KT77 worth it?

turnitdown

turnitdown

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I have a very nice, clean Hammond AO-58-1. This is the licensed-to-Hammond copy of the Dynaco ST70. I put all new matched tubes (EL34) in it and it really sounds great driven by the pre-amp in my Luxman R117.

Are KT77s a real step up or is this a case of whichever sounds best to you?

$370 for a quad of KT77s is a steep price for an experiment.
 
Those should give you good performance. I don’t personally think 77’s would sound any better. However, the EH EL34’s and reissue Tung-Sol EL34’s have great reviews.
 
EL34 vs KT77

The KT77 has higher plate impedance (23k) compared to the EL34 (15k). Also if you look at the screen current it's less than the EL34 by 5mA for the same operating point which would indicate the grids are aligned unlike a EL34 being a true pentode will have non grid alignment. In the same circuit they should perform differently, whether this is good or bad I have no idea and depends on the circuit and if you like more/less distortion.

What's weird is the EL34 vs EL34L that JJ offers. They show the same exact plate characteristics graph for both tubes and yet they have different Vg1-k parameters for the same operating point. Something doesn't smell right and I doubt they have the same characteristics. Again whether this is good or bad depends on the circuit and what you subjectively like. Numbers-wise try them in circuit and see which measure better or just use your ears. But your standard real Pentode EL34 vs KT77 will give different performance given the same circuit. I went through this whole thing like 15 years ago and don't remember the details. I was making a Mullard 5-20 type circuit and ended up going with the KT77 if that's of any use lol. As I said I don't remember why I went with them vs the EL34 but I did. In a Dynaco circuit which uses a different Ra-a load impedance I can't say my experience will align with yours.
 
I've used several EL-34's in my VTA ST-70. I ran some JJ KT-77's for a few years also. I personally preferred the KT-77's over the EL-34's I tried. Everyone has there own preferences though. No two sets of ears are identical. But in the end the EH 6CA7's won out over all of them, including some KT-88's. If your happy with how the amp sounds now, then that $370 may not be worth it. I think I payed around $160 to $180 for a quad of the KT-77's back then.
 
I found a relation between tubes that have grid alignment sounding better in ultra linear amplifiers. Since non-aligned grids pull much more screen current, you'll get more screen grid distortions when the plate gets pulled down close to ground.

In full pentode operation with a regulated screen supply combined with flat output stage loading (zobel network) the problem isn't there and the amps sound great.

So no surprise really that these other low screen current tubes sound better in UL amps vs the true pentode EL34.
 
I used JJ kt77's for a while and wasn't wowed... They sounded good but not better than my Russian Mullard quad. +1 on the EH6CA7'S though.

P.S. I have an updated ST70
 
I did some testing with my collection of EL34 tubes, and oddly enough the JJ's actually performed and sounded most like my old Mullard tubes. The bias points and all were right there, the Russian ones need more negative voltage, the Shugang need less.

The EH 6CA7 are "brighter" than any of my EL34 tubes, so I run them in an amp that is a bit challenged on the top end. The Shugang are kind of soft, so I run them in a pair of amps that tends to be bright. The Mullard and JJ are right in the middle, which gives them the unfortunate position of not being ideal in either amp. I do actually have the JJ's installed right now because my bench somehow ate one of the Shugang EL34 but the JJ's were out so in they went. I guess it says a lot for my general state of disaster when I can lose a vacuum tube, but find 4 of the same type in a different brand.


also if it matters, the amp the 6CA7 are in is a UL design, the other is a pentode design.
 
Myself, I didn't care for either the GL KT77, or JJ KT77. The GL KT77 can have a bright edge as well. Both lack the classic EL34 midrange. Eh.........no thanks.
In my Prologue 4-even the stock old PL EL-34 sounded much better then either KT77. The Sino EL34B(2 halo getters), the new PSvance EL34C sound great-plenty of space and detail without being bright. No lack of bass. I ordered a set of PSvane EL34-UK-s sound be interesting. A bigger bottle then the EL34C's.
Agreed the JJ's are a good sounding EL34-but in my Prologue 4-they aren't the best-a bit one dimensional. Besides that-very musical and well rounded.
My KT88 Prologue 5-the JJ KT88's sound very good-interesting bass to them. Musical and nice wide sound to them.
Again the Shuguang KT88/98 still seem to have the best overall sound-so far. Have not tried the UK series Psvanes yet.
 
UL here too. I am experiencing with EH KT90 at the moment.
Of course the heater requirement makes it impossible to run in a amp designed for EL34, unless you supplement with a additional filament PT which I did.
But the result is super boldly and worth the effort.
 
turnitdown said:
I have a very nice, clean Hammond AO-58-1. This is the licensed-to-Hammond copy of the Dynaco ST70. I put all new matched tubes (EL34) in it and it really sounds great driven by the pre-amp in my Luxman R117.

Are KT77s a real step up or is this a case of whichever sounds best to you?

$370 for a quad of KT77s is a steep price for an experiment.
Click to expand...
$279 shipped from Upscale Audio-on the GL KT77's
I just moved a set here not to long ago for around $200-low hours.
IMHO stick with the EL34's if they are sounding as good as you are saying.
 
If I gotta have a push pull pentode amp I definitely prefer the KT88/6550 over the EL34.

It's hard to not take the more power into consideration but I just think they slam better.
 
turnitdown said:
I have a very nice, clean Hammond AO-58-1. This is the licensed-to-Hammond copy of the Dynaco ST70. I put all new matched tubes (EL34) in it and it really sounds great driven by the pre-amp in my Luxman R117.

Are KT77s a real step up or is this a case of whichever sounds best to you?

$370 for a quad of KT77s is a steep price for an experiment.
Click to expand...
As a technical point : KT77 needs a smaller grid resistor in order to never redplate. It might work in a Dynaco st70 but as
the grid resistors are 270k you are outside the safe area.
 
automojo said:
Myself, I didn't care for either the GL KT77, or JJ KT77. The GL KT77 can have a bright edge as well. Both lack the classic EL34 midrange. Eh.........no thanks.
In my Prologue 4-even the stock old PL EL-34 sounded much better then either KT77. The Sino EL34B(2 halo getters), the new PSvance EL34C sound great-plenty of space and detail without being bright. No lack of bass. I ordered a set of PSvane EL34-UK-s sound be interesting. A bigger bottle then the EL34C's.
Agreed the JJ's are a good sounding EL34-but in my Prologue 4-they aren't the best-a bit one dimensional. Besides that-very musical and well rounded.
My KT88 Prologue 5-the JJ KT88's sound very good-interesting bass to them. Musical and nice wide sound to them.
Again the Shuguang KT88/98 still seem to have the best overall sound-so far. Have not tried the UK series Psvanes yet.
Click to expand...
I didn't care for the KT-88's in my ST-70. The bottom end was good though. The midrange just didn't sound right to me. But in the M-125's they sound much better.
 
peterh said:
As a technical point : KT77 needs a smaller grid resistor in order to never redplate. It might work in a Dynaco st70 but as
the grid resistors are 270k you are outside the safe area.
Click to expand...

just as a further point on this, the datasheet says with fixed bias and plate dissipation less than 28 watts, 500k is fine. Above 28 watts not more than 250k. Dyna ST-70 runs around 23 watts.

https://frank.pocnet.net/sheets/086/k/KT77.pdf
 
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