Ultra-linear vs. triode mode for Luxman MB3045 (with KT-88)

[tutor_turtle]

I have a pair of Luxman MB3045 with the KT-88 modification, currently in Ultra-Linear mode.
They are driving a pair of the very efficient Klipsch Cornwal IV's.
I don't use all the power the Luxman is capable of delivering in UL.
The change to Triode mode is a simple resistor change and location.
Would the mode change result in a notable improvement in detail / dynamics?
Has anyone made this change in their MB3045?
If so, what are your thoughts?

 

[gadget73]

I had opportunity to try these in both modes a few years ago. They actually make the same power in both modes, and sonically i really didn't notice much difference. Just my 2 cents, but i freely admit to a bit of tin ear.

 

[Nyjblbob]

I prefer triode run tube amps,
with all my horn speakers.
Not only that but tube rolling
Can also be added to the mix .

 

[gadget73]

Also i should mention these don't actually run ultra linear, though I'm aware what the instructions say. There aren't any taps on the transformer for the screen, its actually in pentode mode.

There should be less gain in triode so less feedback, but the distortion measurements are so low in both modes that only your ears might ever know the difference.

I don't own a set and I'm probably too cheap for that to change but I've worked on two sets and listened to them. Lovely pieces of gear.

 

[tutor_turtle]

I prefer triode run tube amps,
with all my horn speakers.
Not only that but tube rolling
Can also be added to the mix .

Thanks, good advice.
I've had these about 30 years now.
Given how straight-forward there mod is, it sounds like it's worth a shot.
That 100 ohm resistor: looks like 1/2 watt should work? (I have a customer with an old Luxman stereo amp who wants me to implement this change)
Did you use a film resistor? I have a good supply of MIL-Spec 1% film @ 1 watt.

Tube rolling:
I like the Ampex Bugle Boys in the V1 position (12AX7).
I just discovered the 12BH7 is a great swap for the V2 (12AU7) and I am happy to report, yes it is.
This is currently a Psvane. The plan is to find some NOS at a reasonable price. So far, no joy.

For V3 & V4 I have a good stock of NOS 6CG7's from RCA and GE. I'm not hearing a notable difference between the GE & RCA.

KT88 Outputs: I like the Gold Lion for Classical, instrumental, and female vocalists. The Tungsol is the better choice for rock-n-roll.
I loved the Winged "C" tubes when they where in production, but they didn't seem to last more than a few years before one would fade.
Still have a decent set of three .

I did try the Tungsol KT120's at one point. Didn't sound any different from the Tungsol 88's (to my ears), that, and they were too tall for the cage.

 

[gadget73]

Half watt is fine, its not going to dissipate anything significant.

The trick with a kt120 is they use more heater current. I don't know how much extra capacity there is in the transformer. They don't run hot so it's probably not a concern. Not honestly sure what the original tubes used

 

[kward]

The original amp ran 8045G’s I believe. As near as I know it was developed by NEC for Luxman. And I believe they ran them in triode mode. I can imagine they delivered a smooth and sweet sonic signature.

 

[gadget73]

Right, but i don't happen to know what the current draw is vs a kt120.

The original were strictly a triode. Possibly it was a beam tetrode internally connected as a triode but definitely triode mode.

 

[tutor_turtle]

Any thoughts about rolling 6GU7 (Sylnania) in place of 6CG7 (6240G spot).
Picked up some NOS at Tubes and More (.com) for a song.

 

[tutor_turtle]

Right, but i don't happen to know what the current draw is vs a kt120.

The original were strictly a triode. Possibly it was a beam tetrode internally connected as a triode but definitely triode mode.

Given the transformer was designed to drive the big sweep tubes with the same current draw, I tried a set of KT120 (Tungsol- Russian).
My ears were unable to hear any difference.
Caveat: I biased them at the same 0.5 V. Should I have kicked up the bias to 0.75v? Like the old sweep tubes?
If some has been down this path, please tell us about your experience.
BTW, the cage won't fit with the 120's installed, they are about 3/4" taller.
You can rest the cage on he screws.

 

[gadget73]

In my one amp that can run them I haven't noticed much difference but it may not be the case here. Either way I think you'd be OK to sub them for one another, they aren't identical but they are similar enough that it shouldn't cause any fuss. 6GU7 is said to be the same as a 12BH7, just permanently in 6v mode. Physically they look different to me, longer plates on my 6GU7 than the single 12BH7 I own, but I haven't studied the curves too close. They aren't drawn at the same voltage spacing so it makes it a little harder to do.

they are a cheap tube with decent looking curves though.

Only concern I'd have with the KT120 is possibly the heater current, so long as its not greater than the 8045G you're fine

Don't really think the bias is going to change it much but give it a go. Worst case it won't do anything useful. I don't tend to notice vast differences between KT88 and KT120 in my amp that can run them, at least nothing more obvious than I get going from one KT88 to another. The KT88 have a little better bottom end, the EH KT88 are a little nicer on top, the Gold Lion are as good as the KT88 on the bottom and as good as the EH on top, so overall its a better sounding tube but its not "a whole new sound" or anything. That amp is quite different from the Luxman in terms of circuit though.

 

[Blue Shadow]

The Japanese spec sheet for the 8045G says 6.3V and below that 2.5A. I couldn’t read the wording. Thain, you have a copy sent by email years ago, 4 pages.
The transformer inside the amp is marked as 2.5A for each winding used for the heaters. It is also on a following page of the attachment.

 

[kward]

Any thoughts about rolling 6GU7 (Sylnania) in place of 6CG7 (6240G spot).

So I have tried a GE 6GU7 in place of a Sylvania 6CG7, where the amp was designed for 6CG7 in that spot. That spot being the input voltage gain tube of an EL84 push pull amp. Not your exact scenario I know, and in my amp the 6GU7 worked just fine, no issues whatsoever.

But for sound presentation the Sylvania 6CG7 beats the GE 6GU7. I’m thinking that has more to do with the Sylvania brand than anything else. An early 60’s Sylvania 6CG7 is kind of the holy grail, hard to beat. It would be telling to sub a Sylvania 6GU7 in for a Sylvania 6CG7.

 

[gadget73]

thank you Google Translate.

anyway if the 8045G is a 2.5 amp heater, no worries on the KT120 heater load.

So I have tried a GE 6GU7 in place of a Sylvania 6CG7, where the amp was designed for 6CG7 in that spot. That spot being the input voltage gain tube of an EL84 push pull amp.

Mine is in a long tail pair inverter, so lots of local feedback making the tube itself not very critical. Not surprised that an input voltage gain spot is more sensitive to tube differences.