3 spring 10 ohm reverb tank, in a 8 ohm

[mikepukmel]

Thanks Enzo, thanks Juan.

[bob p]

Mike asks a good question about the reverb attenuator, and I agree with Juan's response that in the big picture the exact value really shouldn't matter if it varies to the next value in the resistor series ... but then I look at a couple of the current Fender schematics and I feel like I've been kicked in the teeth by some of the things that they are doing.

Take a look at the following schematic that itemizes the differences between the current production 65 Princeton Reverb Reissue (BF) and the 68 Custom Princeton Reverb Reissue (SF).

fender-custom-65-princeton-reverb-schematic-vs-68.pdf

It's evident that they're selling these two different versions of the same amp as being voiced for different types of players. Of course there are speaker changes that are going to result in huge differences in the amps' overall tone, but they've made some electronic changes as well:

Preamp:
* re-scaled the bass section of the tonestack by halving the value of C23 in the 68 Custom
* changed the value of the reverb attenuator (F30) by doubling it in the 68 Custom

Power Amp:
* change in feefback factor (R10)
* change in HPF knee frequency (C10, C16)

Looking at that feedback attenuation resistor, they're using a value of 470k in the "BF" version while they double that value to 1M in the "SF" version, which is going to dry up the wet signal somewhat.

Some of these changes seem pretty backwards to me. They're selling the BF cosmetic amp as the clean version and the SF cosmetic amp as the early distorting model. I tend to think of old Fenders in the opposite way.

[mikepukmel]

The circuit has a lot to do with how good a reverb sounds and many amp-based reverbs don't have enough control - just an output level that determines how much reverb gets mixed in with the dry signal, and even that has a preset maximum. Very often any additional post-manufacture dwell control mod is just a level control on the input that can go from zero up to the existing pre-set level set by the circuit topology and really does nothing to enhance the reverb. Kind of like a control to give you much less than you started with. I like to be able to drive the tank really hard with the dwell at maximum and I've spent endless hours looking at scope traces to get a better drive circuit. For me, a tank really comes to life with a much higher drive level than amp manufacturers provide. In addition, I like to be able to shift from 100% dry to 100% wet and anything in between.

There are other considerations, too; the frequency band that is chosen to drive the tank, the high-pass filtering on the output to reduce feedback and rumble, plus any resonant capacitance that the output coil 'sees' in parallel to itself.

For my money the same tank in a standalone reverb (say, a 6G15) will always sound a lot better than in an amp, because in general the amp is always compromised in how much circuitry is given over to the reverb section.

It comes down to personal listening preference and how much the reverb needs to be there just as a support, or an effect in its own right. I sometimes like to push my reverb to get the same sound from guitar as the (keyboard) reverb in the theme to 'Get Carter'.

Not having enough EE background, that is what I thought "dwell" meant: the bit of the circuit around that 3.3meg + 10pf cap, what looks to me the part of the ckt that mixes dry with wet. I though there should be a pot there someplace near that 3.3meg resistor to 'tune' either from 100% (or very high) dry, to 100% or very wet. I read a post on one of the other amp blogs that said something like "If you replace the stock 2 (4) spring with this long 3 (9) tank, you'll need to add a dwell pot ... but they go on to explain to replace that 1 meg grid to ground on the input side of the 12AT7 with a pot. That won't provide "dwell" the way I understood it (maybe incorrectly) as wet-dry mix, but only attenuate what is going in to the tank driver. So you still end up with the same mix of dry/wet, but the tank driver input is attenuated. All that said, I don't know what the effect on the sound will be either way.


Shouldn't there be a switch someplace to switch between 1, 2,3 (2, 4, 6) springs?

[bob p]

switch? no. every one of the 3 springs in the 3 spring tank is comprised of two springs hooked end to end. there's no going through one spring without going through the other.

as far as 2 spring (4 spring) and 3 spring (6 spring) tanks are concerned, there's no switching between them. 2 spring tanks always use both springs (4 elements) and 3 spring tanks always use all 3 springs (6 elements).

[g1]

The dwell is just an attenuator for the drive like Mick described.
You won't end up with the same mix of wet/dry if you change the amount of wet thrown into the mix. Everything through the tank is wet. If the mix ratio is constant, adding more wet to the mix ends up with a more 'wet heavy' mix.

[mikepukmel]

Thanks everyone.

[Chuck H]

JM2C...

I've used 10ohm tanks interchangeably with 8ohm tanks many times. I can't detect any significant difference in tone or useful signal at any point in the circuit.

re: Two spring (4?), three spring (6?) long, short, etc. these are my personal experiences...

I haven't tried a new manufactured reverb tank yet that wasn't more microphonic than the old school Accutronics product. And any old Accutronics product may have become microphonic with age. So we're sort of hosed there. In my experience it is pretty much impossible to use a three (6) spring long tank in any combo amp due to microphony. You just can't insulate/isolate it enough. My experience with new, long two (4) spring tanks is little better, but worse is the spring selection and matching seems poor on all of them so the actual reverb reflections, interaction and overall tone is poor. At least when compared to that old Fender tone. Two spring short tanks are strictly out because they're much worse in this regard. I get my best results from the short three spring tanks. The reverb reflections and interactions are complex enough (though not on par with the golden age) and the microphony is more manageable. I've had some proximity noise and hum issues with new tanks that seem worse than it was with the old tanks. The short tank gives you a tad more distance from the PT and sometimes allows for more creative mounting when necessary. Of course, I'm trying to get a full, familiar reverb tone out of these mediocre tanks and that's no small task. I've noticed that most newer design amps pinch off more low end and/or reduce overall available wet levels. I have to assume this is to accomodate the available reverb tanks and avoid product run problems. I've gone through as many as three tanks for a build culling for tone and/or gross microphony. Good luck.

[bob p]

http://music-electronics-forum.com/t32785/

[Chuck H]

I'm so bad about getting back to old threads for conclusions sake. I did get a MOD tank. Three spring short. And I've used two others (but purchased four) since then. I ruined one of the leftovers attempting a hum abatement trick and the other will collect dust until I get tired of looking at it. It's a cull, yes. But it IS a new reverb pan. It may serve as a "better than broken" repair for an acquaintance some day or something.

[stokes]

Try these tanks,Chuck. Reverb Tanks I posted this earlier.Best tanks I've seen in years.Somebody said they thought they were MOD's,but I dont think thats the case.A world of difference in my experience.

[bob p]

where are they located? i can't tell from the site.

[Chuck H]

Try these tanks,Chuck. Reverb Tanks I posted this earlier.Best tanks I've seen in years.Somebody said they thought they were MOD's,but I dont think thats the case.A world of difference in my experience.

I did go to the link. They look exactly like the MOD tanks with a different color plastic. But that can't be taken at face value either. Not when you consider that companies like Ruby and TAD are keeping us in tubes, Mostly the same tubes as anyone else, but selected or refined, when most of the other vendors are selling junk from the same factories!?! I'll give those tanks a try for certain. Though I don't know when it will come up right now.

[stokes]

where are they located? i can't tell from the site.

Florida

[stokes]

where are they located? i can't tell from the site.

Florida

[mikepukmel]

Try these tanks,Chuck. Reverb Tanks I posted this earlier.Best tanks I've seen in years.Somebody said they thought they were MOD's,but I dont think thats the case.A world of difference in my experience.

Thanks Stokes, ive seen the Studio Electronics site, don't know the parts enough to know the brand names. Any idea who makes Revisit? They make other stuff too.