Shuguang KT-66 Any good

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colin.hepburn
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#1 Shuguang KT-66 Any good

Post by colin.hepburn »

Ok so whats the verdict on these Shuguang KT-66 valves any good as i can buy it now match pair for £37.00 :shock:
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#2

Post by Prince of Darkness »

I've been using some in my SE amp, seem good to me :) Look just like original GEC's as well.
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#3

Post by colin.hepburn »

Yep I figured at that price It was worth a punt so ordered a set let's hope they get here in one peace :)
http://www.ebay.co.uk/itm/220808008910? ... 1438.l2649
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#4 KT66 Spec Help Please

Post by colin.hepburn »

Hi All
Well just received my KT66 valve from china
And just want to confirm that I can safely use them in my single ended JE EL34
Which has an anode to ground HT voltage of 405 volts HT and Cathode to ground 30volt so?
Cathode 30v/560R=53mA
I see from the kt66 spec sheet aV is 500volts
But for single ended triode connection its either 250volt or 400volts this is what's confusing me
So am I ok and within the kt66 safety limits
With HT @405 volts and 30/560R=53mA
See kt 66 spec sheet
http://www.r-type.org/pdfs/kt66.pdf
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#5

Post by Mike H »

The sheet is only suggesting various examples of usage, depending what power is desired, single or p-p etc.

The limiting factor (as always) is anode power dissipation, you can have high Voltage, but not high current, or high current, but not high Voltage.

Also as per EL34, I'd prefer to run it less than maximum Pa as it should prolong working lifetime - for example on one of my KT66 data sheets it says 8,000 hours for Pa 25W, and 10,000 hours for Pa 21W.
 
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#6

Post by Mike H »

PS: the 500V max. rating will include the peak signal Voltage on the transformer primary, that is, HT plus max. positive signal swing, e.g. EL34 is supposed to be 800V.
 
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#7

Post by colin.hepburn »

Mike H wrote:PS: the 500V max. rating will include the peak signal Voltage on the transformer primary, that is, HT plus max. positive signal swing, e.g. EL34 is supposed to be 800V.
So i can just plug them in them yes
HT 405 volts
30v/560R=53mA
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#8

Post by pre65 »

Personally, I would run them a gnats lower, like with a slightly bigger value cathode resistor.

But you won't blow them up as is. :wink:
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#9

Post by colin.hepburn »

Yep the original amp with cathode resistor was 880R says I can just plug it in but I changed it to 680R then it was changed again to Richards's recommendation to this 560Rwhich it is still at this value
But 53mA is still under the 400v 63mA so ok then as I just want to see if they work
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#10

Post by Mike H »

I make that a gnat's eyebrow under 20W, so should be fine.
 
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#11

Post by colin.hepburn »

Mike H wrote:I make that a gnat's eyebrow under 20W, so should be fine.
OK thanks mike just been giving them a spin they sound promising 8)
So giving my HT of 405 volts and the 30v cathode
So as there now Running @ 30v/560R =53mA
Would you change this and if so to what value cathode resistor for optimum results
I think we are getting back to this load line stuff but i just seem to get lost in there at the moment need to go find my MJ book me thinks :)
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#12

Post by Cressy Snr »

colin.hepburn wrote: Would you change this and if so to what value cathode resistor for optimum results
I'd sort those speakers first Colin :D

One thing at once or you could drive yourself crazy :wink:
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#13

Post by colin.hepburn »

SteveTheShadow wrote:
colin.hepburn wrote: Would you change this and if so to what value cathode resistor for optimum results
I'd sort those speakers first Colin :D

One thing at once or you could drive yourself crazy :wink:
Yep I think your right there Steve I do tend to run before I can walk But I am getting there I think :P
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#14

Post by Mike H »

colin.hepburn wrote:So as there now Running @ 30v/560R =53mA
Would you change this and if so to what value cathode resistor for optimum results
Depends what you mean by "optimum", but avoid going too low, as it will start going non-linear where the valve is getting close to cut-off.

You can also try tweaking the DC to find the OPT sweet spot, if any, this is where it best matches the air gap size. Although 50mA is not a lot so might make it slightly worse if going much lower than that. So balancing those two, + Pa, problee 43 - 53mA is it.
 
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#15

Post by colin.hepburn »

Hi All
Info Question pleas
Has anyone compared the Shuguang KT-66 with the Sovtek KT-66 as they are a similar price for matched pairs plus the Sovtek are available in UK what are you views on both plus which KT66 would you consider your favourite :)
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