1961 reverborocket R12R trem trouble.

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1961 reverborocket R12R trem trouble.

Postby ceeya68 on Fri Apr 15, 2016 9:24 am

Hello, I am new to the forum and I am searching for help with my 1961 reverborocket. Wish I could put a vid with this post. But anyway the tremolo does not work properly. Everything else does. When you hit the switch it tries to go you can hear it trying but it's very short and weak. I'm stumped. I switched tubes out, that's not it. I'm thikin it's gotta be a cap but I don't know what one or two maybe. It's got the old red Astron caps and the green Tropicaps and the pink tiny chiefs caps. I found a schematic on line and mine has part of the schematic on the back panel. But I am no good at reading a schematic. I am schematic illiterate. If anyone can help and lead me in the right direction I sure would appreciate it. I'm a do it yourselfer. I wanna do it myself I just need a little help. Thanx much in advance. I hope I can get it working! The reverb works great!
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Re: 1961 reverborocket R12R trem trouble.

Postby slider313 on Sat Apr 23, 2016 4:33 pm

I find the problem is usually one of the three .05 oscillating caps in the trem circuit. I would change all three. They are on the far left when looking at the back of the amp above the first pre-amp tube.
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Re: 1961 reverborocket R12R trem trouble.

Postby Jack Hester on Sat Apr 23, 2016 4:54 pm

In the schematic for this amp, find the Tremolo footswitch in the oscillator circuit. There should be a cathode capacitor next to it labeled C16, a 25uf-25v. This little devil will more than likely be the source of your problem. It's an inexpensive electrolytic cap that needs to be replaced, anyway, on an amp of that age. If it starts to oscillate and dies to nothing, I'll bet that this is it.

Jack
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Re: 1961 reverborocket R12R trem trouble.

Postby ampcabinets on Sat Apr 30, 2016 7:48 pm

I am glad you guys posted this.
I am fixing to start on the trem on that b12-xt-C.
I suspect the tube, but if anyone has tackled this, on one of these, please let me know.

I am sure of this, after exhaustingly going over and over one tremolo circuit, averything kept checking out, and I exchanged 4 other preamp tubes inside the amp, to no avail, and then took a NEW tube and stuck it in, and it worked perfectly.
I went back over and over those 4 other tubes and could find absolutely nothing wrong with them. They work in any other part of the circuit, and withoue any problems or microphonics.
So, my theory is, if all of the parts check out for values, it is probably more linked to a tube, or something else. New parts usually have plenty of smoke inside.

I am telling you, I replaced every part, rewired and rerouted grounds, until I felt stupid. Then got smart, or close, anyway. Fixed the problem and put everything back as it was before I had the brain fart.
Nothing changed and it still works.


thanks
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Re: 1961 reverborocket R12R trem trouble.

Postby Dean Jr. on Thu May 05, 2016 4:25 pm

IIRC< that tremolo is a bias vary trem that operates on the power tubes. IF the bias is too high on the power tubes, the trem effect will be weakened. ....if the bias is too hot, the trem could cease to function altogether.
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Re: 1961 reverborocket R12R trem trouble.

Postby ceeya68 on Fri May 06, 2016 6:29 pm

Update: I did replace the .05 caps (qty 3) and also the 25/25 electrolytic cap in the trem circuit with .05 Jupitor caps. Lord behold the trem came to life. I have read on the forum that people thought the trem was weak in these amps. But I find that the trem in this particular amp is quite nice. I am going to replace some of the other old caps along the circuit board. Some these old Astron caps look as if they have cracks in the plastic and the paper is splitting and coming off the caps. There is a large .5 400V cap in the center of the board that is extremely waxy and just yuck. The amp has some small popping and crackily issues. I am going to mark it up as tubes. Because the amp believe or not still has the factory tubes in it. All the tubes have the Ampeg logo on them and they seem to be pretty dang old. I do not have replacements at this time but I will get some eventually and my hope is that the pops and cracks will be over with new tubes. I did reflow all the heater connections and blew out the sockets with good cleaner. And I found a spider nest in the amp also. Wolfy I think. Any more ideas on your folk's end still is more than appreciated. Good Day, Cheers!
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Re: 1961 reverborocket R12R trem trouble.

Postby ampcabinets on Thu Jun 02, 2016 9:38 pm

just did work on that b12-xt-c tremolo and pulled the same thing you did.
Replacing those .05's and that 25uF, and a couple of others did the trick.
The spragues I put in ought to last a while.
Ampeg, was really bad about using less than 100% parts and their life duty was strained because of it.

Those green caps are very notorious for going out, although I haven't really seen 'that' many bad ones in these amps.

The tremolo does sound weak, but, also, sounds almost like a chorus.

I used the list found in some 'vibrato repair kits' for ampeg amps. It's about 8 or 9 caps, altogether. And I changed a couple more for good measure in the same circuit.

Before ever working on the tremolo, I had to learn lesson #(1) about tremolos on the ampeg b12 and b18 series.
It ONLY works on CHANNEL ONE. The one on the left as you look at the front.
It's the REVERB that works on both channels.
The tremolo controls being on the same side as channel 2, would leave you to believe that is the channel it works on and you would be wrong.
Although that can be changed, we chose to leave them both as they are suppposed to be. The b-18 and the b-12xt-C I worked on recently (both recently).
Only 'slightly' confusing.


I might mention ampeg, also, used some sticky dark glue sunstance down the middle of some boards. The stuff on these last 2 amps just flaked off it was so old and dry.
no phone, no pool no pets....I ain't got no cigarettes!...............Roger MIller
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Re: 1961 reverborocket R12R trem trouble.

Postby ceeya68 on Fri Jun 03, 2016 11:33 am

I fixed the tremolo in my R12R Reverberocket by replacing the .05 caps with those Jupiter caps. I thought I would give them a try. They worked great. There about the same size and the sound is good I think. I also purchased some NOS NIB GE tubes thinking that it would improve the sound of the tremolo. It did not!! They made the tremolo very weak and light sounding. I paid a hefty price for them also. They came out and the originals went back in. Now the tremolo sounds great and thick and very forward. Like it is supposed to be. My Reverberocket has great trem. I would not trade it in for anything else. My amp also has the rubber cement in the chassis. It's a pain but I know why they did it to keep all the wires from vibrating around and try to keep things stable in the chassis. There so many wires in these amps their worse than a bowl of spaghetti!
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