71 Super Reverb Slow To Engage Vibrato

[keithb7]

Although my troubleshooting skills were limited, I do believe, for whatever reason, the centre cap that I replaced last, was the fix here. It certainly was the last part I changed out before I got the results I wanted. I should have changed all three when I was initially in there and changed the other two caps. I did test the amp after I made any part changes, or just repaired some connections. Only the last cap change made a difference. All 3 caps were tested for capacitance with my DMM and were within the 10% rating. However maybe all combined, the problem compounded. I don't think there was a cold solder problem that I happened to repair when I changed the last cap. The amp was dead quiet and there was no cracking or popping that I have experienced in other amps with cold joints. Only a theory here, it is possible.

I left the amp over night. This morning I clicked on the foot switch before I turned on the amp. As soon as the amp started producing sound the vibrato was on, and working perfectly. Under the same circumstances, previously it took up to a minute to start pulsing. So this confirms that when working properly, there is no audible ramp up time for the vibrato to kick in on this amp.

[52 Bill]

All 3 caps were tested for capacitance with my DMM and were within the 10% rating.

Unfortunately testing caps on a DMM will not always find a bad cap. The DMM will never come close to simulating the in circuit conditions of a cap in a tube amp.

[Chuck H]

True. But I'll bet there's nothing wrong with them that can be tested for with average, if not standard measurement tools found on a typical amp repair bench So this still leaves it in guru-land.

[keithb7]

I'd be curious to know the measured values of the three caps? Justin

Justin I just measured the 3 caps here they are:
Spec .02 10%. Actual .02348
Spec .01 10%. Actual .00979
Spec .01 10%. Actual .00986

Regards.