Another Project?

[bgadow]

If it is just a filament winding I would say that wouldn't be so bad. Should be space for a beefy filament transformer somewhere in there, and I don't guess they cost too much.

[jeyurkon]

Originally Posted by bgadow

If it is just a filament winding I would say that wouldn't be so bad. Should be space for a beefy filament transformer somewhere in there, and I don't guess they cost too much.

If it really is a shorted filament secondary, then a separate filament transformer won't help much since the short will still overload the transformer.

I agree with wa2ise though that ohming the secondary isn't a reliable test.

John

[leadlike]

Well, this thing failed the dimbulb test days ago, I just forgot to mention that. I'd say it is pretty dead, since even with all of the tubes pulled, the simple act of powering it on with "no load" is enough to overload the transformer, as it rapidly heats up and makes a fairly audible hum to boot.

I hope to get into this a little more tonight-disconnect the tf leads and really see what is happening here, before going through transformer replacement hell.

[leadlike]

I removed the transformer tonight and pried the bells off to see if I got lucky and it was just shorting out a bit inside the case. What a mess! The transformer is charred, with bits of ash raining out of the case. Whoever last powered this up must have left it on for quite a while before giving up, and I'll bet their house smelled great when it was over. Now that it is isolated, I can ohm it out much better, and it appears the failure is on the center tapped 5y3 secondary, but there is a lot more damage here than that.

On removing it, I found another item-a mystery winding that goes to the radio section. Looks like the transformers for the 801 (which I have the service info for) and the 802 are different. Guess I'll have to finally track down the SAMS for that. GE really loved packing in a lot of stuff in this transformer, I see that they used some shims to give the end bells the clearance they need.

My strategy now would be to make a power chassis, which would slip in where the record player used to be. I will probably have to buy two transformers, something like a 350-0-350 and a 450-0-450 and run them up to the main chassis through an umbilical cable. I can't be sure until I get the SAMS.

[Eric H]

Sent you a P.M. concerning the schematic.

[wa2ise]

Be sure to check for what might have killed that transformer, like a shorted filter cap or such. It's possible the transformer killed itself, but you want to be sure there isn't a problem that would ruin a replacement transformer.

[leadlike]

I've checked over the set's power supply, and I keep going back to the multisection filter caps. They all test bad, using my Heathkit cap checker. Certainly the e-cap section that was tied into the video IF bias supply was bad enough to cause a 2 watt power resistor to burn up into two pieces. The primary filter cap in the 5y3's filament string had also belched its guts out as well. So for now, I would just say that the transformer was killed recently by someone who powered it up with bad caps. After all, the set's owner was given this set for free, so it is possible the previous owner toasted it, knew it was badly damaged and gave up on it.

This leaves me with looking for a replacement power supply. Here is how the 802's tf broke down:

The plates of the 5u4 and 5y3 are shared on a single center-tapped to ground secondary.

The low voltage windings go to the 5u4's plates and put out 270 volts.
The higher voltage windings go to the 5y3's plates, supplying 440 volts.

There are two 5v windings for the rectifier filaments.

There is a center-tapped winding dedicated to the two filaments related to the phono preamp tubes.

There are two more pairs of filament secondarys, these are not center tapped:
The first filament secondary supplies 8 tube filaments and the dial lamps. This is all for the radio.

The second supplies 13 tube filaments for the television tubes.

So, I suppose to find the current handling of this transformer, I need to sit down with my tube manual and add up all of the filament currents in each string? Do the same for the plate/screen currents for the rectifier plate windings?

[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