Loadline Tools

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Paul Barker
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#1 Loadline Tools

Post by Paul Barker »

A lot has happened while Ive had my eye off the ball.

https://www.vtadiy.com/loadline-calcul ... alculator/
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pre65
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#2 Re: Loadline Tools

Post by pre65 »

I had a quick look at GK71 in triode mode, and it seems they suggest the load as 4K, and I can't see a way to alter it to 5K, as that is the OPT I use. :?
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Paul Barker
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#3 Re: Loadline Tools

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you put it in place of the 4000 down where the input boxes are.
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#4 Re: Loadline Tools

Post by pre65 »

Paul Barker wrote: Tue May 26, 2020 10:57 pm you put it in place of the 4000 down where the input boxes are.
I did that, but did not see how to reset the graph.

I think I've got in now, pretty neat site. :D
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#5 Re: Loadline Tools

Post by pre65 »

It seems for GK71, that in single ended triode mode, it assumes the ultralinear tap on the OPT is used, but my OPT does not have ultralinear taps. :?
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Paul Barker
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#6 Re: Loadline Tools

Post by Paul Barker »

You select pentode ultra or triode.

You set Anode voltage and cathode current and you put load impedance in.

You look at where Loadlines then displays relative to max power curve (a lot for bottle size 125 watts).

Then you check out different voltages and currents you’re aiming to get you’re quiescent point with an equal number of grid lines either side if possible and make you’re driver strong enough to 1/ provide all the voltage swing for full power with margin (headroom). 2/ low impedance driver and plenty of current to deal with grid current + some. Then from gk71 you will set the scene for very strong amp.
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#7 Re: Loadline Tools

Post by Paul Barker »

Here is the data I put in (note I can go more current but it stresses output transformers). You have to cut you’re coat according to you’re cloth. The system calculated quiescent grid voltage.

The ultra lines percentage in shaded box ignore it doesn’t feature when using triode mode. Likewise screen voltage.
Image
Image
If you get lost as to what grid voltage line voltages are: put curser on that grid line it will text box the voltage first followed by other parameters not relevant at that place:-
Image
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#8 Re: Loadline Tools

Post by Paul Barker »

The power output class A1/A2 is the figure for us. It’s rather optomistic. I don’t know if he’s got his formula wrong. One thing I do is not include in the power output any power which involves extreme visual evidence of distortion. What’s the point claiming output power full of distortion. Some people quote max power at (whatever distortion they deem small enough to keep claiming power output.) 3% 5%? You decide! If you apply that concept you won’t come to 44 Watts!
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#9 Re: Loadline Tools

Post by Paul Barker »

The usefulness of the tool is you can visualise different load and different quiescent point , how much dc current you think you can subject your opt to before you degrade its performance. Pointless max powering the operating point on Loadlines only to saturate you’re transformer at 15 watts.
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#10 Re: Loadline Tools

Post by Cressy Snr »

Here’s mine for the KT77 amp:
Image
It estimates a 275R cathode resistor for the conditions I measured the other day. Mine is 270R so I’d say it’s a pretty good little calculator. 5 and a bit Watts is what I worked out using the long winded method. The calc gives 5W

We can see that the KT77 works OK with 2K5 output transformers, which vindicates my choice to make my amp work optimally with the KT77 to the exclusion of everything else.
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#11 Re: Loadline Tools

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I’m glad you’re enjoying it Steve.

I did a calc for you’re power output using 338v Swing at 2.5k = 5.7 Watts but ... have you seen plenty of pinching bottom right. Doesn’t look like a SE design at full power.
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#12 Re: Loadline Tools

Post by Paul Barker »

3 watts with 250v PP swing is 3 watts nice sweet sound.

If you’re opt can handle more current it’ll lift the loadline to where you get more power at low distortion in this valves case. With a DH true triode that pinching is less acute.

Or make the loadline more impedance if that’s an option to lift the right side out of the pinch zone.
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#13 Re: Loadline Tools

Post by Cressy Snr »

Paul Barker wrote: Wed May 27, 2020 5:27 pm I’m glad you’re enjoying it Steve.

I did a calc for you’re power output using 338v Swing at 2.5k = 5.7 Watts but ... have you seen plenty of pinching bottom right. Doesn’t look like a SE design at full power.
Yep, I’m under no illusions about the power this thing produces. Probably 3 Watts before distortion takes off. But I have 100dB/W speakers, in a 13 x 12 room, so I’m not too badly off. Owston or similar would be as farcical as ever.

I can make it a 5K loadline as I’ve brought the 4 Ohm setting out to the rear sockets. And as these OPTs are the older Hammonds where you parallel the secondaries rather than simple tap-offs, coupling should not be as badly affected.

Seem to have overlooked the rule that higher voltages require higher impedance transformers to keep the right hand side out of the non-linear zone. With the OPT limitations I have regarding impedance, it might be more prudent as you say, to lower the voltage and raise the current.

That’ll give me something else to do. :)
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#14 Re: Loadline Tools

Post by Paul Barker »

Worth trying.
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#15 Re: Loadline Tools

Post by Mike H »

Oooo interesting ... :shock:
 
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