Art Welter --
Are you still looking at this oil-can?
>
the signal to noise ratio is about 1/1S/N is about the media, the Drive Level, and the recovery losses.
The tube circuit has oddities but is not hard to read.
The input is two HIGH-gain stages. The obvious intent is to bring e-guitar up to about 100V rms into a very high impedance load (prehaps less than 50pFd, plus some megs of trim-pots). You won't get this level from line-amps or line transformers; indeed transformers work poorly into such loads. The "simple" answer is to build the tube-amp. If you have Line (not e-guitar), only the 2nd stage is needed. Set peak level near clipping.
The recovery amp is very specialized, and may be your bigger problem. The 4.7Meg grid resistor is boot-strapped by the cathode, and a second cathode. Counting on thumbs it looks like 50 MEGS input impedance. Chewing the computer, I get numbers like 30Megs with less than 1pFd(!) input capacitance. It's odd, and surely necessary to recover signal from such a hi-Z source.
You will not get this level of light loading from any common studio preamp. A condenser mike head-amp could work, or something like that simplified to bootstrap JFET on 18V-24V supply. Or the tubes. The teeny grid capacitance suggests that (like a condenser mike head) the stray wiring capacitance must be VERY small, the recovery amp should be up-against the tank, and room-buzz will be a problem.
There were, however, 25V transistor versions:
http://www.el34world.com/charts/Schematics/files/effects/tel ray_delay_echo_reverb_oilcan.pdf
http://www.el34world.com/charts/Schematics/files/effects/tel ray_echovolume_evo-1_oilcan.pdf
http://www.el34world.com/charts/Schematics/files/effects/tel ray_electrostatic_delay_line_oilcan.pdf
The disk surface must be a thin insulator on a conductor. VERY low self-leakage. Preferably with high dielectric constant. Your disk is Aluminum. The obvious surface treatment is anodize, Aluminum Oxide, much like an electrolytic capacitor except without (necessarily) a conductive liquid electrode. Indeed patent 2,892,898 cites aluminum oxide on aluminum. (Patent 3,072,543 rubs glycerine into AlO... dang-near an electrolytic cap.)
Surface must be DRY. Oil must be dry.... high-voltage oil is commonly heated above the boiling point of water for a few hours before final use. Scratches do little harm. Water on a soft cloth with a good dry does no harm. Harsh scrubbing will remove the anodize film, and the raw aluminum in everyday air will grow-back a coarse self-anodize which will work poorly or not at all.
Oil VooDoo may be the trick which raised the can from a toy into a product. Dry-rub wears the surface or wipers, and upsets electrons. Lubrication helps life, and also can improve dielectric coupling.
In addition to the basic delay, there is system-stuff. Input audio is tapped to a "Direct Signal" pot and mixed to output. Recovery amp is tapped for "Echo Level" pot mixed to output. Basic stuff, though the 0.01u+5K in the echo out path suggests EQ.
And then there is regeneration. The double cathode follower second plate (to bypass Miller trouble) has a high-gain output potted onto the same line used for Direct output. This works because the input first stage plate is very high impedance. The regen pots look to be wired backward (wiper-in), it works better this way.
The "mudflaps" should touch the surface more like "windshield wipers". The contact area must be large for good energy transfer. The length in direction of motion must be small for good high frequency response. Same as tape: the gap is 0.1" one way and 0.001" the other way. And like tape, the play azimuth must be aligned with the record azimuth. This must be difficult with rubber mudflaps.
http://www.google.com/patents -- 2892898 - 3072543 - 3215911
http://web.archive.org/web/20050419134852/http://www.geociti es.com/tel_ray/pictures.html
http://www.el34world.com/charts/Schematics/files/effects/tel ray_ad_n_echo_oilcan.pdf
http://www.el34world.com/charts/Schematics/files/effects/fen der_echoreverb_II_oilcan.pdf
http://www.el34world.com/charts/Schematics/files/effects/fen der_echoreverb_III_oilcan.pdf
http://www.el34world.com/charts/Schematics/files/effects/tel ray_deluxe_organtone_oilcan.pdf
http://www.el34world.com/charts/Schematics/files/effects/tel ray_echo-ver-brato_oilcan.pdf
Side-note: "
I don't think ESD conductive rubber was around in the 60's"-- in the 1962-1965 timeframe I was shown a bumpy rubber plate the size of a punch-card, told it was mildly conductive, and that it was part of a card-reader. Also patent 2,892,898 speaks of "elastic conductive" material and "neoprene impregnated with graphite"; patent 3,072,543 mentions "conductive rubber". Tire-rubber has been doped with powdered carbon since forever; not to the point of great conductivity (they put other stuff in also), but enuff so that sorta-conducting rubber would be obvious.