KT 88 Driver Stage Alternatives.

[AP@1992]

The KT88 tube has a punchy & incisive sound....

No brand of KT88 will mimic a 300B

If you are looking for a vastly more mellow sound, you will probably need yo change your amp to one that uses different output tubes... these will most probably be lower powered output tubes.

Within the KT88 sound signature boundary, I would recommend the 6550 Tube.

The 6550 is electrically Identical to the KT88, and is the USA's equivalent of the KT88.

The 6550 tube tames the bite of the KT88, leaving the same drive & punch.

Thank you for your suggestion.

I am currently playing around with the input/driver stage to see if I can get tame the KT88's. I will look into a 6550 or a 6CA7 going forward. And yes, KT 88 do have a signature sound which lowered powered tubes can match and vice versa.

 

[reignofchaos]

I have a set of KT88 (shuguang) and a set of NOS GE 6550 tubes for my amp. The GE tubes are super expensive but far superior to the KT88. More resolution across the board and much tighter bass

 

[AP@1992]

I have a set of KT88 (shuguang) and a set of NOS GE 6550 tubes for my amp. The GE tubes are super expensive but far superior to the KT88. More resolution across the board and much tighter bass

The shuhuang, I also felt they are inferior. I run Sovtek KT88. They are a better made amongst the KT88's

 

[reignofchaos]

The shuhuang, I also felt they are inferior. I run Sovtek KT88. They are a better made amongst the KT88's

Yes they aren't the best - looking to get something better but they are ok as a daily driver. For special occasions I use the GE 6550.

However the best KT88 - the NOS Genalex Gold Lions which are the best go for obscene money. Apparently the reissues by new sensor aren't anywhere as good and also have short lives.

 

[yogibear]

Try Sovtek or Svetlana 6550. They should be good. Nos available.

 

[AP@1992]

Yes they aren't the best - looking to get something better but they are ok as a daily driver. For special occasions I use the GE 6550.

However the best KT88 - the NOS Genalex Gold Lions which are the best go for obscene money. Apparently the reissues by new sensor aren't anywhere as good and also have short lives.

Obscene .

In many posts regarding my specific amp, there is an unanimous feeling that the best out there is the KT 88 GG Lions or its 6550 NOS.

My amp has a spirited character, this is independent of the KT 88's own signature. So in search of a tamer/milder tube which doesn't put out a puchy, incisive show.

 

[AP@1992]

Try Sovtek or Svetlana 6550. They should be good. Nos available.

Someday when they are not obscenely prized....

 

[reignofchaos]

Anything with NOS in its name is obscenely priced these days.

Prices of tubes has more than doubled since the Ukraine war.

 

[Hari Iyer]

EH is heavenly for the KT88.

 

[AP@1992]

Update on the tube rolling with Cayin AT88-mk2

System 1: Kt88 Sovtek + Stock 6ns7 and 6sl7
Sound had slam and punch. Bass was terrific, so was the treble. Overall the sound was detailed, clear and precise with great separation of instruments. The midrange, particularly voices were so crystal clear and tangible that it felt like a centre channel is installed. However, the voices sound dry, without a lot of texture and kind of tiny and not very intimate. There was total lack of warmth with the voices as well. With certain tracks voices had a harshness and sort of sibilant.

System 2: Kt88 Sovtek + Russian NOS 6H9C + 6H8C
All the pro’s of system 1 remained. However the midrange, particularly the voices had bit more warmth. Smoothness also increased. The voices sounded little bigger and lil more forward and were slightly more intimate.

System 3: Kt88 Sovtek + Russian NOS 6H9C + PS Vane UK 6NS7

All the pros of system 2 remained same. Additionally midrange warmth increased even more. Voices now had a nice texture to them and they no longer sounded tiny. They sounded more open, big and nicely forward and intimate.

At this point, I realised I have matched Quad of PS vane El34C lying unused, which came as stock with my Boyuurange.

System 4 PS EL34C+ Russian NOS 6H9C + PS Vane UK 6NS7

Sounded very different. That warm, smooth tone of EL34 made its presence felt. Voices had a lot of texture, Sounded big, warm, smooth and nicely forward. Bass articulation, separation of instrument, treble extension, clarity, pace, punch small were all less than System 3, but with rights songs this rich, warm, and lush tone is really addictive. Midrange/voices clarity was also great and there was nothing to be desired, but this was not at the same level as system no. 3 which was in some other level.

To put it in a “philosophically audiophile” lingo, System 3 pleases the mind whereas system 4 pleases the heart.

Also, Cayin A88T Mk2 , in general, and irrespective of the kinds of tubes I put, did a great job with bass, mid-range clarity (both voices and instruments) and treble performance. I am really surprised at the quality of these amps. Very well made amp too. The current iteration i.e. CS-88A is exorbitantly priced though.

Lastly, amazed at how tube rolling can meaningfully effect and get you the sound you prefer.

 

[Yelamanchili manohar]

Update on the tube rolling with Cayin AT88-mk2

System 1: Kt88 Sovtek + Stock 6ns7 and 6sl7
Sound had slam and punch. Bass was terrific, so was the treble. Overall the sound was detailed, clear and precise with great separation of instruments. The midrange, particularly voices were so crystal clear and tangible that it felt like a centre channel is installed. However, the voices sound dry, without a lot of texture and kind of tiny and not very intimate. There was total lack of warmth with the voices as well. With certain tracks voices had a harshness and sort of sibilant.

System 2: Kt88 Sovtek + Russian NOS 6H9C + 6H8C
All the pro’s of system 1 remained. However the midrange, particularly the voices had bit more warmth. Smoothness also increased. The voices sounded little bigger and lil more forward and were slightly more intimate.

System 3: Kt88 Sovtek + Russian NOS 6H9C + PS Vane UK 6NS7

All the pros of system 2 remained same. Additionally midrange warmth increased even more. Voices now had a nice texture to them and they no longer sounded tiny. They sounded more open, big and nicely forward and intimate.

At this point, I realised I have matched Quad of PS vane El34C lying unused, which came as stock with my Boyuurange.

System 4 PS EL34C+ Russian NOS 6H9C + PS Vane UK 6NS7

Sounded very different. That warm, smooth tone of EL34 made its presence felt. Voices had a lot of texture, Sounded big, warm, smooth and nicely forward. Bass articulation, separation of instrument, treble extension, clarity, pace, punch small were all less than System 3, but with rights songs this rich, warm, and lush tone is really addictive. Midrange/voices clarity was also great and there was nothing to be desired, but this was not at the same level as system no. 3 which was in some other level.

To put it in a “philosophically audiophile” lingo, System 3 pleases the mind whereas system 4 pleases the heart.

Also, Cayin A88T Mk2 , in general, and irrespective of the kinds of tubes I put, did a great job with bass, mid-range clarity (both voices and instruments) and treble performance. I am really surprised at the quality of these amps. Very well made amp too. The current iteration i.e. CS-88A is exorbitantly priced though.

Lastly, amazed at how tube rolling can meaningfully effect and get you the sound you prefer.

Thanks a ton for the insightful and excellent write up

Tube amp designs have been out there for decades. And their circuits are simple. With small but meaningful modifications being done to the circuits overtime. So, there is no rocket science involved in the same. And component quality decides the end sound quality in these implementations, without the need for reinventing the wheel. And the chinese have the advantage of cheaper labour and component costs compared to the west. So they can make a tube or SS amp of comparative quality for a lot less. Companies like Cayin, Willsenton, LM, Shanling, Reisong, Mingda and many more are all making excellent and comparable amps to the west. Good luck trying to get a point to point hand soldered amp made in the west. The labour itself will be a scary sum.

 

[AP@1992]

T

Thanks a ton for the insightful and excellent write up

Tube amp designs have been out there for decades. And their circuits are simple. With small but meaningful modifications being done to the circuits overtime. So, there is no rocket science involved in the same. And component quality decides the end sound quality in these implementations, without the need for reinventing the wheel. And the chinese have the advantage of cheaper labour and component costs compared to the west. So they can make a tube or SS amp of comparative quality for a lot less. Companies like Cayin, Willsenton, LM, Shanling, Reisong, Mingda and many more are all making excellent and comparable amps to the west. Good luck trying to get a point to point hand soldered amp made in the west. The labour itself will be a scary sum.

Thank you.

 

[coaltrain]

@AP@1992
Thanks for your detailed listening impressions.
I must confess, I’ve recently been tempted to try EL34s in my amp out of sheer curiosity. Your observations have saved me some money
On another note, I would urge you to try different NOS options for the preamp stage. As I’d mentioned earlier, according to Cayin the 6SL7 has the greatest sonic impact in your amp; and the Russian and Chinese tubes are usually brighter and drier. I’m pretty sure that any NOS tube of European ancestry will give you the midrange magic you seek. Do check with @yogibear for some sound advice, and also the link below:

6SL7 VACUUM TUBES IN STOCK

@Yelamanchili manohar
Totally agree with your take on Chinese tube amps.
Of the brands you mention, Cayin and Line Magnetic in particular are taking their lineups to the next level. Check out Cayin’s latest flagship that incorporates KT170s in a 2 chassis setup:

 

[yogibear]

It’s the onus of the designer / maker of the amp to clearly specify tubes to be used. 6SL7 is high gain and low current tube and 6SN7 is opposite. So the real sonic impact will depend on the biasing of the amp. I would still urge to try 6CA7 tubes in place of KTs or 34. And driver stage tube as stated by the amp maker.

My own favorite driver stage tubes are 6SN7 (Russian) and 6N2P. I find 6CA7 to be more pleasant sounding than EL34 in every way. Details and instrument separation was staggering.

 

[Yelamanchili manohar]

@AP@1992
Thanks for your detailed listening impressions.
I must confess, I’ve recently been tempted to try EL34s in my amp out of sheer curiosity. Your observations have saved me some money
On another note, I would urge you to try different NOS options for the preamp stage. As I’d mentioned earlier, according to Cayin the 6SL7 has the greatest sonic impact in your amp; and the Russian and Chinese tubes are usually brighter and drier. I’m pretty sure that any NOS tube of European ancestry will give you the midrange magic you seek. Do check with @yogibear for some sound advice, and also the link below:

6SL7 VACUUM TUBES IN STOCK

@Yelamanchili manohar
Totally agree with your take on Chinese tube amps.
Of the brands you mention, Cayin and Line Magnetic in particular are taking their lineups to the next level. Check out Cayin’s latest flagship that incorporates KT170s in a 2 chassis setup:

Thanks for sharing that video, that cayin is grogeous

 

[Hari Iyer]

I agree with "reignofchaos'" Post #22. A NOS GE 6550 truly is very neutral / good.

In Post #11, you tell us your amp has adjustable manual biasing. Great!

There are several factors that weigh on the sound of a tube amp. An obvious one is the choice of Vacuum tubes. Less obvious, but possibly equally important, is how precusely, and at what level, the Finals tube is biased. No one has mentioned this at all in this thread ! Let us not be oblivious.

Most Manufacturers specify high current operation, possibly to meet advertising claims of power output. Done often, with little consideration of " other " factors.

What unwanted negative factors occur, with high-current Final tubes' operation???


1) Unwanted thermal stress on the metallurgy inside the tubes. (It actually sounds stressed.)

2) Stress on the amp's entire Power Supply, under dynamic conditions, as reflected / heard directly in the sound of the high-current-draw Finals' tubes.


You can change tube-types until you are blue in the face, or you are broke.

But you are not fully hearing any of these Final tubes in your amplifier until you manually optimize by ear, each tube's operating current.

In many cases (versus a Manufacturer's stock settings), an amp will sound better, more relaxed, less stressed, more natural, with reduced current in the Finals.

YOU alone must carefully take control of this!

If your amp has a manual bias adjust pot, you can easily, manually adjust the bias current lower in steps. Listen to music playback, with each increment, to hear these differences. YOU need to select the bias level that sounds best overall to you, on your speakers, when playing back your music. It will, almost always, be lower than commonly thought. Listen and decide.

Sometimes, the optimal sound is heard at about 62% of the Finals tube Maximum power rating ( AKA maximum "plate dissipation"). This percentage happens to be nature's "Golden Ratio". One does not use a scope etc. for such determinations, but rather, your ears. Incrematically, and systematically lower the Finals bias by your own ear, until you discover the best sounding setting - playing the music back to you.

That setting becomes your amplifier's new long-term tube bias / use point!!

In almost every case, you will receive a big advantage of much longer tube life, ( perhaps with a KT88 tube, up to ten times ) while hearing your amp's playback in total, at its sonic-best in your own home.

In my KT88 amp, with 6FQ7 driver, I run my KT88 happily at only 43.5mA and only 12.45 Watts of plate dissipation. This is versus the tube's published 42 Watts of rated maximum plate dissipation.

 

[grindstone]

...

In my KT88 amp, with 6FQ7 driver, I run my KT88 happily at only 43.5mA and only 12.45 Watts of plate dissipation. This is versus the tube's published 42 Watts of rated maximum plate dissipation.

Hey, if it's not double-top-secret, is that into 5K? So maybe ~280V p-k?

 

[Hari Iyer]

Hey, if it's not double-top-secret, is that into 5K? So maybe ~280V p-k?

Yes it's 12.18 watt dissipation to be precise. Direct Couple voltage is 205vdc

 

[AP@1992]

@AP@1992
Thanks for your detailed listening impressions.
I must confess, I’ve recently been tempted to try EL34s in my amp out of sheer curiosity. Your observations have saved me some money
On another note, I would urge you to try different NOS options for the preamp stage. As I’d mentioned earlier, according to Cayin the 6SL7 has the greatest sonic impact in your amp; and the Russian and Chinese tubes are usually brighter and drier. I’m pretty sure that any NOS tube of European ancestry will give you the midrange magic you seek. Do check with @yogibear for some sound advice, and also the link below:

6SL7 VACUUM TUBES IN STOCK

@Yelamanchili manohar
Totally agree with your take on Chinese tube amps.
Of the brands you mention, Cayin and Line Magnetic in particular are taking their lineups to the next level. Check out Cayin’s latest flagship that incorporates KT170s in a 2 chassis setup:

I agree. The input/pre amp tubes do have a huge impact. I also felt that the UK 6NS7 by PS Vane was of the main change which brought that midrange forwardness, depth and intimacy in my system. The same was than bolstered by the EL 34 C from PS Vane.

As per company specs, that UK 6NS7 by PS vane is indeed a replica of the 6NS7 of old European mades


So far as 6sl7, I am yet to try anything better than the h Russian NOS's.

Will update on this, if I can lay my hands on some NOS 6sl7 european makes.

 

[AP@1992]

I agree with "reignofchaos'" Post #22. A NOS GE 6550 truly is very neutral / good.

In Post #11, you tell us your amp has adjustable manual biasing. Great!

There are several factors that weigh on the sound of a tube amp. An obvious one is the choice of Vacuum tubes. Less obvious, but possibly equally important, is how precusely, and at what level, the Finals tube is biased. No one has mentioned this at all in this thread ! Let us not be oblivious.

Most Manufacturers specify high current operation, possibly to meet advertising claims of power output. Done often, with little consideration of " other " factors.

What unwanted negative factors occur, with high-current Final tubes' operation???


1) Unwanted thermal stress on the metallurgy inside the tubes. (It actually sounds stressed.)

2) Stress on the amp's entire Power Supply, under dynamic conditions, as reflected / heard directly in the sound of the high-current-draw Finals' tubes.


You can change tube-types until you are blue in the face, or you are broke.

But you are not fully hearing any of these Final tubes in your amplifier until you manually optimize by ear, each tube's operating current.

In many cases (versus a Manufacturer's stock settings), an amp will sound better, more relaxed, less stressed, more natural, with reduced current in the Finals.

YOU alone must carefully take control of this!

If your amp has a manual bias adjust pot, you can easily, manually adjust the bias current lower in steps. Listen to music playback, with each increment, to hear these differences. YOU need to select the bias level that sounds best overall to you, on your speakers, when playing back your music. It will, almost always, be lower than commonly thought. Listen and decide.

Sometimes, the optimal sound is heard at about 62% of the Finals tube Maximum power rating ( AKA maximum "plate dissipation"). This percentage happens to be nature's "Golden Ratio". One does not use a scope etc. for such determinations, but rather, your ears. Incrematically, and systematically lower the Finals bias by your own ear, until you discover the best sounding setting - playing the music back to you.

That setting becomes your amplifier's new long-term tube bias / use point!!

In almost every case, you will receive a big advantage of much longer tube life, ( perhaps with a KT88 tube, up to ten times ) while hearing your amp's playback in total, at its sonic-best in your own home.

In my KT88 amp, with 6FQ7 driver, I run my KT88 happily at only 43.5mA and only 12.45 Watts of plate dissipation. This is versus the tube's published 42 Watts of rated maximum plate dissipation.

This is a new direction of advice. Will definitely play around with the biasing and report my changes.