in there that would mute the reverb. Easy enough check. (Well, in my R12R the tank is on the floor of the cab. But if yours is on the side, then that's a bit more work as I would assume you would need to pull the chassis....)

Thanks, I'll try switching the tubes and go from there; I do have a spare set of 6SN7 tubes. BTW, we replaced the 6SN7 preamp tube with a 6SL7. The result was more volume, but I didn't like the tone as much, so back in went the 6SN7.

[Hangman]

You may want to take a look at the tank too. You never know, some bozo could’ve replaced the tank years ago with the wrong tank. It wouldn’t be the first time I saw that happen.

[journeyman]

You may want to take a look at the tank too. You never know, some bozo could’ve replaced the tank years ago with the wrong tank. It wouldn’t be the first time I saw that happen.

Well, the amp is working great now, except for the reverb. I changed tubes as well as rotating the existing ones; no change. Last night I removed the tank and everything looks good there. I put rubber washers between the tank and the cabinet and can run the control up full now without interference from cabinet vibration, but the reverb is just weak. I'll have to take it back to my tech and get him to go through the circuit again; maybe he missed something. Otherwise, a nice sounding amp.

[journeyman]

Pull the tank again and hit the solder connections with your iron. You may want to use an alligator clip for a heat sink because the wires are very thin and could damage the transducer. If that doesn't work then a new tank may be in order.

The tank is fine and actually sounds nice. I hooked my Reverberocket 2 up to this tank and it sounded great. So, something has drifted or burned out in the circuit. Dropped it off at my tech's today. I'm sure he'll find the problem. It did have OK reverb level when I first got it a few weeks ago, but the amp hadn't been used for a long time; maybe many years judging from the amount of dust that had collected in it. I suspect that something has burned out since I've been playing it and running voltage through it again.

[journeyman]

The reverb is back, and quite a nice reverb at that. There was a resistor that was way off, and simply replacing it with the proper value value did the trick. Nice little amp; not as gainy as I had expected, but it sounds good and will make a nice jazz amp; nice to have the on-board reverb. Tonight I had a restaurant gig (guitar and bass) and all I took was my guitar, the R12R and one patch chord; very convenient.