Odd OPTs

[EWBrown]

I recently (and cheaply) glommed onto a pair of "odd" 6BQ5 OPTs, these are marked "Baldwin Electronics" and from rough measurement techniques, the impedances are thusly: Secondary 8 Ohms, Primary 1 (plate to plate) approx 8,000 Ohms CT , Primary 2 (or secondary 2?) 77 Ohms CT. No UL taps, I would make a SWAG that the 77 Ohm CT winding is for cathode feedback? THese would be a good try-out with SV83s, as they need reduced screen voltage (200V). I doubt that this 77 Ohm CT winding would be proper for feeding the screens, but it might make for an interesting experiment (or a lot of electro-smoke).

These do seem rather small as compared to Z-565s or Hammond 1650Fs,
so either the power capability is lower (10 Watts) or the freq response will not be as good.

The only "Baldwin" I can immediately think of is Baldwin Organs. :?

/ed B in NH

[Shannon Parks]

Secondary 8 Ohms, Primary 1 (plate to plate) approx 8,000 Ohms CT , Primary 2 (or secondary 2?) 77 Ohms CT. No UL taps, I would make a SWAG that the 77 Ohm CT winding is for cathode feedback?

Ed, is this 8k ohms DC resistance?

The only "Baldwin" I can immediately think of is Baldwin Organs. :?
/ed B in NH

Yeah, I immediately thought of a Lowery organ we used to own. Unfortunately, I discovered it was all solid state when I went to rip it apart.

Shannon

[EWBrown]

The 8K is impedance, not DC resistance. I use the simple method of applying a known low (16VAC) voltage on the primary, and making voltage measurements on the other windings, and determining the
impedances as being a square of the ratio of the voltages, So, an (assumed) 8 Ohm secondary would show about 0.5 VAC, the 77 ohm winding about 1.56 VAC, etc.

I've also used this method to test the HWT trannies, and found that their claimed plate load impedances aren't always accurate, the 10K SE OPTs
proved out to be closer to 8K primary for a 4/8/16 ohm secondary.
The PP trannies I tested this way were within tolerances.

/ed B in NH

[Shannon Parks]

The 8K is impedance, not DC resistance.

That second primary of 77 ohms had me confused. :?
Thanks!

Shannon

[EWBrown]

I figured the 77 ohm winding was too low a ratio for screen UL usage, and too high for speakers, possibly they used cathode feedback. I have a couple of PC boards pulled from an SCA-35, I might twy setting up one or both of these with the Baldwin OPTs and try them in various configurations. Including using the 77 ohm winding, connected to a 200 VDC source, for the SV83 screen grids' lower voltage requirements. Maybe it won't really be UL but it's worth a try. And it anything does go "critical" it will just be old semi-retired phenolic dyna-boards and not a nice new DIY board. So far, I have been lucky, no power on catastrophes yet. :? I have taken a few 360 VDC "hits", I guess my caution has been made complacent by dealing for so long with low VDC circuitry. 12 or 24 VDC doesn't really bite, but 360 (and higher) definitely packs a wallop... :shock: :shock: :scrambleup: :crazyeyes: :shocked!: :onfire:

/ed B in NH