Help needed determining which reverb tank for an amp.

[Thegtrzan]

Hey everyone. Here's my dilema. I have a 1973 Earth Sound Research Revival 410 tube amp I'm restoring. Model number M1954. All my "research" says this amp was a direct rip off of the second phase of the 1970's "Peavey Vintage" series amps. There were two versions of the Peavey Vintage, and like the Earth Sound Research amp I'm working on, the second phase Peavey Vintage had a solid state preamp exactly like the Earth Sound Research amp I'm working on. (In other words this is NOT not the Peavey Vintage with that bizarre internally mounted dual tube preamp.)
This amp I'm working on has four 6L6 only, with a solid state pre amp. I've looked at a photo of the said Peavey Vintage and but for minor differences on the big capacitors by the transformers, indeed they appear to be identicle.
Everything works great on the Earth Sound amp as is but for one problem; someone had swapped out the original reverb tank with an unsuitable unit. This is blatantly obvious for two reasons.
One, the reverb barely works at all as is with the tank I got it with; it's barely audable. Two, the tank thats in it has a retail price tag sticker on it from some defunct old electronics supply store in Michigan, so it was definitely replaced. It was absolutly put in second hand. The tank thats in it is an Accutronics 8BB3C1B. Its gotta be way off spec for this amp. Here's why I say that:
I pulled the long spring reverb out of my Peavey Delta Blues amp just to give it a short trial run in the Earth Sound. It's an Accutronics 4EB2C1B. Immediately the Earth Sound reverb came alive, and the reverb worked well. At least tenfold better than the tank I got it with. Yet it's still not what I'm looking for. I want more of a Fender Twin kinda reverb, deep and thick. I'm considering an Accutronics type 9 three springer...
* Problem being; how do I determine what the proper input and output impedances for this amp should be, when the original tank is long gone? I have the schematic for the amp, but it doesn't tell me anything as to impedances for the reverb circuit, or which jack is the input and which is the output. And if it does, I'm not near knowledgeable enough to know how to tell from a schematic print.
Now when I reversed the leads on the reverb tank using either the tank it came with, or the Delta Blues tank, it sounded exactly the same; no difference at all either way. From all I've read online, thats not altogether normal either. So uh, say huh? Shouldn't this make a big difference? Because it doesn't sound any different to my ears....or three of my guitar player friends who were here with me.
* That said:
A) How do I determine what impedances tank to order?
B) How can I determine which is the input and which is the output on the amp....when it's not labled on the chassis?
I did note that one jack has a single wire going to the center conductor inside, and the other jack has a shielded cable soldered on to it, but the sheild wire is not connected at the circuit board end if this is any help.
Common sense dictates the impedance of the above Peavey Delta Blues tank is a much closer match to what the amp needs, simply because it works and functions. It's also notable to add that it sounds strikingly the same when installed in the Earth Sound amp as it does installed in the Delta Blues its actually for. In either amp the reverb is clearly there, but by no means as lush or deep as I'd like it to be in either amp. That being said, I'm guessing its close to being the right impedance for the Earth Sound amp simply because it sounds close to the same as when its in the amp its for.
But "close to right" isn't my objective. One hundred percent correct or close as I can get to spec is my objective is. So again:
A) How can I determine what input and output reverb tank to order when the original reverb tank is missing?
B) How do I determine which is the input and which is the output on the amp when the chassis is not labeled?
C) Why does it sound the same no matter which way the leads are connected?
Any help graetly apreciated. Thanks much
Thegtrzan

[Enzo]

Let's see if we can condense all that.

You have an amp that is a Peavey copy. the reverb is bad. You subbed the 4EB2C1B reverb from another Peavey, and it worked. So you need a new 4EB2C1B reverb.

Comments:
This amp reverb should sound a lot like any other Peavey amp reverb. If that is not what you want, sorry. The type 9 pan versus the type 4 pan is not the difference between a FEnder surf reverb and something else. The two spring and three spring reverb pans make the same amount of reverb, the three spring is just a bit more complex sounding.

Other than a very small number of transformer drivien reverb circuits, Peavey has used the same 4EB2C1B is all their amps. No reason to think Earth did anything different.

The wrong reverb type works equally poorly in both directions. OK, so what? Don;t waste time trying to fathom that out. The wrong thing doesn't work right. And twice a day, the blinking 12:00 on my VCR display is the correct time.

You have two cables to the reverb pan. Turn the amp on and the reverb up. Touch the tip of each cable plug. One should make hum when you do, that is the return cable. Plug it into the OUTPUT jack on the pan. It must be shielded cable. The other end is the drive cable, and connects to the INPUT jack on the pan. It doesn't have to be shielded, but can be.

The 4EB2C1B has an insulated INPUT jack, the shield side is not grounded. If your chassis end reverb cable connetions are not made, you ground the return cable shield, but the shield or "ground" side of the drive cable is not chassis grounded.

If someone can get a Fender/surf reverb out of these thing, bless their hearts. But that is not the natural sound in the Peavey reverb. The Fender tube drive is a small power amp, and it won;t sound the same as the op amp drive that has worked for decades too.

[Leo_Gnardo]

Currently available reverb tanks have small circuit boards behind their jacks, on those boards are solder pads, you can attach or detach ground connections with a drop of solder.

Exact replacement? What Enzo says, not likely you're going to get a grand canyon echo*. Another point, even if you could identify an "exact" part number, reverb tanks vary one to the next in spite of the assumption they should all sound the same even with the same part number. I used to buy 'em by the dozen, sure enough some sounded fantastic, most were perfectly suitable, and typically one dud out of the bunch. And even that last one eventually found a home.

Only one thing seems obvious, you need a tank with medium or high input impedance. I'm leaning towards high from your description of "one direction sounds same as the other" with the tank borrowed from the Peavey.

*You have a choice of 2 spring and 3 spring tanks. Some dealers refer to these as 4 and 6 spring, since each spring is made of two springs joined in the center. That being said, you'll have a better chance of getting a long lush reverb with the 3/6 spring variety. I ordinarily avoid these in guitar amps as the reverb seems to never end, has a "playing in an indoor stadium" quality. But if that's what you want, more springs is better.

Antique electronics, tubesandmore.com is my go to source these days. (I'm not an employee or owner just satisfied customer.) They're not much for long winded conversations, no salesman is going to take 45 minutes to discuss reverb tanks and their relative qualities, descriptions - for what they're worth - you can read on their online catalog, please pick an item and buy it. MOD & Belton are the current brands, I've had good luck with the MOD. Belton now stamps some of their tanks "Accutronics" and charges a couple more bucks. Are they better? Do they really sound like the Accutronics we used to buy and love 20+ years ago? I don't know. Belton bought the brand name, that's all I know.

[Thegtrzan]

Let's see if we can condense all that.

You have an amp that is a Peavey copy. the reverb is bad. You subbed the 4EB2C1B reverb from another Peavey, and it worked. So you need a new 4EB2C1B reverb.

Comments:
This amp reverb should sound a lot like any other Peavey amp reverb. If that is not what you want, sorry. The type 9 pan versus the type 4 pan is not the difference between a FEnder surf reverb and something else. The two spring and three spring reverb pans make the same amount of reverb, the three spring is just a bit more complex sounding.

Other than a very small number of transformer drivien reverb circuits, Peavey has used the same 4EB2C1B is all their amps. No reason to think Earth did anything different.

The wrong reverb type works equally poorly in both directions. OK, so what? Don;t waste time trying to fathom that out. The wrong thing doesn't work right. And twice a day, the blinking 12:00 on my VCR display is the correct time.

You have two cables to the reverb pan. Turn the amp on and the reverb up. Touch the tip of each cable plug. One should make hum when you do, that is the return cable. Plug it into the OUTPUT jack on the pan. It must be shielded cable. The other end is the drive cable, and connects to the INPUT jack on the pan. It doesn't have to be shielded, but can be.

The 4EB2C1B has an insulated INPUT jack, the shield side is not grounded. If your chassis end reverb cable connetions are not made, you ground the return cable shield, but the shield or "ground" side of the drive cable is not chassis grounded.

If someone can get a Fender/surf reverb out of these thing, bless their hearts. But that is not the natural sound in the Peavey reverb. The Fender tube drive is a small power amp, and it won;t sound the same as the op amp drive that has worked for decades too.

Thank you so much for the fast reply Enzo! I was kind of leaning towards that conclusion on the tank myself, but hearing it from someone with considerable more knowledge than myself is very comforting. I was concerned about damaging something in the amp due to its age for one, and due to it being a rather questionable project to begin with being what it is. The numbers on the op amps in it look old and may be obsolete and difficult to cross reference and replace were something to happen due to incompatability. But what you said makes perfect sense if Peavey has used the same pan on most of their amps, and this being a Peavey copy as everything indicates it is. All I've read about this company indicates Peavey basically gave them the choice of closing shop on the Revival amp series they had nicked from them, or going to court. They stopped making them and went out of business a few years later. Thanks for helping determine which is the input and which is the output. I was at a total loss being a rookie. I am greatful for this wonderful site and resource. What a big help!!! Thanks again!

[Thegtrzan]

Thanks Leo. I think I'm gonna stay with what I know works and sounded good and just buy another 4EB2C1B for it as Enzo suggested. I for sure don't want an overbearing reverb that washes out the detail. I actually use reverb sparingly for the most part, but wanted it to sound nice come time to sell the amp.

[g1]

As far as your question about why the wrong tank sounds the same no matter which way it is hooked up:
The 2nd and 3rd characters in the tank code (BB or EB in this example) denote the input and output impedance of the tank. With the BB type tank, the impedance is the same at both ends. That's why it sounds the same when hooked up 'backwards'.

Edit: above is incorrect. I forgot the part that the letters denote different impedances depending on whether they are at the input or output end. An EB type has closer impedances at in and out than a BB type.

[Thegtrzan]

That I did figure out by going to Accutronics and looking over the impedences...but it doesn't explain why the 4EB2C1B out of my Delta Blues amp sounded the same either way, the input and output are quite different, the input being 600 ohms and the out 2575 or the like. Hm....well, it worked and thats the good part! Ill take Enzos advice and stick with it. Thanks so much to everyone!

[Enzo]

Not quite, but inviting to think. They both have B impedances, but B means high impedance on the OUTPUT end, 2k-something ohms, but on the INPUT end, B is next to lowest impedance.

[Thegtrzan]

The difference between the two tanks is striking. I'm not any tech thats for sure, and don't pretend to be. My research said it was a Peavey copy and I happened to have a Peavey tube amp to test another pan. Common sense told me it might be closer to spec and what Enzo said confirms that. I so wish I had the knowledge you guys do. But fear not, I am smart enough to know when to leave good enough alone, and take it to a pro. I'm well aware of the dangers involved and have no wish to destroy my gear or fry myself trying to do any kind of modifications or the like. I totally admit, I do not know a thing beyond how to swap parts out and replace a capacitor or resistor correctly if I had to. Now that much I do know. But beyond that and very basic repairs like fix a bad solder joint, no thank you. I'd absolutely take the long way home, and call a pro like yourself!

[Enzo]

Advice we give around the shop: if the amp works, stop fixing it. Go enjoy your amp.

[Thegtrzan]

"If it ain't broke; don't fix it!"

[Thegtrzan]

I just registered this morning. Soon as I figure out the site I"ll post some pics. Did a total cabinet rebuild and upgrade and getting ready to put the tweed down soon. Actually got very lucky and found two NOS speakers for this on eBay from a wholesale warehouse that have the right date codes and all. What are the odds of that? It had been stored in a wet basement or garage and had water damage to the bottom of the cabinet that ruined the two bottom ten inch speakers. I made a new birch ply baffle board for it, installed new maple bracing etc.. Its nice and solid now and should look pretty OK when done. Didnt add any weigh really. Actually is not a bad sounding amp. I like it almost as much as my 78 Fender Twin reverb. But note the "almost" part well!