New tremolo circuit for Marshall Bluesbreaker Tremor-nator?

[Apexelectric]

I have a 50W Marshall Bluesbreaker 1961 clone on the bench with a non-functional tremolo circuit that’s missing components and was wanting to rebuild a new tremolo circuit for the client. I have read that the circuit that Marshall used on the 50W amps left a lot to be desired so I was looking for a suitable replacement and was considering Sluckey’s Tremor-nator as a possibility. Has anyone out there implemented that tremolo design in this amp or have any suggestions as to where to tap the preamp with it where it wouldn’t pull down the signal too much? The Marshall design used two 12AX7 triodes so I have what I need and then some for the oscillator.

[Apexelectric]

I did give it a go yesterday and got it to work but not well. Used the stock schematic for the Tremor-nator and inserted it right at the grid on the first triode. I bled signal through a 100k resistor and a .02 cap before entering the LDR. When the tremolo works the tone is a bit dark. Tremolo intensity only works  on the upper end of the range of the 50KRA pot and needs to be a bit stronger so I probably need to figure out a better way to tap the circuit and still make this have one channel that is not a Tremolo channel.

[ac427v]

I am very pleased with this method of connecting the Trem-o-nator. Note that the Intensity Pot does not directly connect to ground when used with a non-Black panel circuit.

[Apexelectric]

Thanks for that!

 I think that might be where I went wrong with the intensity pot. Will play with it a bit more and post my results later.

[sluckey]

ac427v's method is proven. Another option is to insert the tremolo just prior to the PI input cap. As always, you may have to experiment with the INT pot value and actual wiring.

[Apexelectric]

That definitely did it. Had my intensity pot wired to ground. Only issue I’m having is the oscillator will sometimes take a while to restart after the speed is turned down. Seems like if I increase the resistance of the 100K resistor off the speed pot it might help and possibly increase the .01 cap to a .02 to slow it that way? Thoughts?

[sluckey]

What B+ voltage are you operating at? I use node B (screen node) in my BandMaster and it supplies 434V. I have no oscillator drop outs for the entire speed range.

You can also experiment with the 10K cathode resistor. Its purpose is to keep the oscillator running when the footswitch is turned off.

[Apexelectric]

I’m getting around 450V on the B node and passing it through a 470k resistor to the plate of the oscillator triode as per the schematic

Changing the .01 cap to a .02 only made the situation worse.

[Apexelectric]

I do have an additional unused triode, would wiring it in parallel make for a more robust oscillator or would that be overkill?

[sluckey]

Changing the .01 cap to a .02 only made the situation worse.

Yes, that's because it is dropping out on the low speed. The bigger cap just made the low speed even lower.

Parallel triodes ain't gonna help. A stronger tube would probably help.

But we don't even know what your speed range is. Can you measure the frequency with a scope, or maybe even a good DMM. My Fluke 87V measures the low freq. very well. Once you get down to 3Hz the oscillator gets a little iffy.

[Apexelectric]

Will check it out but I don’t think it was that slow. Brand new JJ 12AX7 tube, guess it’s possible that it’s a tad weak. The circuit is the fairly stock .01uf/.01uf/.02uf configuration for the oscillator and a 3MRA speed pot with the 100K to ground off the end but with a 250kra for the intensity control. 10K cathode resistor and the 1M resistors to ground off the two oscillator caps.

[Apexelectric]

It drops out at about 4.5hz. I’d need about an 820K resistor off the speed pot to prevent it from dropping below that. Does that seem odd based on the values of the rest of the circuit components? Or do I just chalk it up to the way it behaves in this amp?

[sluckey]

It drops out at about 4.5hz. I’d need about an 820K resistor off the speed pot to prevent it from dropping below that.

That doesn't make sense to me. The 100K on the speed pot sets the fast speed limit. If you increase the size then the upper speed limit would be slower.

That doesn't quite seem like my circuit. I have .02, .02, and .01 caps. There's only one 1M to ground. The other 1M connects to the cathode.

I would not be satisfied with a slow speed of only 4.5Hz. Something ain't right. The oscillator doesn't care what amp it's in.

[Apexelectric]

It’s your circuit shy of the 50K intensity pot and only one .02 cap like the stock Fender tremolo oscillator. There is 820k from wiper to ground on the speed pot when it’s oscillating at 4.5hz right before it drops out. The wiper and ground terminal on the pot are jumpered.

[sluckey]

It’s your circuit shy of the 50K intensity pot and only one .02 cap like the stock Fender tremolo oscillator. There is 820k from wiper to ground on the speed pot when it’s oscillating at 4.5hz right before it drops out. The wiper and ground terminal on the pot are jumpered.

You are having speed problems and all the changes you made affect the speed. Make the oscillator look exactly like my circuit and reevaluate. INT pot is not a factor.

[Apexelectric]

The only part in the oscillator that’s different than yours is the .01 cap. Instead of the second .02 cap. When I did swap it for a .02 it made matters worse. The intensity pot worked better at a 250kra than the 50kl that I had in it originally. I double checked all the resistor values by reading with a meter not just trusting the bands and it’s exactly like your schematic values including the 10K cathode resistor. So I’m at a bit of a loss as to what might be causing the issue. Probably can try swapping out the oscillator caps just to be sure.

[Apexelectric]

Changing the .01 cap to a .02 only made the situation worse.

Yes, that's because it is dropping out on the low speed. The bigger cap just made the low speed even lower.

Parallel triodes ain't gonna help. A stronger tube would probably help.

But we don't even know what your speed range is. Can you measure the frequency with a scope, or maybe even a good DMM. My Fluke 87V measures the low freq. very well. Once you get down to 3Hz the oscillator gets a little iffy.

Looks like my problem might have something to do with the grounding scheme in that area of the circuit.  I got some varying results using different ground points for the oscillator.

[Apexelectric]

Well I’ve tried a handful of different things including swapping out the Vactrol, changing the value of the 10k resistor, playing with the grounding scheme and still no luck in getting the oscillator/tremolo to not stall. The oscillator is on the output ground and the LDR is grounded at the preamp.  Using the footswitch to turn it off and on is a good way to get it restarted. Turning the speed all the way down is a good way to get it to stall.

There are times when it seems as though the oscillator is working but the effect is not and there are times it seems the oscillator is not working too using my meter to check the frequency.

All resistors, caps and tube test good.

Wondering if the insertion point has anything to do with my issue. I’m going from the wiper on the volume pot to the end of the intensity pot with no cap or resistor between the two.

[sluckey]

Wondering if the insertion point has anything to do with my issue. I’m going from the wiper on the volume pot to the end of the intensity pot with no cap or resistor between the two.

No. The VTL5C1 totally isolates the oscillator operation from the insertion point. What is the slowest speed you have before the oscillator drops out? What is the fastest speed you have?

[Apexelectric]

[/quote]No. The VTL5C1 totally isolates the oscillator operation from the insertion point. What is the slowest speed you have before the oscillator drops out? What is the fastest speed you have?
[/quote]

The range seems to be 3 to 10hz

Dropout happens at the slow end usually around 4.5hz. But there have been moments where I’m able to get it lower before it drops out.

[sluckey]

Disconnect the LED side of the VTL5C1. Now connect a red LED between the oscillator cathode and ground. Does the LED continue to blink for the entire speed range? And what is the min and max speed?

[Apexelectric]

Disconnect the LED side of the VTL5C1. Now connect a red LED between the oscillator cathode and ground. Does the LED continue to blink for the entire speed range? And what is the min and max speed?

Thanks for the tip. The visual of the blinking led made it much easier to get to the root of the problem which was the cliff jack. The switch contact wasn’t very solid. Changed it out to a new one and had the same issue, switched it out to a switchcraft jack instead and that resolved the issue.

[sluckey]

Footswitch jacks get overlooked too often. Never occurred to me on this amp. And I wasn't suspicious when I suggested using the LED. I was thinking about the VTL5C1 (long shot). Anyhow, glad it's working. So, what is your min/max speed range now?

[Apexelectric]

Footswitch jacks get overlooked too often. Never occurred to me on this amp. And I wasn't suspicious when I suggested using the LED. I was thinking about the VTL5C1 (long shot). Anyhow, glad it's working. So, what is your min/max speed range now?

It worked great so I didn’t bother to check exactly but I’m pretty sure it slows to under 3hz and just above 10

[sluckey]

When you are happy with the way the TON works, maybe you could post a schematic showing exactly how you integrated it into the Bluesbreaker circuit. And if you don't mind I'd like to include your circuit on my Trem-O-Nator page. I already have several different adaptations and think that adding more successful circuits could be helpful to others that may be considering the TON.

[Apexelectric]

When you are happy with the way the TON works, maybe you could post a schematic showing exactly how you integrated it into the Bluesbreaker circuit. And if you don't mind I'd like to include your circuit on my Trem-O-Nator page. I already have several different adaptations and think that adding more successful circuits could be helpful to others that may be considering the TON.

It was the stock configuration except the intensity pot so nothing really new to report there and the insertion point was at the volume control of the tremolo channel. The Cliff footswitch jack seems to be a weak link, I’ll be using Switchcraft in the future.

[sluckey]

Is the Bluesbreaker the same as a JTM45 1961 model?

[66Strat]

Is the Bluesbreaker the same as a JTM45 1961 model?

Either 1961 or 1962. I think that the 1961 may have been a 4-10 model and the 1962 configured as 2-12.

schematic
https://el34world.com/charts/Schematics/files/Marshall/Marshall_jtm45_lead_45w.pdf

[sluckey]

Thanks

[Apexelectric]

Is the Bluesbreaker the same as a JTM45 1961 model?

With all the talk about how lousy the tremolo was on this amp, both the originals and the reissues, and how everyone just disconnected it from the circuit to prevent all the tone suck from happening, this tremolo design was a great alternative. My customer wanted me to add a bypass switch and I told him it was a waste of time since turning down the intensity pot accomplished the job. Really pleased once I got rid of the gremlins.

Thanks, as usual, for the assist.