[mgandalf]

I have an old 511 I found at auction. I inspected the underside of the chassis and can see that the caps were all replaced. As I understand it, the radio sat for at least 10 years unused, however.

The radio powers on fine and tunes stations well. The sound is loud. Everything seems to work well. The unit looks to be drawing between 80 and 90 watts at 120v. Is that typical? In all of my research I've only found one mention of power draw and that person mentioned 50w.

After about 15 min. or so, the transformer starts putting out a slightly sweet smell. I looked at the bottom of the transformer and I don't see where anything has leaked out. I'm guessing the smell isn't normal and may be indicative of overheating due to current draw.

Can anyone tell me how many amps these things are supposed to draw?

Thanks, Mark.

[klondike98]

Welcome to the Phorum!
:wave:
I dont have any experience or info on the 511 but someone will chime in soon.

[Steve Davis]

Hi Mark,

 Welcome to the Phorum!
 
The transformer should not get so hot the you can't hold your hand on it. If it does, remove the rectifier and try again, the transformer should barely get warm. If the transformer gets hot with the rectifier removed, it is bad. 


Steve

[mgandalf]

Thanks Steve. I'll give that a try. I know it's not hot enough with the shield in place, but I haven't tried taking that off.

[mgandalf]

I pulled the rectifier tube and powered it up for a few minutes. The transformer barely gets warm, but I still noticed the smell, which got me thinking. Could it condenser can? I understand that guy is full of tar. Does it mean anything that it smells when operating? I'm guessing yes.

[Arran]

Put your hand on the condenser can, as well as the filter choke, if something is smelling whilst the set is power up, and it is not the power transformer, it has to be one of the other two. Someone may have installed new capacitors but that does not mean that the old caps were taken out of circuit, a lot of people had a bad habit of bridging old components with new components rather then disconnecting the old ones first.
Regards
Arran

[Steve Davis]

With the rectifier pulled, there won't be any voltage on the condensers or the choke. The smell must be coming from something else.

Steve

[Phlogiston]

The sweet smell is probably the bee's wax used in the transformer.

If the transformer is already damaged, other than rewinding it, there is nothing you can do to fix it.

If it runs without getting warm for 15 minutes, it is a tough call. Most with shorted windings will begin to smoke/bubble by that time. Still it could have a few shorted windings in the HV secondary.

With the rectifier removed and the radio unplugged, measure the resistance from the AC input pins on the rectifier socket (2 of them) to the chassis ground. It should be nearly equal. If there is a difference of more than 5 - 10% one side of the HV winding probably has shorted. The readings will be in hundreds of ohms. This can be done to the other windings as well but is far less likely to find a problem since they are going to be in the 10 ohms or less range.

Lastly run the transformer as you have SUPERVISED, for an extended time - with the rectifier removed. If it is shorted it will eventually smoke. Don't let it continue. Don't attempt this unless you have the time to watch it carefully. Don't want a smelly mess or worse. If it fails, it was going to fail anyway. Look for a new one BUT (!) check out the radio thoroughly before installing a new one. Many people ignore every component except the caps. a bad resistor can cause excess current to flow in an output tube - enough to cause power transformer failure.

Lastly, don't do any of this unless you understand the dangers involved with servicing high voltage equipment.

[codefox1]

Agree, most likely a partial short in the secondary winding, and ultimately could be a hazard. Of course you could carefully note and disconnect all windings, remove the transformer, open the bells, gently loosen paper shielding and inspect connections from leads to windings. They often corrode, dunno why, but at this junction you have little to lose. Well, you can always resolder 'em, and replace the leads if they are worn or ratty. Not familiar with this model, but if you have enough space, any transformer that is roughly electrically equivalent (or better) and will physically fit in the set can be used.

[mgandalf]

Many thanks for all the feedback. Where can I find out what the voltages are supposed to be on all the windings, assuming I opted for replacement?

- Mark.

[codefox1]

Well, let's assume the primary is 115 or so. Filament windings would probably be two, one for the 6.3 volt string, the other, more heavily insulated a 5.0 voltage for the rectifier. HV windings (sometimes red, red/yellow/red) should be very close when measured by a reasonably good meter out of circuit. These readings would be with the set operating normally under the designed load factors.