Reverb Circuit has now killed two reverb drivers. Please help!

[nickb]

For each case:-
Where is 0V?
What is the vertical scale?

[Gaz]

For each case:-
Where is 0V?
What is the vertical scale?

Nick, I didn't take note, so I retook some shot with my small digital scope and 100X probe. I also compared equivalent Accutronics and MOD 3-spring tanks. The AC primary voltage went up over 100V RMS with the MOD tank. I don't know if that's of any interest... Here are the shots with the on-screen measurements (God forbid if the uploader rotates my photos again ;/)

[TimmyP1955]

As to the danger of running the reverb circuit without a tank: I've had innumerable amps come in with the input of the tank open owing to broken internal wires (the cause of 90% or more of our tank issues). I've replaced one reverb transformer.

[SoulFetish]

As to the danger of running the reverb circuit without a tank: I've had innumerable amps come in with the input of the tank open owing to broken internal wires (the cause of 90% or more of our tank issues). I've replaced one reverb transformer.

I've had a couple of reverb transformers go bad, but I've pretty much seen the same thing as you, Timmy. I can't tell you how many either broken transducer wires, rca jack oxidization, bad cables which have opened the secondary and they have survived.
But obviously, Nick's theory is sound and I have no good explanation for why these audio transformers hold up under no load conditions.
I dunno', what is the typical leakage inductance in these little transformers?

[nickb]

Sorry for delay. Been away and the and WiFi was broke...

I see that you get about 1.4KV. Given this is probably not a worst case test I would not be surprised to see something higher. I suggest two things, one add an MOV to clamp to a max of 1KV and second reduce the drive. It seems like you might be driving it a bit hard. This was done with 100mV input and a real guitar can put out quite a bit more than that.

On the reverb transformers failing it's certainly a rare thing. Where I have seen it I can only think of once where it was total fail. In the other cases it just made faint noises, I guess insulation starting to go. OTOH the excessive drive in this case means failure is more likely.