Ampeg Tremolo Module "TM1"

[KingCameron]

Guys,
I have a GS-12R built similar to the attached schematic. (vintage)

This amp has a tremolo module called "TM1". This module appears to be some kind of LDR, or photoresistor set-up.

Can someone tell me how to test it?
Can I replace it with the Fender LDR? Other versions? (if needed)

Any other info on this little gizmo would be great

[Bruce / Mission Amps]

Guys,
I have a GS-12R built similar to the attached schematic. (vintage)

This amp has a tremolo module called "TM1". This module appears to be some kind of LDR, or photoresistor set-up.

Can someone tell me how to test it?
Can I replace it with the Fender LDR? Other versions? (if needed)

Any other info on this little gizmo would be great

Yes it is an LDR but quite a bit different in values then the Fender type. They are not interchangeable.
I'm actually working with another person to see if we can duplicate these things but at a more reasonable price... depending on which kind you have, you can buy something like it from Flip Tops.
http://www.fliptops.net/catalog/index.php?cPath=25_56
Regardless, it's hard to test that damn thing because it is a closed up device and the resistance is really really REALLY high... like 30M to 40M and the turn on (high to low resistance) "slew rate" is wacky.
Not just any cell will even come close to working.
But you can "kind of" check one part of it if you make sure all the light is blocked and then read the resistance across the two cell leads.
Since most bench ohm meters can't read as high as the cell is... it should read like an open circuit, but if you have a decent meter and put a "KNOWN" (and I mean measure it first) 10m resistor in parallel with it, you should see that the two in parallel is much less then 10M.... etc.
The blinky light thing is a little hard to tell if it is working.
For the casual repair... after checking the other parts of the circuit, I'd just assume it is the cell and replace it with what is available.

[KingCameron]

Ampeg LDR "TM1"

Bruce,
As always, thank you very much for your responce. You're awesome!

Please let me know if you ever come up with a replacement for TM1. I would be very ineterested to get one. I am not sure the one I have is bad, yet. But, if there was a reasonably priced replacement, I'd probably swap it out anyway.

I will also look at the web-page you recomended.

Thanks,
Cameron

[KingCameron]

Fliptop's TM-1

Bruce,
I looked at Fliptop's version of the TM-1. It does not look the same, and is $35, but may be electrically functional.

I think I'll get the rest of the amp dialed in first, and make sure the tremolo LDR is the issue, before drop the dough on this one...

although it is nice to know there is a back-up available

[KingCameron]

TM-1 (Ampeg Tremolo Circuit)

Here is a picture of the Tremolo Module in the Ampeg GS-12R

I'd like to get a new one of these.

[Bruce / Mission Amps]

Here is a picture of the Tremolo Module in the Ampeg GS-12R

I'd like to get a new one of these.

Yeah those are stinkers.
Possibly their VM-1R model will work in your amp.
Call them and see what they say.

By the way... if you can replace all the those blue e-caps (could be Ducati) on your circuit board.

[KingCameron]

Ducati Caps

Yup. They're Ducati caps...why should I change them? (Other than the obvious) Are they known to be bad?

Thanks for the tips..

[darrellcheng]

Age will dry out e-lytics. The old ones probably stay in value for 10-20 years max. new ones will last 30+. You can measure capacitance to see if they've drifted.

[glp]

Reverberocket....

Age will dry out e-lytics. The old ones probably stay in value for 10-20 years max. new ones will last 30+. You can measure capacitance to see if they've drifted.

I too have a 66 Reverberocket, came in as a basket case....... replaced the main electrolytics and tubes and all seemed to work great. It wasn't long after that the amp went dead?!

Finally found one of the small wires from the TM-1 to the intensity pot had broken off the TM-1. $43 delivered later the TM-1 arrived from fliptops.com. Installed it and the amp was very weak?
I chopsticked around the intensity pot connections and the amp came back to life? Made me think the pot needs to be replaced? I removed the pot (4meg) cleaned it straightened the connecting eyelets, reinstalled.
Amp not only came up dead again but in a minute the 10k resistor (looks like at least a 2 watt?) that goes back to pin 10 on the 6U10 started smoking??

scratching my head on this whole deal??

Any thoughts??

[52 Bill]

Amp not only came up dead again but in a minute the 10k resistor (looks like at least a 2 watt?) that goes back to pin 10 on the 6U10 started smoking??

The 10K 2 watt resistor is the plate resistor for one stage of the 6U10. The trem module and depth control are only connected to the audio path and to a 12AX7 oscillator.

There may not be any connection to the two events other than you. The 6U10 is used for the reverb section and in the phase inverter. If it fails then the entire amp can die or only the reverb can die. Do you have another tube to sub in?

[glp]

The tube tests great in an emissions tester.. I do happen to have another.

The whole trem circuit thing is getting me? I found a 4meg pot, but without a switch. I'm thinking I can put it in anyway? JUst to see if I can get this thing running again.

[52 Bill]

The whole trem circuit thing is getting me? I found a 4meg pot, but without a switch. I'm thinking I can put it in anyway? JUst to see if I can get this thing running again.

Yes any 4 meg pot will work as a replacement to see if it works, but I doubt that it is the cause of the resistor overheating.

The trem works by sending the audio signal through the paralleled combination of the 4 meg pot and the light dependent resistor of the trem module. When the control is set to a high resistance level, the audio signal is reduced by the resistance of the pot until the trem circuit lights up the ldr reducing its' resistance which allows more audio signal to pass through to the next stage. When the control is set to a low resistance, the signal just passes through to the next stage, regardless of the resistance value of the ldr.

If you think that the pot is bad either read the resistance level with a meter or temporarily jumper across the pot.

[glp]

Hey Bill,

I appreciate your support on this one...... I am suspecting the pot because originally, I could chopstick the teriminals on this and the amp would be weak, dead or perfect.... just by wiggling the terminals.
Got it running and played it for about 20 minutes, the amp just died........... no sound. When I opened it up this time I noted the broken wire right at the base of the TM-1. After I replaced the TM-1 the amp sounded very weak on fire up. Chopsticking the pot terminals again it came back to to life..... a little MORE chopsticking and it went dead. So I removed the 4 meg and all (rather sloppy) connections. Cleaned it up and reinstalled. It was at that fire up the resistor started to smoke. I have since fired it up once more breifly (about a minute) no smoke. But still dead!

[Queen*Son]

If anyone is still around I've been working on my gemini 1 and I'm not sure about the 4m ohm intensity pot. Do you guys have a different schematic than I do? Mine says 3m ohm.