Hello,
Can please someone explain what happens when SE:SE interstage transformer DC rated current is exceeded?
For example, Hammond 126C interstage is rated for 15ma unbalanced DC current, what happens if there's 20ma flowing through it?
Does it saturate the core and low frequency response is affected (essentially inductance become lower)?
Thank you,
Igor.
Can please someone explain what happens when SE:SE interstage transformer DC rated current is exceeded?
For example, Hammond 126C interstage is rated for 15ma unbalanced DC current, what happens if there's 20ma flowing through it?
Does it saturate the core and low frequency response is affected (essentially inductance become lower)?
Thank you,
Igor.
Yes, but mostly you get hysteresis distortion.
https://www.voltech.com/support/tec...g the,with the area of the B-H curve enclosed.
Gapped cores are used to propone saturation.
https://www.voltech.com/support/tec...g the,with the area of the B-H curve enclosed.
Gapped cores are used to propone saturation.
The amount of saturation is according to . . .
1. The amount of un-balanced DC current
2. And is proportional to:
The amplitude of signal voltage (or signal current) / the frequency.
The lower the frequency, the earlier the saturation will occur at a given signal voltage or signal current.
And,
Something to remember . . . Global Negative Feedback that comes from the output transformer secondary, can not fix the saturation effect, it only makes it worse in an attempt to correct it.
1. The amount of un-balanced DC current
2. And is proportional to:
The amplitude of signal voltage (or signal current) / the frequency.
The lower the frequency, the earlier the saturation will occur at a given signal voltage or signal current.
And,
Something to remember . . . Global Negative Feedback that comes from the output transformer secondary, can not fix the saturation effect, it only makes it worse in an attempt to correct it.
an interstage transformer has current in the primary, the secondary do not have current flow to speak of when running classA1, class A2 is different in that the grid draws current, so depending on what you really want to do you can have problems...so show us the complete picture so we do not speculate...
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Thanks everyone!
I was planning to use both triodes inside 6SN7 in parallel for lower effective plate resistance as a driver, which leaves me with only 7.5mA per triode. However, I have since read that apparently 6SN7 works fine even at smaller plate currents.
Does it mean that transformer "behaves" better at lower frequencies with smaller voltage swings?
Thanks, very clear explanation. I've seen some manufacturers e.g. Lundahl even provide available flux density values in Tesla in their datasheets.
The amount of the magnetization of the core is dependent on the Ampere x Turns of the primary.
10mA DC on the primary has a particular amount of magnetization.
20mA DC on the same number of primary turns has 2x the magnetization.
Think of a signal frequency that is lower, and lower, and lower, then you get "near" to DC.
The more signal voltage you drive the primary with, the more it adds to the magnetism that is there from the quiescent DC current.
Lower frequencies can become a problem, long before any midrange frequency can become a problem.
Over a decade ago, Shishido ran transmitting tube grids with some quiescent DC current through/from the interstage transformer secondary.
That current times the secondary turns; and the current times the primary turns was in opposite directions according to the phase connections of the interstage transformer.
That trick cancelled the quiescent magnetism, and so the Single Ended Interstage Transformer did not need an air gap in the lamination assembly.
Genius!
10mA DC on the primary has a particular amount of magnetization.
20mA DC on the same number of primary turns has 2x the magnetization.
Think of a signal frequency that is lower, and lower, and lower, then you get "near" to DC.
The more signal voltage you drive the primary with, the more it adds to the magnetism that is there from the quiescent DC current.
Lower frequencies can become a problem, long before any midrange frequency can become a problem.
Over a decade ago, Shishido ran transmitting tube grids with some quiescent DC current through/from the interstage transformer secondary.
That current times the secondary turns; and the current times the primary turns was in opposite directions according to the phase connections of the interstage transformer.
That trick cancelled the quiescent magnetism, and so the Single Ended Interstage Transformer did not need an air gap in the lamination assembly.
Genius!
then i suggest you use the 6n30, or the bigger triodes of the 13fm7, ea7/6em7 etc...
to me paralleling tubes meant you run out of options..
Interstage transformer coupling was dropped ~100 years ago because RC coupling does not have the high frequency self-resonance, the low frequency inductance shorting attenuation, hysteresis distortion, hum pick-up, bulk and expense that transformer coupling does. Transformers have advantages at the microphone input and in some cases the speaker output, but those are of little use in the middle of the amplifier. No amplifier that uses an interstage transformer qualifies as "hifi" today, including "solid state" amplifiers. Perhaps I should envy those who have time and money for antiques, but I'm far too frugal for such things in my home. Getting rid of junk quickly becomes a serious problem.
7.5mA per triode of the 6SN7 is plenty good, especially considering the 105H inductance. If the transformer is in spec it should be able to swing undistorted 75-80 Vrms down to 20Hz if there is enough anode voltage. FR down 3 dB around 6 Hz. One single triode running well at 15 mA could be the 6H30.
No need and likely no benefit in running at 20 mA (with reduced inductance). It is the product of DC current and inductance that sets the max output voltage at a certain frequency.
No need and likely no benefit in running at 20 mA (with reduced inductance). It is the product of DC current and inductance that sets the max output voltage at a certain frequency.
Very clever indeed, just that the interstage must be a bit special, as it needs to invert the phase. Bifilar's do not like that, maybe others do it better?
I believe Shishido used highly specialized interstage transformers designed to be used in inverting mode. I've had this idea about trying i pair of LL1671 as inverting interstage transformers to drive transmitter tubes, possibly connected as 2:1 or even 4:1 to get the best frequency response as possible when used out of phase.