Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chip on September 03, 2012, 12:12:55 pm
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Just double checking how to hook up a Hammond 272HX Power Trany with 5u4gb.
Secondary: 300-0-300 V, 200 Ma Red—Red/Yel—Red
Filament winding #1: 5 V, 3 A CT Yel—Yel/Blk—Yel
Filament winding #2: 6.3 V, 6 A CT Grn—Grn/Yel—Grn
1) Does the CT (Yel/Blk) of the Filament #1 not connect to anything?
2) Yel’s of Filament #1 goes to 5u4gb pin 2 and 8 and pin 2 or 8 also to CT of OT?
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Just securely tape off the YEL/BLK lead and tuck out of the way.
Connect one YEL to pin 2 of the 5U4. Connect the other YEL to pin 8 of the 5U4. Pin 8 is the B+ output from the rectifier. It usually connects to the first filter cap (maybe thru a STBY switch) and the OT center tap connects here as well, ***IF*** you don't have a STBY switch.
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The intent of the Hammond 5v CT is this:
You wire the yellows to the rectifier filament pins as usual. At this point, you'd typically run a wire from one of the filament pins to the first filter cap.
Hammond's thought is you could forgo adding the extra wire, and use the yellow/black CT to run to the first filter cap, with no extra wires from the rectifier socket.
Problem is, you wouldn't ask if you already knew this. And if you didn't know it, you might follow a layout and add the extra wire between the rectifier socket and filter cap, which is going to tend to short one-half of the filament winding.
So you can use it if you're very careful to verify what you're doing. Or you can so what Sluckey said and tape it off and stay out of trouble.
If I had that CT I'd use it, but that's just me.
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> Does the CT (Yel/Blk) of the Filament #1 not connect to anything?
Do what Sluckey says: secure that CT wire away from trouble, just use the 5V leads.
> Pin 8 is the B+ output from the rectifier.
5U4GB is a naked-filament rectifier, no cathode. Either 2 or 8 (not both!) may be "B+ output". It is perhaps conventional to grab pin 8 since that's where the cathode is on most other Octals.
As HBP says, you can save one wire-end *if* the 5V has a CT. *AND* in principle taking a winding CT here nulls the 60Hz component of the ripple you get when you take one end. I recall somebody being prodded into actually 'scoping this..... the difference is nearly invisible at ~~400V, and certainly moot.
The CT was common in the 1930s, when speccing a CT lead was cheaper, the wiring was neater, caps were much more expensive, and B+ voltages were a lot lower.
The main reason to ignore (hide) the CT: that connection is SO uncommon now, that the next guy to work in there (could be you years from now) will not understand, which leads to misconnection, which leads to smoke, perhaps costly PT smoke.