Dimensions and availability of Dowdy choke?

[Jim R.]

Hi Mike,

Can you tell me/us the dimensions of the dowdy choke and what typical delivery time is?  After being set straight by some fellow bottleheads and PJ, this does appear to be a good upgrade for the SR-45s I bought from Doc.  BTW, space probably isn't as much of a concern as I'm rebuilding my SR-45s (eventually) on some 8" x 11-1/2" copper plates and in the "portrait" orentation, so there will be some extra room to the new front and back of the power transformers.

Thanks,

Jim

[xcortes]

Jim, they're 28 by 27.4 (cm of course!). They do fit (very tightly) in a Paramount/Paramour chassis. Better mount them on the driver tube side.

[Paul Joppa]

The location of the chokes is chosen to minimize magnetic induction from the power transformer. What's important are the perpendicular coil axes, and the symmetrical fore-and-aft location.

[Jim R.]

Just sent in my order for a pair of the dowdys.

Paul, can you clarify one thing about what you mean when you say symmetrical?  Do you mean that the opt on one end of the pt and the plate choke on the other need to be the same distance from the pt core, or do you mean aligned on center lines?  Or both?

Also, can the bpc-15 in the sr-45s be recycled into the s.e.x. 2.1 -- with the appropriate adjustments?

Thanks,

Jim

[Paul Joppa]

I meant fore and aft, which I think you meant by "aligned on center lines," for the transformers. It's strenuous to imagine the magnetic field lines in three dimensions, but as an engineer/scientist yourself I expect you will - how shall I put this - enjoy the challenge. Yeah, that's the ticket, "enjoy"!

The regular BCP-15 makes 40 henries, same as the stock SEX 2.1 plate choke. The Magnequest BH-2 (and the BCP-15 gapped for 40mA instead of the usual 50mA) makes 50 henries. Except for this relatively small difference, they all work the same in the circuit. Personally, I would not bother changing the parafeed capacitor for this small difference. If you have more than one option on hand, it would be a very interesting and educational exercise to listed for any differences, and we would all appreciate you sharing of the results if you do so.  :^)

[Jim R.]

Oh, you have no idea how much time I've put into coming up with a good 3d mental map of the flux lines around various transformer cores. :-)

Yup, we're talking the same thing as fore and aft is given with you thinking the standard layout with the plate in the landscape orientstion.

I plan to make mine, if it were in the same orientation, an inch wider, hopefully with the binding posts centered on the top directly fore'n'aft on the output and between the OPT and the edge of the chassis base.  Also going to put the rca jack near enough to the driver tube so the grid stopper resistor is the only thing between the rca hot and the grid pin.  Then the power inlet and power switch  near where the binding posts and rca input are in the standard layout.  Then I'm going to turn it all 90 degrees so that it is deeper than wide and then all the connections come in the back and also pretty much stay out of each other's way.  And yes, I'm trying to get a good handle on the flux lines near the corners of the PT too.

If the mounting hole positions for the dowdy and the existing bpc-15 line up, then it will be super simple to A/B the two chokes in these amps, but I'm not likely to go drilling a second set of holes in this nice piece of copper I have.

Of course this is for the future and I'm first just going to enjoy the SR-45s -- which I surely hope to setup with the Nagas next week.  The final big moving day is Friday of this week, and then at least everything will be at the new place -- yesterday myself and a couple of friends moved all the audio gear and most of the computer gear over, so at least I don't have to trust that to the movers.  It's all safe and sound just waiting for me to come over and set it up -- but unless the rest of the junk is going to pack itself, then that won't be until after the move and unpack.

-- Jim