[DaleHCook]

For something like your rusty transformer housing my preferred approach is a Dremel abrasive buff, They are plastic sponge wheels bearing one of three grits of abrasive. They are much less drastic than wire wheels.

On using a dimmer, I would discourage you from feeding anything but a pure sine wave into a chassis under test. Dimmer outputs are too jagged and noisy. My custom bench AC power supply uses a Variac (if it isn't GR it isn't a Variac) and a true isolation transformer. See:

https://plymouthcolony.net/starcity/radi...tml#variac

and

https://plymouthcolony.net/starcity/radi...tml#wp-26a

[jrblasde]

Boy howdy, that’s some nice custom testing equipment! I really do need to invest in a variac. I also have a tube tester on my wish list. I currently have no way of testing tubes other than eliminating all other problems first.

I removed the bells from the transformer today, and the innards are looking more promising. I was able to clean up the two bells with the use of a couple of wire wheels. I’ve got a bigger, more powerful wire wheel on my bench top grinder, and then one which I can use on my drill. I then applied a layer of baking soda paste and let that sit for a couple of hours before rinsing and drying. Finally, I used some JB Weld Steel Stick putty to reconstruct the missing rivet holes where the transformer is riveted to the chassis. I’m letting that set for 24 hours, and then I’ll sand the putty flush to the metal and drill new holes. The bells should then be ready to repaint.

I will clean the exterior of the laminated metal tomorrow. I also need to reinsulate the wire leads. Tonight I plan to order the sleeves. The leads go into the windings of the transformer as one continuous wire; because the leads are not soldered onto terminals inside the bell, I am stuck with the original wires. But that is okay, I’ll get them cleaned up and install new sleeves.

By the way, I got a quote back from Edcor. I had reached out to them before I settled on repairing this unit. Their quoted price was even worse than Hammond’s!

[DaleHCook]

I currently have no way of testing tubes other than eliminating all other problems first.

Bear in mind that no tube tester can tell you if a tube is good - it can only tell you if it is likely or definitely bad.

[morzh]

Second that.
Had a superbad reaction of my McIntosh amp to ECC83 tubes that tested perfectly well. Redplated KT88s, blown up fuse...

[Arran]

Again I don't think a custom made transformer would have been necessary in this case since the set uses your typical 6.3 volt AC tubes and a 5 volt rectifier, the main difference might be in how much voltage the H.V winding puts out. Most are a 350-0-350 affair but some are higher, others lower, it really depends on what audio output tubes they used, how much they drive them, and how much current is needed. In most cases you can find something off the shelf that will work, especially with the vertical mounted style transformers. Where you might need their services is if you had a radio with a type #50, those were 7 volts, but needed 500 vdc to really work, or one that has motor driven tuning and a winding for the motor, I think they were 24 vac. There were also some oddball sets that used combinations of 6.3 volt AC tubes, and the older 2.5 volt style, I think there was a Silvertone and a Lafayette brand radio that did.
From what I remember reading Edcor has an engineering charge for custom winding transformers, but if they find they already have the specs on file they will refund it.
Regards
Arran

[morzh]

...or one might keep checking eBay, swapmeets. Power xfmrs from Philco often pop up. And though the price of them is sometimes unreasonable, it is still way better than what Hammond suggested.

But again, first try too clean this one.

[jrblasde]

Well, I have cleaned up the transformer and repainted the bells. It's looking much better, but I have a new concern. During AC testing, I heard a loud buzzing or humming sound. It does not go away after about 20 seconds. I got so far as to test the secondary voltage (336 volts for each half--a little higher than the 320 I would expect, but it looks good). Is anyone aware of what might cause this hum?

Another update. I got a quote from Heyboer. They actually gave me a GREAT price. It's on par with most standardized power transformer replacements. No ridiculous markup for a custom design. If we exhaust all other options, I will at least have that in my back pocket.

[jrblasde]

Sorry, meant to upload a photo of the cleaned up transformer. 

   

[jrblasde]

Alright, I feel like a dummy at this point. I moved the transformer to a different surface and plugged it back in. This time no rattle. I took it back to the first table, and the rattle resumed. Turns out that the magnetic field had been rattling a little piece of metal that I didn't see at first!  

So now there is no humming sound, and voltages look good! I left it plugged in for five minutes, and it did not overheat. Not even warm to the touch. So I have a usable transformer!!!

I'd like to thank everyone for their guidance on this transformer restoration. I had absolutely no idea that these could be cleaned up and the wires sleeved.

[morzh]

Heyboer do great job; it's just at some point someone here said they quit doing custom orders.
They did two transformers for my 38-690.
Screwed up both, two times, but eventually did everything right, and charged me what they said they would, and even gave me some money back, as the output transformer, even though wound right, had some other issues (they took two stabs at it) , but it worked great.

If they still do custom jobs, they are good people.

[Chas]

Joseph,

Very well done!

Because the radio has some chassis corrosion, do solder or re-solder all chassis connections including those riveted to the chassis. Despite rivets, dissimilar metals over time will corrode and and give problems...

Chas

[TV MAN]

Very nice work on that transformer! Now you can move on to the next steps. +1 on not using the dimmer control. They do introduce tremendous noise. Dim bulb is simple, cheap and works well. You can change the load limits by simply changing the bulb (incandescent). I used a socket with a couple clips for some time, but later got a couple metal boxes from the construction store, a box for a ceramic (or plastic) light socket, about $2, a double box for an outlet and switch to bypass, a cord, something to connect the two boxes. I'm sure I have less than 10 in all of it, and you might have most of it in your garage! Variacs are readily available on the auction site, and would be a good idea to have. Also, you might want to take a look in the future for an isolation transformer. Hamfests are a good source, as is the auction site, but they are kinda heavy, so shipping may be a little more. You really dont need that until you start working on things without a power transformer.

All it is- power cord hot to the bulb, then hot from the other side of the bulb to the outlet hot (gold, small slot). then neutral to the neutral (silver, long) side of your outlet. Then, wire your switch across your bulb. This can bypass your bulb if you want to jab it. Just remember, this is only a current limiter/fuse, not isolation.

Edit: I have a couple Heyboer transformers (used) patterned after the Dynaco ST70 and they seem like very good quality transformers, so I recommend them highly.

[jrblasde]

I do already have an isolation transformer. I got that before aligning my 49-906 since it’s an AC/DC set. I didn’t dare to connect an oscilloscope or function generator to it without isolation!

Good call on the rivets and chassis connections. I do have a riveter hand tool, so I’m able to replace any which are corroded. There’s a couple as well which look to be mashed up. I’ll probably drill those out and put some fresh rivets in place. I’ve recently learned about naval jelly, so maybe I will give that a whack when I clean the chassis up. It’s got some rusted areas.

[DaleHCook]

I suggest stripping all electronics, including sockets, from the chassis. That way you have a completely free hand to use any method to clean the chassis.

[Arran]

Another trick I learned of to remove any of the thick crusty rust that our little rodent friends tend to leave on a radio chassis, is a wad of paper towel soaked in vinegar placed right over the corroded area. I did this in a few sets and it got the crust off and the chassis down to bare steel, of course the plating is also gone but our rodent pal already ruined that. One point to make, you don't have to completely strip the chassis down, only the top deck of it, the sockets can be pushed down inside after the rivets are removed, rather then removing them entirely. The front end parts like the band switch, are a little more difficult unless the set has a sub chassis that can be pulled out in whole by snipping a few wires, fortunately those usually have the tuning condenser mounted on top so the chassis was more protected there, potentiometer type controls are pretty straight forward.
Happy Christmas
Arran