Help with weak Tremelo Ampeg Gemini l

[punkykatt]

Hello all, anyone here fimilar with Ampeg tremelo circuits? I have the Gemini l (G12) amp on the bench. Did a complete cleaning & service and replaced all the electrolytic caps. The amp sounds fantastic except for the tremelo (the owner said the tremelo did not work when he dropped it off). I ordered a new tremelo module (M-1R) from Fliptops. I installed it following their instructions. The tremelo was very  weak , so I replaced all the .047 caps in that circuit, plus the .22 cap, lifted all the resistors and checked for spec.(all are within spec),  both the intensity and speed pots read good. Checked all grounds with my ohm meter. The voltages on that triode all read normal. I called Bruce at Fliptops and told him what I did and the weak tremelo, he sent me another module, I installed it and Im still getting weak tremelo.  Do you think its possible to get two defective modules?  My Brother-in-law has this model Ampeg and the tremelo kicks you in the chest.  Any input is much appreciated. 
Punky

[Leevi]

What do mean by weak tremolo?
Are both intensity(depth) and speed weak?
/Leevi

[punkykatt]

What I mean by weak is you have to have the intensity knob up have way or better before you can hear any trem effect at all and full up is not  anywhere near where my Brother in-laws Gemini l was.  The speed is a bit faster in the slowest position  compared to the other amp.   Thanks Leevi

[Leevi]

I would first test by removing the intensity pot from the circuit i.e. disconnect one of the pot wires.
If the tremolo is still weak then the cause is in the oscillator or in the LDR-module.

Then you could decrease the 390K (going to the module) resistor value e.g. by soldering one resistor (100K-500K) over it. 

A more clear schematic below
http://www.schematicheaven.com/ampegamps/g12.pdf

/Leevi

[rzenc]

did you try a new tube?? According to Merlin - http://www.freewebs.com/valvewizard1/trem1.html -:

"It is worth mentioning, that of all the stages in an amplifier the trem' oscillaor is the most sensitive to valve ageing. If you have a very weak sounding tremolo it can usually be ammended by plugging in a new valve."

JJ ECC803S worked flawless in this position, however, on your schem V7 is shared. Don't know how you will like it though.

Hope this helps
Best regards

Rzenc

[RicharD]

The speed issue is simply a function of the RC network involving that 120K resistor and the 500k pot.  You can play with that 120k resistor to set the limits of the speed.  I'm running on 1/2 a cup of coffee, but IIRC, and increase in ohms = an increase in speed.

It seems fairly obvious that both of your roaches are good.  Basically the oscillator flashes a lamp and the resistance across X & Y changes.  There is a 4M pot in parallel with X & Y.  When it's dialed to short, the signal passes right through and the roach has no effect on the signal.  4M is effectively open as compared to the resistance of the roach, so when the pot is dialed the opposite direction the signal has to pass across the roach.  I question the linearity of the 4M pot.  Bust 1 end of the pot loose, and listen to the intensity.  It should be at maximum.  Now with your ohms meter, sweep the 4M pot slowly.  Is it sweeping linearly? 

[punkykatt]

Thanks guys for the great responses.  Yes I did check the tube, I put three known good tubes in.  I think Butterylicious hit the nail on the head. Its got to be the sweep of the intensity pot.  Leevi`s test suggestions determined the module and oscillator circuit are working.  I cant thank you guys enough for all your help.  Im onna fiddle that 120k speed resistor to slow it down.  Thanks again
Punky