Power Tube Replacements for Ashdown CTM 15

[bongostealth]

I have an Ashdown CTM 15 (CTM 15). It is powered by (1) ECC83 preamp tube and (2) EL84 power stage tubes.

To me, the amp sounds awful. Even with the gain all the way down and the treble all the way down, increasing the volume past 8 'o clock just makes the amp sound complete shrill and abrasive. I don't like the tone. I find it too harsh. So I replaced the stock ECC83 preamp tube with a Mullard 12AU7. This tamed the amp a little bit but it's still too harsh for my tastes. I much prefer warm and gooey low-gain tone. Are there any replacements for the EL84 tubes that I can use to get the tone I am looking for? Or will replacing the EL84 tubes not make a difference?

 

[ahbass2500]

I swapped mine to Gold Lion EL84 (already had them in a drawer, so figured I should use them). There was some change, but if you do not like the inherent sound of the amp, it is not going to shift significantly from that.

It sounds like you want an Ampeg PF20T or PF50T. The Ashdown can do warm with little/no overdrive, but it has one setting for that. The Ashdown prefers to overdrive a bit. The Ampeg has a wide range of settings that are basically all warm with little if any breakup.

I used to have the Ampeg PF50T and prefer it to the Ashdown. I am also not a fan of the overdrive nearly all the time design of the CTM15. Only reason I kept the Ashdown over the Ampeg is form factor. I use it on top of a Phil Jones Compact 2 and the Ampeg was too big for that.

 

[KevInDaBassment]

Those with more know-how will probably chime in later, but to my understanding you aren't going to be making a world of difference if your current tubes are in working order. If they are defective or dying, that could cause audible issues, where changing to a healthy set would help.

Past that, nope, I doubt you'll really hear much difference. What speakers are you putting the amp through? How about the rest of your signal chain? This could be a cabinet that's just a bad fit for that amp head.

 

[ahbass2500]

What speakers are you putting the amp through? How about the rest of your signal chain? This could be a cabinet that's just a bad fit for that amp head.

Worth checking on this part, but in this case, I think it is the nature of the head. I like the CTM 15 well enough (relative to what I paid for mine), but the EQ section is weak and outside of setting the gain near 0 it will overdrive. Makes for a severely limited amplifier if you are not into overdrive.

I am not OP, but I have hooked my CTM15 to Phil Jones Compact 8, Phil Jones C2, and Genzler Bass Array 10 Series 2 cabinets. Some character changes across each setup but the amp's desire to overdrive is there on all of them.

I have tube swapped mine. NOS preamp tube (GE if I remember correctly) and Gold Lion Power Tubes. Slight change in sound profile. While it was a change for the better, the character of the amp is still what it was before the swap.

 

[bongostealth]

Worth checking on this part, but in this case, I think it is the nature of the head. I like the CTM 15 well enough (relative to what I paid for mine), but the EQ section is weak and outside of setting the gain near 0 it will overdrive. Makes for a severely limited amplifier if you are not into overdrive.

I am not OP, but I have hooked my CTM15 to Phil Jones Compact 8, Phil Jones C2, and Genzler Bass Array 10 Series 2 cabinets. Some character changes across each setup but the amp's desire to overdrive is there on all of them.

I have tube swapped mine. NOS preamp tube (GE if I remember correctly) and Gold Lion Power Tubes. Slight change in sound profile. While it was a change for the better, the character of the amp is still what it was before the swap.

This is what I have been suspecting. It's just the inherent character of the amp.

 

[Wasnex]

Which version of the CTM15. I don't know about later versions, but there seems to be quite a few comments that the first version was not very good for bass (too thin sounding and too prone to drive). Supposedly it was better for guitar. I believe it had a solid state buffer on the input, so it may not like being pushed hard with a hot bass, clean boost, or tube screamer.

The LB30 and CTM30 are good for bass, but their tone and overdrive characteristics can vary significantly from one production run to the next. I have an LB30 from the original production run and also a Mk2 which was made much later in the UK Custom Shop. They sound totally different. I also have a CTM30 Little Stubby that sounds great with bass.

Some circuits respond to tube rolling and some do not. Any changes that occur tend to be subtle. If the original tube was a 12AX7, a 12AU7 should reduce the gain but it won't necessarily give you more clean headroom. 5751 is considered a low gain 12AX7. JJ makes a medium gain ECC83S. 7025 and ECC803 are also 12AX7 types.

Rolling EL84s may give you some subtle changes as well. I believe these amps are cathode biased (self biased), so changing the EL84s is pretty much plug and play.

As far as reducing preamp drive, try turning down the tone controls. The LB30 and CTM do not have a gain control and the volume control comes late in the amp. The preamp in my Mk1 LB30 distorts if I turn the tone controls above a certain level. The Mk2 LB30 preamp has a lot more headroom and is always clean even with the tone controls maxed. The output sections of both have about the same amount of clean headroom.

The CTM 30 Little Stubby has a gain and master, so you can set the headroom in the preamp for clean or drive.

The Ampeg PF50T and the PF20T also have a gain and master. The PF50T has plenty of gain to push the preamp into drive if you like. A lot of people say their PF20T stays clean pretty much wide open.

 

[agedhorse]

I wouldn't expect there to be enough of a difference (for better or for worse) to overcome what you are describing...

 

[SC Bassboy]

I have an Ashdown CTM 15 (CTM 15). It is powered by (1) ECC83 preamp tube and (2) EL84 power stage tubes.

To me, the amp sounds awful. Even with the gain all the way down and the treble all the way down, increasing the volume past 8 'o clock just makes the amp sound complete shrill and abrasive. I don't like the tone. I find it too harsh. So I replaced the stock ECC83 preamp tube with a Mullard 12AU7. This tamed the amp a little bit but it's still too harsh for my tastes. I much prefer warm and gooey low-gain tone. Are there any replacements for the EL84 tubes that I can use to get the tone I am looking for? Or will replacing the EL84 tubes not make a difference?

I bought one from Sweetwater when they first came out a few years ago. It was sent back in short order. I agree with everything you said, it simply didn't sound good and I found the output volume to be so low it was borderline unusable. My hope was that it could replace my trusty SWR IOD (it's basically the same piece of equipment) but it fell far short of that desire. Regarding tubes, I pretty much use JJ or Mullard tubes when needed. If you want a thick, rich focused sounding 12AX7, the Mullard is a great choice. I rolled through a bunch of tubes before settling on those for my turntable phono amplifier. Very warm, hi-fi sound.

 

[agedhorse]

Different circuits impact how a tube might sound, some might not sound any different and some might sound even worse. Every tube swap doesn’t make an improvement.

 

[bongostealth]

Different circuits impact how a tube might sound, some might not sound any different and some might sound even worse. Every tube swap doesn’t make an improvement.

Yeah, I'm starting to learn that.