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  #211  
Old 07-23-2011, 09:43 PM
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leadlike leadlike is offline
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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?
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  #212  
Old 07-24-2011, 12:05 AM
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Quote:
Originally Posted by leadlike View Post
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.
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  #213  
Old 07-24-2011, 02:15 AM
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Quote:
Originally Posted by miniman82 View Post
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

Last edited by Kevin Kuehn; 07-24-2011 at 02:31 AM.
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  #214  
Old 07-24-2011, 07:49 AM
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Quote:
Originally Posted by miniman82 View Post
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?
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  #215  
Old 07-24-2011, 09:21 AM
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cbenham cbenham is offline
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<---> 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
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  #216  
Old 07-24-2011, 09:50 AM
kvflyer kvflyer is offline
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Originally Posted by cbenham View Post
...
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.
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  #217  
Old 07-24-2011, 11:04 AM
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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

Last edited by Penthode; 07-24-2011 at 11:18 AM. Reason: updated
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  #218  
Old 07-24-2011, 01:57 PM
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No, only an isolation transformer off the heater string that supplies all the other tubes.
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  #219  
Old 07-27-2011, 01:42 PM
DrRick DrRick is offline
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Please let me know what else you may need for the power supply. If I have anything you need, it's yours for the shipping cost.
I have, literally, a ton of PS iron, etc..

Rick
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  #220  
Old 07-27-2011, 03:25 PM
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OK, thanks for the offer! Right now I have the chassis Bob gave me, with a pair of tranformers that look like they are up to the task, twin ST glass 5U4G rectifiers and enough stuffable caps to build something useful. If I need anything more, I'll keep you in mind.
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  #221  
Old 08-29-2011, 08:53 PM
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Update: I may have a line on a very nice cabinet for this chassis. It's a 9-T-79, which uses the 19" tube. It's got 4 doors, 2 for the screen and 2 for the speaker. Very classy. The seller says it's 24" deep, which should be more than enough to hold the entire color chassis without any of it sticking out. Only question is, will I be able to make a nice bezel to adapt this cab to the smaller 16" pix tube mask?
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  #222  
Old 08-29-2011, 10:07 PM
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I've already got an idea on how to make a mask for it, we could whip one out in less than a day. ( If nothing goes wrong :3 )
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Last edited by zenithfan1; 08-29-2011 at 10:11 PM.
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  #223  
Old 09-04-2011, 08:56 PM
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Here's the set in question:

http://nashville.craigslist.org/fuo/2520420291.html





I already sent a payment through Paypal, but she has never used it before so we'll see if it goes through OK. If so, I have a job up on U-Ship right now to get it here. There is also another potential Bob alerted me to, this time on Ebay:

http://www.ebay.com/itm/RCA-Victor-T...item45fcd745e4



Of the 2, the second one would be better since it has the smaller 16" pix tube. The developmental tube would fit right in, no mods at all. I have to admit though, I really like the looks of the 19" one with it's double doors and all. I suspect I will end up with both, and I'll have to choose. I have promised a friend first crack at whatever I don't need (tubes/chassis), anything else will be offered here at a very low price.
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Last edited by miniman82; 04-15-2012 at 03:01 PM.
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  #224  
Old 09-04-2011, 09:01 PM
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Looks like two 16" sets to me...?
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  #225  
Old 09-04-2011, 09:06 PM
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I thought so too, but she looked at the back of the first set at my request: it's a 9-T-79, which uses the 19AP4.
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