A midbass transformers with fast core

Design and use of the various types.
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Romy The Cat
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A midbass transformers with fast core

Post by Romy The Cat »

Hey, David, long time no see…

I think I will have a project for you. I am contemplating to have a single-ended transformer made foe my new midbass channel (not lower bass). I would need it to be bass-transformer only. Not too crazy on inductance as my current bass transformer. I would say 10Hz clipping at full power would go. It shall be 20W. The upper knee roll off might be anywhere above 1.000Hz. I would need to load a full 6C33C (100-120R on plate) with 1500R-1700R, driving 15R driver. I would prefer to keep DCR of primary as low as possible, in teens of the Ohm is preferable. The transformer has to be made from relatively fast core, faster than M3 steel. It has to be able to handle 350-400mA of plate current. So, will you have such a large chunk of core?

Rgs, Romy the Cat
dave slagle
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Post by dave slagle »

Hello Roman,

I'm not clear what you mean by a fast core but CV has approached me with this question several times before. Of course he was thinking SE 212's but the end result, I suspect is the same. We usually ended up looking at the amorphous materials and everything you propose seems doable.

dave
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Romy The Cat
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Post by Romy The Cat »

Yes, I was thinking about something like amorphous or your Nickel cores, that what I call “faster” core then regular steel.
dave slagle
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Post by dave slagle »

what frequency range are you considering for this specific situation?

dave
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shinebox
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Post by shinebox »

Yo shines here,
CV pointed me in the direction of this thread... I think Romy meant 1kHz, not 1.000 Hz, so 2 decades...

Romy - your actual Idc is 200-220mA, right? If you quote 350-400mA to Dave, I'd guess (only slightly kidding) you might end up with an airgap good for 1A... Similarly, are you really going to get 20W out of that loading on the 6C33?

With other manufacturers, I would spec exactly as you have done, but with intact I'd tell them what the actual Idc and power output is, and discuss optimising air gap and headroom afterwards...

cheers
shines
Romy The Cat
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Post by Romy The Cat »

shinebox wrote:Yo shines here,
CV pointed me in the direction of this thread... I think Romy meant 1kHz, not 1.000 Hz, so 2 decades...
Shinebox, and what in your view difference between 1000 Hz and 1kHz?
shinebox wrote: Romy - your actual Idc is 200-220mA, right? If you quote 350-400mA to Dave, I'd guess (only slightly kidding) you might end up with an airgap good for 1A... Similarly, are you really going to get 20W out of that loading on the 6C33?
I usually specify current that I would like to have and it is up to manufactures to figure out how it gets converted in air gaps. I would like to have my midbass channel to be loaded to 1500R, this will make, if I am correct, 1:5.3 transformer driving 15R driver. The tube is driver at 220-270 mA, with a perspective to do 300mA, so 350-400mA transformer will not hurt. This transformer shall not be as crazy as my current one that goes to 7.5Hz at 22W. I think 15Hz at full power will do with a lot of reserve. The channel is high-passed at 20H and it also will never see a full power (109dB horn)
shinebox wrote:With other manufacturers, I would spec exactly as you have done, but with intact I'd tell them what the actual Idc and power output is, and discuss optimising air gap and headroom afterwards...
I do not know yet what will be the optimum current. For this channel I idea the 6C33C very heavy, burning power and harmonics and gaining damping. With a faster transformer (higher permeability core) , I might load a tube a bit heavier or use less current (higher plate impedance). I do not know yet. It is not a DSET transformer, se there is not objective in HF. Why do not take a larger chuck of code and to have some reserve?
dave slagle
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Post by dave slagle »

Hey,

Sorry for the late reply. Things were busy for be getting ready for RMAF.

I generally shoot for equal extension on either side of the frequencies in question so until we nail that down along with the other basics I cannot select a core size.

Big Amorphous would be my choice for this application.

dave
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Romy The Cat
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Post by Romy The Cat »

Dave it looks like I have finally found what I need. The transformer need to be amorphous core, 9:1, be gaped for 370mA and to have inductance good for 12-15Hz at 20W. It shall have sub 15R primary (lover is better) and no sections on secondary – just a single coil. The upper roll of this thing I would like to be no higher then 1000Hz (lover is better). I do not care about size and appearance of the transformer, sure I care about price (lover is better :-). So, what will you say? Wonna try?
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Post by dave slagle »

This meand your expected 6C33Rp will be around 180 ohms?

What is the driver impedance it will be seeing?

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Romy The Cat
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Post by Romy The Cat »

It will be seeing 15R driver. I am planning to drive 6C33C at 50-55W and I anticipate plate impedance will be around 100-120R for 6C33C and around 80-100R for 6C19C.
dave slagle
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Post by dave slagle »

I think I have everything I need to do some calculations / experiments to see what needs to be done in this case.

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Romy The Cat
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Post by Romy The Cat »

Dave, hold for now with calculations / experiments. I have put in there a 9.35:1 transformer with a regular M6 core that roll at 800Hz and I eliminated my power limitation but because of more tube load I got too long harmonic tail. I was forced to roll of this tail with shaper filter but I got some time alignment delay with 3rd order. My concern is that in this configuration if I introduce a faster core transformer then it will be wide open to 20K and would force me to go for even sharper filters – the option the I do not think I have. Let me to put the faster core transformer ide on hold for now and I need to think a bit how I would accommodate it.
suqun1
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Post by suqun1 »

Of course he was thinking SE 212's but the end result, I suspect is the same. We usually ended up looking at the amorphous materials and everything you propose seems doable.
carkifelek
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Post by carkifelek »

@Romy the Cat, You can hold it off for now but I think you’ll have to go with this idea sooner or later. A faster core, one having greater permeability will certainly make you change some of the parameters in your circuit and you’ll have to tune a few values of resistors but in the end you’ll have a much better circuit than you have currently and will be according your requirements of a midbass transformer.
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