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6SL7 VS 6SU7 VS 6188 SETTING THE RECORD STRAIGHT

75.83.55.174
Posted on July 19, 2024 at 15:56:21
MP62
Dealer

Posts: 91
Location: CA
Joined: November 15, 2020
 I have been reading up on the 6SL7 Type tubes - specifically, the 6SU7GTY, the 6SL7GT and the 6188 tube.

While the 6SU7GTY is commonly recognized as a premium 6SL7GT with a micanol base (that does not absorb water vapor and is a very good RF insulator) and factory matched triodes, the 6188 is often referenced as being the same as the 6SU7GTY.

Like the 6SU7GTY, the 6188 does have the micanol base and the factory matched triodes, but the advantage they have over the 6SU7GTY is the plate impedance - which is about 50% lower in the 6188 (25K Ohms vs 50K Ohms).

That makes a huge difference in drive capability - especially with a 300B tube. Likely, the 6188 drives the 300B better than any 6SL7 type tube ever made!

 

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RE: 6SL7 VS 6SU7 VS 6188 SETTING THE RECORD STRAIGHT, posted on July 19, 2024 at 16:15:45
Tre'
Industry Professional

Posts: 17554
Location: So. Cal.
Joined: February 9, 2002



I have some 6188s. I'll have to test them.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

The 6su7gty also has a plate resistance of 44K, posted on July 19, 2024 at 19:16:07
Tre'
Industry Professional

Posts: 17554
Location: So. Cal.
Joined: February 9, 2002



.
Have Fun and Enjoy the Music
"Still Working the Problem"

 

Drive Capability, posted on July 19, 2024 at 22:14:12
Triode_Kingdom
Audiophile

Posts: 10181
Location: Central Texas
Joined: September 24, 2006
 "That makes a huge difference in drive capability"

If that's the goal, two low-Rp triodes in cascade will perform better. The second in the series could also be choke loaded to maximize the voltage swing.

 

RE: The 6su7gty also has a plate resistance of 44K, posted on July 27, 2024 at 18:13:06
MP62
Dealer

Posts: 91
Location: CA
Joined: November 15, 2020
 I saw that too!

Still Gordon of Wavelength noted this in an interview with Stereophile-

"But the 6188s are actually a little different. The plate impedance of a 6SL7 is roughly 50k ohms, but the 6188 is more like 25k ohms, and so it's got a better drive capability. It's an extremely nice tube—detailed and very fast. Because of the low plate impedance and high gain, it drives the 300B better than any other 6SL7 we've ever tried, including the 5691."

 

RE: The 6su7gty also has a plate resistance of 44K, posted on July 29, 2024 at 07:58:27
Tre'
Industry Professional

Posts: 17554
Location: So. Cal.
Joined: February 9, 2002
 The data sheets for the 6su7gty, 6188, 6113 and the 6sl7 all show a plate resistance of 44K
I don't know why Gordon would have said what he said.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: The 6su7gty also has a plate resistance of 44K, posted on July 29, 2024 at 10:13:43
MP62
Dealer

Posts: 91
Location: CA
Joined: November 15, 2020
 I hear you and I read the same, so I emailed Gordon - here is his response:

The 6188 is a much better tube. That was used in the original Cardinal
and the new Cardinal ST. I never had many of the Tung Sol so I really
can't comment on how good they were. I have a couple hundred of the
Sylvania 6188 and the 6SL7WGT and the 6188 have so much better drive and
detail in my circuit.

 

RE: The 6su7gty also has a plate resistance of 44K, posted on July 29, 2024 at 13:03:41
Tre'
Industry Professional

Posts: 17554
Location: So. Cal.
Joined: February 9, 2002
 "much better drive" To my understanding that would indicate a lower plate resistance yielding a lower output impedance for the stage (all other things being the same).

I wonder why the datasheet doesn't reflect that?

It would be easy enough to measure the output impedance of a 6sl7 stage with a 6sl7 and then a 6188 in there.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: The 6su7gty also has a plate resistance of 44K, posted on July 29, 2024 at 15:03:02
PakProtector
Audiophile

Posts: 12388
Joined: May 14, 2002
 IIRC, the esteemed Mr. Rankin also had some issue with what sort of loading a PP output transformer applies.

I would suspect just a simple bit of mis-translation he picked up. An overlay of plate curves would show the difference. I have a few 6188's and a handful of 6SU7GTY and ooodles of 6SL7's. When I had an amp with a LTP input stage phase splitter, all of them biased up in a group. General random variation IOW... :)

Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: The 6su7gty also has a plate resistance of 44K, posted on July 31, 2024 at 23:13:40
MP62
Dealer

Posts: 91
Location: CA
Joined: November 15, 2020
 Anything is possible.

I did conduct a few preliminary listening tests between the 6SU7GTY Circa 1959 and the 6188 Circa 1972. Here are my findings:

1. The 6188 puts out greater DB on the same songs/passage compared to the 6SU7GTY by 2.5 DB - 3 DB.
2. The 6SU7GTY had a slightly "thicker" sound - in the mids especially.
3. The 6188 were very slightly more transparent, but thinner sounding in the mids. The highs seemed more extended.
4. The two tube types sounded very similar!

 

Cascaded triodes to achieve a pentode without feedback? , posted on August 1, 2024 at 02:46:52
Cleantimestream
Audiophile

Posts: 7579
Location: Kentucky
Joined: June 30, 2005
 !
The Mind has No Firewall~ U.S. Army War College.

 

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