Tube rolling for Cayin A88t MK2 limited edition.

[Rayq]

Hi! Everyone, 

 

I just bought a new tube amplifier, Cayin A88t mk2 limited edition 6550. I would like to ask for suggestions on tube rolling. 

 

1) Would power tube rolling has more effect then driver tube? 

2) My amplifier has 6550 as stock power tube. Would it be better to upgrade to kt88 tube? What will be the difference between 6550 vs kt88?

3) what is the recommended tube for the driver tube rolling?

4) which power tube rolling is recommended?

 

This is my 1st post here. Thanks so much for the reading the post and advice! 

[muon*]

Welcome, Raymond

 

Tube rolling is personal, some like one type of tube some another, same for select replacements of any given tube type. Generally folk suggest that the small signal tube changes are more noticeable though myself I'm undecided and think it depends on the circuit and tubes swapped in.

 

Personally I prefer the 6550's to the KT88's, but my staple is the EL34 in my amp as It's designed for it.

 

I guess I noticed more with power tubes as I have a limited choice where 6H30 in fron are concerned.

Edited November 29, 2020 by muon*

[xlr8or]

Congratulations on the purchase of the Cayin A88T Mk2 SE tube amplifier - they're are certainly going to be some fun times ahead.

 

Just adding to Ian's comments, the way in which the circuit has been designed to run a specific power tube type will determine the best power tube type to use in circuit. In this specific case this looks to be the KT88. Between different KT88 makes (both vintage and modern) you'll find changes in sound signature - some you will like more than others. However, moving to a 6550 will result in a larger change in sound signature that you may well prefer. Certainly this is something worth trialling in your tube rolling journey. In particular, if the power tube can be biased up and down.

 

Normally rolling the input tube followed by the power tube and then the driver tube will have the largest influence in changing the sound signature; in that order.

 

Here is a general blurb of how the KT88 versus the 6550 sounds. The KT88 will sound more extended in the top end with harmonically accurate mids and bottom end. In contrast, the 6550 will sound more dynamic and warmer across the midband with a more fleshed out bloom. The bottom end and mids will also have a certain level of pace and rhythm when compared to the KT88. Both tube types have their strengths and weaknesses. However, the strengths will outweigh the weaknesses in a big way.

Edited November 30, 2020 by xlr8or

[LX_4_MAN]

Just to add some options in the a88t has a little switch on the back to switch to configuration to run el34's if you would like to head in that direction 

[Rayq]

Thanks so much for the reply! Really a very friendly and helpful forum that which I am so glad to join in.

 

After playing it for a few hours, it starts to open up and i quite like the stock 6550 and the stock input tubes. 

 

Thought of tube rolling but now i don't where to start. Thinking of trying KT88 tube or should i just upgrade the 6550 tube. 

 

Or should i just upgrade the input or driver tube. I don't know which is input tube? 6SL7 or 6SN7. 

 

1st time having tube amplifier so there are many things for me to explore. I seem to like this amplifier than my SS Musical Fidelity M5si as the mid is fantastic on Cayin A88t mk2 even though it is not burn-in yet. No regret of buying it. 

[xlr8or]

Let the amp burn in for a minimum of  200 hours before assessing the sound signature of each tube. Allow the amp to warm up for 90 minutes for optimal assessment. The 6SL7 is the input tube and would be best to roll first. I'm biased towards vintage tubes and would recommend a 1940's or 1950''s Tung Sol 6SU7GTY black coated glass brown micanol base tube for this position.

 

Reference photo attached.

 

Edited November 30, 2020 by xlr8or

[aussievintage]

7 hours ago, Rayq said:

Thought of tube rolling but now i don't where to start. Thinking of trying KT88 tube or should i just upgrade the 6550 tube. 

 

Or should i just upgrade the input or driver tube. I don't know which is input tube? 6SL7 or 6SN7. 

 

 

If it were me, I would stick with the 6550 tubes (which I already know I like), and try different input tubes.  That will make the most difference and save you a lot of money.  Also, there's lots more options that way.

[Rayq]

I am thinking of trying out the KT88 power tube rolling first then input or driver tube.

 

Currently, although my amplifier is still new and not burn-in but i can hear that i like the vocal and the warm sound of the 6550 but the clarity or some vocalist like Diana Krell doesn't sound right. It is not a accurate assessment for the amplifier is still new. So far, i quite like 6550. 

 

My logic is that i don't know how KT88 sounds on my amp. If it is better than 6550 then i will try to look for 6sl7 and 6sn7 that pairs well with the power tube that i like. 

 

Will this be good? 

[muon*]

Be patient.

 

Lots of other parts in the amp are also running in apart from the tubes.

 

How many hours does the amp/tubes have up approximately?

[Rayq]

Hi Muon,

 

Maybe around 15 hrs only.

 

You are right, I am not patient enough. I always eager to optimise or tune to my liking. Keep thinking stock tubes not good enough to hear the capability of the amplifier. 

 

How do people usually tube rolling? Start from input/driver tube or power tube?

[aussievintage]

5 hours ago, Rayq said:

How do people usually tube rolling? Start from input/driver tube or power tube?

 

The input.  The further up the chain towards the source, the more you will hear the change.  Many people are rolling preamp tubes ahead of their power amp.

 

6 hours ago, Rayq said:

Currently, although my amplifier is still new and not burn-in but i can hear that i like the vocal and the warm sound of the 6550 but the clarity or some vocalist like Diana Krell doesn't sound right. It is not a accurate assessment for the amplifier is still new. So far, i quite like 6550. 

 

It could just be the preamp valve causing this.  

 

6 hours ago, Rayq said:

My logic is that i don't know how KT88 sounds on my amp. If it is better than 6550 then i will try to look for 6sl7 and 6sn7 that pairs well with the power tube that i like. 

 

My logic would be that you should start with the preamp 6SL7. You may find that's all you ever need to do and changing power tubes is expensive. 

[muon*]

These are one of the best sounding 6SL7 variants, very detailed but liquid smooth and very open and not aggresive.

https://www.ebay.com/itm/2PCS-6N9S-6H9C-6SL7-1579-MELZ-TUBES-NOS-METAL-BASE-TESTED-RARE-50S-/143326808606

 

The Metal base MELZ from the 1950's

 

Might find them cheaper somewhere on ebay, usually come from Ukraine or the Russian Federation.

Edited December 2, 2020 by muon*

[Rayq]

Today, i bought the Tung sol 6sl7gt Black glass NOS and Raytheon JAN CRP 6sn7gt VT231.

 

The vocal is very clear and i don't hear the vocal sounds too warm or bloated. It does sound more accurate. But now, some music with vocal sounds too sterile. Maybe it is the recording is not good so it is able to hear it.

 

Will the new tube i bought today will still change the sound signature when further burn-in?

 

Now, it seems i like the 6550 as i think if i use KT88, it might be even too sterile. Might even consider EL34. But i think i will stick with 6550. Might consider changing the power tube for 6550. The current sound is good as the bass is good and warm enough with good and accurate vocal.

 

 

Edited December 2, 2020 by Rayq

[muon*]

All new and NOS (new old stock) tubes will have an initial burn in time where the sound will change noticably, usually around 30+ hours.

[xlr8or]

Patience is a virtue with tube rolling. You'll find the tonal character changing with time when you're using NOS tubes. If you're seeking a quicker turnaround time in hearing a tonal change then UOS tubes maybe your best bet. It takes approx 200 hours for NOS tubes to burn in. As mentioned prior, allow 90 minutes warm up time before assessing the tonal character of a tube.

 

If the 6550's don't suit and are too clinical sounding then yes go to the EL34's to bring out more midrange magic.

 

There are a couple of things to further consider in your specific case. Am I listening in triode or ultralinear mode? Have I also biased the power tube change? These parameters will change the tonal character of the amp further. Triode mode may sound more accurate and pleasing with a loss of dynamics. Ultralinear the reverse. Not biasing the power tubes correctly will also have a consequence - too cold or too hot sounding if not dialled in correctly.

Edited December 2, 2020 by xlr8or

[Rayq]

Today, i play with the bias. There is a zone that i cannot set under or beyond the zone. I notice that that when i set the level a bit to the left instead of middle, the treble is not harsh or sibilance in the vocal. It sounds smooth and right to me. I don't know if the left is hot or cold in the bias but it is within the zone. Didn't expect the bias also have a effect on the sound. 

 

With this bias setting, i feel 6550 is good for me. I intend to buy the GE 6550A power tube from a seller which i read that it is discontinue. Many reviews raves about it. I don't want to miss the opportunity to get it.