Maybe it’s my handwriting maybe your skills to read it but you found out that it is a SE transformer with a total of 1960 windings 😉 .
There are 3 layers of 4 Ohm, each with 0,53mm wire but the “8” Ohm has a trifilair winding of 34 windings and also 3 layers. When the 80 winding and 34 winding are in serie you get the real 8 Ohm tap.
Probebly presspahn, you are right but because of all laquer impregnation any other isolation would be fine too.
Afterall it measures not that bad, the copperlosses are high (i have to look at my notes but i guess about 0,4dB) but sqw is good enough and frequency response too. I have seen a lot worse transformers but anyway this is not my cup of tea.
Let me add. In the transformer world, minimum should be replaced by "optimal" (for the needed situation).
I did some simulations on this OPT. I don't know the core height to width ratio, so I put parameters of a 2:1 bobbin ratio of 28x56mm. The Afe considering 0.95 stacking factor is ~15.
MLT ~ 216
Average layer length ~ 45mm
Rdc primary ~ 100Rdc, considering the input of 0.3mm with 0.03 lacquer coating
Rdc secondary for full 6 layers assumed as 4R - 0.2Rdc, considering 0.58mm wire with 0.03 lacquer coating
Calculated Ls ~ 6.5mH, considering Rp to Ls roll-off at ~63kHz. In reality it will be slightly worse due to secondary layers Rdc imbalance.
In practice consider Ls roll-off to be higher due to rising speaker impedance.
In terms of Ls, not necessarily far from Hi-Fi. In terms of overall frequency response, of course the capacitances and their distribution are needed for a better picture.
Now, power. Considering
Primary impedance 2600R
Gapped at 12H for an unloaded -3dB response at 8Hz, 600R driver (close to 2xEL84 PSE), excluding primary and secondary ohmic losses.
Primary Idc @ 150mA. Headroom for more linear SE operation, bla bla. This gives us 0.66T Bdc and 29W (losses excluded)
Voltage swing of 255Vrms. This gives us 0.65T @ 30Hz and a power of 25W (losses exluded)
If the core is capable of 1.31T, why not?
The second to the right picture is an excellent example of how roll-off dominates over potential resonances. Roll-off could be either Cp, Ls, or both dominants. We observe a small kink @ 150kHz which would be more or less visible when altering test conditions.
There are two types of resonances (by shape) in HF response - peaks or dips. Peaking is caused by clumped parallel capacitance to Ls (series RLC) and is easiest to treat externally. Dipping however occurs due to Ls resonating in a variety of Cs capacitance bridges and their distribution of values. In some projects even coil to core and coil again capacitance should be taken under serious consideration.
There are two types of resonances (by shape) in HF response - peaks or dips. Peaking is caused by clumped parallel capacitance to Ls (series RLC) and is easiest to treat externally. Dipping however occurs due to Ls resonating in a variety of Cs capacitance bridges and their distribution of values. In some projects even coil to core and coil again capacitance should be taken under serious consideration.
The bobbin is 44x38mm and 52 long.
I think it was original for 3 EL84. Those tubes never are able to give 25W.
3 layers of 4 Ohm, not 6. And serie 34 winding for the 8 Ohm (3 layers each layer 3 wires= triflair)
Primary 150mA? Not with EL84. Btw it was indeed original for 2 EL84, but the transformer i had was uses with 3. The former owner did a modification. The 600R is closer to 3 EL84 in triode mode.
I can design an OT with the data you gave but we would need the exact dimensions of the winding case because this aspect is extremely important
Thanks.
The winding case/bobbin is very inefficient
Space is 48 x 10,5 mm.
If I make one myself which i don't like space could be 52 x 12 mm.
I guess 4000 P and 160 S.
Is the height of the bobbin to core 10.5mm?
Prepare some space for winding bowing, at least 2mm to be safe.
Prepare some space for winding bowing, at least 2mm to be safe.
In my books, sectioning for this project (5k on SM85B) of P6-SS-P6 is good enough. You are free to split primaries further and reverse their direction for better capacitance distribution. For example you could do a (P4(rev)+P2 )- (SS) - (P6(rev)
Primary wire max raw diameter: 0.36 (12 layers of 125 turns) (1500 turns overall)
Secondary wire max raw diameter: 1.06 (Full layer of 42 turns for 4R, bifiliar 21+21 for 1R). Making the bottom layer 4R and the top 1R will give you 4R and 9R output capabilities.
Approx Rdc primary - 66R
Approx Rdc secondary for 2 paralleled 4R windings - 0.085R
Gap to taste Idc vs primary inductance ratio.
Primary wire max raw diameter: 0.36 (12 layers of 125 turns) (1500 turns overall)
Secondary wire max raw diameter: 1.06 (Full layer of 42 turns for 4R, bifiliar 21+21 for 1R). Making the bottom layer 4R and the top 1R will give you 4R and 9R output capabilities.
Approx Rdc primary - 66R
Approx Rdc secondary for 2 paralleled 4R windings - 0.085R
Gap to taste Idc vs primary inductance ratio.
This is an SM85b that seems to match the case data given by you, can you confirm ?
Attachments
P.S. I was wrong on P4(rev)+P2. You could simply go P6-SS-P6(rev). Connect Anode to core closest primary layer and B+ to closest to the secondary layer of the second reversed section. IRRC, such example of P-S-P(rev) is depicted also in Crowhurst/RDH4 examples. You will get lower Cs value and could go with simpler dielectrics (higher dielectric constant). Primary to secondary capacitance factors of reversed primary is 0.29 instead of 0.5. That results into 1.72 times less capacitance.
The drawback in such case is the higher primary to core to primary capacitance factor, which in projects with higher primary turns can cause a bad dip resonance, but not in this project with low amount of primary turns.
The drawback in such case is the higher primary to core to primary capacitance factor, which in projects with higher primary turns can cause a bad dip resonance, but not in this project with low amount of primary turns.
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Thanks. I am surprised by the low windings count of 1500. The foto looks like the core I have.
If you confirm it is a 2 x SM85b with a rated catalogue Afe of ~11.32sq.cm, then yes. It can handle 6W @ 25Hz output capacity with 1500 turns.
And then if you need more power = more primary turns.
And then if you need more power = more primary turns.
So this is correct. With the stacking factor (varies with different manufacturers) goes to ~11 cm^2
As for the secondary, it's advisable to go to 3 layers: Two 4R layers of 42T and one bifiliar 18T+18T will give you the ~8R tap.
By giving two layers on the 4R, you are equalizing Rdc to impedance ratio for both secondary taps.
So final sectioning looks like...
con.A-P12(rev)-- (right to left)
-------P11(rev)-- (left to right)
-------P10(rev)-- (right to left)
-------P9(rev)---- (left to right)
-------P8(rev)---- (right to left)
B+----P7(rev)---- (left to right)
------------------ Capacitance factor ~0. Select dielectric mainly by DC breakdown.
8R--S18+18T--4R (left to right) (connect all 4Rs together) (18T+18T) connected in parallel.
gnd----S42T---4R (right to left) (connect all 4Rs together)
gnd----S42T---4R (right to left) (connect all 4Rs together)
------------------ Capacitance factor 0.293. For MLT of 190mm, layer length45mm, and 0.3mm presspahn with DC of 3.5, that gives us ~260pF
con.A----P6--- (right to left)
----------P5--- (left to right)
----------P4--- (right to left)
----------P3--- (left to right)
----------P2--- (right to left)
Anode---P1--- (left to right)
As for the secondary, it's advisable to go to 3 layers: Two 4R layers of 42T and one bifiliar 18T+18T will give you the ~8R tap.
By giving two layers on the 4R, you are equalizing Rdc to impedance ratio for both secondary taps.
So final sectioning looks like...
con.A-P12(rev)-- (right to left)
-------P11(rev)-- (left to right)
-------P10(rev)-- (right to left)
-------P9(rev)---- (left to right)
-------P8(rev)---- (right to left)
B+----P7(rev)---- (left to right)
------------------ Capacitance factor ~0. Select dielectric mainly by DC breakdown.
8R--S18+18T--4R (left to right) (connect all 4Rs together) (18T+18T) connected in parallel.
gnd----S42T---4R (right to left) (connect all 4Rs together)
gnd----S42T---4R (right to left) (connect all 4Rs together)
------------------ Capacitance factor 0.293. For MLT of 190mm, layer length45mm, and 0.3mm presspahn with DC of 3.5, that gives us ~260pF
con.A----P6--- (right to left)
----------P5--- (left to right)
----------P4--- (right to left)
----------P3--- (left to right)
----------P2--- (right to left)
Anode---P1--- (left to right)
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