Ampeg GU-12 tremolo problem

[Brotherkite]

I just got an Ampeg GU-12 from the early 70's, and it is in fantastic shape except for one thing: the tremolo works, but it is just barely there. Very faint. I'm trying to figure out if the trem module needs replacing or the caps. Can anyone help?

Patrick

[rf7]

Typically, the caps in the tremelo oscillator circuit go bad. I'd replace them first.

[Brotherkite]

Okay, next question: They appear to be CDE .047uF 400v polypro caps (PM4S47). Trouble is, I can't locate these anywhere online. Are there any decent substitutes I can could use without messing the amp up?

[Steve Conner]

Any 0.047uF 400v polypropylene cap will work. The make and model aren't important.

[Brotherkite]

Jeez, another question!

Alright. The past few days with the amp have been interesting. The discoveries:

1. The reverb has a tendency to feedback on itself when the "dimension" knob is over 12 o'clock (I replaced the reverb driver tube, but no change).

2. When warmed up and the volume is around 2-3 o'clock, it is pretty loud, but if I hit a strong chord, the volume will jump down and get way quieter, but no less overdriven. When I stop playing, there is a one second pause before it jumps back up.

Any thoughts?

[Enzo]

Turn the reverb off. Play something through the amp. Ball up your fist and whack the top of the amp. Does the whacking affect the amp in any way? If it does there is a loose connection. A first place to look is the tube sockets.

[Brotherkite]

I tried the "whack the top" method, but still nothing. It has been staying in the quiet, "lower power" stage for the last few days, and pretty securely so: I've been gently wiggling tubes and knobs while playing, and nothing seems to happen. Would this have anything to do with the filter caps?

And an update on the tremolo circuit: I replaced the caps, but it is still faint like before. I noticed that the module is not the TM-1, but the Fender-type black one that looks like an insect. Could this be at fault, or did I replace the wrong caps (I replaced [3] .047uF polypro caps, C5, C6 and C7)?

The schematic is here:
http://www.freeinfosociety.com/media/images/674.gif

Sorry about all the questions, but I am new at this, and I appreciate all of the help!

[melvin]

as far as tremelo caps go, the cathode bypass cap may also be bad....

[Brotherkite]

update.

So, I've replaced the cap can, electrolytics, and most of the poly caps on the circuit board, and the overall sound seems to be more stable, but the tremolo is still faint as always. However, I noticed that, with the tremolo on, if you strike a chord and turn the standby switch off, you can hear the effect as it should be as the sound fades away. Any thoughts?

[spy]

Hey, what did you do with your tremolo problem? Did you fix it?
I have the same problem with a Gemini II. It has TM-1 module.

Fliptops has tremolo modules but are a little bit pricey. Does anyone know if it's possible to find a substitute?

[Brotherkite]

trem problem

The only thing I haven't done yet is replace the actual trem module, which is the fender one, strangely.

Yeah, those TM-1s on fliptops are a bit pricey. I was planning on putting one in the gu-12, but the only reason I haven't is because of the price. I plan on resuming soon, so when I crack the case, I'll post what happened.

[spy]

Does anyone know if the 7ender LDR will do the job in Ampegs?

[Queen*Son]

10 years later I hope you figured it out! was it a bad intensity pot?