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Alternative Dynaco ST70 upgrade

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Posted on February 17, 2016 at 21:57:26
Gera
Audiophile

Posts: 244
Location: Illinois
Joined: April 23, 2000
 I've had a K&K board upgrade (triode mode) ST-70 for a few years. I like it lot but something evil inside me recently began to stir and I looked around other options. I found this suggestion by Joe Rasmussen who used it on an ST-70.
http://www.customanalogue.com/jlti_el34.htm
this has a so called "Virtual Triode Mode"



and L.E.M. module to "induce Permeability so it never drops below our defined level"




So now my question is does this make a worthy alternative upgrade that makes technical sense or can this be incorporated into my K&K ST-70 to further improve it's sound quality? Your thoughts on this modification?

Herman

 

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RE: Alternative Dynaco ST70 upgrade, posted on February 18, 2016 at 05:29:08
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 The "Virtual Triode Mode" output stage configuration seems to create a different bias point for the screen grid than connecting it through a diode to the plate. What voltage value of zener diode to use to get the best sound would require some experimentation to determine. You might find some info to this end amongst the wealth of info in the link. I suspect that the idea came from this link info.

I have no idea what the small "L.E.M." circuit board does, so I can't comment on the applicability of that.
Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Alternative Dynaco ST70 upgrade, posted on February 18, 2016 at 11:41:49
nerdorama
Audiophile

Posts: 439
Location: Eastern WA state
Joined: February 2, 2002
 Could be related to or directly from this idea:
http://www.t-linespeakers.org/tubes/triode-trick.html

I've done it several ways: a simple 100ohm resistor, a resistor with a diode, and with the Pearl triode trick. I don't really think the triode trick sounded different or better than the resistor with diode. I think the diode does make a small improvement over just a resistor.

John
De gustibus non est disputandum

 

L.E.M. circuit description, posted on February 18, 2016 at 22:34:39
Gera
Audiophile

Posts: 244
Location: Illinois
Joined: April 23, 2000
 Again, below is a quote from website but I bring it up because I would like to know if it makes sense and worth try to incorporate into the ST-70 with K&K board.

"Induced Permeability: This technology was in fact patented during the Second World War and then subsequently forgotten. What a pity. According to our foremost researcher on tube transformers, Menno Vanderveen (from the Netherlands and designer for companies like Plitron), the major shortcoming of tube output transformers is the lack of Permeability at low signal levels, leading to lack of resolution in a similar way to DACs (Digital to Analog Converters) suffer from at low levels (this fact will stun quite a few pro tube aficionados). High Permeability cores can be used to offset the problem, but these saturate at about half the power and the so-called amorphous cores are very expensive indeed. A 50 Watt transformer will be derated to 25 Watts or it distorts badly.

THE SOLUTION:
The solution is highly imaginative; make use an unused portion of the transformers bandwidth (very high frequencies) and then excite the transformer at a specific level that does no damage to the speaker and yet is high enough to stop the Permeability sliding to dangerously low levels below that. We also do not suffer from saturation and poor power performance as the transformer is not derated. The module fitted is called an L.E.M., Linearity Enhancement Module, and the result is to induce Permeability so it never drops below our defined level.

The result is superior definition and a marriage made in heaven when combined with Super Linear Triode Mode.

This combination, the Super Linear Triode and the L.E.M. is the crux of the story here, taking a modest tube amplifier and make it perform like little else out there does."

 

RE: L.E.M. circuit description, posted on February 19, 2016 at 12:50:15
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 I understand the principle of operation for this product, but I can't comment on its effectiveness, because I've never tried it. Things that sound like they should have a serious positive effect don't always have that kind of effect, and likewise, things that you don't at first think very likely to be effective are sometimes surprisingly positive. This is first and foremost an endeavor where much empirical work stands on the back of less knowledge than we like to believe we have.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: L.E.M. circuit description, posted on February 23, 2016 at 21:48:07
Gera
Audiophile

Posts: 244
Location: Illinois
Joined: April 23, 2000
 Hello Kevin,

Generally, I do not to like to ask for this kind of thing but the seller of this LEM module is willing to help me instruct on where to install it in the K&K version of the Dynaco. And he is asking to look at the schematic to identify where it would need to go. Now, I have the schematic in the manual but without your approval I will not disclose any part of it unless you agree or point to what I can and cannot disclose. I am interested in trying the LEM module but do not feel good to go for it without guidance from designer and approval from you. Also, I can blank out the component values if that makes a difference to you. Either case, let me know how you feel about this.
thanks,
Herman

 

RE: L.E.M. circuit description, posted on February 24, 2016 at 04:53:06
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 I have no problem with you sharing the schematic with the seller. Let us know how it works out, if you proceed.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: L.E.M. circuit description, posted on February 24, 2016 at 08:14:44
Gera
Audiophile

Posts: 244
Location: Illinois
Joined: April 23, 2000
 Thank you Kevin, will do!

 

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