Leslie 147 -> running a EL34 and a 6550

[danotron]

A freind dropped off the old Leslie today, says it blew up. Soundd like a bad tube to me. He hadn't changed the tubes in years (10 or 20) so I pulled them out.
One was a 6550, what I was expecting but the other was an EL34.

Could this realy have worked for so many years with the wrong tube in it? The Leslie always sounded great and was nice and loud.

Anyone seen this before? How bad would this be on the op tranformer?

[Wayne]

Seems to me I saw in an old textbook (maybe RDH?) where they did an analysis of a PP amp running two different types of triodes to extole the virtue of push-pull and demonstrate how it cancelled out many of the differences between unmatched tubes. On paper, I think it resulted in (surprise, surprise) a bit more distortion, but I don't think anything "blew up". Then again, that was on paper - can't say I've ever seen this in real life.

W

[selloutrr]

I guess the question now is do you put in a matched set or retube how it was? if you go matched which tube do you pic 6550 or el34 to get the sound back to its former glory.

[briane]

I think you need to get a schematic and do whats original. I thought they were 6550, but I would have to check.

I've been meaning to do that to my 147 as well, but its pretty far down the waiting list.

[CaseyJones]

A freind dropped off the old Leslie today, says it blew up. Soundd like a bad tube to me. He hadn't changed the tubes in years (10 or 20) so I pulled them out.
One was a 6550, what I was expecting but the other was an EL34.

Could this realy have worked for so many years with the wrong tube in it? The Leslie always sounded great and was nice and loud.

Anyone seen this before? How bad would this be on the op tranformer?

The larger Leslies like the 122, 145 and 147 use very close to the same amp. I like the 145 because it uses a slightly shorter cabinet, easier to carry but then again road cases are more readily available for the 122/147. Anyway... they're one rugged SOB. I don't expect there's very much wrong with yours. We usually replace all the coupling caps, the electrolytics and maybe the bias resistor, re-tube 'em and send 'em out the door. However: Those old green Cornell-Dubelier .1ufs are rock solid, usually they're right on value and they don't leak. The electrolytics hold up o.k., it's hit or miss with the old ones. We replace all of them so it's bulletproof on the road.

Mixed tubes? Hell, yeah! My favorite is when they come in with only one output tube and the owner says, "It's low and distorted." Ya think?!

Stock they use 6550s. The original Tung-Sols last just about forever. They don't die, they fade away unless you stick yer big ol' boot in there and kick 'em out. Then they die! The old ones get ratty and bluesy. Many of 'em test great and match well but they still sound ratty. NOS ain't cheap but it's the way to go. Don't screw around with KT88s or KT90s, some of them arc and they will take your transformers with 'em. Argue if you must, I learned that the hard way.