Calming down a Reverb Tank (Offboard)

[jukelemon]

Hi all.

I have a Kendrick Reverb unit/tank.  Actually like serial # 109 or something which is kind of cool.  I have had it many moons and love, absolutely love, the tank.

My issue though, and I have written about this before and tried suggestions, is that the Mix pot is useless i.e. it is so washed up after 2 that I typically have to finess it between 1.5 and 1.5489990909 to get a useable sound.

I have tried changing the pot to a different value. I have tried a 6k6 versus the 6v6.  I have tried different preamp tubes as drivers. Nothing seems to calm that lack of range down.

The Kendrick, as far as I know, is an exact copy of Fender minus the offering of a 2nd input (more treble/sparkle).

Any ideas?

Not sure if you recall, but I actually called Kendrick and asked about it and was told that is just the way they are...which is fine I guess.  But I would like to really have a more useable Mix pot.

Any suggestions?

I just picked up a 1990 Bassman Reissue....different story but damn it sounds nice. Original speaker. WELL broken in. I didn't have to do much. Someone had already put in a bias pot and a 5u4. I replaced the 5U4 with a 5R4 and then cut out the 44ufd preamp filter and changed it back to the spec'd 8ufd.  What a change and what a tone.

Anyway, point is that I am gigging with that now and therefore need my tank..again..and again trying to resolve the Mix issue.

Thanks all.

Jason

[terminalgs]

So I'll use the 6G15 schematic's 250K mix pot.

set the mix pot to the point where it is at your maximum usefulness.  lets say "2".   Measure how much of the pot's swing is left on the "reverb" side.

Lets pretend it's 225K.  so the other side of the pot should be about 25K.   

Replace the 250K pot with a 25K pot, and install a 225K resistor between the pot and the "reverb" side.  On a 6G15, that would be the .00025 cap.  (If you can't find a 225K resistor, -and you won't- use a 220K resistor).

In essence, you've take that "0" to "2" usefulness of the 250KL pot, and made "10" on the new pot the "2" on the old pot.  of course, "0" is still "0".

your other option is to leave the 250KL as-is, and measure the percentage of usefulness range.  continuing with the 25K/225K example above: that means usefulness is 10%.  so leave the 250K pot in place and install a 2.2M resistor "on top" between the top wiper and the .00025 cap.  I like this idea less than the first b/c it might effect overall output impedance (tho I'm not sure how).

[PRR]

Schematic?? (Not all of us have low-number Kendricks.)

> finess it between 1.5 and 1.5489990909 to get a useable sound.

So it's too wet?

Add a "volume" pot between the reverb recovery amp output and the mix-network. Set that around "3", then you have 0-8 of smooth control on the mix knob.

[eleventeen]

Maybe you have an audio taper pot in there for the mix pot instead of what I'd imagine would/should be a linear? A manufacturing error, either picking out the wrong part at Kendrick or at CTS (!) putting the wrong stamped-can on the back of the pot. Yes, it's far fetched but not impossible. 

Hey, you build a lot of stuff with diodes and you will find some that are labeled backwards. Can drive you nuts, trust me.

It seems very odd that a "mix" pot would be as sensitive as you say. Picturing a mix pot as selecting between two roughly equivalent signals at either end of the pot...there really shouldn't be this giant threshold as some point in the lower-middle, but there COULD be if you had an audio pot in there. So I am guessing by the symptom. Measure it as you slowly rotate it. Probably you'll be able to do so without disconnecting anything, but if you have to, you have to. If it gets to full value with only fractional rotation, maybe the pot is mislabeled or the actual pot is audio taper when it wants to be linear.

[echuta13]

I borrowed my friends Kendrick Reverb last weekend and I ran into the same issue (little to no range).  Played with it one night and gave it back. 

[jukelemon]

Schematic?? (Not all of us have low-number Kendricks.)

> finess it between 1.5 and 1.5489990909 to get a useable sound.

So it's too wet?

Add a "volume" pot between the reverb recovery amp output and the mix-network. Set that around "3", then you have 0-8 of smooth control on the mix knob.

Hi. Yeah, its a copy of the 6g15 I believe.

That's an interesting idea.

[jukelemon]

I borrowed my friends Kendrick Reverb last weekend and I ran into the same issue (little to no range).  Played with it one night and gave it back. 

Yeah, I am told though that Fenders are like this...no?

I will go back and look at the pot but the Audio v Linear is something that I have already done..I think.

I will take a peek.

[jukelemon]

OK.

There is an Alpha B500k in there now as the Mix pot.

And I found my post back in 2008!!

Geez the cycles..

There are a few other things I may do..

[PRR]

> a copy of the 6g15 I believe.

That can be a very ripe cave, but can also be used subtlely. Wonder how the copy differs?

First: if the recovery stage has a cathode cap, snip one end. That's half the reverb for no cost and little labor.

Still wet? Temporarily tack a 100K Lin pot between last-stage coupling cap and the tone pot. Just adding 100K here will get the maximum wetness down another few dB. Then you can turn-down the pot to half, quarter, tenth, whatever you need to balance the box's wetness against your musical climate. If you can be happy, decide if you will drill the box for a user knob, or hide the pot inside as a pre-set.