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Understanding load on triode and impedance matching
Understanding load on triode and impedance matching
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Old 12th June 2019, 07:37 AM   #51
johnsurnamerobinson is offline johnsurnamerobinson
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The use of load lines is invaluble when aiming for max power transfer.However as I posted before in your case you need to make sure the o/p transformer has ample iron so as not to saturate when passing anode standing current +max signal.A good transformer manufacture will work this out for you as it depends strongly on core material.BTW a class A push pull output stage is far more forgiving in this regard as standing current is cancelled in the transformer.
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Old 12th June 2019, 07:37 AM   #52
TonyTecson is offline TonyTecson  Philippines
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Understanding load on triode and impedance matching
powering headphones, you will actually see much much less power than the graphs showed...

btw, speakers that are nominally rated at 8 ohms is only 8 ohms at one frequency and goes all over the place with different frequencies, i suspect that headphones are not much different...
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Old 12th June 2019, 07:58 AM   #53
johnsurnamerobinson is offline johnsurnamerobinson
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More on output transfomers.Care also needs to be taken when including a CUSTOM o/p transformer in the negative feedback loop.Thats a whole new world of pain!!!!

Re your point about headphone amps. I am an old timer and over the years can recall seeing many designs for valve headphone amps in the UK hobby press.Since almost everything ends up on the net these days they should be out there.I am no expert on google you may need something more specific. As I recall most seemed to use small signal triodes with No o/p transformer they were cap coupled. Really sorry I cant provide links.
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Old 12th June 2019, 04:32 PM   #54
PRR is offline PRR  United States
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> intended loads of about 64-300 ohms, .... .... I can't decide between 5K:16 (17.7:1) and 5K:32 (12.5:1).

Use 5K:32.
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Old 12th June 2019, 04:37 PM   #55
itsikhefez is offline itsikhefez  United States
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Understanding load on triode and impedance matching
Thank you
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Old 12th June 2019, 08:55 PM   #56
Tubelab_com is offline Tubelab_com  United States
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Quote:
Use 5K:32.
Without actually testing anything, that would be my best guess too. Unfortunately I have been busy slinging asphalt and ripping one of the heads off my dead lawn mower lately.

I would get the amp working with the 32 ohm transformer using a cheap speaker as a (mismatched) load, then try the headphones. Once working you can play with resistors in PARALLEL with the headphones to adjust the load seen by the tube for the best balance of power and distortion. Something between 33 and 1000 ohms will be the best.

As I stated before, I believe that a 5K to 8 ohm OPT will be marginal at putting enough power into 300 ohm phones without getting the 45 too close to clipping. The 32 ohm OPT will have enough voltage on its output to feed the cans, and enough reserve power to feed a resistor, while keeping the 45 in its happy zone around half a watt or less on peaks.
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Old 12th June 2019, 09:06 PM   #57
itsikhefez is offline itsikhefez  United States
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Understanding load on triode and impedance matching
Thanks for the input George, much appreciated.
I will proceed with this and report my findings, but that will take a while.
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Old 14th June 2019, 09:15 PM   #59
johnsurnamerobinson is offline johnsurnamerobinson
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You are really lucky to have so many good people reply to your post.All of them have given sound advice. I do understand your desire to learn and can only say learning drives us all forward.
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Old 14th June 2019, 11:16 PM   #60
TonyTecson is offline TonyTecson  Philippines
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Understanding load on triode and impedance matching
learn by doing, less talking.....
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