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Old 16th November 2009, 12:27 PM   #1
bst is offline bst  United States
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Default James OPT connections?

Purchased a pair of unused James JS-6236HS push-pull output transformers last weekend. These are 30W, 6.6K units. Unfortunately, they came with no datasheets or other documentation. I'm puzzled by the input-side connections, and would appreciate any enlightenment.

There are four output terminals, labeled 0, 4, 8, and 16 ohm. That's straightforward enough.

Next are six input terminals, labeled P1, S1, B1, B2, S2, and P2. This seems pretty clear as well, with one exception. P1 and P2 obviously connect to the plates of the output tubes, and S1 and S2 to the respective screen grids.

Now the rub: why two separate B+ terminals? All other OPTs I've used have only one for each transformer. I've perused several other manufacturer's datasheets (Tango, Tamura, Magnequest, One Electron, Edcor, Hammond, et al.), and find only single B+ feeds on the input side. However, Sowter does show a PP OPT datasheet with two separate B+ leads.

Questions: what is the purpose? How should they be connected to the power supply; can I simply tie them together? Are there two separate windings which need some kind of splitter resistors or pot to balance them?

Your help in solving this head-scratcher is much appreciated.
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Old 16th November 2009, 01:08 PM   #2
Join Date: Dec 2001
Location: Schaffhausen Switzerland
Simply connect the two B+ terminals together and attach to your B+.

Why they bring them out seperate who knows, don't fuss over it, I just know they work/sound wonderfully!

Regards, Allen
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Old 16th November 2009, 05:17 PM   #3
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Separate 'inputs' for B+ may be handy if you use DHT tubes with their cathodes fed in parallel, such as in the karna amplifier by Lynn Olson. As you can see, there is no possibility to measure individual currents in the cathodes, so you can measure current in the anodes by feeding each B+ through a 10R resistor (and measure voltage over this resistor). This is one example, surely one can think about other examples as well.
my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!
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