Standel Oil can Echo

[gmoon]

I scored a Standel Duette II "Oil Can" echo unit yesterday from Craigslist.

Seller said it didn't work, but (lucky twice) it really just needed a new belt!

Also, it seemed a little weak, but the "dry" signal also dropped off when hitting the footswitch. So I pulled the 7199 and tried the 6GH8A and adapter combo from my Ampeg Gemini--loud and clear. Guess I'll have to grab a couple NOS 7199's, 'cause the tube and adapter won't fit in the shield (or even the cabinet).

Rather than clog up the forum with more photos, here's a gallery:
https://picasaweb.google.com/evendistempered/StandelDuetteIIA

[Willabe]

Very cool!

What do they sound like? Like echo or verb or somewhere in between?


        Thanks,     Brad     

[gmoon]

Brad, it's a spacey or maybe "underwater" type effect. Not very subtle--although you can dial down it down (but it's fun not to!).

Effects the pitch also, at some settings...

[Willabe]

I think Billy Gibbons has one. G. Weber was kinda fascinated by it's design.


          Thanks,       Brad        

[gmoon]

It is fascinating, in a cludgy way. Can't get much more "analog" than this.

There's quite a bit of info on these things out there--a dedicated forum; R.G. wrote a "Tech of" article about them, etc. The "oil" in the cans has been identified for sure (and is available and safe) but other stuff--the recording disk surface, for instance, is somewhat mysterious.

Re: the sound. I've been playing with it a bit. It's definitely a delay/echo, with adjustable regeneration feedback. But the individual echos are so "approximate" that the playback audio fidelity is low... Low fidelity, but still very very interesting, if you're into this kinda thing. Really sounds out there.

This Standel is pretty rare, I guess. But the circuit, tank, controls and even the cabinet looks identical to the Tel-Ray Ad'N'Echo.
Schematic: http://www.el34world.com/charts/Schematics/files/effects/telray_ad_n_echo_oilcan.pdf

A question:
What's the purpose of the zeners in this? (guess: a clamp to limit voltage to the oil drum).

[HotBluePlates]

I think you're right with your guess about the zeners. As drawn, regular diodes might work, depending on the max signal level the drum can handle. They look like they are intended to clamp the input signal to avoid overdriving the drum.

[gmoon]

OK, thanks. The Standel Duette II schematic (not here in Doug's library) specs those zeners at 35V, which seems about right (considering I know very little about the oil can technology).

[PRR]

The mechanism was sold to several companies.

The surface is "just" anodized aluminum. Yes anodizing is a tricky process.

The frequency response "can" run from below audio to (like tape) a limit set by media linear speed and the width (and alignment) of the heads (wipers). The high end is probably not that high. In many versions, the low end is cut-off in the electronics.

The signal to noise ratio is not clear. The insulator thickness against the recovery amp input impedance sets some fundamental limit. It appears that in practice friction causes excess noise. It is also susceptible to hum/buzz.

Long-term pitch should be exact. Short-term, bad bearings and belt will add wow and flutter. Think of it as a phonograph (if you are old enough). It's a pretty cheezy phonograph.

7199 is again available but will always be a rarer tube. I wonder if the driver could be a 6AU6. Then a 12AU7/12AX7 could be the recovery stage; or an FET. (It really begs to have the FET inside the can right AT the pickup wiper.)

[gmoon]

Yeah, PPR, these are (and sound) very different compared to other delay technology. I've been reading up a bit. The patents are available.

From what I gather, no one has replicated the anodized surface of the disk correctly...although one poster claimed that coating the anodized surface with PVC glue (or alternately, Teflon) did the trick.

There is a pitch component to the effect, definitely. Due to the mechanics, it apparently varies from unit to unit.

If 7199's run dry (again), the 6GH8A is considered an excellent replacement (with a bit of rewiring). It was the substitute of choice for Ampeg amps when the 7199 was out of production. These are pentode/triode pair tubes. But there are plenty of other oil can circuits out there, both tube and SS.

It would be fun to make a working unit from scratch...nearly everything is known, other than the secrets of the anodizing process.