CT on single ended OT?

[johnnyreece]

So, I'm working on converting an old organ amp, when I see something interesting on the OT...it's a single ended 6V6, but the OT has a CT, and it's grounded by a 220 ohm resistor in series with a 100 ohm in the schematic. What's funnier, the actual wiring is (what appears to be) a 560 ohm resistor (color bands green blue brown silver) to a 100 ohm. Here's the schematic:

http://aronnelson.com/gallery/main.php? ... alNumber=2

I'm eventually shooting for a Magnatone 410. Any reason I couldn't just leave the CT disconnected? I appreciate any guidance!

[Stevem]

Well two things!
1) the manufactuer must have got a killer deal on a truck load of those OTs on surplus which made them have to do that strange resistor deal, and 2, the winding impeadence from the B+ input to that resistor grounded center tap must be quite high to not short out the B+ voltage.
The schematic using two separate resistors instead of one makes me really wonder what the designer was smoking that day!

[johnnyreece]

*sigh* lesson learned...don't believe everything you read on the internet. I've attached a copy of the official schematic, which will make things easier...Looks like NFB to me. Not sure why the value is more than double the schematic, but hey, why not?

[Firestorm]

That's an impressive error on a redrawn schematic! So in the actual amp, is the feedback connected properly or is there really an extra primary tap?

[johnnyreece]

That's an impressive error on a redrawn schematic! So in the actual amp, is the feedback connected properly or is there really an extra primary tap?

Well, that's the thing...there's a white wire that comes from the OT and goes to the speaker, a bare wire that goes to ground (a black wire is connected directly to the chassis and goes with the white wire to the speaker), and a green wire that is connected to those resistors (which, other than the value being different, looks like it follows the schematic). I've not measured the OT for continuity yet, but, if the schematic is correct, I should get almost no resistance from the green and white wires. Yeah, that is quite an error. Think I'm going to just toss that version of the schematic.