KT88 and 6550

[Cygnus X1]

Are these the same tube?
If not, then what would be the difference?

I am going to be building an AX84 style Hi Octane SEL guitar amp, and it calls for a KT88, but I have four 6550's without a home.

Finding real info at AX84 is difficult.
And, a lot of dead links, too.

[skyboltone]

Are these the same tube?
If not, then what would be the difference?

I am going to be building an AX84 style Hi Octane SEL guitar amp, and it calls for a KT88, but I have four 6550's without a home.

Finding real info at AX84 is difficult.
And, a lot of dead links, too.

What kind of 6550's? And as far as I know the KT-88 and 6550 are pretty much interchangable. Have you looked at the Allen Class Act? It's the SEL I'm kinda gearing up to do. It'll run just about any octal with the 6L6/kt66,88,6550,6k6 layout. I posted the scheme yesterday in the Garage section. Look for "Is IMG turned off".

[Cygnus X1]

Hey, sky.
Yes, I was just looking at the schem you posted in my other thread, about a potential dlite or 18 watt build.
The Allen looks like another good one to try.
I have the parts for the AX84 SEL coming to me as we speak.
Looking forward to your experience!

The 6550's are (junk) Audio Classics, a brand new quad set I stupidly bought
20 years ago for an Ampeg V4 project. No one wants them, and I want to try them, rather than tossing them out.

Is biasing the same? I can just pop it into the KT88 designed circuit, and bias as usual?

[jjman]

KT88:

http://tdsl.duncanamps.com/show.php?des=KT88

6550:

http://tdsl.duncanamps.com/show.php?des=6550


At 1st glance the look pretty similar.

[skyboltone]

Hey, sky.
Yes, I was just looking at the schem you posted in my other thread, about a potential dlite or 18 watt build.
The Allen looks like another good one to try.
I have the parts for the AX84 SEL coming to me as we speak.
Looking forward to your experience!

The 6550's are (junk) Audio Classics, a brand new quad set I stupidly bought
20 years ago for an Ampeg V4 project. No one wants them, and I want to try them, rather than tossing them out.

Is biasing the same? I can just pop it into the KT88 designed circuit, and bias as usual?

Yes. The 6550 has a touch more plate dissapation allowance but otherwise it's pretty much the same tube. Tung-sol is the holy grail on 6550s. Genelex on the KT-88. I've bid unsuccesfully $45 on tung-sol pulls. I'd use a Valve Art KT-88 before I'd plunk down more on a pull unless I knew the source very well and it was an McIntosh 275 owner with OCD.

[Cygnus X1]

Thanks, sky.
Those 6550's are just sitting there, unused, so might as well try them.
Actually, I'd love to know what an EL84 would do in the SEL circuit.

I'm going for low volume, shredder gain.

[dartanion]

Going with a big bottle output isn't really going to be "low volume shredding", unless you have hearing damage already A regular champ through a 12" is loud.

[Cygnus X1]

Going with a big bottle output isn't really going to be "low volume shredding", unless you have hearing damage already A regular champ through a 12" is loud.

Myself, I want to also try a 6V6.
That ought to tame things a bit.

The SEL circuit has nasty gain built into the preamp, with two pots for gain stage control. I'm looking everywhere for what I want, and people keep putting me on the path back to the same places, which is closer to "blues tube overdrive" territory, (which I love, btw), but not real high gain in lower wattage territory. The AX84's seem to have gone there, so I'll give a shot.

[dartanion]

You can try something like the Moonlight amp which is ultra low watt push pull triodes (6SN7) and mate that to a high gain preamp. Depending on your power supply, you can be good for up to a couple of watts, although 1 watt is plenty for bedroom shredding. Remember that any flavor that a speaker lends to tone is greatly diminished when not being driven much. Use a very low wattage speaker here, about 15W max.

[Ears]

6550A and KT88 are significantly different in terms of allowable screen and plate voltages (and dissipations).
Don't just treat them as interchangable.

[Cygnus X1]

So, in a given schematic that shows a KT88, what would I change to accomodate a 6550? (Or 6L6, 6V6, etc)?
Just biasing?

[Cygnus X1]

You can try something like the Moonlight amp which is ultra low watt push pull triodes (6SN7) and mate that to a high gain preamp. Depending on your power supply, you can be good for up to a couple of watts, although 1 watt is plenty for bedroom shredding. Remember that any flavor that a speaker lends to tone is greatly diminished when not being driven much. Use a very low wattage speaker here, about 15W max.

Interesting.
Could you point me to a schematic?
I'm still in the kit building level of experience, I can't design my way out of a wet paper bag!

I have several NOS 6SN7's that are for sale, but I'll keep them if I can use them. I have Autocad 2000i, if that helps with posting a schematic.

Thanks!

[tubetek]

The KT88 (REAL NOS) can handle 800DC on the plates; the GE6550A specsheet says 600DC plate. Also, the KT88 is limited to LESS screen voltage than the 6550...compare the specsheets. The '88 also uses a little more filament current than the 6550. They are a close enough match to use the same OT. Hope this helps
tubetek

[muchxs]

We've assumed that KT88s are a direct 6550 sub in organ amps... and were quickly proven incorrect.

Old burnt Tung-Sol 6550s last forever in Leslies, new KT88s don't.

My question would be, "If you have a matched quartet of 6550s why break a quartet?" Sell them to Slash to use on his clean side... except his tech "insists on Groove Tubes."

The Hi-Octane is a wonderful little amp when built with a 6AQ5, 6BQ5 or 6V6 depending on what your supply voltages are. For an inexpensive build with low voltages use a 6AQ5, for higher voltages use a 6V6s with alternative bias resistors if you want to keep the possibility of a 6550 open.

[Cygnus X1]

Because the Audio Classic 6550's have a dirt poor reputation, for some reason. I don't know, I have never used them, and nothing to check them out in. Water under the bridge. I paid around 100 dollars for them a very long time ago.