James 6123 OPT Wiring Help

[kstylianos]

I'm currently at the point of wiring up the OPT and have a couple of questions.

I'm building Derek Waltons JE Labs 300b MK-II variant.

http://www.iol.ie/~waltonaudio/mk2300bmk1.html

I understand the secondary markings but have a few questions regarding the primary.

Question #1) The original JE labs uses an opt w/ a 2.5k primary. Dereks latest variant uses a Plitron with 3.5K. The James has 2.5, 3.5 and 5K windings. Any thoughts on which to use (and why)?

Question #2) The OPT has the following markings: 2.5-5K, B and S (I understand the others). The 436v from the power supply goes to the 2.5-5K pin, and the 300B goes to the "B" pin.....is this corect? Also, anyone know what "S" is?

Thanks for any help.

Here is a teaser pic:

[dsavitsk]

In general, lower primary impedance means more output power, higher means, perhaps, better sound ... though not always. Depends on the particular tube and the particular transformer. It is worth experimenting.

S means screen grid.

[kstylianos]

In general, lower primary impedance means more output power, higher means, perhaps, better sound ... though not always. Depends on the particular tube and the particular transformer. It is worth experimenting.

Thank you.....

So my previous thinking:

The 436v from the power supply goes to the 2.5-5K pin, and the 300B goes to the "B" pin.....

is correct?

[danFrank]

B is B+ or where your +436 volts go, 5K goes to the tube if you want to use the transformer as 5K primary imped., 2.5K if you want to use it as a 2.5K imped. S is the screen tap if you are using the transformer with a SE pentode.
Daniel

[ray_moth]

It looks great but I hope those can caps are not too close to the hot tubes. In the original, there seems to be a greater distance between them.

[Ciscokid]

Hi,
Nice looking amp! Any shots of the underside? Where are you planning to put the power trannies?

dg

[Sherman]

Excellent job on a nice looking amp!

Daniel has the markings down, just follow his advice. You won't be using the 'S' connection with 300B valves. Just decide on whether you want to go with 3.5K or 2.5K primary Z. As Dave said, lower primary Z gives more power and more distortion, higher Z gives lower power and lower distortion.

You could experiment both ways and decide what sounds best to you.

The James OPT you are using is a great OPT, especially for the price. I've got a pair in my KT88 monoblocks and they sound very good.

[kstylianos]

Thanks guys......I'm going to use the 3.5k taps.

I'll post a pic of the underside when shes complete.

The power trannys (Angela Universal) sit in the back corners. They were off in the picture as they were apart for shielding of the AC runs.

Just curious as to what affect cap proximity could have on the tubes?

Off to Radio Shack to get a few minor items. Hopefully it'll be singing this eve.

[dsavitsk]

Originally posted by Sherman
As Dave said, ...

Doug

[Sherman]

Originally posted by dsavitsk


Doug

Sorry Doug, I just got back from a trip with a Dave, and was talking to my wife about it while answering. (That's my story and I'm sticking with it! )