Roger's Output Transformers
Designed by
phone/fax: +46 31 252345

This second generation special cored low leakage symmetrical wound KE57613-B tube output transformer prototype, which almost meets Williamson's specifications from 1947, has the following design parameters:

Primary windings (50W):
- 2X115V@20Hz (Imax=0.22A)
Secondary winding:
- U0=6.5V, Imax=5A
Miscellaneous data:
Dimensions/Weight: 52X100mm/1kg
Total primary inductance: 45H@5V/50Hz
Leakage inductance: 47mH (42kHz@KT66 p-p drive)
Total primary DC resistance: 233Ohm
Maximum power input: 50W@230V/20Hz
Inductance vs DC unbalance:-

KE57613-B, My Second Generation Output Transformer Prototype

Which makes the transformer useful as for instance:
- Standard Williamson OPT using push-pull KT66/807/6L6GC/EL34 drive with 8Ohm speaker load only (15Wsin@807).
- Boosted Williamson OPT using push-pull KT88/6550/PX25/300B drive with 4-8Ohm load (Psqr@6550>30W, +/-30% Class AB if biased@6R).
- Custom tapping at outermost secondary may however also be used but is not recommended.
- May also even be used as mains isolation transformer for f.i tube preamps (<230V@0.2A, 13V@0A)

More info:
KE57613-B, Independent OPT Test Results