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JMcS - Help, please! - - XK-3 tube replacement

David Loving

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I read in some posts about upgrading the tubes in the xk-3 with nos rca tubes, etc. Has anyone actually done this? How do you get to the tubes in the console? It sounds like a good idea, but from looking at the case it seems daunting.
"Forget it, Jake. It's Chinatown."
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The 4 screws across the back of the case and the 4 small headed screws to the right and left of the drawbars come out (the two larger headed screws at each end stay in). Then just lift the lid off. The tubes are held in place with wire clips (these just keep them from working loose when the XK-3 is being carried around). Just slide them off the top of the tubes - the ends stay attached to holders on the pc board. Gently pull up on the tubes, rocking them a little may help. Use a finger on the edge of the pc board to keep it from flexing particularly when you insert the new tubes. Using a little de-oxit helps the tubes slide into the sockets easier, but isn't required. Slide the wire holders back on and you are good to go. The lid can be a little snug when putting it back on. Just make sure it is lined up properly and press down gently. Give the new tubes 20 minutes or so to really warm up. Start playing right away, but you may find that the tone improves even more after a few minutes. If you want to hear a really big difference, after you have played the XK-3 with the new tubes for a while (45 minutes to an hour), put the original ones back in. As great as the XK-3 sounded before you put the new (old) tubes in, you'll wonder where the tone went. The tone is in the tubes. Also, after you put the new tubes in, play with the preamp settings (Pg. 71). Try different crossover points and blend settings etc. Preamp Dual 2 seems to give the fullest sound.


Setting the Expression - Min. Level (Pg.60 #12) to -60 and both Exp. - Limit LF & HF to 0 (Pg. 60 #'s 13 & 14) changes the tone a little also. With these settings, the tone of the Digital Leslie changes when it switches from slow to fast. I think this is the change in higher frequencies that some people feel Leslie Sims don't get right. Try other settings of these parameters as well. Each setting provides an obvious difference.


The XK-3's service manual, along with others, is available from here:


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My guess is that they would work and sound great. There is some info regarding the 6681 here:


and here:



From the descriptions, the added benefit seems to be that they would handle getting bumped around some if the XK-3 is moved often. This might be the "gigger's tube".


I have tried GE 12AX7's and GE 5751's and they both sounded great and very similar. The only difference was that the 5751 had a little less gain so there was a little drop in volume when switching from preamp off to preamp on. When the overdrive knob is turned all the way up, the volumes are equal. Since I never turn mine off, that wasn't a problem. The benefit is that as the overdrive is increased with the 5751, the volume also increases some. This is due to the fact that the tube circuit has a gain limit. This is probably so that you can't put higher gain tubes in, I think 12BZ7's are kind of higher gain 12AX7's, and send too hot a signal to the effects section. I currently have a pair of Amperex tubes in mine, I like them, and they are different from the GE's, but I'm not sure they are "better". So far, nothing "sings" better than the GE's.


I like the GE tubes because they have a great overdrive tone, but also really keep the individual notes distinct before they overdrive. Chords and lower frequencies don't get muddy. Also, there is a wider area of tone change as the overdrive is turned up. That area where they sing before they scream. The RCA tubes that I tried sounded very good, but they went from very little overdrive to a lot pretty quickly. The Raytheon and Sylvania tubes I tried sounded good but not as good as the GE's (to me). Both of those tube pairs were used so I don't know how strong they are or how much life is left in them.


The other thing you might try is to take some of the leakage noise and motor hum out of a tonewheel set. I described what I did in the XK-3 tips thread. I think that the tonewheel set I came up with is what a new 50's/60's B3 would have sounded like before it spent years on the road. This is just my guess, but I think that since the new production tubes tend to roll off the high and low frequencies, leakage noise and motor hum were left kind of high to compensate. By taking the noise out of the tonewheels, you send a nice clean tone into the preamp and you aren't overdriving noise. Let the old tubes do the work. Also, cleaning up the noise made the notes seem more powerful for lack of a better term.


If you try those tubes, please post back with your impression.


Good Luck.

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Would using the "Real B3" type - see p. 98, manual, do about the same thing? "This template simulates the B3classic model in good condition. It contains low motor hum and some leakage noise." I am using the Noisy template now. I'll go ahead with the GE tubes and report back. Thank you for the help. It is much appreciated.
"Forget it, Jake. It's Chinatown."
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I think that tonewheel sets four and five match the Real B3 tonewheels. I adjusted TW set four so that the leakage and hum are greatly reduced. When you listen to each tonewheel through headphones, I think you will be surprised at how much noise there really is. And how much better the overall tone gets with it gone. At least I like it more but thats why it is adjustable. Everyone gets to pick their own. The way mine is set now, in order for TW set four to sound close to the Real B3 TWs with RB3 @ 888000000, TW 4 is 688000002.


I posted this elsewhere, but it gives more detail regarding adjusting the tonewheels etc. I played around some with the resonance and decided to take it back out. I may add some back in after a while, but to me it doesn't need much. Although, I think I prefer adding a little resonance rather than the leakage noise.


Something you might try is to tweak a set of tonewheels. I set B Type

#4 based on how the manual describes the way the tone changes as

each parameter is adjusted. For example, I adjusted Cutoff Freq. -

LPF (pg. 65 #5) down until there was very little leakage noise but

not so that the volume started to drop. Using headphones really helps

to hear the subtle changes. (Turning the resonance up close to 100

really makes the point where the noise is gone easy to hear. I have

been turning turning up the resonance, dialing in the LPF and then

turning the res. down to about 25.) I adjusted the Cutoff Freq. - HPF

(#7) so that there was very little motor noise but not so that the

sound thinned out. (Maybe what I end up with is what a B-3 sounded

like when it was relatively new.)


Each tonewheel/parameter has a range of about 4 or 5 that fits those

descriptions. As I went up the tonewheels the setting that sounded

right (to me) usually increased some. The following is a list of some

of the tonewheels so that you can see what I mean. Although the LPF

on tonewheels 37 and 49 are both set at 74 for example, TW 41 might

be 77, and TW 46 might be 70. Also, the level on tonewheels 93 - 96

is set at -2. Setting them at 0 seemed to make them too bright. (I

have since added a little resonance.)


TW1:1C Lev. 0, LPF 54, Res. 0, HPF 10

TW2:1C# Lev. 0, LPF 57, Res. 0, HPF 10

TW3:1D Lev. 0, LPF 52, Res. 0, HPF 10

TW13:2C Lev. 0, LPF 55, Res. 0, HPF 29

TW25:3C Lev. 0, LPF 60, Res. 0, HPF 40

TW37:4C Lev. 0, LPF 74, Res. 0, HPF 56

TW49:5C Lev. 0, LPF 74, Res. 0, HPF 73

TW61:6C Lev. 0, LPF 88, Res. 0, HPF 84

TW73:7C Lev. 0, LPF 106, Res. 0, HPF 100

TW85:8C Lev. 0, LPF 108, Res. 0, HPF 111

TW96:8B Lev. -2, LPF 116, Res. 0, HPF 121


To get to the top and bottom tonewheels by using the drawbars, turn

the foldback off. You can get to them via the knob as well. Any of

the settings I chose probably sounded about the same if the setting

was +/- 1 or 2. This kind of "cleaned up" the tone of each note and

although it really didn't change the tone when playing single notes

very much, (holding down a note and changing tonewheel sets from 1 to

4 doesn't produce a big difference - but it is obvious) it did have

an effect on how the notes in a chord blend together. The other thing

it did is it improved (to me) the tone of the overdrive. It reduced

the high freq. buzz and gave it more "beef". This is probably the

biggest change that the tweaking produced.


Another experiment you might try with TW set #5 is to turn the Lev.

to +2 on all but the top 3 (or so) tonewheels. This really affects

the tone of the overdrive. I have not changed the LPF and HPF

settings on this TW set yet, but I did change the Res. setting to 0

when it was above that per the note on pg. 65. I didn't notice any

distortion when the overdrive knob was turned down. (I have since set

this set of TW's LPF and HPF settings similar to the ones above.)


In my opinion, the tweaking I have done improves the tone by taking

out the unnecessary noise. By removing most of the leakage noise, the

overdrive is even beefier than it became by installing the GE or

other old tubes. I think that overdriving the leakage noise

adds "buzz" to the tone. There is a similar effect with the motor

noise, it muddies up the bass. I prefer to send a relatively clean

signal into the preamp and let the tubes work their magic. A side

benefit to this is that the overall tone is improved in a way that

adds more body/fullness - more "Leslie" to the Digital Leslie it

seems to me.


Have Fun.

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