EL34 vs. KT88/6550

Papa Lolo

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Has anyone here played a plexi with KT88 or 6550 tubes installed ?
I have read that Jimmy Page had his amps modded to take these tubes and that Jimi Hendrix also used them but did not mod his amps.
The reason I ask is not only am I a huge fan of both of them and their sound but also because my son has an Ampeg Lee Jackson amp that is supposed to be based on a Lee Jackson modified Marshall design. It has a switch that allows you to use either EL34's or KT88/6550 tubes and I really like the sound of the big tubes. I dont play hi gain and it seems there is more punch and clarity to the notes with the big tubes. My amp is a 50 watt plexi that has already been modded, it has a Mercury Magnetics transformer which seemed to increase headroom and punch compared to the stock and I was thinking that the tube mod might take it alittle further.
I have to take the amp in to have the fx loop looked at and was considering the tube mod while it's in the shop.
 

william vogel

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KT88’s in a plexi 50 watt are easily swapped. The 220k bias dropping resistor before the diode needs to be changed to 150k and the 2 220k bias feed resistors need to be reduced to 100k. KT88’s give you more headroom and tight bottom end. Power output usually doesn’t change much but the feel of the amp is bigger. Overdriven, the KT88’s are awesome. Also, I bias KT88’s at 28 watts dissipation
 

Papa Lolo

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KT88’s in a plexi 50 watt are easily swapped. The 220k bias dropping resistor before the diode needs to be changed to 150k and the 2 220k bias feed resistors need to be reduced to 100k. KT88’s give you more headroom and tight bottom end. Power output usually doesn’t change much but the feel of the amp is bigger. Overdriven, the KT88’s are awesome. Also, I bias KT88’s at 28 watts dissipation

Good to know
Thanks
 

Dogs of Doom

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I have an Ampeg VL-501 (Lee Jackson 50 watt 1 channel) amp.

In the VL amp's, 6550 make the amp bigger. I've heard some people say, that, in their Marshall, they didn't like the 6550, because it didn't break up soon enough & made the bass a little muddier.

IMO, the EL34 in the VL sounded thin & brittle, although, the VL has so much gain, compared to a plexi, or even a JCM amp. I don't think Marshall makes an amp w/ that much gain...

It has more than the DSL & JVM, by far...

I like 6550s, but will concede that there may be times where I'd opt for EL34...
 

tallcoolone

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Has anyone here played a plexi with KT88 or 6550 tubes installed ?
I have read that Jimmy Page had his amps modded to take these tubes and that Jimi Hendrix also used them but did not mod his amps.
The reason I ask is not only am I a huge fan of both of them and their sound but also because my son has an Ampeg Lee Jackson amp that is supposed to be based on a Lee Jackson modified Marshall design. It has a switch that allows you to use either EL34's or KT88/6550 tubes and I really like the sound of the big tubes. I dont play hi gain and it seems there is more punch and clarity to the notes with the big tubes. My amp is a 50 watt plexi that has already been modded, it has a Mercury Magnetics transformer which seemed to increase headroom and punch compared to the stock and I was thinking that the tube mod might take it alittle further.
I have to take the amp in to have the fx loop looked at and was considering the tube mod while it's in the shop.
I've been in Zep tribute bands forever and I've converted 2 50w 1987 clones to KT88s. If you really want to nail the TSRTS tone it is a must IMO.
 

Pete Farrington

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KT88’s give you more headroom ... Power output usually doesn’t change much
If headroom isn’t power output, what is it?
https://www.fender.com/articles/tech-talk/keeping-it-clean-what-is-headroom
The vol control will need turning higher with KT88 because they require a higher bias voltage.

I bias KT88’s at 28 watts dissipation
A 35W design max rating is equivalent to about 30W design centre. So idling KT88 at 28W is equivalent to idling EL34 at nearly 23.5W.
 

william vogel

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TheB3Bob

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Has anyone here played a plexi with KT88 or 6550 tubes installed ?
I have read that Jimmy Page had his amps modded to take these tubes and that Jimi Hendrix also used them but did not mod his amps.
The reason I ask is not only am I a huge fan of both of them and their sound but also because my son has an Ampeg Lee Jackson amp that is supposed to be based on a Lee Jackson modified Marshall design. It has a switch that allows you to use either EL34's or KT88/6550 tubes and I really like the sound of the big tubes. I dont play hi gain and it seems there is more punch and clarity to the notes with the big tubes. My amp is a 50 watt plexi that has already been modded, it has a Mercury Magnetics transformer which seemed to increase headroom and punch compared to the stock and I was thinking that the tube mod might take it alittle further.
I have to take the amp in to have the fx loop looked at and was considering the tube mod while it's in the shop.
Has anyone here played a plexi with KT88 or 6550 tubes installed ?
I have read that Jimmy Page had his amps modded to take these tubes and that Jimi Hendrix also used them but did not mod his amps.
The reason I ask is not only am I a huge fan of both of them and their sound but also because my son has an Ampeg Lee Jackson amp that is supposed to be based on a Lee Jackson modified Marshall design. It has a switch that allows you to use either EL34's or KT88/6550 tubes and I really like the sound of the big tubes. I dont play hi gain and it seems there is more punch and clarity to the notes with the big tubes. My amp is a 50 watt plexi that has already been modded, it has a Mercury Magnetics transformer which seemed to increase headroom and punch compared to the stock and I was thinking that the tube mod might take it alittle further.
I have to take the amp in to have the fx loop looked at and was considering the tube mod while it's in the shop.
There is a white 100 watt Marshall Plexi reissue on YouTube that was modded by Scott Splawn. It has KT88's, Mercury Magnetics transformers, a master volume and a foot switchable gain boost, and solo boost.
Has anyone here played a plexi with KT88 or 6550 tubes installed ?
I have read that Jimmy Page had his amps modded to take these tubes and that Jimi Hendrix also used them but did not mod his amps.
The reason I ask is not only am I a huge fan of both of them and their sound but also because my son has an Ampeg Lee Jackson amp that is supposed to be based on a Lee Jackson modified Marshall design. It has a switch that allows you to use either EL34's or KT88/6550 tubes and I really like the sound of the big tubes. I dont play hi gain and it seems there is more punch and clarity to the notes with the big tubes. My amp is a 50 watt plexi that has already been modded, it has a Mercury Magnetics transformer which seemed to increase headroom and punch compared to the stock and I was thinking that the tube mod might take it alittle further.
I have to take the amp in to have the fx loop looked at and was considering the tube mod while it's in the shop.
There is a white Marshal 100 watt head on YouTube. it was done by Scott Splawn with KT88's. It has the most incredible sound I've ever heard
 

Tjohn8573

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I've been in Zep tribute bands forever and I've converted 2 50w 1987 clones to KT88s. If you really want to nail the TSRTS tone it is a must IMO.
Hey tallcoolone. I’m building a Marshall 1968Super Bass now and have another 1987 build I would like to change to KT88 for the Jimmy Page thing. Would you have any advice on doing this mod as far as what components I would need to change or should change. Thank!
 

tallcoolone

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Hey tallcoolone. I’m building a Marshall 1968Super Bass now and have another 1987 build I would like to change to KT88 for the Jimmy Page thing. Would you have any advice on doing this mod as far as what components I would need to change or should change. Thank!
Sorry I’m no tech, I’ve always had someone do the swap for me. It’s def not plug and play tho
 

playloud

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Several "plexis with KT88s" were made under the Park name in the 60s. Johan plays an example here (looks like it's running Tung-Sol RI 6550s):

My friend owned a 2203 that ran KT88s for a while. My abiding memory is of it being loud. I also recall we made a "wall" of all our amps combined once, for recording purposes, and ended up basically turning off everything except for my Germino Club 40 (JTM 50 clone) and his '65 Princeton Reverb (original) - so it obviously didn't make the cut for whatever reason!
 


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