AB763 Bandmaster Skyliner Tonestack Help

[Jake1524]

Hi,

I have an old Bandmaster that I have been using to explore different mods and to learn more about amplifiers. Another member on here reccomended implementing the Skyliner tonestack. I have done a decent amount reading, looked through the dumble files and have developed a very rudimentary understanding of what this entails.

Is there any information out there on how to implement this in an older fender amp? This is where am getting lost. Perhaps someone has an annotated layout or schematic? I am hoping someone can point me in the right direction here.

[martin manning]

Which Bandmaster? And, are you looking to include the Rock/Jazz and PAB functions?

[Jake1524]

Which Bandmaster?

It is an AB763 dripedge non reverb bandmaster. I believe it is a 68.

[martin manning]

Do you want Rock/Jazz and PAB? Mid boost?

[Jake1524]

Do you want Rock/Jazz and PAB?

No need for PAB and on the fence about Rock/Jazz. If adds a lot of flexibility, might as well include it.

[martin manning]

Basically you would be replacing what is in the red rectangle. The full implementation needs three switches (including Bright) plus the PAB relay, but if you use an 0n-0ff-0n for the Rock/Jazz you can have PAB in the middle position. There are a couple of additional parts, and I don't know how easy it would be to add two more switches to your amp. Of course you'd be drilling holes in a vintage chassis and faceplate too. In any case, the easiest would be Rock only, with no Mid or Preamp boost. I would see that as a tighter version of the Fender stack.

[Jake1524]

Basically you would be replacing what is in the red rectangle. The full implementation needs three switches (including Bright) plus the PAB relay, but if you use an 0n-0n-0n for the Rock/Jazz you can have PAB in the middle position. There are a couple of additional parts, and I don't know how easy it would be to add two more switches to your amp. Of course you'd be drilling holes in a vintage chassis and faceplate too. In any case, the easiest would be Rock only, with no Mid or Preamp boost. I would see that as a tighter version of the Fender stack.

Hey Martin, I got that much.

Im just not sure of the exact values to use, and if the pots need to be rewired etc.

My goal is to make the amp as clean, clear and warm as possible. There is always this inherent sizzle that I have with fenders that I would like to dial out.

[martin manning]

You have two threads going on the same topic.

Here is the bare bones Skyliner stack. You are short a mid pot, too. But, there are other ways to reduce some high end. An easy experiment would be to place a large resistor in front of the second triode's grid at pin 7. Try a 220k right at the tube socket, iike Dumble did on ODS amps. He had a 500p in parallel, but try it without that first.

[Jake1524]

You have two threads going on the same topic.

Here is the bare bones Skyliner stack. You are short a mid pot, too. But, there are other ways to reduce some high end. An easy experiment would be to place a large resistor in front of the second triode's grid at pin 7. Try a 220k right at the tube socket, iike Dumble did on ODS amps. He had a 500p in parallel, but try it without that first.

Apologies for multiple posts. I was not sure where the best place to post was.



I have used this layout in the past. I know a couple of the values are different from the stack you posted, but when I used the attached, I did not notice any meaningful changes. Would there anything to be gained from trying the schematic you just posted?

[WhopperPlate]

That’s a classic stack . Significant differences. Sky liner uses .01uf mid cap , 250k mid pot , 500k bass pot , 10k tail resistor off bass pot , .001 cap across bass pot, with 220k/500p grid stopper v2B.

[Jake1524]

That’s a classic stack . Significant differences. Sky liner uses .01uf mid cap , 250k mid pot , 500k bass pot , 10k tail resistor off bass pot , .001 cap across bass pot, with 220k/500p grid stopper v2B.

You have two threads going on the same topic.

Here is the bare bones Skyliner stack. You are short a mid pot, too. But, there are other ways to reduce some high end. An easy experiment would be to place a large resistor in front of the second triode's grid at pin 7. Try a 220k right at the tube socket, iike Dumble did on ODS amps. He had a 500p in parallel, but try it without that first.

I just drew this up. Do you guys see anything that’s missing or incorrect?

[martin manning]

If you want to do the whole #124 Skyliner clean channel in Rock mode it would look like this.

[Jake1524]

If you want to do the whole #124 Skyliner clean channel in Rock mode it would look like this.

Amazing! Thanks so much for this. What values change if I want to try it in ‘jazz’ mode?


I’ve tried the 220k resistor you mentioned, and didn’t notice much effect. I love the amp with the treble turned up, as it makes the amp much more percussive and punchy. Unfortunately, along with that, the sizzle I’m attempting to dial out gets worse. It almost seems to be a sort of clipping?

End goal is a amp that is clean, clear, and bright without the harsh raspiness that comes with fender amps.

[martin manning]

I love the amp with the treble turned up, as it makes the amp much more percussive and punchy. Unfortunately, along with that, the sizzle I’m attempting to dial out gets worse. It almost seems to be a sort of clipping?

It's very possible that the sizzle is a parasitic oscillation that kicks in when the treble is turned up. The cause is usually related to lead dress (routing).

Does you Bandmaster have a mid pot? The Fender schematic doesn't. Jazz mode requires another resistor and cap, plus a DPDT switch if you want to go back to Rock. It's shown in the layout you posted above. That could be done with a pull pot.

[Jake1524]

I love the amp with the treble turned up, as it makes the amp much more percussive and punchy. Unfortunately, along with that, the sizzle I’m attempting to dial out gets worse. It almost seems to be a sort of clipping?

It's very possible that the sizzle is a parasitic oscillation that kicks in when the treble is turned up. The cause is usually related to lead dress (routing).

Does you Bandmaster have a mid pot? The Fender schematic doesn't. Jazz mode requires another resistor and cap, plus a DPDT switch if you want to go back to Rock. It's shown in the layout you posted above. That could be done with a pull pot.

The sizzle I’m referring to is present pretty much every fender amp I’ve tried. It’s one of the few things I really don’t love about fenders. It also seems to get better the less the amp is pushed.

I actually have mid pots on my bandmaster. One of the first things I did when I bought the amp. I was planning on replacing the bright switch with a DPDT if I were to implement this.

Just to clarify, jazz is just adding the .005 cap to ground? Where exactly does the 100k resistor go? The layout above also includes a boost which I would not include or use.