Donor power section question

[luthierwnc]

Hi Guys,

I am thinking about the "winter project" and am looking at a big 4-tube Baldwin organ as a donor. I have what I am pretty sure is the schematic. There are actually four schematics on the diagram. Three have a pretty conventional filter choke arrangements. The one on auction has this set-up. The center tap of the power trannie goes through a big-assed choke to ground. The B+ goes to the center tap of the output trannie and through the usual dropping resistor cap string to the screens and inverter tube.

Has anyone seen this before? If so, how does the choke smooth the waveform? Again, the choke is a 4-bolt dude almost as big as the OT.

Thanks, Skip

[Steve Conner]

It's just an ordinary CLC filter. Note the 4uF cap before the choke, and there should be another one hooked up to the OT center tap.

The only difference is that the choke has been relocated to the negative line instead of the positive one. Maybe they did this to reduce voltage stress between the choke's windings and its core, but from an electrical point of view it behaves just the same.

[luthierwnc]

Here's the full schemo. I haven't seen the cap between the HV supply before. I'm sure I can make it work but was mostly concerned what going off the reservation would do to the B+. There are four 4-tube versions of these that come up on Ebay fairly often. This is the only one that isn't stereo or dual power section. Thanks, sh