Marshall 1987x 50w Plexi KT77s?

[jasonmaska]

I have a Marshall 1987x plexi 50w head and I love the warm tone I'm getting from it. It currently was just re-biased in June 2024 with EL34s and 12AX7s. I changed out the V1 12AX7 to a 12AY7 because I enjoy reducing the gain and getting some more warmth out of the head - which I believe this does the trick. Despite the lower gain pre-amp tube, I still notice some early breakup and have been exploring KT77 or the KT "family" of tubes. Has anyone tried them specifically in this amp? Do you still hear the nice warmth from the amp with them in it? Does it provide extra headroom? Was it worth the change from EL34? Any other power tubes you might recommend?

 

[Creach]

Hello jasonmaska,

On the 1987x you have a 330uF cathode bypass capacitor on inputs 2, so you can use a 12ay7, simply as a Fender amps.
When you plug into input 2 you will have a cleaner sound than inputs 1. Don't use input 1 for clean.

If you want more range of clean sound just let less signal go to the phase inverter (v3), insert a volume control in the effect loop (like an EQ, volume box, boost...).

 

[Up The Steen]

Easiest way is to jump the channels mainly using the normal channel and blending the tiniest bit of the bright channel in for some sparkle.

These amps do break up very early by design.

 

[GIBSON67]

Early Breakup is now probably coming from the PI tube distorting. Change to a 12AT7 for cleaner sounds and a 12AU7 if you want to crank the volume more.

 

[jasonmaska]

Folks, thanks for the contribution so far but - a bit of clarification on what I'm looking for.

I've picked the preamp tubes I plan to stick with. I wanted to see if anyone specifically had experience with KT77s in this amp and if you like them over the EL34 tubes. How did they fare for the headroom and tone? Do you still get warm tone out of the plexi amp with KT77s? I'd like to get more bass out of the tone, headroom, and clarity if possible.

I've tried 12AX7, 12AT7, 12AY7, and 12AU7 in the V1 spot of my amp and I've chosen the 12AY7. I'm probably going to invest in some 5751s for V2 and V3, but specifically wanted to know about power tubes.

 

[guitarbilly74]

KT77s do add a bit more bass and headroom, but it won't be a night and day difference, as far as that goes. The midrange on the 34 is sweeter.

The 1987 is designed to be a lead amp and IMHO early break up and tight bass is what the 1987 is all about. Trying to change that is trying to make the amp something it's not, and ultimately, I am not sure if you will ever be completely satisfied with the results. I'd say a JTM45, Bassman or even a SuperBass / Bass 50 would be more in line with what you are looking for.

I think using the Normal channel low input and jumping the inputs is a good suggestion, as far as getting a more mellow tone out of the 1987, other than that, idk. The 1987x is an aggressive amp by design.


But tubes are relatively inexpensive so give it a shot. There is a difference, but I don't know if it'd be enough. Probably not.

 

[JohnnyBandera]

Folks, thanks for the contribution so far but - a bit of clarification on what I'm looking for.

I've picked the preamp tubes I plan to stick with. I wanted to see if anyone specifically had experience with KT77s in this amp and if you like them over the EL34 tubes. How did they fare for the headroom and tone? Do you still get warm tone out of the plexi amp with KT77s? I'd like to get more bass out of the tone, headroom, and clarity if possible.

I've tried 12AX7, 12AT7, 12AY7, and 12AU7 in the V1 spot of my amp and I've chosen the 12AY7. I'm probably going to invest in some 5751s for V2 and V3, but specifically wanted to know about power tubes.

Sounds to me, and I’m a novice when it comes to different tubes in Marshalls, like you’re after the kt66 tubes that you would find in something like a vintage modern. Someone had put in el34s in my 2466 before I bought it and it sounded alright, especially when pushed in the high dynamic range mode, but I swapped for some kt66s and they spanked the el34s up and down the block like you’re talking about especially edge of breakup, dirty.

But it may have been the tubes or they weren’t biased properly because my experience with el34s in different plexi style amps is they can deliver similar tones depending on the design/mods etc.

 

[jasonmaska]

KT77s do add a bit more bass and headroom, but it won't be a night and day difference, as far as that goes. The midrange on the 34 is sweeter.

The 1987 is designed to be a lead amp and IMHO early break up and tight bass is what the 1987 is all about. Trying to change that is trying to make the amp something it's not, and ultimately, I am not sure if you will ever be completely satisfied with the results. I'd say a JTM45, Bassman or even a SuperBass / Bass 50 would be more in line with what you are looking for.

I think using the Normal channel low input and jumping the inputs is a good suggestion, as far as getting a more mellow tone out of the 1987, other than that, idk. The 1987x is an aggressive amp by design.


But tubes are relatively inexpensive so give it a shot. There is a difference, but I don't know if it'd be enough. Probably not.

Fair points, but I already have the 1987x and generally like it, especially in the studio. I'm just looking to see if there's ways to spruce up the existing tone. I realize I'll have to get it re-biased when inserting KT77s so I wanted to ask around before committing.

 

[Pete Farrington]

I still notice some early breakup and have been exploring KT77 ... Does it provide extra headroom?

By 'extra headroom', do you mean that the amp volume needs turning up more before it overdrives?

Guitarists seem to use the term 'headroom' to cover both system gain and power output.

The KT77 looks to have been designed to be Marconi Osram's competitor to Philip's EL34, as they have fairly similar operating conditions and capabilities for typical applications.
So all else being equal, for a given amp, swapping between them shouldn't affect system gain or power output much.

The KT77, being a typical beam pentode design, has somewhat higher anode resistance than the EL34 suppressor grid pentode. So into a loudspeaker load, its tonal balance may tend to be more bass and treble.

https://frank.pocnet.net/sheets/084/k/KT77_GEC.pdf

https://frank.pocnet.net/sheets/129/e/EL34.pdf

 

[Trouble Free]

6550s FTW

 

[FRED]

I have a Marshall 1987x plexi 50w head and I love the warm tone I'm getting from it. It currently was just re-biased in June 2024 with EL34s and 12AX7s. I changed out the V1 12AX7 to a 12AY7 because I enjoy reducing the gain and getting some more warmth out of the head - which I believe this does the trick. Despite the lower gain pre-amp tube, I still notice some early breakup and have been exploring KT77 or the KT "family" of tubes. Has anyone tried them specifically in this amp? Do you still hear the nice warmth from the amp with them in it? Does it provide extra headroom? Was it worth the change from EL34? Any other power tubes you might recommend?

For about 8 years now, I’ve been using a 12AY7 in the V2 position of my ENGL Thunder 50. I think it’s a great idea for people whose amps have more than enough gain for their needs.

For my use, this combination gives me a sweeter mild overdrive sound in the crunch (mid-gain) mode and a much more usable (a little more compressed feel) in the clean mode especially when the gain is set high.

I’ve tried a 5751 for a little while (a little more gain than the 12AY7 but (I thought) not as sweet. At one point I also tried JJ ECC823 and an ECC832 (one of those is a custom order, don’t remember which). Those have one stage of each type, in different positions.

I eventually went back to just one 12AY7 and the rest 12AX7’s though. But it was great fun searching all the possibilities.

 

[Ricky610]

I have a Marshall 1987x plexi 50w head and I love the warm tone I'm getting from it. It currently was just re-biased in June 2024 with EL34s and 12AX7s. I changed out the V1 12AX7 to a 12AY7 because I enjoy reducing the gain and getting some more warmth out of the head - which I believe this does the trick. Despite the lower gain pre-amp tube, I still notice some early breakup and have been exploring KT77 or the KT "family" of tubes. Has anyone tried them specifically in this amp? Do you still hear the nice warmth from the amp with them in it? Does it provide extra headroom? Was it worth the change from EL34? Any other power tubes you might recommend?

I installed a set of kt66 tubes in my origin 50. It has a solid state pre- amp. The very first Marshalls used KT 66 power tubes , then later went to the EL 34 ( I think it was because they were more available in the UK.)

 

[jasonmaska]

By 'extra headroom', do you mean that the amp volume needs turning up more before it overdrives?

Guitarists seem to use the term 'headroom' to cover both system gain and power output.

The KT77 looks to have been designed to be Marconi Osram's competitor to Philip's EL34, as they have fairly similar operating conditions and capabilities for typical applications.
So all else being equal, for a given amp, swapping between them shouldn't affect system gain or power output much.

The KT77, being a typical beam pentode design, has somewhat higher anode resistance than the EL34 suppressor grid pentode. So into a loudspeaker load, its tonal balance may tend to be more bass and treble.

https://frank.pocnet.net/sheets/084/k/KT77_GEC.pdf

https://frank.pocnet.net/sheets/129/e/EL34.pdf

When I say 'extra headroom,' I am talking about the amp volume being turned up more before it overdrives, i.e. the ability to have clean tone at high volume. I'm also very interested in more bass and treble in my sound. I also acknowledge that a new speaker might help, but the description of a KT77 still sounds great to me. Just wondering if folks have hands on experience or if there are blaring obvious things that people like about KT77s over EL34s.

 

[Pete Farrington]

When I say 'extra headroom,' I am talking about the amp volume being turned up more before it overdrives, i.e. the ability to have clean tone at high volume. I'm also very interested in more bass and treble in my sound.

Ok, your goal may be best served by a valve type with a lower u than EL34 then.
From http://www.valvewizard.co.uk/bias.html

EL34 = 10
EL84 = 20
KT66 = 7.5
KT77 = 11
KT88 = 7.5
6L6GC = 8
6V6GT = 10

Hence on the face of it, KT77 look to be your worst feasible option .

KT88 / 6550 have a lower u but, having beefier anodes, have equivalent anode resistance.

So KT66 look your best option, as they have the combination of lower (hence lower system gain, thus requiring a higher volume setting) and having a higher anode resistance, hence more bass and treble.
In practice, the standard Marshall 3k4 OT impedance is a bit low for them, but setting the amp 1 step below the cab impedance sorts that out.
eg with an 8ohm cab, set the amp to 4ohms.

A potential downside is that without a small (1 resistor) modification, the amp may not have enough range on its bias trimmer to accommodate lower u valves.

 

[Trem man]

You might consider a NOS 5751 in the V1 preamp slot, still sounds like a 12AX7 but with less gain. As for the power tubes, the EL34 is really the sound of the 1987 amp. KT66's sound great in a JTM45 but that also has a tube rectifier. When they nailed the short lived 50 watt Black Flag and the 45/100 plexi circuit sthey kept the tube rectifier and eventually went to EL34's which were more mid forward and sparlier on the top. To me that's the quintessential Hendrix sound. But hey they all sound great.

 

[jasonmaska]

You might consider a NOS 5751 in the V1 preamp slot, still sounds like a 12AX7 but with less gain. As for the power tubes, the EL34 is really the sound of the 1987 amp. KT66's sound great in a JTM45 but that also has a tube rectifier. When they nailed the short lived 50 watt Black Flag and the 45/100 plexi circuit sthey kept the tube rectifier and eventually went to EL34's which were more mid forward and sparlier on the top. To me that's the quintessential Hendrix sound. But hey they all sound great.

I have a 12AY7 in V1 and plan to put 5751s in the V2 and V3 spots but I'm waiting on a shipment. I might try the KT77s first to see if I notice any difference. KT66s will require significant changes to the amp as far as I'm concerned. I'm not familiar with biasing or maintaining an amp myself so I'd have to take it to a tech.

 

[Pete Farrington]

KT66s will require significant changes to the amp as far as I'm concerned

Probably just 1 10p resistor

I'm not familiar with biasing or maintaining an amp myself so I'd have to take it to a tech.

As with any change to the particular output valves fitted in the amp, swapping in the KT77 will require a bias check, hence in your case, a trip to the tech bench. May as well tweak the bias circuit so that it can accept KT66 (or even KT88) as well as EL34 / KT77.

 

[jasonmaska]

Probably just 1 10p resistor

As with any change to the particular output valves fitted in the amp, swapping in the KT77 will require a bias check, hence in your case, a trip to the tech bench. May as well tweak the bias circuit so that it can accept KT66 (or even KT88) as well as EL34 / KT77.

That's very good to know. I purchased the KT77s and am waiting for the shipment, but now you're starting to convince me on the KT66s. At the very least, getting the bias circuit changed to accept a KT66/88 sounds great in case I want to upgrade to one in the future.

 

[Creach]

I have a Marshall 1987x plexi 50w head and I love the warm tone I'm getting from it. It currently was just re-biased in June 2024 with EL34s and 12AX7s. I changed out the V1 12AX7 to a 12AY7 because I enjoy reducing the gain and getting some more warmth out of the head - which I believe this does the trick. Despite the lower gain pre-amp tube, I still notice some early breakup and have been exploring KT77 or the KT "family" of tubes. Has anyone tried them specifically in this amp? Do you still hear the nice warmth from the amp with them in it? Does it provide extra headroom? Was it worth the change from EL34? Any other power tubes you might recommend?

I forgot to ask wich one of the 1987x you have... Because I readed el34 i assumed it was the one with the effect loop.
Because there is 2 different 1987x, one is from the 90's without effect loop, the other from the 00's with an effect loop.

 

[jasonmaska]

I forgot to ask wich one of the 1987x you have... Because I readed el34 i assumed it was the one with the effect loop.
Because there is 2 different 1987x, one is from the 90's without effect loop, the other from the 00's with an effect loop.

This is the newer one with the FX loop, but I almost never use it.