[Bob Andersen]

I already have a thread going in the cabinet restoration forum but figure I'd start this one for the electronics.

This tombstone came with a chassis heavily modified for AC operation. Every socket had been replaced to accommodate different tubes and some new ones were even added. Tube were also missing and I gave up on trying to restore it. Out of the blue, someone tipped me off the a 643 chassis on ebay and I won it

Here they are side-by-side.

[Image: http://farm7.static.flickr.com/6139/5919...9776_z.jpg]

[Image: http://farm7.static.flickr.com/6021/5919...180b_z.jpg]

That left the speaker. Just a few weeks later I spied this Philco 624 speaker on the same auction site with no bids. I ended up winning it for all of $ 0.99.
[Image: http://www.bobandersen.com/images/philco...peaker.jpg]

Only problem is that it arrived looking like this
[Image: http://farm7.static.flickr.com/6147/5983...c8d6_z.jpg]

[Image: http://farm7.static.flickr.com/6004/5983...3f3f_z.jpg]

Luckily, a little fabric glue fixed it up and when I tested it in another set it sounded just fine
[Image: http://farm7.static.flickr.com/6030/6009...6d59_z.jpg]

[Bob Andersen]

Nuts! The 32-7472 audio output transformer is open on one side of the center tapped primary

I find it curious that the schematic specifies that it's mounted on the speaker frame but mine is mounted on the chassis. It's also depicted mounted on the chassis in Philco service bulletin No. 226.

I also noticed that it was soldered in crudely. Perhaps it was already replaced or someone tried to repair it ?

I suppose I could try melting out the tar and look for the break
[Image: http://farm7.static.flickr.com/6002/6010...71803e.jpg]

[Image: http://farm7.static.flickr.com/6018/6010...937422.jpg]


Luckily, the speaker I picked up just happens to have a good 32M-9248 output transformer mounted on it's frame. So I'll try using that, but it would be nice to find a good 32-7472 someday.

Who knows maybe I'll find one at the ARCI swapfest later today ?

[Ron Ramirez]

Did you notice the date on that transformer? "11-39." It was made in November 1939, roughly four years after your 643 was built, so that transformer is a replacement unit. That would explain the crude soldering you mentioned.

Hmmm. Unusual...not unheard of for an audio output to fail that soon in a set's life, but unusual...

[TA Forbes]

I feel your pain re: the speaker. I came across a complete AK 318 chassis/speaker, I needed the speaker for my 318 console. The seller shipped them loose in a box with 6- 4"X 6" plastic "bubbles" to pad them. Speaker was trashed, chassis damaged......

[Ron Ramirez]

Unfortunately, some eBay sellers are clueless and/or don't give a rat's behind about proper packaging. As long as they get that money in their hot little hands, that seems to be all that matters to them.

Recently, when I have had occasion to win a speaker on eBay, I have contacted the seller and requested them to package the speaker as follows:

Get a large piece of cardboard, and lay the speaker face down in the middle of this cardboard.

Fold the cardboard over the back of the speaker, cutting the cardboard as necessary, until the speaker is tightly encased inside this cardboard "cocoon."

Then place this inside a suitable box with at least two inches of packing material completely surrounding the cardboard-encased speaker.

I have found this is the best way to ship speakers.

Bubble wrap is too flimsy to reliably protect a speaker, and just tossing the speaker into a packing peanut bath will guarantee a destroyed cone. Cardboard works every time.

[Bob Andersen]

Thanks for the great tips!

This seller put chunks of foam in a box, placed the speaker cone down against it and piled on more foam. Of course, the foam chunks tore right through the cone.

Ah, I hadn't realized that was a date code on the output transformer. So it seems both the original and the replacement failed. I sure hope the one on the speaker doesn't burn out too!

[TA Forbes]

I started using Ron's technique after I recieved a speaker from him. It's simple and bulletproof.

Yep. Emulation is the best form of flattery.

[Bob Andersen]

I'm slowly making progress on the chassis. I discovered that the audio coupling transformer is also a replacement but tests OK. The same cannot be said of the antenna coil though

[Image: http://farm7.static.flickr.com/6183/6106...ecdd_z.jpg]

What I find really strange is that every tap of this coil is open. Someone had connected a low ohm flexible resistor from one tap to ground. I assume that was an attempt to restore reception.

Surprisingly, the antenna coil in the modified chassis is good. So I have the option of repairing this one or swapping it out. Either way, it's not going to be fun. So many connections to deal with ...

[TA Forbes]

Could be the result of a lightning strike, that is the reason for many bad antenna coils.

If it is the same item, why not replace it? Sounds like the path of least resistance, so to speak...

[Ron Ramirez]

As Tom said, if the antenna coil in your parts set is good, might as well swap them out and be done with it.

[Bob Andersen]

I was thinking lightening strike too. I'll pull them both out and see what the condition they're in.

My concern was that the good coil might go bad too from age. I restored a Philco 60 recently and ended up rewinding come coils.

[Ron Ramirez]

The coils in the larger 1936 Philco models seem to be exceptionally well built, and appear to have avoided the use of the nitrocellulose insulation that breaks down with age, causing the winding directly above it (and sometimes, the winding below it) to corrode and fail.

In all of the years I've been working on radios, I've only had to replace one of those coils. It was either an antenna or an RF coil in a model 620 or 630.

I'm not saying they will last indefinitely - who knows how long they will last - but they do not seem to suffer from the issues that the older coils do. As an example, it should be considered standard operating procedure to count on having to rewind both the antenna and oscillator coils in a Philco 60.

[Radioroslyn]

Add model 80,81,84,& 37-84 to the list too.
Terry

[Arran]

You can usaully tell if the coil has been smoked by a lightning strike, the whole primary winding will look black. I recently ran into this in a lake 40s Viking battery radio (Dominion Electrohome) although it is broadcast band only so it doesn't have any extra taps. I'm not sure why they would connect a resistor between a dead coil and ground, the usual quick repair is to connect a capacitor from the antenna terminal to the secondary in some way. I've also seen this happen with an oscillator coil, a paper cap shorted out between the top of the winding and the B+, since most coil windings are made of very fine wire the internal resistance causes them to burn up. It was a rather stupid design in my opinion, much like the tone controls with B+ on the wiper capacitor.
Regards
Arran

[Bob Andersen]

Here's the antenna coil from my donor chassis. I really hope it works out as rewinding looks like a nightmare

I'll have the old one out soon and try to determine why it might have failed.

[Image: http://farm7.static.flickr.com/6181/6126...da86_z.jpg]