reverb tank in/out power?

[olddawg]

Yeh, I've done some searching and what I'm finding is really generic as far as "which diode". I'm interpreting that the foreward voltage drop exhibited by any typical diode doesn't even start to conduct until that voltage is reached... Is this correct??? My concearn was how to figure the voltage I need PLUS the voltage drop and how any given part # would effect that (since I'm working with such small voltages). But I guess that's not the case. Seems pretty simple at this point if I understand this right.

Chuck

Yeah pretty much thats it. The diodes won't conduct until they reach their propogation voltage. For example if you want to clamp the input not to exceed 1.3v you use 4 diodes, two in series with the pairs biased in both directions across the input. A simple limiter for about 20 cents.

[jbefumo]

I'm just putting some finishing touches on a little (8") combo that I designed with a Fender-style reverb in mind, although, due to space limitations, figured I'd use a 12DW7 (AU7 side to drive, AX7 side for recovery). Have been testing it using a full size Accutronics 'A' (10-Ohm) tank on the bench. I had some smaller tanks that fit the cabinet perfectly laying around, but I just put the meter on the inputs and the DC reading is 178.5-Ohms, which I suppose would put them somewhere between an Accutronics 'E' and 'F'. Had I checked first (duh) I would have simply designed the driver to forego the transformer, but as it stands now, it's kind of late for redesign, so, my question is: what are the ramifications of using this higher impedance tank with the mismatched transformer? Or should I bite the bullet and just buy a new short tank and save these for a future project?

The circuit is attached.

Thanks.

Joe

[jbefumo]

Oh yeah - I KNOW these reverb tanks must have some kind of special mojo, because they say: "Manufactured by Beautiful Girls in Milton, Wis., under controlled Atmosphere Conditions" . . .

[jbefumo]

Just came up with this:

Non-accutronic's Reverb tank impedance question? - AMPAGE Archive

It is, indeed, a type-56, and came out of an old Baldwin organ . . . waste not, want not ;^)

[jbefumo]

So, here's a follow up question -- is there any better tube I could use than the AU7? I could easily substitute the 12DW7 for a 12AX7 or a 12AT7, or . . . ?

[Chuck H]

Use the DW7! It's a brilliant tube for a single dual triode reverb and mates fine with the standard "Fender" reverb transformer. Here's a schem that inclunes how I've implemented a 12DW7 reverb. I need to trouble shoot some buzz/hum but otherwise it's working great!!!

[jbefumo]

Use the DW7! It's a brilliant tube for a single dual triode reverb and mates fine with the standard "Fender" reverb transformer. Here's a schem that inclunes how I've implemented a 12DW7 reverb. I need to trouble shoot some buzz/hum but otherwise it's working great!!!

Thank you much! I will study the schematic! I always keep several DW7s and their mirror-image versions (ECC823) on hand. I find them particularly useful in topologies like the Marshall, where 1/2 of a single bottle is used for a gain stage, and the other is a cathode follower. Depending on how the socket is wired, one of these usually works very well. In the current project, it suddenly occurred to me that I was using TWO DW7s . . . Uhhh . . . so I just rewired for one 12AX7 and one 12AU7 . . . linear thinking strikes again!

Will post my complete schematic as soon as I clean it up and bring up to date with on-the-fly changes . . .

btw - it's a 45-W 1X8 combo with foot-switchable reverb and overdrive in a package smaller than a Champ. I wanted something that I could grab and go, carry in one trip with my guitar, stuff in the trunk of my Ford Escort, keep up with a band, and have the main functionality I want without the necessity of pedals, extra cables, etc. Speaker is an absolutely brilliant EOS Celestion Vintage 8, rated for 60W. Haven't been able to find anything else like it. To move more air, I have a matching 2X12 box.

Joe

[jbefumo]

So, am I correct in my interpretation that VR5A and VR5B are a dual ganged pot, set up so that turning down the reverb level simultaneously increases the resistance seen by the dry signal to avoid volume reduction when adjusting the reverb? Brilliant!

[Chuck H]

So, am I correct in my interpretation that VR5A and VR5B are a dual ganged pot, set up so that turning down the reverb level simultaneously increases the resistance seen by the dry signal to avoid volume reduction when adjusting the reverb? Brilliant!

Thanks! Depending on how you look at it, that's pretty much it. The summing stage is wired as a virtual earth mixer with the reverb signal variably bypassing the local NFB to achieve amplification from that stage while the dry signals don't. It's a very clean way to mix things like this. Using a linear pot with this circuit results in very audio pot like operation.

[jbefumo]

To paraphrase the late, great Milton Berle: 'I know a great [joke] circuit when I steal one!"

[Chuck H]

Well I certainly didn't invent the VE mixer. I may have invented that coupling circuit, maybe not, I dunno. Not much new under the sun really. I wouldn't have posted it if I was worried about it being used by others. Pilfer as it suits you.

[jbefumo]

Thanks again -- Personally, I always feel complemented when someone benefits from my work (e.g.: this guy's vid) -- though lots of people get really proprietary about their ideas. The way I look at it, ideas are easy -- making something that works is the tough part.

Joe