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Toroidal transformer as OutPutTransformers (300b) & as mains trafo too

Hi all here :deerman:

I'am in for building an SE 300B amp. (to be specific it's Tubelabs SE II) https://www.diyaudio.com/forums/tubelab/331038-14-run-tse-die.html, and while gathering information about the use of toroidal transformers as OPT's & mains i was encouraged to ask the quistion here in tube/valve forum.

I'am for being honest some confused, i think i had to many input's and maybe been reading to much :D about the thing, so i really need some clarification.

Well for a start the Tubelab SEII need the following specifications for normal EI-core OPT's :
D.C. Primary Current ~100mA (tubes are biased no more than 80mA)
SE with airgab to reject DC
Primary impedance around 3.2K
Secondary impedances at 4 or 8 ohm. (My spk. for now is 8 ohm)

I had some email conversation with Toroidy, which are making such toroidal transformers, and they tell me that they are full capable as SE OPT's toroids, as they have glued airgab on they're core.
There are two specific transformers i have looked at, and the links are provided here:
TTG-EL34SE - Tube output UL transformer [3,2kOhm] EL34 / 6L6 SE - Shop Toroidy.pl
This one are having specs, like i want to i think, why they are not listed as for 300b i donno through. (See link eventually)
Intended for Single Ended
Core type Toroidal
Ultralinear tap 43%
Nominal Power 40W
Nominal anode current 100mA
Frequency bandwidth (-3dB) 10 Hz - 56 kHz
Secondary Impedance 4 and 8 Ω
Primary Impedance 3,2 kΩ
Turns Ratio (Np:Ns) 28,28:1 (4Ω) , 20,00:1 (8Ω)
Primary Inductance Lp 51,2 H
Primary Leakage Inductance Lsp 0,73 mH
Total Primary DC Resistance 112 Ω
Effective Primary Capacitance 11,2 nF

The other opt are this one TTG-KT88SE - Tube output UL transformer [3kOhm] KT88 / 300B SE - Shop Toroidy.pl
Intended for Single Ended
Core type Toroidal
Ultralinear tap 43%
Nominal Power 40W
Nominal anode current 250mA
Frequency bandwidth (-3dB) 10 Hz - 56 kHz
Secondary Impedance 4 and 8 Ω
Primary Impedance 3,0 kΩ
Turns Ratio (Np:Ns) 27,39:1 (4Ω) , 19,36:1 (8Ω)
Primary Inductance Lp 39,5 H
Primary Leakage Inductance Lsp 10,88 mH
Total Primary DC Resistance 85,4 Ω
Effective Primary Capacitance 7,6 nF

But this one are for 250mA Anode current, IS THIS the same as DC primary current? I guess so?
Some other forum member told me, that i proberly? don't want 250mA's when not needed, as the primary inductance reduces when transformers are getting bigger, which could also be seen at the data on them two i listed here!

I've been trying to figure out what the data listed means, but i am confused as when trying to compare the data to EI-core, i find it hard to find data listed the same way, some manufactors call things one word, another manufactor calls the same thing another thing :confused: ... So i was hoping someone can help me make the right choise here.

And now for the Main transformer; this is needed :
Primary:
230 vac
~220 - 250VA
Secondary's :
325 - 0 - 325 at 175mA minimum (I prefer at least 200mA here)
5 volts at 2 A or more
6.3 volts at 4 A or more (center-tap on the 6.3 volt winding is not required, but doesent hurt)

I had some more email conversation with Toroidy, and i can have the mains transformer wound as this for 107Euro (119$) :
> 325 - 0 - 325V (250mA)
> 5V (3A)
> 3,15 - 0 - 3,15V (5A)
With such secondary's i should end up with around 380v B+.
Also i asked them, how much load regulation there is on such transformers. The load regulation is ~12-15%, and the specified voltage will be there at approx. full load, so this is very good i think.
Are there any considirations on this transformer i should think of, or am i good to go with it?

I know it's a lot of quistions, but it's like that in my head right now :rolleyes:...
- Please bare with mw, and hey have a nice Xmas too very soon.

-- Jesper.
 
Hi Jesper!
Thermionic state at last? That reminds me I need to make some progress in the solid state domain...:D
The first OPT seems just fine. The second one does higher anode/primary current using the same core size obviously, which can take fewer turns of the thicker wire, so lower inductance. That reflects to turns ratio and primary impedance. But you can see both transformers can do the same frequency response if driven properly. And this is something to keep in mind. 3,2kohm to 8ohm or 3kohm to 8ohm? Probably none of them. Your speakers impedance is 8ohm nominal. In reality may be something else, usually around 5-6ohm(?). You can only tell if you take an impedance measurement. And then you could pic the OPT that reflects 3,2kohm to the 300b anodes. And then change everything if use other speakers... Otherwise, the first OPT.


The power transformer is OK.
 
Hi Jesper!
Thermionic state at last? That reminds me I need to make some progress in the solid state domain...:D
The first OPT seems just fine. The second one does higher anode/primary current using the same core size obviously, which can take fewer turns of the thicker wire, so lower inductance. That reflects to turns ratio and primary impedance. But you can see both transformers can do the same frequency response if driven properly. And this is something to keep in mind. 3,2kohm to 8ohm or 3kohm to 8ohm? Probably none of them. Your speakers impedance is 8ohm nominal. In reality may be something else, usually around 5-6ohm(?). You can only tell if you take an impedance measurement. And then you could pic the OPT that reflects 3,2kohm to the 300b anodes. And then change everything if use other speakers... Otherwise, the first OPT.


The power transformer is OK.

Hey Magic! :)

According to the manufactor the speakers are 4ohm up until 600Hz, then 8 ohm, and max 16 ohm at 3 Khz. - The chief at Audiovector DK also tells me that they tried 300b amps. on them back when they where in production. He tells me that they are good with 8 ohm OPT's.

I'am glad that you chimed in here also...

Jesper.
 

disco

Member
2006-04-17 6:27 pm
Holland
SE outputs can have two shortcomings in the frequency domain: Low rolloff and High rolloff. The number of turns determines the primary inductance, dropping with input level and exeeding DC-current. One should calculate the necessary inductance at 25Hz (0dB) for an absolute minimum. As DC-current fluctuates under load, one should increase this absolute minimum to allow for the effect of diminished inductance because of higher DC-current.
So, primary inductance varies under load. To minimalize this variation the core gap should be wide and turns number should be high. This can diminish HF response because of higher parasitic properties from capacitive coupling between layers and increased resistance. Because of this contradictive property, it is best to choose an OT for constant inductance characteristic suitable for the exact DC-current you want to apply and not for a higher current. HF response should be at least 35KHz at 0dB.
 

disco

Member
2006-04-17 6:27 pm
Holland
Regarding the mains transformer these thoughts.. Where a toroid can excel in frequency response as an OT I prefer (for exact this reason) the good old EI core for power. Take a large unit of double the VA you'll ever need and be done with it. Yes, it's more expensive but they will last forever, running cool and giving the best regulation there is while doing a good job to keep mains originated pollution out. Find a unit with separate primary and secondary chamber for the least HF coupling.
 
disco:

it is best to choose an OT for constant inductance characteristic suitable for the exact DC-current you want to apply and not for a higher current. HF response should be at least 35KHz at 0dB.

So your'e saying that by the data of the first OPT (the 100mA one) this is my best option?
Nevertheless i don't have more data on them as pasted here.

Regarding the power transformer, i take it into account, but i also have to say that i bought from them before, and the quality is really really good.

Jesper.
 
Evening all.

effective capacitance 11,2nF??? really???

Whilst quoting a -3dB point of 56 kHz? Yes, I don't understand this either.

Althrough i can't tell if those numbers are unrealistic, but as i wrote before they are serious
with everything toroids, so i cannot see if and why they will paste some unreal data?

Well i ordred two OPT's + a mains toroid yesterday, and around mid january i will have them at hand.

I am very excited to see/hear compare it to my AlephJ-miniature amp.

Merry Xmas

Jesper.
 
Yes, something about those figures does not match.

The capacitive reactance, Xc, at 56kHz of 11.2 nF is only 254 Ohms.
The 300B plate resistance, rp, is 700 Ohms.
Driving the primary with a 50 Ohm generator will get you to 56kHz, but only if the leakage reactance is low enough.

Either the capacitance is lower than 11.2nF, or the bandwidth with 700 Ohms driving the primary (300B) is less than 56kHz.
 
I tried to figure out what could be expected from the 80W push-pull CFB transformers from "Toroidy".
When I compared the datasheets of this model with primary impedance of 2k, 4k and 8kohm I found something disturbing.

They all have either exactly or almost exactly the same data:

Primary Inductance Lp 579 - 580H
Primary Leakage Inductance Lsp 4,21 - 4,54 mH
Total Primary DC Resistance 65 - 65,5 Ω
Effective Primary Capacitance 1,8 - 1,9 nF

That looks to me like the primary winding is at all 3 different primary impedance levels the same and only the primary/secondary winding ratio is changed.
 
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disco

Member
2006-04-17 6:27 pm
Holland
I'd say the constant primary DC resistance is a clue. Then again if the secondary has less windings, so should the leakage be less. The winding technique should have a near perfect push pull balance, probably on a non-gapped core allowing for little tube imbalance, hence the high self inductance. You could compare the numbers to VanderVeen or Amplitron toroids (if you can find published specs), these will probably not much depart.