My schematic of a 76 tube driving a 45 tube specifies a Primary impedance and Secondary impedance of 20K, and 1mA. It can be 1:1 or 1:2.
Most interstage transformers are described in terms of inductance.
I have been unable to find a calculator where the crosswalk between these specifications can be done by plugging in these values.
Can someone point me to such a calculator?
In the alternative can someone point me to a tutorial on how to calculate this manually or just recommend the right interstage transformer value in Henry's.
Thank you in advance.
Most interstage transformers are described in terms of inductance.
I have been unable to find a calculator where the crosswalk between these specifications can be done by plugging in these values.
Can someone point me to such a calculator?
In the alternative can someone point me to a tutorial on how to calculate this manually or just recommend the right interstage transformer value in Henry's.
Thank you in advance.
'Crosswalk....'
Do you mean, Crosstalk....?
Dunno!
Are you stuck on using an IT?
Personally, I dont like using 'em--At All! They only used 'em in the day--when there was no alternative.
These days, there's lots of different things to use instead of a chunk of iron with all its attendant issues, --not least the Cost for a GOOD one.
A simply implemented alternative would be a MOSFET DC coupled to the O/P tube grid, set bias by value on the Mosfet gate.
Simple, and IME sound/test better than an expensive chunk of iron!
Do you mean, Crosstalk....?
Dunno!
Are you stuck on using an IT?
Personally, I dont like using 'em--At All! They only used 'em in the day--when there was no alternative.
These days, there's lots of different things to use instead of a chunk of iron with all its attendant issues, --not least the Cost for a GOOD one.
A simply implemented alternative would be a MOSFET DC coupled to the O/P tube grid, set bias by value on the Mosfet gate.
Simple, and IME sound/test better than an expensive chunk of iron!
Inductive Reactance Calculator ? 66pacific.com
Let say if you have interstage transformer says it has Pri 5.6K:Sec 600, and you want to know if it works down to 10Hz, if the pri inductance is 84H, then
XL = 2piFL
= 2 x 3.141592653 x 10 Hz x 84 H
= 5.3E+03 ohms (to 2 significant digits)
= 5,278 ohms
Sec inductance is (600/5600)*84H=~9H
The inductance ratio is same as impedance ratio, say 33:1, don't mistaken as turn ratio, it is sometimes not clearly written, in this case it can not be a turn ratio because Impedance = sq(Turn ratio)=33*33=1089, if sec = 1H the pri would be 1089H, that is not practical.
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>No, crosswalk is right. I need to figure out the equivalent transformer. My schematic specifies the interstage transformer values as 20K impedance on the primary and secondary. Most manufacturers list the inductance in Henry's for interstage transformers. So, the Lundahl transformer site, which is very complete in terms of specification, is hard for me to navigate because they present the transformer values in terms of Henry's.
>I am not stuck doing anything. I do feel badly that your experience with "iron" has been so disappointing. My experience is that characterizations of "iron" or "silicon" or "op-amps" or whatever rarely contextualize the implementation so these declarations are pretty limited. I do respect that you are well intentioned though. I will likely experiment with the circuit over time and see which interstage solution I like better. Thank you.
I really appreciate this generous, maybe heroic tutorial. And, I am concerned that I did not ask the right question or maybe don't have the brain to recognize the answer.
My schematic specifies an interstage transformer that has a primary impedance of 20K ohms and a secondary impedance of 20K ohms. I want to know the equivalent transformer when they describe it in inductance and not in impedance. This Inductive Reactance Calculator calculator seems to be doing something else. But it is the sort of plug values in contraption that I was looking for. I want to pop in the values of 20K impedance primary, 20K impedance secondary, and have the cross walk specify the transformer that is equivalent. We all know about giving a man a fish and not teaching, or expecting them to fish. But, honest, I would not feel at all patronized if someone took these 20K impedance values and recommended a Lundahl or Sowter interstage crossover. As an example I am attaching this Lundahl spec sheet that I don't currently understand relative to the requirements of a 20K impedance interstage transformer. Thanx.
Transformer impedance (20K,10K,5K etc) is usually based on lowest (sec open, or un-terminated) frequency response, be it 10,15,20Hz or more. Say you want 20K @20Hz, you just vary the inductance until you get impedance near 20K
XL = 2piFL
= 2 x 3.141592653 x 20 Hz x 160 H
= 2E+04 ohms (to 2 significant digits)
= 20,106 ohms
20K impedance equivalent to 160H primary inductance @20 Hz, and if 20K:20K, the secondary is also 160H.
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"....
But, honest, I would not feel at all patronized if someone took these 20K impedance values and recommended a Lundahl or Sowter interstage crossover. As an example I am attaching this Lundahl spec sheet that I don't currently understand relative to the requirements of a 20K impedance interstage transformer...."
Or are you saying why 20K (or 160H) and not 5K (80H) for instance? The higher the impedance is the lesser is distortion, esp in zero feedback amp.
But, honest, I would not feel at all patronized if someone took these 20K impedance values and recommended a Lundahl or Sowter interstage crossover. As an example I am attaching this Lundahl spec sheet that I don't currently understand relative to the requirements of a 20K impedance interstage transformer...."
Or are you saying why 20K (or 160H) and not 5K (80H) for instance? The higher the impedance is the lesser is distortion, esp in zero feedback amp.
Why don't you post your question on the K&K Audio site. Kevin Carter, the U.S. distributor of Lundahl transformers is very helpful and can steer you to the appropriate Lundahl product.
Maybe I spoke too soon. LOL. You are a great communicator. I am not understanding something.
I appreciate your patience. The schematic for the amp I want to build has the 76 driving the 45 with an interstage transformer between them. I need to buy a couple transformers to build the 2 channels. The bill of materials requires an interstage transformer that is 20K primary impedance, 20K secondary impedance, and 10mA current. I don't understand how to use the formula or calculator that you so generously shared to find an equivalent Lundahl or Sowter transformer to build this circuit. The specs on the example Lundahl 1671.pdf I uploaded does not describe the 1671 in terms of the impedance values I have spec'd. Rather, they spec the 1671 in terms of inductance.
I understand that this has audible frequency consequences and the use of an interstage transformer in this circuit will attenuate the top end of the amplifier, but I am not trying to calculate the frequency consequences now. I am trying to buy a transformer whose values I can't translate from impedance to inductance.
Thank you for your help.
I appreciate your patience. The schematic for the amp I want to build has the 76 driving the 45 with an interstage transformer between them. I need to buy a couple transformers to build the 2 channels. The bill of materials requires an interstage transformer that is 20K primary impedance, 20K secondary impedance, and 10mA current. I don't understand how to use the formula or calculator that you so generously shared to find an equivalent Lundahl or Sowter transformer to build this circuit. The specs on the example Lundahl 1671.pdf I uploaded does not describe the 1671 in terms of the impedance values I have spec'd. Rather, they spec the 1671 in terms of inductance.
I understand that this has audible frequency consequences and the use of an interstage transformer in this circuit will attenuate the top end of the amplifier, but I am not trying to calculate the frequency consequences now. I am trying to buy a transformer whose values I can't translate from impedance to inductance.
Thank you for your help.
Asking Kevin would indeed be the best option. He is also a member of Diyaudio, so maybe send a PM?
If you really require only 1mA, probably even a LL1660 PP would be good. All Lundahl PP transformers do have a small gap to account for imbalance between the tubes, and this is probably enough to handle 1mA. The PP transformers have a 290H primary inductance, reactance (2*pi*f*L) of 36k at 20Hz.
Cheers, Erik
If you really require only 1mA, probably even a LL1660 PP would be good. All Lundahl PP transformers do have a small gap to account for imbalance between the tubes, and this is probably enough to handle 1mA. The PP transformers have a 290H primary inductance, reactance (2*pi*f*L) of 36k at 20Hz.
Cheers, Erik
As a rule of thump, we must have 20H for every 1K primary impedance, if this is your question.
Avoid 1:2 configuration. The unity ratio minimizes distortion.
Cheers!
Avoid 1:2 configuration. The unity ratio minimizes distortion.
Cheers!
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The generic 20k figure would be representing the impedance of the primary inductance at some frequency, usually the lowest usable frequency, with the general rule of thumb having Zpri >2 Rp at the lowest usable frequency it would suit a 10k tube like Type 76.
The 1mA primary current would be a typo, surely enough, 10mA is what you would be looking for.
If you haven't already bought into Type 76, and don't have the high primary impedance transformers on hand, try another driver with lower Rp (~2k) as it allows for the use of a better transformer (in every way) and a better result.
LH/S
The 1mA primary current would be a typo, surely enough, 10mA is what you would be looking for.
If you haven't already bought into Type 76, and don't have the high primary impedance transformers on hand, try another driver with lower Rp (~2k) as it allows for the use of a better transformer (in every way) and a better result.
LH/S
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I agree with you, that a tube with a lower Rp is to be preferred - at least I would do it!
And of course that I didn't think right about operating the 76 at 1mA: 10mA would be better and a properly gapped IT would be needed.
Hmm, Looks like I'm not the only one who has Never heard of this term!
Please Define EXACTLY what you mean by it--in Plain language if possible.🙂
(TBH--I'm thinking its some daft Audiophool term some idiot in some Blog or Magazine has dreamed up to make himself look knowledgeable....)😉
My information is that a 76 tube has too high Rp for using it in combination with an IT. I solved this by putting a C3M pentode (used as triode) between the 76 tube and a LL1660 transformer. I did it with a 1624PP amp but it can of course also be done in a SE amp.
I don't travel in audiophile circles, so maybe there is specific jargon. But the transformers I use for various purposes all seem to be listed in terms of impedance to impedance. Not hifi, but example data sheet:
http://www.alliedelec.com/images/products/datasheets/bm/PARALLAX/70218235.pdf
or
Allied - 6W68HF - MAX DC 30MA 10K CTOHMS SEC IMPED : PRI 10K OHMS INTERSTAGE UDIO TRANSFORMER - Allied Electronics
http://www.alliedelec.com/images/products/datasheets/bm/PARALLAX/70218235.pdf
or
Allied - 6W68HF - MAX DC 30MA 10K CTOHMS SEC IMPED : PRI 10K OHMS INTERSTAGE UDIO TRANSFORMER - Allied Electronics
I saw that explanation yesterday, and I think it is indeed quite clear what Bruce meant.
The Lundahl LL1660/10mA has a specified inductance of 130H, equivalent to 16k at 20Hz. This will probably be enough for the 76. Hammond makes the 126C, gapped for 15mA and 106H. Bifilar (dua bobbin!) and cheaper than Lundahl.
The Lundahl LL1660/10mA has a specified inductance of 130H, equivalent to 16k at 20Hz. This will probably be enough for the 76. Hammond makes the 126C, gapped for 15mA and 106H. Bifilar (dua bobbin!) and cheaper than Lundahl.
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