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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 27 Sep 2012, 19:08 
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@Steve: I would assume the KT120 amp will run in triode mode though I haven't tried it. Lately I have been enjoying two amps in UL mode. My Luciano (807) amp designed by Suncalc and my latest EL34 amp retro-34UL. My big SET rig is my 300BSE again designed by Suncalc. Though I think triodes have there place I'm leaning heavily toward the sound of the UL based amp. The EL34 amp recently made and now sold (driving electrostatics believe it or not) was an exceptionally nice amp to listen to. I think mostly due to some nice EL34 Svetlana tubes.

I would definitely build the amp UL with the triode switch. You get about 3db more power/volume in UL mode and you may even find the sound, in your system, is better.

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PostPosted: 27 Sep 2012, 19:26 
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Thanks Mark. Is it easy to find a suitable switch?


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PostPosted: 27 Sep 2012, 19:30 
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7_V wrote:
Thanks Mark. Is it easy to find a suitable switch?

The switch only has to handle very low levels of current. I use small quality DPDT power switches.

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PostPosted: 28 Sep 2012, 19:06 
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Out of interest, do I have to turn off the amp before switching from triode to UL or vice-versa?


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PostPosted: 28 Sep 2012, 20:54 
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7_V wrote:
Out of interest, do I have to turn off the amp before switching from triode to UL or vice-versa?

It is a very good idea to have the amp in triode or U/L mode prior to turning it on. If you have a standby switch (which I think all amps should have) you can cut the HT (filaments stay hot), wait a 30 seconds, throw the triode switch and then take the amp out of standby. That way the tubes stay hot and ready to go. Less wear on the tubes too. My standby switches allow manual switching of the HT to all tubes.

This means when the amp is on just the heaters come up. Wait a few minutes then turn on the HT. Cathode stripping can occur if tubes are cold when the HT comes on. This way that effect is reduced. Not only that when you want to shut the amp down turning off the HT allow the caps to be bled (standby switch before first filter cap). This is good for the caps and safety.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 29 Sep 2012, 13:08 
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So would the standby switch open the circuit before the 0.47uf metal film on your schematic? I'm afraid I need it spelled out.


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PostPosted: 30 Sep 2012, 07:19 
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Also, I thought I'd try these new style 'Tomiki' OTs (http://www.ebay.co.uk/itm/180873138457? ... 1439.l2649), as I've heard good things about them. They're rated at '12W, 18W maximum' which is a bit vague, but the seller's English isn't perfect. Is this enough power for the KT120 in ultralinear mode?


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PostPosted: 30 Sep 2012, 07:27 
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I would go for something heavier.
Hpw about a pair of LM-9911U-B from http://www.vt4c.com/shop/program/main.p ... group_id=7
Or check Edcor.

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PostPosted: 03 Oct 2012, 08:19 
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I think Magnus has the better selection.

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PostPosted: 04 Oct 2012, 04:56 
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You may well be right. I'm told though that the Tomikos use the latest Japanese Z11 nickel core, and Hitachi (occ) wire. They might be worth trying at the price.


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