Help on KT100’s, 8417’s & EL156 for guitar amps

[Samaru]

Hey guys, just joined this forum. I’m interested in exploring the 3 powertube types mentioned above for some of my guitar amps that were designed to use KT88, KT90, KT120’s and 6550’s in them. I want to know if these powertubes can safely be used interchangeably in those guitar amps of mine. Also would I need to bias them to different values than I would with KT88’s or 6550’s? I know EL156’s would need adapter sockets for them, but otherwise would it work ok in the amps? Thanks in advance!

 

[Samaru]

Anyone?

 

[Campo007]

I have an Orange AD200 MK3 bass head which was running KT88's and i threw KT120's in it. It was a superb move. So much more head room.
But i would contact the manufacturer and asking the question, before making that change. That's what i did.

 

[Samaru]

I have an Orange AD200 MK3 bass head which was running KT88's and i threw KT120's in it. It was a superb move. So much more head room.
But i would contact the manufacturer and asking the question, before making that change. That's what i did.

The problem is the amps I’d wanna try them with are no longer made amps or brands where I can contact them and even for some past amps I had where I did the amp maker wasn’t familiar with the tube and just said advance at my own risk. Not what I wanted to hear

I liked KT88’s slightly more than KT120’s in the amps I had them in, but preferred KT90’s and 6550’s to both

 

[Samaru]

Anyone?

 

[213Cobra]

It's difficult to give a cut-and-dried answer without knowing details about your amp(s). KT90 can be swapped in place of KT88. The distortion yield is different with the KT90, which in hifi yields less linearity if plugged into a KT88-optimized circuit, but for guitar that can be desirable. You generally will get higher midrange THD at a given volume. I had Mesa MkIV and MkV amps, and could make that swap just fine.

KT100 can be interchanged with KT88, and some of what are labeled as KT100 are virtually same as KT88. I don't think that swap will matter much to you, sonically.

KT120 has a higher filament current draw than KT88, and can provide more headroom, but whether or not your power transformer can take the higher filament draw will depend on the amp. It's likely to be OK in a Mesa, not sure about others without knowing their PS specs. Get a sense for how warm your power transformer gets with KT88 installed, and try KT120 for a short time -- it the PT feels significantly warmer/hotter, abandon the trial.

EL156 is generally compatible electrically, but the German pin configuration and type is radically different from an octal socket, so you'll need to buy socket adapters. You can find them on eBay, usually out of Asia.

8417 is also hard to say. That tube has been out of production for a long time. In hifi amps that used the 8417, most owners have since been forced to have KT88 conversions done, which required B+ and bias alterations. THE 8417 had a higher B+ operating point than a KT88 can tolerate. Going the other way, putting an 8417 into a KT88 circuit, you may not be able to reach the 8417's proper operating point without modification (IF the given guitar amp's PS can supply the higher voltage ~580V.

6550 for KT88, no problem.

Modern KT88s have some significant differences in tone and voicing. A Shuguang Black Treasure KT88 has a darker, denser sound than the typical Russian produced KT88, and there are a lot of sonic variations among several Chinese brands, and the non-Russian Euro brands. You can get sonic varietals out of experimenting within the KT88 family alone, even before you get into vintage/NOS 6550 (different era Sylvanias, for example) or real, British Gold Lion KT88s.

Phil