Woohoo KT88s

[Steve Conner]

Look what I got!

There is a story behind them. Years ago, I salvaged three from a high voltage power supply that I found in my old work's junk heap. Then last week a friend mentioned that he found the same kind of power supply in his work's junk pile too. I asked if I could have the tubes out of it, and what do you know

They aren't for sale. I've seen GEC KT88s fetch stupid prices on Ebay, but they were sold as NOS matched sets. These have been used a little, and probably don't match too well, though I suspect they'll be good enough for rock'n'roll with individual bias pots. I'm saving them for my 300w bass amp project.

[Alex/Tubewonder]

Lucky you. Now go and buy a lottery ticket. And send me the tubes to increase your chances of winning the lottery.

[dai h.]

wow that's cool. You should try finding more of this stuff. Save it from the landfill.

[Sir Cuitous]

Impressive set of tubes there... I am really interested in that 300W bass project. Please post details when you do it.

[Steve Conner]

Hi guys

Just an update on this: I tested the tubes at the weekend. All six work, and the closest four match within about 15%, with two odd ones left over. One runs really hot and the other really cold. (Anyone want to swap for a brown base GEC KT66? I have one good one looking for a mate.)

So it looks more like a 200w bass amp than 300.

I'm still at the research and component gathering stage for it: I have the output and interstage transformers from a Fender 300PS, and a couple of different PTs to try: one from a 250W tube ham transmitter, and a 500VA 1:1 toroidal that was meant as a medical isolating transformer for 240V line voltage. I can use that with a doubler like in the original 300PS.

One other thing I had problems finding was a chassis large and strong enough. If I go down to 200W, I guess I could more or less squeeze it all into a Plexi cabinet from TAD, if I reinforced it a bit and added a fan.

I'm also still deciding what kind of preamp to bolt onto it. I've considered everything from a SVT clone, to my Ninja Toaster preamp with the parametric EQ, or even the simple approach with an Alembic F2B clone. That would have just four controls: volume, bass, treble and earthquake magnitude.

[bob p]

Nice score, Steve! I got lucky and found a pair of GE 6550 (branded as Hewlett Packard), and a pair of Sylvania 6L6GC by cannibalizing old regulated power supplies. I'm still thinking about the high watt tube amp, but I'm resigned to the fact that I'd have to do it with new production output tubes.

300W out of a sextet? I guess you're planning on pushing those KT88 for all they're worth with high B+ in class AB1?

[stokes]

Steve,you should be able to use all six in a 3 on a side PP out put.Just match them up so the total draw of 3 on one side is close enough to the total draw of the 3 on the other side,no?Or are they that far off from each other?

[Robert M. Martinelli]

Hi folks,
I still have the original KT88s I pulled out from my beloved 1966 Vox UL4120, and they' re from the same manufacturer; sadly, I only have 4 of them....Steve, you' re a lucky guy indeed!

( well, telling the truth I think to be a lucky guy too... there aren't many 4120s left, as someone said, they' re rarer than hen's teeth... )

[outtahear]

Bastard!













congrats!