Prototype set is here

[miniman82]

Might have a potenial power supply, it's from an old organ. Thanks to Bob G for the parts. Top transformer is the B+ stuff, bottom is filament only. Should have enough power to do the job, I think.

[leadlike]

Yeah, building a power supply like that will really show you how much power those filaments need. I think I had to use a 15A filament transformer to run my GE 802's power supply, where the filaments consumed something like 12A. What's the filament draw on your set going to be?

[miniman82]

Originally Posted by leadlike

What's the filament draw on your set going to be?

No idea, but this filament PTX came from an organ which always have a bazillion 12AU7's in them. I don't think it will be a problem as far as that goes, I just hope I can come up with all the B+ supplies it's gonna need. I think right now I'm looking at a 250-ish rail, 380-ish rail, some yet unknown B- supply (maybe around ~100), and possibly a small positive bias supply. Interestingly, one of the filament windings on the B+ PTX is 6.6v center tapped... I guess I could always run 5U4's at a volt more than normal, but perhaps 3DG4's would be more appropriate? Then again, it's entirely possible that the voltages will get a little lower once the thing is loaded down really good.

[earlyfilm]

Originally Posted by miniman82

Interestingly, one of the filament windings on the B+ PTX is 6.6v center tapped... I guess I could always run 5U4's at a volt more than normal, but perhaps 3DG4's would be more appropriate?.

Since the early vacuum tube TV days, the ubiquitous 5U4 has gone from the lowest-priced commonly-replaced bottle to being quite dear today. I'd say running those babies at 6.3 volts could get expensive in a hurry. I wonder if they make 1.3 volt 3 amp pilot lights?

On a twin-tube "B" supply, if one tube opens a filament, the other tube promptly melts before the user notices and can shut the system off. On 5U4's this problem seemed to be worse with the fat G's and first generation GT's than with the GB's

If the filaments were wired in series, this would protect the second tube.

Are the tubes in the picture from the organ? If not, any idea what tubes the organ used?

[cbenham]

Originally Posted by earlyfilm

<---> On a twin-tube "B" supply, if one tube opens a filament, the other tube promptly melts before the user notices and can shut the system off. <--->

Someone in this forum pointed out several years ago that wiring a 5U4's plates in parallel and connecting to *just* one side of the B+ winding, then doing the same thing with a second 5U4, but with both tube's filaments connected in parallel to the 5 volt PTX winding, will possibly save the other tube and the PTX in the event of a failure.

The idea is that if one tube shorts and blows the filament open, the remaining tube will be the only load on the transformer. The B+ will drop, but the transformer will not be overloaded.

A 6.6 volt filament winding is sometimes used if the power supply is on one chassis and the load circuitry is on another separated by 2 to 4 feet of heavy cable. The voltage drop through that cable can be in the range of ~0.3 volt if the filament draw is substantial.

Cliff

[kvflyer]

Originally Posted by cbenham

...
A 6.6 volt filament winding is sometimes used if the power supply is on one chassis and the load circuitry is on another separated by 2 to 4 feet of heavy cable. The voltage drop through that cable can be in the range of ~0.3 volt if the filament draw is substantial.

Cliff

And you can use larger wire for the filaments.

[Penthode]

Because the damper tubes in those days may suffer cathode to filament breakdown, was there originally in the prototype previously provision for a separate filament winding for the damper?

Terry

[Kevin Kuehn]

Originally Posted by miniman82

Might have a potenial power supply, it's from an old organ. Thanks to Bob G for the parts. Top transformer is the B+ stuff, bottom is filament only. Should have enough power to do the job, I think.

So, I guess what we've got here, is an organ donor?

Sorry... late night humor

[dieseljeep]

Originally Posted by Kevin Kuehn

So, I guess what we've got here, is an organ donor?

Sorry... late night humor

Nick! I was looking at the schematic for the first Westinghouse. It shows two B+ supplies, using three 5U4's. Two of The 5U4's are connected in parallel and supply the 280 volt source. The remaining one supplies the 390 volt source. The original transformer had a tapped HV secondary plus two five volt rectifier windings. I would also go with a different power supply chassis, like from a Magnavox radio.