MV60SE with KT88

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Joethekid72
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MV60SE with KT88

Post by Joethekid72 »

Hey all,

I got a set of KT-88 tubes and put them in my MV60SE to try out..electro harmonix KT-88's
When I turn the bias screws to bias them the light goes off at about the 10 O'clock position.. Is that normal for kt-88's? The 6550's I have, even as old as they are, the light goes off at about 1 O'clock..
Also, I thought I'd get maybe more bass out of the KT-88's than I'm hearing..
Are they just not a good match for this amp??
Big Dog RJ
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Re: MV60SE with KT88

Post by Big Dog RJ »

G'day mate, from down under

The MV60SE will accept 6550's, KT120's and KT88's. The Bias settings that you have done are normal, as long as all LEDs are off just as you set the bias.
Sometimes 6550's may need less bias due to their current requirements, being more powerful tubes like KT120's, they would set more easily. KT120's in the MV60SE will make your amp sound very different, almost like solid state bass.

The owner's Bias settings on CJ amps are not actual bias adjustments, rather a small amount of current (milli amps) applied to the circuit for output tubes to reside at their idle current. During start up, the circuit is "asleep" so biasing according to the LEDs just going off sort of wakes them up and they're ready to go. Other amps such as Manley and VTL, this is where the owner is required to make actual Bias settings using a multi-meter (and is also a pain in the butt when you have more than 20 output tubes per amp!), plus it gets very hot down there.

With CJ's LED based bias adjustment circuitry, it makes biasing a breeze!

The actual bias setting is done at the CJ factory, and is usually based around the 4 ohms, thereby allowing CJ amps to drive most real-world speakers without strain. Of course the best sound or lets say "effortless drive" will come from a speaker with an easy impedance load and high efficiency.

These are my findings with the following output tubes on the MV60SE:
6550 - powerful sound, with clean and smooth highs, smooth midrange and good bass. Overall a good power bean pentode with plenty of headroom to drive reactive a load impedance as well (specially good with electrostats).

KT88 - top end quite good, open midrange and very transparent in the midband (widely used by McIntosh and Quad amps) known for their musicality in the midrange). Not that great on bass, rather a tuneful bass with all the details but cannot deliver the same bass as compared to 6550 or KT120.

KT120 - very powerful, plenty of headroom and will be cruising along in the MV60SE. Very smooth from top to bottom and the bass is awesome. Overall an excellent power beam tube to have in the MV60SE and will make the amp sound like no other. Some prefer the 6550 tube due to less over-tones, which the KT120 does. It makes the sound fuller with plenty of weight and if you are into this type of sound, the KT120 will deliver.

I have used all these types of tubes in my MV60SE, and I preferred the KT120 over the KT150. The KT150 was made solely for audio applications and was introduced widely into Audio Research amps and Ayon. Although slightly more powerful, there was an "overblown" factor in tones that I didn't like nor could listen to for long periods. Hence did not allow me to relax, sounded more like solid state on steroids. Plenty of drive and massive soundstage but seemed exaggerated to a large extent. Not my preference at all. Also the KT120 & 150 are nearly based on the same specs, however ARC and others who use the KT150 maximise the parameters on the tubes, resulting in this over-blown sound. Some do actually prefer it...

The KT120 will make your MV60SE sound its best, and you will be quite amazed and what the amp delivers.
Cheers, RJ
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