The LL1691 and LL1691B are our most popular SE transformers for high impedance high power tubes.

However, so far these transformers have only been available with an 8 ohms secondary.
With a minor modification we have now been able to extend the above range with:
LL1691D (10k : 4, 16 ohms) and LL1691E (20k : 4, 16 ohms)

Read more about them here: