Relay board with 6.3VAC center tapped and bridge?

[Mickey_C]

I corrected the relay board, as it would make the tranny get warm (though it didn't blow fuses) when connected to a 6.3Vct filament winding.

Both sides of the bridged voltage are tied to ground with 100R resistors.

I admit, I lifted this idea from Kevin O'Connor TUT1.

Anybody know why or how this works?

Mickey

[mhuss]

Does the 6v3 CT winding have the CT grounded? If so, you're just doing the DC version of the 'virtual center tap' thing with the two 100R resistors, the same as if you were doing it AC-wise with a non-CT 6v3 winding.

If you directly connect the - side of the bridge to ground, then the left two diodes are conducting half of the secondary current (3.x volts) directly to ground every half-cycle -- this will warm up your PT a bit.

--mark

[David Root]

If you're using the TUT book design, the pair of 100 ohm resistors replaces the CT as a means of referencing the 6V3 to ground. The TUT method leaves the AC unreferenced (CT not connected to anything), and references the DC after rectification. Using 1% resistors on the DC side forces very good balance. I have put them before and after the tube string, doesn't seem to make any difference.
DC circuits can actually hum if they're not set up right! Hard to believe I know.

[Mickey_C]

Thanks Mark - that makes sense. It actually works!

David - different drawing. I know about that method, this is the drawing for the brown-out relay power supply, in the switching section, that I lifted it from. The resistors are placed as shown. I think it works for the reason Mark pointed out.

Best part of all is I can ground the common-ground of the relay board now, which helps reduce noise.

[drz400]

Thanks Mark - that makes sense. It actually works!

David - different drawing. I know about that method, this is the drawing for the brown-out relay power supply, in the switching section, that I lifted it from. The resistors are placed as shown. I think it works for the reason Mark pointed out.

Best part of all is I can ground the common-ground of the relay board now, which helps reduce noise.

Dont those 100ohms get hot?