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    What about KT-66?

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    MarcVBelgium

    Posts : 83
    Join date : 2013-12-06
    Age : 63
    Location : Antwerp, BELGIUM

    What about KT-66?

    Post by MarcVBelgium on Sat Apr 25, 2015 5:05 am


    Early last year, I found a Dynaco Stereo 80 (PANOR), normally designed for EL-34, but this one came with KT-66 (Shuguang).
    I did change these with Gold Lion KT66 and all driver tubes are now NOS.

    The amp sounds great (not like the ST-120, but still very good) and is a pleasure to look at. However, lately, I have been searching more information on EL-34 alternatives (I like "big" bottles) and this was 6CA7 and.... KT77, not KT66

    Can someone shed some more light on the interchangeability between EL-34/6CA7/KT77 and KT66

    The amp biases perfectly, but still I am wondering if putting KT66 on it is "right", doable and safe.

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: What about KT-66?

    Post by peterh on Sat Apr 25, 2015 7:39 am

    MarcVBelgium wrote:
    Early last year, I found a Dynaco Stereo 80 (PANOR), normally designed for EL-34, but this one came with KT-66 (Shuguang).
    I did change these with Gold Lion KT66 and all driver tubes are now NOS.

    The amp sounds great (not like the ST-120, but still very good) and is a pleasure to look at. However, lately, I have been searching more information on EL-34 alternatives (I like "big" bottles) and this was 6CA7 and.... KT77, not KT66

    Can someone shed some more light on the interchangeability between EL-34/6CA7/KT77 and KT66

    The amp biases perfectly, but still I am wondering if putting KT66 on it is "right", doable and safe.
    According to the datasheet from m-o they recommend G1 resistor <= 250kohm
    http://www.mif.pg.gda.pl/homepages/frank/sheets/086/k/KT66.pdf
    st-70 has 270kohm, it's on the thin line.

    MarcVBelgium

    Posts : 83
    Join date : 2013-12-06
    Age : 63
    Location : Antwerp, BELGIUM

    Re: What about KT-66?

    Post by MarcVBelgium on Sat Apr 25, 2015 1:08 pm

    According to the datasheet from m-o they recommend G1 resistor <= 250kohm
    http://www.mif.pg.gda.pl/homepages/frank/sheets/086/k/KT66.pdf
    st-70 has 270kohm, it's on the thin line.
    [/quote]

    Thanks for your comment.

    In the schematic of the Stereo 80, I can find the 270 kOhm resistor leading to the bias circuitry.
    Further than that, I have no clue, not being technical enough.

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: What about KT-66?

    Post by peterh on Sat Apr 25, 2015 2:07 pm

    MarcVBelgium wrote:According to the datasheet from m-o they recommend G1 resistor <= 250kohm
    http://www.mif.pg.gda.pl/homepages/frank/sheets/086/k/KT66.pdf
    st-70 has 270kohm, it's on the thin line.

    Thanks for your comment.

    In the schematic of the Stereo 80, I can find the 270 kOhm resistor leading to the bias circuitry.
    Further than that, I have no clue, not being technical enough.
    [/quote]
    That's on the spot.
    But i guess that if the tubes arn't driven into clipping it won't bee a problem.

    Bob Latino
    Admin

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    Join date : 2008-11-26
    Location : Massachusetts

    Re: What about KT-66?

    Post by Bob Latino on Sun Apr 26, 2015 9:07 am

    I have used KT66's in the original Dynaco ST-70 and a number of customers use them in the VTA ST-70. The KT66's IMHO are fine to use in either amp. The only downside to using modern KT66's is that they are expensive ... maybe 3 times the cost of EL34's. I have a feeling that the higher pricing involved in using KT66's may be slightly offset by increased tube life of a KT66 over an EL34. Personally, the best tube I have heard in the VTA ST-70 amp is the Gold Lion KT66. The Tubestore online store has a comparison of the various KT66's available today at the link below ...

    KT66 reviews at the Tubestore online

    Bob

    MarcVBelgium

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    Join date : 2013-12-06
    Age : 63
    Location : Antwerp, BELGIUM

    What about KT-66

    Post by MarcVBelgium on Sun Apr 26, 2015 2:04 pm

    Peter & Bob,

    Thanks, my mind is "at ease" now :-))

    Bob, for a quartet of high quality EL34's like TAD STR Premium I would pay the equivalent of 120 $ and the Gold Lion KT66 are about
    175 $ through Tube Amp Doctor in Germany. The Gold Lions have to be compared to the best EL-34 available. The 55 $ difference is IMHO justifiable.

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: What about KT-66?

    Post by sKiZo on Sun Apr 26, 2015 3:54 pm

    Just be aware that the "Gold Lions" that TAD sells are probably made by Shuguang.

    Not saying that's bad. The tubes are built to TAD's specs - that's what the "STR" stands for, "Special Tube Request" - and TAD also tests and burns every tube and rejects anything that doesn't meet their standard. I've got a quad of their KT88's and what impresses me is the weight of these things. Thicker glass and all that.

    Here's a comparison with my Psvane's - a good head to head as these are also special production from Shuguang:



    Difference is obvious in the base, but the internal structure is also somewhat different. Top spreader is spun 90 degrees, and certainly some changes in metal alloys used in the structure.



    You can see the TAD also has a side getter for better evacuation control. Wonder if this has anything to do with the orientation of the top spreader ... Hmmmmmm ...

    Anyway ... The TAD's are quite tasty ... I think you'll like their stuff.

    MarcVBelgium

    Posts : 83
    Join date : 2013-12-06
    Age : 63
    Location : Antwerp, BELGIUM

    Re: What about KT-66?

    Post by MarcVBelgium on Sun Apr 26, 2015 4:40 pm

    sKiZo wrote:Just be aware that the "Gold Lions" that TAD sells are probably made by Shuguang.

    Anyway ... The TAD's are quite tasty ... I think you'll like their stuff.


    Hi Skizo

    TAD also has a section "other brands/OEM" and these Gold Lions are, well....... Russian made Genalex Gold Lions (the ones that I have on the Stereo 80 at the moment.)
    http://www.tubeampdoctor.com/en/shop_Other_brands_OEM_Tubes_GENALEX_Gold_Lion/

    For my ST-120 I have a set of matched TAD 6550A-STR that I like very much indeed. TAD is a thrustworthy company and their tubes are great . And their delivery is within 48 hrs (at least here in Europe), amazing. :-))

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