Another Project?

[leadlike]

Wow, I knew that this thing would eat a lot of power, but this is pretty excessive:

The tv tube filaments alone add up to 9.4 amps!

The radio filament string will require 2.7a

The phono filaments, .6a.

The 5y3 plates will need to supply 440v @ 85ma, the 5u4, 270v @ 160ma.

So now, where to get something like this? Playthings of the Past has a nice list of spares here:

http://www.oldradioparts.com/2a23efl.txt

The closest thing that I own in my spares is a transformer to an rca T120 from the late '40s. It boasts a lot of tubes, but seems to fall short for my purposes:
700vct @.22adc, two filament strings: 1.2a and 9a

[leadlike]

Still working away at this thing. The 802 has so many secondaries the best I could come up with for a replacement is to build a massive power chassis, which will require three transformers, and two large wirewound tapped power resistors to get the B+ in line. I plan to fit all of this into the space where the turntable once was. The two transformers that I need will ship tomorrow, and then I'll begin building the power supply, which has so many taps and such a high amperage rating that I'm sure it could be adapted to power any 1940's television.

[RDusel]

Wow, you are definitely dedicated to reviving this set. Keep posting on the progress, it's very good reading.
Too bad there wasn't a spare chassis hanging around for you to steal the transformer but I guess that chassis from these consoles are pretty rare.
Rob

[rca2000]

I happen to ahve a spare 801 chassis--with tranny, I think. I bought it off of the bay a coupe of years ago, when I got my 801 set. But my set has an OK tranny.

let me know--.. I know where the chassis is--and it is accseeible.

[leadlike]

Will it work? Yes and no-it will certainly power 95% of the set, so you will definitely be getting a pm from me.

The 801 tranny lacks the secondary to power the filaments for the two tubes in the phono circuit. While this would be okay, as the phono is missing, on of those two tubes is an audio IF tube, which tells me the tv will be without sound. But still, wiring in a tiny filament transformer versus building that massive power supply would seem to be the way to go.

I also just realized that GE failed to put a fuse anywhere on this set-probably another reason for all of this heartache decades later. You can be sure this set will have at least one once I am finished.

[miniman82]

Sounds like it has some sort of B+ voltage doubler, could you just sub in a B+ transformer that puts out the voltage you require? I can think of several tube amps off hand that would make around 450 VDC at that current output (or more) from only a single 5U4 rectifier. Just something to think about.

[leadlike]

Well, my power transformers arrived-I highly recommend Playthings of the Past-he sent me a photocopy of the datasheet for the one tranny, and heavily labeled the other one to ensure proper installation.

Somehow, I made a mistake, and the one transformer produces a bit more voltage than I really need-350v instead of 240v. So, maybe someone can check my math:

The final B+ needs to be 240v @160ma. My calculations show I need a 687.5 ohm 17.6w resistor to drop those 110v, from a 350v supply voltage.

The B++ line needs to be 315v@85ma. I figured I need a 411 ohm 2.95w resistor to drop that from a 350v supply voltage. Do these figures seem to work?

[Reece]

Re: phono preamp: this must have been one of the sets where G.E. used their new (for the time) variable reluctance pickup rather than a crystal.

[leadlike]

Finally! I think this is the first bit of good news I have had since I started this thing:

Over the past week I mounted my transformers to an upside-down 9x13 cakepan, and began to wire that up, as well as to rewire the tv chassis to accept a large terminal block to wire the power supply into. Well, tonight I finished all of that, and hooked up the filament string only. After a few tests, I was confident enough to place all of the tubes on the chassis, and I was greeted with their heavenly glow:

edit:
sorry no photo, but I am having some net issues.


I would like to continue to power this set up in this manner, a bit at a time, adding on one transformer secondary source after another.

[bandersen]

Cool. Glad to hear that it's starting to come together.

[leadlike]

I got the power resistors today, only there is a single problem: they don't do anything to the voltage. For example:

A few posts up, I figured to drop a 350 volt supply voltage to 240 volts, I would need 687.5 ohms to do the job. Well, putting a 700 ohm resistor on each secondary arm (leaving the center tap to go to ground) gives me about 330 volts (measuring AC from one secondary arm to ground, or the center tap). Removing those resistors, I still have 330 volts. Absolutely no change. Putting on several Kilohms of resistors doesn't change anything, either.

What do I need to do to drop the B+ here? These resistors were the very first thing the transformer secondaries met, before reaching the rectifier circuits or anything else on the tv chassis. I should think these resistors should be able to bake off at least a little voltage, even the electrical engineers at work were on board with my plan. It's all just a bit frustrating.

[bandersen]

Do you have a load attached - how much current ? Your voltage drop will be R x I.

[leadlike]

Oh yeah, the tv was hooked up to it. That should be enough load, I should say.

I found my resistor value by RXI:

for the 687.5, that was found by:

687.5 X .160= 110

the 110 volts is the voltage drop I need (350-240), the .160 is the 160ma that the tv runs under load at the rectifier, and the 687.5 would be the resistance needed. I hope that makes sense.

I even gave this problem to a guy at work, he just started an electrical internship, and is learning the basics of DC. I simply gave him the current and the voltage needed to be dropped, and he got the same answer. He was happy to be working with a "real" problem, rather than one on paper.

[bandersen]

Sorry, I didn't remember your earlier post where you layed out your plan.

Sure, it makes sense. The math is sound so something's screwy here. Did you measure any voltage drop across the resistors? Did they get warm?

You could try adding a single dropping resistor after the rectifier instead.

[7"estatdef]

I had a passing thought that my old '48 Admiral consolette uses a transformer similar to that. I don't remember the specs on it but it does have the dual hv windings. Seems like it has about 270v and 155v output at the currents you are looking for.
Terry