Eros 2 Step-up Transformers

[Paul Birkeland]

Wouldn't the external SUT be easier to shield? I'm thinking about using an external SUT instead of the Sowter/Jensen/Cinemag to avoid shielding issues.

I would suggest considering that we have tested the placement of the Sowter transformers on the Eros 2 to verify appropriate placement and that they don't interact with the power transformer.  You also won't need to deal with another set of interconnects and another drain wire to connect the Eros to the separate box that holds the transformers.

[Paul Joppa]

To amplify (sic) PB's points, Jensen warns that for best performance the secondary load must have very low capacitance - a couple feet of coax (100pF) is more than enough to harm the high frequencies. Eros is especially well suited to use transformers, because it uses a pentode input tube with about 4pF input capacitance.

This is different from moving magnet carts, most of which are designed for 100-500pF in parallel with the 47K input resistor. A 3 to 6 foot cable accounts for about half of that, and the typical triode input stage Miller capacitance accounts for the rest.

[maarten]

Ok I will go for the Sowter! Will try to find them somewhat cheap (in EU)

[maarten]

Just a small question here as my Sowter pair arrives.

In your early prototype picture, you have a 220 Ohm going from pin 9 to the jack. I guess this was changed to 90.9 Ohm later? (You also have an extra heatshrink wrapping on the Right side (in the manual it's only on Left) btw.)

That resistor is a 90.9 Ohm and goes to terminal 2/17 right? There's no need to change it to a 220 Ohm one?

And then, the 47.5k resistors  that used to go from ground to jack, just go to 1-2 (and 16-17).

Thanks for clarifying