Filament Wiring

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W9ZSL:
Dumb or not so dumb question time. Part of my heart rehab has been doing some much-delayed building. I decided to build the parallel 807 amp from the 1957 ARRL Handbook.  It's going to be primarily for AM on 80 and 40. Just finished with a power supply for the RF. While it has a couple 6.3 V filament windings, rather than run the leads from the bottom of the rack, I decided to put a separate transformer under the RF section chassis. It will be about 8" away from the 807s. The diagram assumes 1/2 of the filament winding is grounded and calls for a ground of pins 4 (cath) & 5 (fil) at the socket. The iron has a center tap. If I grounded that instead, could I wire a twisted pair to the tubes (or not twisted) or just ground one of the 6.3 leads at the xfmr and run a single wire to the tubes? Shielded? Is one method better than the other?  I know a twisted pair is common for audio amps. Speaking of which, I have a second (older) 600 V supply for the modulator. That will run a pair of 6146s because I'll get about 95 watts...more than enough to do the job. The 807s will run about 120 watts inpoot.

DMOD:
Here is the way it is some times done with a single 6.3V secondary.

It has a Unipotential (sleeve) cathode so the cathode can be grounded anywhere the filament is grounded.

If the filaments are wired in series then you would need a 12.6 volt filament transformer.

I don't know what schematic you're looking at but the second schematic may be what you're talking about.

Phil - AC0OB

W9ZSL:
The original shows both cathodes grounded at the socket and 1/2 of the 6.3 secondary grounded at the transformer. A single wire feeds each tube and filaments are in parallel.  One terminal of the filament of each tube is grounded at the socket also. My xfmr is 6.3 VCT and I'd like to ground the center tap and then run each side of the secondary to the tubes. They would not be in series. I've seen it done both ways and am wondering if either one has any particular advantage over the other. I'd rather ground the Center Tap and run the other two wires to the filaments. There are only the two 807s in parallel with no other tubes on the chassis. There's only one schematic.

DMOD:
Quote

My xfmr is 6.3 VCT and I'd like to ground the center tap and then run each side of the secondary to the tubes.


It won't work. A 6.3VAC center tapped secondary has 3.15VAC on either side of center tap. Your filaments would be running at 3.15VAC each.

Get a 12.6VAC CT transformer and wire according to my schematic #1.


Phil - AC0OB

KA2DZT:
You can use your filament xfmr with the CT, just don't use the CT.  Leave the CT taped off and follow the schematic you posted.  Filament wiring is usually the easiest part of any tube project and normally doesn't require 20 questions.  Wake us back up when you get to the harder parts of this amplifier project ;D

Fred

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