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Octals-med mu, low plate R

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Posted on January 2, 2017 at 18:13:30
deafbykhorns
Audiophile

Posts: 648
Location: Florida
Joined: October 17, 2003
Well, I moved from the 76 driver looking for a med mu driver for the 300b-GM70
5687 didn't have enough gain, sounded ok but nothing like the 76
7788 oscillates like crazy (probably long alligator clip leads) sounded thin
6e5p with CCS so far has been the best, gain is perfect, low distortion and very neutral

Downside is my amp is drilled for octal, I do have an adapter but curious if anyone knows of an octal with similar characteristics of the 6E5P (low plate R, mu >30)

 

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I'm looking for an Octal driver (mu 40+) for a 300B SET as well..., posted on January 2, 2017 at 18:51:36
Ivan303
Audiophile

Posts: 34807
Location: Cadiere d'azur FRANCE - San Francisco
Joined: February 26, 2001
But not locked into a pure triode.





 

6SL7 with a MOSFET source follower, posted on January 2, 2017 at 18:55:28
Chip647
Audiophile

Posts: 1635
Location: The South
Joined: December 24, 2012
Or a 6SL7 into a 6L6GT and interstage

 

Make a nice socket insert and stick with 6e5p, posted on January 3, 2017 at 03:24:12
andy evans
Audiophile

Posts: 2927
Joined: October 20, 2000
No problem to make an insert to your octal sockets. See for example Thomas Mayer's designs. The picture shows a square insert, but you can make it round the same way. Looks nice and adds isolation.

 

RE: 6SL7 with a MOSFET source follower, posted on January 3, 2017 at 03:43:27
PakProtector
Audiophile

Posts: 11240
Joined: May 14, 2002
LOL...make the MOSFET's do double duty; stack two depletion-mode in cascode and take signal from the lower one's source, aka mu-follower...:)

Or, get off this octal-only idea and examine some of the fine 9-pin single triodes, either real triodes, or strapped pentodes.
cheers,
Douglas

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

 

Looks like the only way to get a little help around here..., posted on January 3, 2017 at 07:22:49
Ivan303
Audiophile

Posts: 34807
Location: Cadiere d'azur FRANCE - San Francisco
Joined: February 26, 2001
is to threaten to parallel a 6SL7? ;-)



 

RE: Octals-med mu, low plate R, posted on January 3, 2017 at 07:34:35
Lew
Audiophile

Posts: 8732
Location: Bethesda, Maryland
Joined: December 11, 2000
Maybe the 7788 "sounds thin" because it "oscillates like crazy" due to long leads, as you say. Not that I know for sure it would otherwise make you happy, but some do like it in LCR phono stages, etc.

 

RE: Octals-med mu, low plate R, posted on January 3, 2017 at 07:47:27
dave slagle
Manufacturer

Posts: 4745
Location: NYC
Joined: April 27, 2001
The 8213 is the obvious choice :-)

dave

 

Dang, nice low plate resistance..., posted on January 3, 2017 at 08:00:50
Ivan303
Audiophile

Posts: 34807
Location: Cadiere d'azur FRANCE - San Francisco
Joined: February 26, 2001
med mu, what's not to like?

Oh wait...



 

RE: I hear ya, posted on January 3, 2017 at 10:19:55
deafbykhorns
Audiophile

Posts: 648
Location: Florida
Joined: October 17, 2003
I wanted to avoid that and just wondering if there's any octals that do similar jobs.
Maybe not due to the size and structure of tube.
For now, I'm sticking with the 6E5P. It runs circles around the most all the 9 pins.
Too much plate resistance on the 6SL7 and gain is twice what I need unless I decide to change the GM70 to a 211 or 845

 

RE: Octals-med mu, low plate R, posted on January 3, 2017 at 10:21:36
Eli Duttman
Audiophile

Posts: 9363
Location: Monroe Township, NJ
Joined: March 31, 2000
Octal only is tough. Would that there was a 6SM7, whose characteristics were like either the 12AY7 or the 12AV7.

Perhaps some "trickery" will help. With its mu of 70, the 6SL7 has too much gain and it's a wimp. Buffering the plate with a DC coupled ZVN0545A MOSFET disposes of the wimp issue. You could set up 6SL7 LTPs to reduce the effective mu to 35. A possible plus to the LTP is the ability to select absolute polarity.

Eli D.

 

RE: Octals-med mu, low plate R, posted on January 3, 2017 at 10:37:06
deafbykhorns
Audiophile

Posts: 648
Location: Florida
Joined: October 17, 2003
Looks like my 6E5P without the G2!
Not an octal but I'll try it out

Edit: Do you buy up all the 8213's Dave? Not an easy tube to find...

 

RE: 6SL7 with a MOSFET source follower, posted on January 3, 2017 at 10:38:26
deafbykhorns
Audiophile

Posts: 648
Location: Florida
Joined: October 17, 2003
Yeah, not something I would be interested in doing.
Dave Slagle had a nice looking tube to try.

 

RE: "Not an octal...", posted on January 3, 2017 at 10:42:03
Ivan303
Audiophile

Posts: 34807
Location: Cadiere d'azur FRANCE - San Francisco
Joined: February 26, 2001
I'm counting eight pins. :-)



 

RE: And an E8 base but a nice looking triode, posted on January 3, 2017 at 10:53:37
deafbykhorns
Audiophile

Posts: 648
Location: Florida
Joined: October 17, 2003
.

 

6SL7s are for bass players with Ampeg stacks.... (nt), posted on January 3, 2017 at 11:57:30
andy evans
Audiophile

Posts: 2927
Joined: October 20, 2000
.

 

RE: Octals-med mu, low plate R, posted on January 3, 2017 at 11:59:32
dave slagle
Manufacturer

Posts: 4745
Location: NYC
Joined: April 27, 2001
I believe I have the entire worlds supply of this tube in my stash... sadly so do you as I have never seen or heard of anyone who has seen one in person.

dave

 

RE: You dirty dog!!!, posted on January 3, 2017 at 12:52:39
deafbykhorns
Audiophile

Posts: 648
Location: Florida
Joined: October 17, 2003
You had me on a treasure hunt ;-)

 

RE: Octals-med mu, low plate R, posted on January 3, 2017 at 21:44:26
tube wrangler
Manufacturer

Posts: 1602
Location: USA
Joined: January 29, 2007
7788, connected triode, should give you
excellent performance.

There is a tendency to assume that when a tube oscillates,
it is the TUBE'S fault. It is usually a result of too much
internal wiring, wiring too long, and wiring too close to another
wire, or a component-- or wiring laced together-- THE WORST thing you can do!.

NEVER bundle ANY wire in with another wire! Remember all
those fancy pictures of spic & span Military and Ham Radio
construction-- all those wires neatly laced together with string?

This is exactly how NOT to build audio equipment. Make every wire separate from
everything else, and separate from any other wire. The farther apart they are, the better the results. Keep wires SHORT-- VERY short.

If you must run a wire across another wire, do it at right angles only.

Work in all 3 dimensions-- you can use silicone products or other
ingenious methods to have components and wire stay where it belongs...

If you get these layout principles right, you will stop unwanted oscillations because you will stop injecting unwanted signals into
the tube that is oscillating....

The use of a "grid-stopper" series resistor is sometimes used on
a tube's grid to damp-out oscillation. Use of this device-- of any
value-- is a sure-fire way to throw away most of an amp's fidelity.

Instead, use the tubes that others are afraid of because they sometimes
find them oscillating. These sound wonderful because they really respond to signal-changes-- they don't damp-out musical expression.

To keep them from oscillating, build the entire amplifier right.

The 7788 should be really good in this application. There is an article,
and discussion on using this tube as a driver, in the old Sound Practices literature-- the "B-52" S.E. amp.

The guy is pretty smart-- why not learn from him?

---Dennis---

 

LOL..., posted on January 5, 2017 at 06:58:01
PakProtector
Audiophile

Posts: 11240
Joined: May 14, 2002
let me know if you find one.

Look at the Russian 6S3 or 6S4. Single triode, 9-pin with mu a wee bit higher than a 6DJ8.
cheers,
Douglas

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

 

RE: LOL..., posted on January 6, 2017 at 08:23:07
Tre'
Industry Professional

Posts: 11955
Location: So. Cal.
Joined: February 9, 2002
I'm not sure anyone would be happy if they found one.

The datasheet says they are meant for cathode follower circuits.

My guess is they are not very linear.


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

 

There is a 6SM7 (well nearly), posted on January 23, 2017 at 16:36:01
Mike C
Audiophile

Posts: 1008
Location: Essex
Joined: November 23, 2000
The 6C8G is in my view 'the 6SM7 that never was'.
Octal with a top cap, mu just under 40, runs nicely at about 4mA and dissipation a bit under 1 watt. Pretty much midway between 6SL7 and 6SN7.

I use this in a mu stage as driver for my best SET amp. The mu stage runs about 10mA total current, from a low impedance, and will swing over 100V both ways, so it'll drive a typical power triode very well indeed.
And it sounds very good! Look at those curves ....

 

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