The owner brought in a Fender Bronco amp for service. The main complaint is that the Intensity control for the tremolo lowers the gain considerably. Thus, the footwitch is not really usefull for shutting off the tremolo because the gain remans too low unless the intensity knob is turned all the way down. After doing a search, I believe this is normal? The circuit appears to be AB764.
I'm wondering if there's a mod for this issue? The only thing I can think of is using the footswitch for controlling a relay which disconnects the wire from the "intensity" pot that goes to the cathode of V1B.
Fender Vibro Champ / Bronco tremelo intensity knob lowers the gain
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Fender Vibro Champ / Bronco tremelo intensity knob lowers the gain
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Stevem
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Re: Fender Vibro Champ / Bronco tremelo intensity knob lowers the gain
In my master volume Proreverb I did away with the boost circuit that was activated by the on/ off switch on the 1m master volume pot and used that switch to open or close the signal feed to the tremolo circuit.
You could replace the Champ / Bronco’s volume pot with the same set up.
On the amps with a tremolo circuit that use a roach there is a huge drop in signal drive level when the feed is hooked up to the intensity pot that makes the drop in gain that your hearing hardly anything!
You might use the same switch set up to un-jump a series cathode resistor added on the first gain stage.
With both resistors in series that would add more gain to compensate for when the tremolo is on.
You can add about 25% more cathode resistance before the plate resistor needs to be changed also.
This mod might provide enough make up gain.
This mod would likely make for a pop being heard when switched and a 1 meg across the switch should take care of that side issue.
You could replace the Champ / Bronco’s volume pot with the same set up.
On the amps with a tremolo circuit that use a roach there is a huge drop in signal drive level when the feed is hooked up to the intensity pot that makes the drop in gain that your hearing hardly anything!
You might use the same switch set up to un-jump a series cathode resistor added on the first gain stage.
With both resistors in series that would add more gain to compensate for when the tremolo is on.
You can add about 25% more cathode resistance before the plate resistor needs to be changed also.
This mod might provide enough make up gain.
This mod would likely make for a pop being heard when switched and a 1 meg across the switch should take care of that side issue.
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Not screaming like the passengers in his car!
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Fender Vibro Champ / Bronco tremelo intensity knob lowers the gain
You have a defective 25 k Reverse audio intensity control. Replace it with a CTS or Alpha 50k reverse audio pot !