Fender Amp "Weak" Vibrato

[Pastortom]

Lookin' for some input.........

Generally speaking, would a "weak" intensity on a Fender Vibrato mean a "weak" optoisolator, or are there more variables that commonly cause the weakness?

Again, it works......but the intensity is just very weak......full intensity (10) acts like a 1 or 2 setting.

What say ye?

[FYL]

Could be a bad solder, a weak tube or a weak neon/LDR module. Begin by checking/reflowing board connections, then try changing the 12AX7 in the oscillator stage with new or known good tubes, then try a new roach. Less probable causes: defective passives - caps, resistors and pots.

 

[bnwitt]

I'd change the tube first.  You need a really strong 12AX7 in that circuit.

[Merlin]

Begin by checking/reflowing board connections, then try changing the 12AX7

Why on earth would you open up an amp and start reflowing joints before just plugging in a different tube?

(It's nearly always a weak oscillator tube)

[EL34]

I have also seen it where the bulb was not lined up with the opto in Fenders

Kind of rare, but it can happen.
You can realign the parts and re-heat shrink them.

[FYL]

I'd change the tube first.  You need a really strong 12AX7 in that circuit.

Agreed, but I've just worked on two vintage DR's suffering from weak vibrato because of board-related problems. Both were fitted with recent tubes and functional roaches, both were fine after a few reflows.
 
Changing the 12AX7 in the vibrato section is usually sufficient with recent amps.

[Tiny_Daddy]

I have seen more than one amp with no cathode bypass cap on the oscillator tube. Result was weak oscillation, slow to start.

[P Batty]

How old is the amp?  The light sensitive resistor in the roach will lose its effectiveness over time, diminishing the effect, but definitely check the tube first.