Mods and tips for Fender Tremolo circuits
Here are a few tips and mods for the tremolo circuit in Blackface and
Silverface Fender amps. These apply to the circuits with the
light bulb/photo resistor trembug, not the tube based bias vary circuit.
the tremolo to make it switchable in and out
I did this mod on my Bandmaster,
and I love it. You get a noticeable
bump in gain when you switch the tremolo out of the circuit. You can
get the pot with the switch from Ted
Here's how it's done:
1. Disconnect the wires from the 50k RA Intensity pot.
2. Remove the pot.
3. Install new 50k RA Intensity pot with SPST switch attached.
4. Solder Brown wire to center lug as before.
5. Solder left lug to pot casing as before.
6. Solder Yellow wire to one side of switch.
7. Solder short length of new wire from other side of switch to right
If you are getting pops when actuating the switch, add a 1 meg resistor
inline with the yellow wire in step 6.
down the tremolo speed
If you're like me you think the speed control on Fender trem circuits
is too fast. There are three caps in the trem circuit: Two .01's and a
.02. You can slow the trem speed down by replacing the .01's with
.02's. Tone wise, I don't think it matters here but I used Orange Drops.
the "Ticking" in Fender Tremolo circuits
This is from the great electronics guru R. G. Keen. For an astonishing
amount of information about tube amps and guitar effects check out his
My Tech Page
- Fiberboard contamination: Dust, dirt, and junk can let the
signal leak into the audio path. Vacuum the dust and dirt away, and if
it still persists, remelt the wax top and bottom with a hair dryer.
- Solder blobs from eyelets touching insulating board:
Sometimes excess solder drips out the bottom of an eyelet and can
intermittently contact the insulating board, can cause ticking. Remelt
the eyelets and examine the board underneath for any blobs dripped
- Funny ground on some SF Fenders; On one of the signal tubes,
the cathode cap was placed on the tube socket, and wired to a ground
lug on the vibrato cancel jack instead of across the resistor on the
fiberboard. The vibrato shares this ground line, and can the vibrato
current can cause audible ticking in the audio path. Rewire the cap to
another ground or relocate it to the board.
- Poor Signal wire layout: signal wires run too close to
vibrato leads can pick up the LFO signal. Move them around and see if
the ticking goes away.
- Bad repair/replacement foot switch cable: the Fender
foot switch cable is not two conductor; it's single conductor shielded,
plus single conductor. The reverb wire is shielded, vibrato wire is
not. This keeps vibrato out of reverb. If you retrofit with two
conductor shielded, you get vibrato ticking onto reverb audio.
- Sharp tick in vibrato oscillator: On neon/LDR Fenders, on
neon bulb side of the module there is a 10M to one side of bulb, 100K
to the bulb; from the 10M straight across the board is the gnd point of
the LDR. Put a 0.02 cap from 10M/bulb to the ground point; this works
by filtering the output of the oscillator.