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Best SE output transformer for 300B - shootout
Best SE output transformer for 300B - shootout
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Old 7th February 2018, 11:57 PM   #181
Perfectusaudio is offline Perfectusaudio  Australia
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type 45 data https://frank.pocnet.net/sheets/021/4/45.pdf
5k is standard load for type 45 tube
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Old 8th February 2018, 05:57 PM   #182
hpeter is offline hpeter  Slovakia
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i think the 10k is just better.
5k is "shooting into knee" , i hate that sonically

same loudness, but not the THD profile !
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Old 10th February 2018, 02:58 AM   #183
soulmerchant is offline soulmerchant  Switzerland
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Quote:
Originally Posted by jpak View Post
Anyone know why such a high 12k primary for the 45 transformer?

Edit: this is in reference to the NP Acoustic transformers.
Me thinks this might be for 801a.
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Old 10th February 2018, 03:00 AM   #184
soulmerchant is offline soulmerchant  Switzerland
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Quote:
Originally Posted by hpeter View Post
i think the 10k is just better.
5k is "shooting into knee" , i hate that sonically

same loudness, but not the THD profile !
I like 7k for the 45, but primary inductance, frequency response, power, etc. all play such important role.

Last edited by soulmerchant; 10th February 2018 at 03:08 AM.
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Old 10th February 2018, 05:06 AM   #185
Hanze Khronye is offline Hanze Khronye  Australia
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Quote:
Originally Posted by soulmerchant View Post
I like 7k for the 45, but primary inductance, frequency response, power, etc. all play such important role.
7kohm load impedance at what frequency?.

Load impedance is a function of primary inductance with respect to frequency. And that inductance figure for air gapped types depends on DC current through the core.

Change the frequency for a given amount of inductance, and the load impedance changes.

For example, I would like load impedance to be 2x Rp at my lowest usable frequency. That makes sense, a lot of sense.

I know of one winder (recent inquiry, US based, self proclaimed winder of 20,000 items sold), who does not understand this as fundamental, he does not specify, but when asked he admits that his 'impedances' are measured at 1kHz. Then again, maybe he does understand and is chasing better HF response due to less capacities (there is more than one internal capacitance involved) within the transformer. Or perhaps its just a matter of convenience and he doesnt really care - take your pick.

If I see primary inductance specification at a given DC current through the core, I am happy - I can work out the loading to my tube at ANY frequency. Simple.

If I see a '3k3' with in circuit measurement utilising 800 Rp tube at 80mA and quotes -3dB(f) as such, I am happy - and I think it is the latter who fully understands that he needs to provide a bridge to those who do not really understand the nature of the relationship between inductance as it varies with DC current through the core, frequency and how this relates to the impedance which then loads the tube.

Again, to specify a transformer primary as simply an impedance by itself is meaningless.

Last edited by Hanze Khronye; 10th February 2018 at 05:36 AM.
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Old 10th February 2018, 02:10 PM   #186
jpak is offline jpak  United States
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Great info, I am definitely in the latter "don't know" camp Any suggestions for recommended reading? Preferably an online source that explains this well.

I am using 6.4k OPT for my 45 SET wound by Electra-Print, this is for a headphone amp where very little power is needed. I am very interested in trying amorphous where low level information is critical for headphone use.

Last edited by jpak; 10th February 2018 at 02:13 PM.
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Old 10th February 2018, 04:36 PM   #187
artosalo is online now artosalo  Finland
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Quote:
7kohm load impedance at what frequency?.

Load impedance is a function of primary inductance with respect to frequency. And that inductance figure for air gapped types depends on DC current through the core.

Change the frequency for a given amount of inductance, and the load impedance changes.
Are you sure ?

Assume we have a typical output transformer with primary/secondary turns ratio = 22.36, which gives the impedance transforming ratio = 500. We connect 8 ohms load at the secondary and measure the reflected impedance from the primary at the frequencies 1 kHz and 2 kHz.

Do we get two different impedance values ?
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Old 10th February 2018, 04:48 PM   #188
waltube is offline waltube  Italy
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Hi

sometimes I remeber this thread about trafos OPT Characterization



Walter
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Old 10th February 2018, 06:48 PM   #189
pieter t is offline pieter t  Netherlands
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Quote:
Originally Posted by artosalo View Post
Are you sure ?

Assume we have a typical output transformer with primary/secondary turns ratio = 22.36, which gives the impedance transforming ratio = 500.
We connect 8 ohms load at the secondary and measure the reflected impedance from the primary at the frequencies 1 kHz and 2 kHz.

Do we get two different impedance values ?
You are missing a point, which Hanze explained in post #185.
Of course the reflected impedances in your example are the same.
However, for a given impedance to be a real one the value of inductance can not be ignored.
In your example of 1 kHz, and the impedance ratio of 500:1 giving a load impedance of 4k at 8 ohm, the value of the inductance should be at least 637 mH (2.Pi.1000.0,637=4k).
This value of inductance at these frequencies is not a problem also for low quality output transformers.
It matters however at low frequencies; in your example the inductance at 20 Hz, with DC current through the primary, should be 31,83 H.
Now we enter territory where we see differences in quality in output transformers.
Another point to realize is the fact that inductance goes up with higher signal levels; a normal inductance meter only gives an estimation of reality.

Last edited by pieter t; 10th February 2018 at 07:08 PM.
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Old 10th February 2018, 07:50 PM   #190
andyjevans is offline andyjevans  United Kingdom
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Coming back to NP Acoustics, I suggested that DIY Audio members might possibly have a discount. The reply, as much as I understand it, is that the first 10 buyers would get a discount. So it could be worth making contact and exploring this.
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