On 11/28/2015 6:49 AM, amdx wrote:
On 11/27/2015 9:00 AM, Christopher Tidy wrote:
Hi folks,

This is a question for people with electrical knowledge, especially in the
field of electrostatics. It's also spontaneous. I'm not sure if I'm going to
build anything yet.


This may be of interest to some folks. Back in the 60's there was an electronic
device for creating an echo/reverb effect for electric guitars and such.

It could replace tape recording devices for a delay effect, at least to some
extent. It was generally referred to as an oilcan echo/reverb


https://en.wikipedia.org/wiki/Echo_chamber

Oil-can delay method

An alternative echo system was the so-called "oil-can delay" method, which uses
electrostatic rather than electromagnetic recording.[1]

Invented by Ray Lubow, the "oil-can" method uses a rotating disc made of
anodized aluminium, the surface of which is coated with a suspension of carbon
particles. An AC signal is sent to a conductive neoprene "wiper", which
transfers the high impedance charge to the disc. As the particles pass by the
wiper, they act as thousands of tiny capacitors, holding a small part of the
charge. A second wiper reads this representation of the signal, and sends it on
to a voltage amplifier, where it is mixed with the original source. To protect
the charge held in each capacitor and to lubricate the entire assembly, the disc
runs inside a sealed can with enough of a special oil (Union Carbide UCON lb65)
to assure that an even coating is applied as it spins.

The effect resembles an echo, but the whimsical nature of the storage medium
causes variations in the sound that can be heard as a vibrato effect. Some early
models featured control circuitry designed to feed the output of the read wiper
to the write head, causing a reverberant effect as well.

Many different companies marketed these devices under various names. Fender sold
the Dimension IV, the Variable Delay, the Echo-Reverb I, II, and III, and
included an oil can in their Special Effects box. Gibson sold the GA-4RE from
1965-7. Ray Lubow himself sold many different versions under the Tel-Ray/Morley
brand, starting out in the early sixties with the Ad-n-echo, and eventually
producing the Echo-ver-brato, the Electrostatic Delay Line, and many others into
the eighties.



http://www.geofex.com/Article_Folder...can_delays.htm

The Technology of Oil Can Delays
Updated 7/1/02

Copyright 1999-2002 R.G. Keen. All Rights Reserved.

Before digital delays, before analog bucket brigade delays, there was an effects
technology that subbed in for tape delays that was portable and relatively easy
to use for floor mounted items. This was the rotating oil can delay, and here's
how it works.

Everyone is familiar with magnetic storage - you move a substrate containing
magnetizable particles past a recording head that has an alternating magnetic
field in it. The magnetic field polarizes the magnetic direction of the
particles on the substrate and an "image" of the magnetic field alternations is
thereby stored in the particles. Reading is the reverse - you run the substrate
past a pickup head with many turns of hair-thin wire and the magnetic field in
the particles causes a voltage to be induced in the coil of wire, reading the
info that was recorded.

There are usually "dual" operations for all magnetic and electronic operations,
interchanging electric field for magnetic field and capacitors for inductors.
This is no exception. If you put charge into a capacitor, it holds the resulting
voltage, a crude form of storage. If you have many incredibly tiny capacitors,
you can start making a fairly good representation of a varying voltage. This is
in fact the way bucket brigade delay chips work.

There is another way to do electrical field storage. Insulating materials can be
given an electric charge, as we all know. Just wear rubber soled shoes and walk
across pile carpeting on a dry winter day, then touch a doorknob. The motion of
the shoes across the carpet stored a charge on the shoes (and then you) that was
expressed visibly and audibly when you touched the doorknob.

In a similar way, if we have a fine brush of conductive wires, and arrange an
insulating belt to be moved past, just touching the brush, we can put a large AC
voltage on the brush and some of the electric field will be captured on the
surface of the belt. Since the belt is an insulator, the charge can't go
anywhere, so the electrical charge forms a replica of the voltage on the brush.
Each tiny area of insulating surface is in fact acting like a micro-miniature
capacitor, storing the value of the voltage from the brush at the instant the
brush moved away from it, just like the magnetic particles in a tape machine
store a replica of the magnetic field from the record head.

The tiny voltage-carrying capacitors are carried off as the insulating belt
moves. The voltage would eventually leak off into the air if we let it. We can
instead choose to keep it in a dry environment for a while, and "read" it later
with a very high impedance amplifier. It turns out that vacuum tubes are ideal
for both the writing (at high voltage) and reading (very high impedance) of such
capacitive storage, and indeed the first oil can delays were tube based. Later
as semiconductor technology got better, transistor and FET read and write
amplifiers were made for the oil can delays.

So why the oil? What's that do? Remember that business about leaking into the
air? The oil provides a sealable insulating layer over the insulating belt so
the charge is trapped inside and has a hard time leaking into the air. The
brushes reach right through it to put in/take out charge, and the voltage is
protected from leaking away.

The oil is the center of a controversy - the original oil is reputed to be a
hazardous material, carinogenic, etc. Is it? Maybe. The best insulating oils
available at the time the oil can delays were designed were transformer
insulating/cooling oils. These were definitely polychlorinated biphenyl based -
the same "PCB's" that are now banned from all use as containing deadly dioxins.
The only question is whether the oil can delay makers used that stuff or
something else entirely.

If you're restoring an oil can delay that is now dry, what oil do you use? I've
heard of using mineral oil from a pharmacy, Singer brand sewing machine oil,
even 20 weight motor oil, all said to work to some degree. However, the reports
have been decidedly mixed.

I recently stumbled onto the Tel-Ray page
(http://www.geocities.com/tel_ray/home.html) where some of my intuitions on oil
can delays were confirmed, and where I found a reference to the original patents
on the technology. You can look them up at the US patent office web site if
you're interested. Look for US Patents 2892898 and 3072543. From what I read,
we might be able to make new, functioning oil cans - they don't look like rocket
science ( as old-hat as rocket science seems now, even ).

The principals in the Tel-Ray page have now confirmed some of my guesses, and
have graciously extended the info a great deal. From the patents, it is clear
that the original oil can delays were just as I guessed, capacitive storage
devices. However, the second and third patents delve further into the
lubricating medium. It seems that by carefully dinking with the
lubricating/insulating oil and doping it with various things to get conducting
particles spread out in the oil, you can make for a higher signal level stored
in the rotating capacitor, and hence better signal recovery, lower noise, and
all-round better performance.

Zak Izbinsky, Richard Bills and Jamie Ray dug out the detailed info, as
displayed at the Tel-Ray site. The "real stuff" replacement oil for the oilcan
effects is Union Carbide "Ucon" LB-65 oil. It is not carcinogenic, and not PCB oil.

This is the exact same substance as was originally used by Tel-Ray in the 60's
as specified on the third patent. It is still available through Union
Carbide/DOW and is reputed to be only $200 a gallon. ... GAK!!!

However, the guys at Tel-Ray have helped out. They bought a supply and will
parcel out just enough for your oil can for about $25. Check them out.

The second method

I've also come across a second method for "oil can" delays. I put the quotes in
because it doesn't use any oil. I got a Vox Echo-Reverb model V807 recently. It
had a typical oil can delay... until I looked further. There's no oil, but not
only that, it looks like there never was any. Multiple spring contacts are held
against a rotating disc in a machined aluminum housing with a counterbalancing
spring mechanism to keep them all just touching. It looks like this one is
intended to get around the Tel-Ray patents. I'll know more when I get the bugs
fixed and get it running.


R.G.