Differences between 6550 and KT88

[fusionbear]

I looked at the data sheets, but I am still learning to interpret. Anybody care to explain the differences? Wiring, power, tone?

The reason I ask is I built this:

https://taweber.powweb.com/store/6s100_schem.jpg

It seems that I could substitute 6550's in there, but might have to decrease the value of the grid resistors (R32,R33) from 220K to ???

Any ideas or advice would be appreciated

[selloutrr]

the easiest way is to google 6550 tube specs and kt88 tube specs and compare them.

tone is subjective because each brand / model has a different sound.

both are great tubes if you buy the right brand.
usually KT88 can handle a bit more voltage.
for the most part they are interchangable.

check the voltages for your application against the make and model you are wanting to use.

happy building!

['67_Plexi]

I looked at the data sheets, but I am still learning to interpret. Anybody care to explain the differences? Wiring, power, tone?

The reason I ask is I built this:

https://taweber.powweb.com/store/6s100_schem.jpg

It seems that I could substitute 6550's in there, but might have to decrease the value of the grid resistors (R32,R33) from 220K to ???

Any ideas or advice would be appreciated

You don't need to drop from 220K, they are fine. Marshall used 150K for 6550's but it is not necessary and makes little to no difference tonally or technically. THe affect on the frequency response is not even noticeable.
The Tuc uses 220K and runs either 6550's or KT88's. 6550's are more stringent feeling whereas KT88's are softer. I find Strat players seem to prefer KT88's in that amp. Results will always vary by the actual end design, but they are my findings. Just a little tip, both these power tubes respond better to a PI that uses a 12AT7 set up correctly for the tubes as opposed to the typical 12AX7 arrangement you might use for EL34's or 6L6's. Even though it's used with 6L6's, a BF Twin Reverb PI will give you a good starting place for a circuit that will drive these output tubes really well. Some designs use more complex PI's with an extra gain stage, but I've found adaptations of the TR circuit to be totally fine and offer a nice smooth master volume sweep. You've played a Tuc....

Alan.

[fusionbear]

I looked at the data sheets, but I am still learning to interpret. Anybody care to explain the differences? Wiring, power, tone?

The reason I ask is I built this:

https://taweber.powweb.com/store/6s100_schem.jpg

It seems that I could substitute 6550's in there, but might have to decrease the value of the grid resistors (R32,R33) from 220K to ???

Any ideas or advice would be appreciated

You don't need to drop from 220K, they are fine. Marshall used 150K for 6550's but it is not necessary and makes little to no difference tonally or technically. THe affect on the frequency response is not even noticeable.
The Tuc uses 220K and runs either 6550's or KT88's. 6550's are more stringent feeling whereas KT88's are softer. I find Strat players seem to prefer KT88's in that amp. Results will always vary by the actual end design, but they are my findings. Just a little tip, both these power tubes respond better to a PI that uses a 12AT7 set up correctly for the tubes as opposed to the typical 12AX7 arrangement you might use for EL34's or 6L6's. Even though it's used with 6L6's, a BF Twin Reverb PI will give you a good starting place for a circuit that will drive these output tubes really well. Some designs use more complex PI's with an extra gain stage, but I've found adaptations of the TR circuit to be totally fine and offer a nice smooth master volume sweep. You've played a Tuc....

Alan.

Appreciate the tips! Thanks! What about a parallel triode cathodyne arrangement with a 12AU7. It seems that that tube has the "gusto" to drive these tubes properly. Like to hear your comments on that.

[FYL]

What about a parallel triode cathodyne arrangement with a 12AU7. It seems that that tube has the "gusto" to drive these tubes properly.

You may consider using a 12AY7 or similar in the cathodyne, with a 12AU7 driver or paraphase follower.

[greiswig]

(SNIP)6550's are more stringent feeling whereas KT88's are softer.

I'll second that. I've tried both in my two-hole Dumble build, and I thought the 6550's had a hardness to them that might be great for some, but wasn't my preference. Sort of a "velvet glove smacking you in the face" approach, where the KT88s felt more like the glove was wielded by a more ardent, feminine hand.

That said, I should try the 6550s out live some time...there's a big difference between what sounds good in the amp by itself versus what works best live. Hmmm...

[JamesHealey]

Ones a kinkless tetrode one isn't. I like kt88 for certain things. Usually big clean amps

[fusionbear]

I played around with both types of tubes and the KT88's feel and sound "nicer" to my ears. So, they will stay.

Thanks for all your comments. I really appreciate them...