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Single-Ended Transformers |
VT1399 | |
| Inter-Stage Coupling Transformer | |
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Order No. VT1399 Price £30.00
Valve inter-stage transformer with four equal separate windings which can be combined for various ratios, including 1:1, 2:1, 1:2 and 1:1.5. Used as transformer drive of output stage valve grids. Size and style same as VT1087. Clamp mounting. Dimensions: 57W x 50D x 49H mm Overall width: 90mm (including feet) Fixing centres: 85mm Weight: 0.5kg Max. power: 5 Watts Max. DC: 30 mA Coupling loss: –2% DC resistance, all windings in series: 1,600 Ohms Possible permutations Volts - turns / impedance ratios: 1:1 / 3.75k : 3.75k 1:1 / 15k : 15k Step-down 2:1 / 15k : 3.75k Step-up 1:2 / 3.75k : 15k Step- up 1:1.5 / 7k : 15k (equivalent to e.g. Hammond 124D type) Interleaving of windings in any order is also possible as well as centre-tapped primary and/or secondary (series 15k connection). As a guide W1 is the first winding on the former, W4 is the last. For more specific connection details see also our VT1399 leaflet (PDF) With all windings in the same circuit it is also possible to make a choke. Max. possible impedance of all windings in series is 60 kilohms, or 200 Henries, however that would be before any DC is introduced. |
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Application Guide
The following diagrams illustrate possible uses:
Single-ended transformer coupling: (1:1, 2:1, 1:2, 1:1.5)
Direct Reactance Drive: (15k - 60k choke)
Phase-splitter for push-pull: (3.75k or 7k or 15k : 15k centre-tapped)
Push-pull driven phase-splitter: 15k centre-tapped : 15k centre-tapped)
Appendix - (14/01/2011)
Better coupling (for best frequency response) may be achieved by interleaving windings w2 and w3 as the secondaries between w1 and w4 as the primary - tag connections as follows:
w2 and w3 in parallel for 2:1 step-down (as shown), or in series for 1:1. This has proved very successful in the Aurora-7 300B SET and various other similar designs.
Note - to ensure best low frequency performance the driver valve should have a low Ra (anode resistance), e.g. preferably less than 10 kilohms where primary is two windings in series.
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