Reverb mellowing mod

[rfgordon]

A client of mine dropped off a bunch of old reverb tanks, some missing springs, some of questionable function, etc.

One of them was a Hammond branded tank, same impedance values as Fenders normally use. This tank had been hard-wired into something (he couldn't remember where it came from).

It turns out it worked. But here's the interesting part. Inside the tank, on the input, there was a 1 watt, 330 Ohm resistor soldered between the input of the RCA jack and the transducer.

Since I tested the tank, via clip leads, to see if it worked, I heard the tank with the resistor. I figured the resistor had to do with its original application, so I removed it prior to prepping the tank to go into the client's old Pro Reverb.

Without the resistor, the reverb is typically dramatic--Fender style. With the resistor, the verb was much mellower, and, one might say, gave a more useful range on the Reverb control of the amp.

Hmmm, says I. So I decided to put a 68 Ohm, 1 watt resistor in the amp on the reverb send RCA jack, in series with the output from the reverb drivier transformer.

It does mellow the reverb slightly and it makes it less "spashy."

I don't know if any of y'all have seen this kind of mod before, but I thought I'd share it. I suppose, in a reverb amp, you could even mount a low value pot next to the reverb send to act as a bit of extra depth control.

This has a different effect than the Dwell control, sind the dwell actually bleeds signal to ground.

Thoughts?

[roberto]

The first reason that comes into my mind is some capacitance of the transducer inside the tank (due to the windings), but to have a 3db cutof at 5 kHz that capacitance should be around 470 nF with the 68 R resistor.

It will cut at around 1 kHz with the 330 Ohm resistor.

But it seems too much, so I think there's another reason.

[rfgordon]

I had wondered if the tank had come from an organ, and the resistor was meant to protect the transducer from too hot a signal. But I just don't know. I do know it has an effect on the verb, though.