CJMV60SE

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Joethekid7
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CJMV60SE

Post by Joethekid7 »

Hi all!
I have a MV60se and I installed tung sol KT-120 power tubes. I have power hungry speaker(dahlquist DQ-20i) so I decided to try bi amping.. Mf200 SS amp on the bottom.. Mv60Se for mids and tweeters.. Sounded great for an afternoon.. The kt120's are dieing! Only had them for 11 months... Is that average lifespan?? I miss the MV55 I used to have.. Anyone know if the gold lion kt-88 is any good?? Will they last longer? Have more if the mid range like the el 34s?
Big Dog RJ
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Re: CJMV60SE

Post by Big Dog RJ »

Hi there,

I used to own the MV60SE both with 6550's and KT120's from Tungsol.

When you say the KT120's are "dieing" what do you mean?
1. Are they red hot (cherry like colour) on the grids? That is red right throughout the grids and not just lit up at the top or bottom of the tubes.
2. They cannot be biased properly?
3. Have you tried biasing them the proper way with volume in mute or absolute zero, turn counter-clockwise until LED just goes off and then back off by slight notch as a counter measure- during AC voltage fluctuations that cause LED's to flash sometimes, which is quite normal but can be annoying.
4. If you have changed the output tubes, you must also change the driver and input tubes as well to make sure that the full set of tubes is new, or have been sourced from the same batch. This is called tube matching and is slightly better to have this config, it is easier to track tube life than purchasing individual tubes at different times.
5. Has the overall sound gone "dull and low level rumble" which means tube require changing (the full set of tubes need changing, not just the output tubes).
6. Tubes can go bad within a few months to few years, nothing is guaranteed.

Therefore, when you say "dieing" what are you referring to?
Also, please ensure that you are turning the amplifier off when not in use or in idle. If it is on idle for long periods, over an hour this will waste tube life!
When the power is turned on, all it takes is just 2-3 minutes for a tube amplifier to get going. 5-10 mins is more than enough to warm up. During playback is the only time tubes begin to really warm up after about 20-30 mins they sound even better.

Many people who own tube amplifiers think that warming up for over an hour is ideal and tubes amps take an awfully long time to warm up... Not at all, they are active amplifier devices and fire up immediately during turn on. They are good to go within 2-3 mins provided they are biased properly.

By the way, the KT120 Tungsol placed into the MV60SE should sound superb! This is one very top notch amplifier on premier standards when matched with the right preamp of equal or higher quality. The MV60SE would not disappoint you, with either the 6550 or KT120 tubes and these give far better sound compared to the KT88 tubes. BUT that is to my ears and most of us out there including cj designers. Therefore, you have to try different tubes and check for yourself which sort of sound you would prefer?

At the end of the day you may actually prefer the KT88... who knows? only you do!
Cheers and hope you can address the above points to help why your amp sounds dull or as you say "dieing".

RJ
Joethekid72
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Re: CJMV60SE

Post by Joethekid72 »

Wow!
Thanks for this reply! Very informative!
As for:
1-the KT-120's get red hot yes but not fire red as you describe.. Do KT-88's put out less heat?
2-I heard distorting out of the right speaker.. I shut the amp down.. Turned it back on, waited, then tried to re-bias with the trim pots.discovered that the power tube closest to me on the right channel the light wouldn't go on at all.. I pulled them and put the original 6550c's that came with the amp back in... Light worked again. Distortion gone.. So I guess it's a dead tube.. They are 11 months old and I do listen to the amp a few hours a day.. So.. I guess it's time .. The one mistake I made I guess was leaving the original 6sn7's and 12ax7's in there .. I only changed the power tubes..
As I mentioned.. I did try bi-amping with the mv60 for the tweeter and mid.. And an MF200 for the low driver.. Sounded great. Maybe with a brand new set of tubes I will use just the mv60.

Thanks for your insight RJ!
Joethekid72
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Re: CJMV60SE

Post by Joethekid72 »

On a side note.. I'm running a CJPv10A ..with a new set of tubes from upscale audio.
Big Dog RJ
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Re: CJMV60SE

Post by Big Dog RJ »

Hi mate,

Ok, now I understand what kind of trouble you had with the KT120's. It sounds like it was just one tube, which definitely this can happen within a matter of few months. I would suggest the following:

1. re-order a full set of tubes for the MV60SE (this includes all driver & input tubes) they don't cost much, "EH"- Electro Harmonix are pretty good.
It is not necessary to order fancy tube brands that cost thousand dollars! This is quality only for short term gain as eventually down the line you would have to replace all the tubes again, therefore there really is no super tube out there.

2. re-order the KT120's, and replace all 4 output tubes. Keep the three other KT120's as back ups, and change as and when required. For example when it cannot be biased properly as you have indicated. Also hold on to the 6550's, this will allow you to have spare tubes just in case a full replacement set is required...

3. By any means- do NOT mix and match tube types- KT120 with 6550 and so on... only use one type at a time (I think you would already know this).
Believe me there are some so called experts who have done this and even swapped tubes whiles the amps were on- have ended up with the fire brigade!

4. Try to get hold of a set of KT88's. Compare the sound of both the KT88 and the KT120- you will be quite surprised!

The KT88 is similar to the EL34 but with added warmth in the midrange, better mid bass slam and very palpable imaging. Lets you sort of reach out and touch the performers... The KT120 takes this whole experience to another level but with a very slight diminished midrange. The KT120 has far greater dynamics, is a more powerful power beam tetrode, has solid impact in the bass, holds the soundstage together extremely well, even on loud passages, and delivers a sort of "fuller sound". Some have found this characteristic to be more bloated, and have preferred the 6550. Some even still prefer the EL34 or the KT88 for that matter. Hence, why McIntosh still uses the KT88 widely. But ARC and CJ now use the KT120 extensively and ARC has also introduced amplifiers using the KT150.

I used all types quite extensively, and for my tastes, since I am not a bass freak, I prefer the subtleties in the highs, the finer details in the mids, the finer resolution in the mid bass, and a well balanced sound that allows me to relax- therefore I have ventured back to the EL34. This is the main reason why I have ordered the CAV45, and another reason why I like the ARTsa in Triode mode so much that uses EL34's.

You cannot use EL34's in the MV60SE, due to the circuit being different for the mains output supply. The standard version of the MV60 does use EL34's, and this was one superb sounding amplifier with the right load. I first heard a MV60 driving a pair of Quads 989's and it was remarkable. I later went on towards the SE version and then so called upgraded to KT120's but I always missed that midrange magic the EL34 can produce. And on Quads or any other stats such as Martin Logan's, this is simply superb!

Let us know how you go, and what you decide with eventually. Who know's you might actually prefer the KT120 according to your listening tastes.
Cheers, RJ
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Re: CJMV60SE

Post by TONEPUB »

Actually, driver tubes usually outlast power tubes by a considerable margin. The NOS tubes are more expensive, always sound "different" and whether that's "better" or not to you is one thing, but where a set of $50 EH tubes might go 5000 hours a $300 set of NOS tubes might go 40-50 thousand hours. They made em a lot better in the old days and the consistency from batch to batch was much better.

I just put new KT-120s in my MV60 SE, and I listen a lot for work, so I'll be curious to see how long these last. Past CJ amps (the MV-50, MV-52 and MV-55 all seemed to go about 2000 - 3000 hours on a set of power tubes. When they no longer hold bias, that's when it's time to get new ones. The driver tubes rarely if ever fail, they usually just get kind of weak, and lose a bit of their "sparkle" on the top end.

My experience with every CJ power amp I've owned (and ARC for that matter) has usually been that the driver tubes wear out at the rate of 1-2 sets of power tubes, if you're not spending the big bucks on NOS. I've got an MV-50 here with Telefunkens that has run for about 12 years and the driver tubes still test at about 95%. So there you go.

As mentioned, Kevin Deal at Upscale is a great resource and has a huge stock. It's always a good idea to drop him a note before you buy, explaining what your putting the tubes in as some amplifiers and preamps have different synergies with different tubes.
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shag57
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Re: CJMV60SE

Post by shag57 »

Assuming you listened to your Cj for 2 hours each day x 30/month x 11......still much less than 1000 hours. I wouldn't waste money purchasing a set of 4. Replacing the good one should work / sound just find. Now if you had 2000 or more hours on all the power tubes I would change them all. As for the other tubes, my experience has been like "tonepub" they should last through several sets of power tubes. Tubes are a funny thing, I've been using them in my many guitar amps since 1971. I've had NOS tube fail within days and had new tubes last for years. The one constant is that most of them will short out in the first 10-15 hours.....so if you purchase tubes burn them in right away for 15-20 hours.......most companies will not offer a replacement after 30-60 days. Enjoy.
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