KT77s in Einstein creating more compression - SOLVED!!!

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ccl117

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Swapped all preamp tubes per Peter's advice and noticed a HUGE improvement in tone in my Einstein Combo. Waited a couple days to replace the Ruby EL34's with JJ KT77's per his advice as well.....and noticed more compression in my tone. This is particularly more noticeable on Ch2 where the notes seems to have a bit less punch than before, and as a result get a bit lost in the mix.

I swapped the tubes myself and biased them to precisely 35ma per tube with a Bias King Pro taking the reading. Based on others reviews of the KT77, I seem to be having the opposite effect of what they are supposed to do for your tone. Might I be biasing them incorrectly? Has anyone else noticed this tonal change? Just curious if there is anything I might be able to do bias wise to open them up a bit before I swap the Ruby EL34s back in.

Outside of that, any other power tube recommendations for a Einstein to tweak a slightly less compressed tone? Thanks all,

Chad
 
What kind of current draw do those have? Depending on that measurement, they'll break up early or late. You might have some that are weaker and compress more. Where did you get them? Also, your bias voltage is going to depend on that number in relationship to your plate voltage. I.E., you could be idling too high and be browning out.
 
Thanks for the response. I don't know draw values unfortunately, or how to get them. The only tools I have available are the Bias King Pro. I bought them from Doug's Tubes as a matched pair with "Average Distortion" (options were Early, Average, or Late). If I am potentially idling too high, would I then lower the ma bias to compensate to test?
 
UPDATE:

KT77 #1
Plate Current: 24.4
Transconductance: 6100

KT77 #2
Plate Current: 25.2
Transconductance: 5970
 
I bought a quad form Valve Queen for my Einstein and they are not more compressed then the 34's I had in there. Maybe Peter with chime in?
 
Thanks Tripstan, I really think it's either something funky with the biasing, or perhaps the specific tube itself. I put the EL34s back in there and re-biased it, sounds outstanding. I just realize that my experience with the KT77s was so different than most others, and wanted to figure out what was the loose string causing it.

Side note, the 12AX7AC5 HG+'s in V1 & V2 literally created an incredible difference in tone for my Einstein. I picked it up used so I didn't know how long the prior pre-amp tubes were in there, but once I replaced the old generic ones this amp was a completely different beast, so much fuller sounding and open. Thanks again to Peter for steering me in the right direction!
 
Weird. Einstein was the one for me (vs hagen,vh4) that the kt77's were kinda passable in. If you like the Rubys stay with them. I certainly do.

Don't put me in timeout Papa! :D
 
ccl117":3s6rfqa8 said:
UPDATE:

KT77 #1
Plate Current: 24.4
Transconductance: 6100

KT77 #2
Plate Current: 25.2
Transconductance: 5970
Click to expand...

That's a fairly low PC. If it was head room you were after, I don't think you will get there with this duet. However, you can bias them higher than 35mA. Take them up to around 42mA and see what that does for you. The 34's that you had in the amp (if it came from the factory with them) will likely be much higher PC, knowing Peter. These will likely provide better results than the 77's.
 
Steve and Slyvren, thank you for the additional info and I apologize for the delayed response. Both very good suggestions, I appreciate them both quite a bit. But before I had a chance to implement, Papa sent me a note recommending I try lowering the bias rate to 25ma to see what happens.

I did, and viola, much more open and crisp sounding! Bass a bit more pronounced, and sweeter highs to my ear. Channel 2 actually has a little more growl to it too. I still love the EL34s and really like what they bring to the table with the amp, but I'm happy to now hear what others were describing with the KT77s.

Cheers, and thank you all for the help guys
 
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