Part 4: The output transformer GIT80

of The Vanderveen Project

The core of the GIT80 is not gapped, therefore the primary inductance LP is large. At low frequencies all the energy from the tube goes into the loudspeaker while the core loss is negligible. Single ended circuits now need quiescent current compensation. The core is large and can handle 80 Watt. The figure shows the windings and their taps plus dimensions and technical specifications.

In every transformer the ratio of primary and secondary impedances is given by (np/ns)2, where np equals the number of primary turns used and ns equals the number of secondary turns used. See the tables for more details.
Single ended: in the circuits 1-9 only the upper halve of the primary is used, the current compensation is connected to tap 5. The primary impedance Za depends on the impedance Zs of the loudspeaker and to which taps this speaker is connected. The single ended amplifiers are designed for Za = 2000. A loudspeaker with 8 impedance therefore should be connected between the secondary taps 1 and 3.
Push pull: the circuits 10-16 use a primary impedance Zaa = 4000 . A loudspeaker of 8 should be connected between the secondary taps 1 and 4. In the circuits 19 and 20 a larger voltage supply is used. There the primary impedance equals 8000. The 8 loudspeaker now belongs between the taps 1 and 3.
Cathode follower: circuits 17 and 18 need a primary impedance Zcc = 900. The 8 loudspeaker should be connected to the taps 1 and 3.

More news to follow soon!