Why did Fender change the cathode cap...

[AdmiralB]

...of the tremolo oscillator in the AA270 revision from 25uF to 5uF?

I could see that 5uF might be enough, but I don't see any disadvantage to 25uF - that tube has to amplify some VERY low frequecies. I guess 5uF components might have been cheaper, but since it's the only place in the circuit that uses them it seems like the operational cost of stocking another component for just that application would outweigh any piece part savings.

[Rick Erickson]

If you rotate the Speed control from slow to fast rather quickly the oscillator will drop out. The 5uF cap. shortened the recovery time of the oscillator without adversely affecting the operation of the circuit. I always use the 5uF (4.7uF) value when rebuilding a Fender trem circuit. Not all changes done in the CBS era were bad - the challenge is to understand which ones were the good ones.

RE

[AdmiralB]

Thanks! I don't think I've ever replaced a 5uF in one of these with anything other, but I wondered why.

[Enzo]

Aha, now that is an interesting bit of data. I never thought about the osc coming to a halt.