Quote:
Originally Posted by vishalk
So i decided to go through all the component values for the ST20.
Now for some reason the components have changed values over the years?
For example on different wiring diagrams and lists of parts:
R5 can be 47k or 100k
R12 470k or 1M
R13 470k or 1M
C5 0.1uF or 0.02uF
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Much of this happened when Leak discovered that they couldn't exceed the EL84's specifications and get away with it (with previous amplifiers the output valves had generous safety margins, but the EL84 doesn't). So they had to change the output transformer design and also some component values to stop the EL84s going into thermal runaway. The 47k/470k/0.1uF values relate to the later amplifiers which had type 8778 output transformers (you may have labels on the bottom of your transformers giving the type number). The earlier amps had type 3921. If your amp was an early one and it has been to Leak for a service then they will have changed the transformers. So the documentation won't necessarily match the transformers you have.
Cheers,
GJ