Reverb trouble with my 112RD50

I have a strange problem with the Reverb on my 112RD50 amp (serial# EN10544 - made in September 1982)
With the Reverb engaged, I can�t hear no Reverb added to the sound, until the Reverb control is up to maximum. The Reverb sounds weak and a loud huming noise is also audible - if I roll down the Reverb control only a little bit down, the noise and the Reverb are gone. This occurs in both configurations - with the footswitch plugged in and unplugged. I x-checked if everything is connected the right way, changed the reverb cable and cleaned all the RCA jacks. When I use the Reverb pot, there is no crackling noise. Any ideas what could be wrong ?

It kind of sounds like your tank took a bite out of crime. If you can bang the cabinet with the reveb turned up and you hear no "crash", chances are the tank's out. If you hear a crash, it's working but not getting fed from the circuit. Try thr crash test first and let us know.

Hi Mike,
thanks for answering ! I did the crash test and received the same results as with the guitar plugged in - until the maximum position of the Reverb pot, I can�t hear the typical "boooing" of the reverb tank when hitting it, at the max position the crashing sound is audible, together with the loud noise in the background.

Pretty much sounds like it's out. There IS a possibility that the driver is out but it's MUCH more common to have a bad tank. They were pretty flimsy. If you have an old Peavey tank laying around, they are sometimes the high impedanace type. You could try subbing it temporarily to see.

Mike, do you have any part or model number for a new reverb tank ? I also have a Peavey Classic 30 combo amp, but I�m not quite sure if it�s a high-impedance tank because there is no imprint or lettering on it. Accutronics tanks are easily available over here for a decent price.

I don't know EXACTLY which tank you have but there is a generic chart here:http://www.stf-electronics.com/Page0014. Html
Try this.
MY tank in one of my old 130s is 4fb3a1b so that at least should give you a clue. There SHOULD be the number stamped on the top of the tank in ink though. I'd pull it out of the bag and look first. If not, the chart will get you close enough. Mike

Hi Mike,
I took the tank out of its bag, and it�s a 9" ACCUTRONICS 8BB2A1B with 3 springs. According to the specs table from your link, it has an input impedance of 190 and and output impedance of 2575. Is this the original reverb tank the 112RD50 came with or is it a substitute from one of the previous owners of this amp ?

Honestly, I don't know. Doesn't SOUND right and the high low spread is extreme for MM's but I don't have a 112-50 to compare it to and MM had no master sheet(that I am aware of) to compare models to. Maybe somebody WITH a 112RD will chirp in and let us know. Mine are all 65 and 130's with tube inverters. I know SOME of the guys here have RD's. I do know that they had to get smaller tanks with the smaller case amps so thet MIGHT be the answer. Mike.

I just has a look at the circuit drawing, and the Accutronics 8BB2A1B with the 3 springs is the stock reverb tank. I also had the chance the try my reverb tank with another amp, and it�s working perfectly !!! So it seems not to be the reverb tank and the cable. Any more suggestions what could cause this problem ?

The jack on the chassis that is connected with the output of the tank is an input. Plug-in an RCA cable and touch the other end of it with your fingertip: you should hear a typical sound (or connect it with some signal output e.g. a CD player, you should hear the music then, with the reverb control adjusting the volume). If not, you must trace back the signal path, maybe a faulty OP amp there)
Ingo

One thing I forgot to tell you is that if the leads are reversed, the damn thing won't work for spit. THe spead is so much that they do practically nothing. Try reversing the elads first, and then what Ingo said is true. This will tell you if the driver/pickup is working.

Hi Ingo and Mike, I did what you suggested and reversed the leads - I get the same strange phenomenon in both directions !!! Afterwards I connected one channel of a CD player to the "reverb in" RCA jack of the amp and I did exactly what Ingo said, I could hear the music and adjusting its volume with the Reverb control pot of the amp, independent on the volume setting of the amp. So I guess the driver stage of the amp is ok and it�s the tank ?!?
@Ingo -> Hey man, welcome at this place. I never expected another german out here :-)

Hi. I got a similar problem on a 112RD 65. The cause was a short circuit on the cable of the foot switch so the reverb was always disabled. I red that you already checked it with the foot switch disconnected, I know that's a stupid question but have you disconnected both RCA plugs of the footswitch? I remember that it's easy to confuse RCA plug of reverb with the one that control distortion.
Bye!

Hi Giorgio, nothing is to stupid when it comes to trace down an error, so thanks for taking care of my problem. Yes, I totally disconnected the footswitch and both RCA plugs. I don�t need the footswitch, because I don�t like the overdrive sound and channel of the amp and with the footswitch of the reverb disconnected, the reverb is engaged - that�s the way I like it :-)

Very strange indeed. If the tank worked with another amp it should be OK, and if you hear music from the CD, the secondary side of the reverb circuit should be fine as well.
There is not much left anymore. The primary side of the reverb path (before the tank) should not matter here because you said you don't hear the typical sound when you bounce the tank, which should be there even if the primary side is faulty.
Hmm, did you check the cable from the tank to the amp, and are you sure the tank is connected correctly (output amp -> input tank, output tank -> input amp, might sound stupid but can easily be mixed up).
Ingo

Hi Ingo, I agree ... very strange thing ! I x-checked the cables once again and changed it completely for another cable that I checked with a DMM before - same strange thing. I also interchanged both cables to make sure that they are really connected the right way, no difference in behaviour. I think I will try to get another reverb tank to make sure that it�s really not the tank ... but not much MM users here in my hometown, so I think I will have to buy one to test this. By the way, where are you living and are you an amp tech ? I�m from Kassel.

Hi Dirk,
I am from Schwerte (near Dortmund). I am not a professional amp tech but after repairing and servicing my amps for a long enough time I am normally confident to fix all possible problems with them.

According to the schematics your reverb tank is the corect one. Try replacing IC-3. The NTE replacement number for the TL072 is NTE 858M. The two driver transistors in the reverb circuit are ZTX109's. NTE crossover is NTE 199. If your reverb tank worked in another amp, the problem lies in the transistor drivers or the op-amp.

Tank works with another amps, so it'OK. And it seems that the second stage of reverb path works too.
To test all amp reverb circuitry I suggest to connect with a RCA cable the input and the output conn. of the reverb (never tried this, but I think it's safe).
That's a kind of try like the CD player one, but you test also the circuitry before the tank. Reverb pot will act as a second volume. Before doing this, reverb-pot should be set to 0 to avoid too much gain (or feedback) at first.

The problem is finally solved !!!! I would like to thank you all for your help and numerous tips. You will never believe, what the reason for my problem was ..... the two pots from the Reverb control and the Volume control from the second (overdrive) channel had been interchanged !!!! It�s obvious from the solder joints, that the amp came from the factory this way. So I had a 1Meg log. pot for the Reverb control and a 25k lin. pot for the Volume control. This was the reason why the Reverb control only worked on the last few millimeters. I interchanged both pots and the Reverb works properly now. Did ever someone had such a strange problem too ?!?

...Simply crazy....
Well done Dirk!