up close and personal...

[MitchK]

So after the "jcm 800 2203 dead..." I've decided I'm going to put a quad KT88s/6550s in both my jcm800 and my 5150. What I've realized though is that the tube sockets in these amps are a liiiiittle close to one another and with the big fat body shape of the kt88s I can get them all in there but they will be all touching one another. this seems like a bad idea to me that would lead to over heating and possibly some glass shattering. Just want to know if this would be the case or what others have done in this situation.

Also the 5150s tubes connect directly from the sockets to a pcb board. detaching this, drilling new spaces in the chassis, connecting new sockets I put in myself to the old pcb seems like a lot of work, I've noticed that "kt90" tubes have a straight appearance like the el34s. should I just save myself a lot of time and get some kt90s in the hope they will sound pretty much the same?

[Matt T.]

I can't remember where but I've seen it somewhere (maybe a tube data sheet?) that states minimum distances between power tubes. If they are that close together I wouldn't do it...can't comment on the KT90s.

[MWJB]

The EH KT90 seems to have quite a recessed top end, a little like a big KT66, smooth, round & bassy. I can't imagine that it's going to sound much like any 6550, or really any KT88 (only tried them for harp not guitar). Some vendors expressly state the EH KT90 is not an instrument tube, I don't agree with that 100% but they can sound dull & lifeless in an unsympathetic circuit. If you haven't heard them I don't know if I would take the risk on a quad? The EI KT90 is pretty well impossible to find quality items of but by all accounts is very different (livelier?) to the EH (the only guy I know that's tried them hasn't had a working pair long enough for me to hear them...or finish a set for that matter!).

What about the straight bottle SED6550 or Sovtek 6550WE/WD?

I seem to remember a National tubes data sheet quoting 110mm centres for KT88s, that's over 4"! Most guys get away running them at typical Fender style 6L6 spacings.