[Ron Ramirez]

Let's start on another, shall we?

[Image: http://www.philcoradio.com/images/phorum...770-01.jpg]

This is the oldest, largest, and heaviest Tropic in my collection. The cabinet alone is surprisingly heavy.

[Image: http://www.philcoradio.com/images/phorum...770-02.jpg]

As you can see, the chassis looks like a typical thumbwheel drive Philco from 1939-1941...only it has no pushbuttons.

[Image: http://www.philcoradio.com/images/phorum...770-03.jpg]

A close-up of the dial scale. Notice that it has four bands with complete "all wave" coverage from 540 kc to 22 mc. A unique feature of this radio is a tuning light, mounted just below the dial scale.

[Image: http://www.philcoradio.com/images/phorum...770-04.jpg]

This is a back view of the chassis.

[Image: http://www.philcoradio.com/images/phorum...770-05.jpg]

The metal model number tag...

[Image: http://www.philcoradio.com/images/phorum...770-06.jpg]

...and a sticker indicating it was serviced in the Bronx, NY. The guarantee expiration date is hard to read, but if you look close, you can just make out the date: Apr. 12, 1942.

So either this set was sold in the USA, the "made expressly for export" on the model number tag notwithstanding, or else whoever originally purchased the set immigrated here not long afterward, and settled in the Bronx (and brought their very cool - and very rare - Philco Tropic with them).

Now let's take a closer look.

[Image: http://www.philcoradio.com/images/phorum...770-07.jpg]

Right away you can spot a problem if you look closely - a tube socket has been mounted from the top of the chassis! I will correct that issue during the course of the restoration.

Now let's look under the chassis.

[Image: http://www.philcoradio.com/images/phorum...770-08.jpg]

Since none of the original paper caps are left underneath, I'm not sure whether or not I am going to install restuffed caps under here.

Who am I kidding, of course I will (if I have enough, that is).

I was warned by my friend from whom I purchased it, that it had a bad coil. Now, I don't remember which one, but I will find out. I hope I can manage to rewind it. It would be great if it were as easy as the AM band oscillator coil in my 42-788, but I don't think I can be that lucky twice in a row.

I could take the easy way out and just stick any 1939-1941 Philco chassis with thumbwheel controls in the cabinet. (Just kidding! I would not do that with a set like this.)

Like the 42-788, this will be no walk in the park. But it should be interesting...

[NostalgiaRadioTime]

Looks to be another great project, Ron. Looking forward to your progress.

[Ron Ramirez]

Thanks, Greg!

I looked up the location of the Armory Radio Clinic, just for fun...

Looks like the most recent business at that address was a furniture store. It's across the street from the NY National Guard Kingsbridge Armory, which is likely why the radio shop was called "Armory Radio Clinic." Maybe the radio was purchased by a soldier and brought back to the USA?

If these radios could talk...

[Arran]

  The use of a tuning light is interesting, Rogers, Canadian Majestic and DeForest Crosley radios used to have a feature like that up until 1936 or so. The lamp is a 25 volt bulb, and it dims when you tune into a station, really dims on a strain station. I will have to study the circuit again but I think it's connected to either the bias circuitry or the AGC, some of the higher end models like the Rogers 10-12 have an extra tube as an amplifier to power the tuning light. It's curious that Philco did not incorporate this feature into more of their sets, it would have undoubtedly been cheaper to use then the shadow meters, more reliable, and they still would have avoided making their sets RCA like by not using a magic eye tube.
Regards
Arran

[Joe Rossi]

Hi Ron, The image links don't work for me. Any ideas? Thanks, Joe

[klondike98]

Hmmmm....photos are working for me.  Try clearing your browser cache...? 

[Ron Ramirez]

+1 what Bob said, plus:

If you're running Windows, try CTRL+F5 to refresh the page.

Working here at 8:59am EST this morning.

[Joe Rossi]

Hi Ron,  I was on my iPad.  They are working now. Thanks.

[Ron Ramirez]

Joe

Were you logged in when you were viewing on your iPad?

If you are not logged in, you will not see the pictures...

[Joe Rossi]

Ron,  I was logged in and couldn't click on the links.  When I logged OUT, the links became active (blue).  No problem this side as I am usually on the PC.  Thanks for responding!  Joe

[Ron Ramirez]

Here's the schematic for anyone wishing to follow along.

39-770 Schematic (655 KB)

[Ron Ramirez]

Man, I really should start studying service info before jumping into a project. I just discovered, much to my dismay, that Philco specifies 1 watt resistors throughout this set, rather than the usual 1/2 watt resistors.

Which means, of course, that I do not have roughly half of the resistors I will need.

I am going to have to replace at least two other tube sockets besides the one that is mounted upside down. One is cracked nearly in half, and another doesn't look so good. In addition, someone removed all of the tube shield bases somewhere down the line. It's a good thing I have some spare junk. I'll be using 1937 tube shield bases to replace the missing bases, so I can use any type of tube I want to and not be limited to "G" types.

And it just gets better...

A quick check with the ohmmeter section of my DMM reveals that half of the primary of the audio output transformer is bad. Well, I still have a push-pull output made for 6F6 tubes...which is what this set uses...so I'm covered there.

On the positive side, it does not appear that this one will be as difficult to rewire as was the 42-788. I hope that turns out to be true.

And the 400 ohm Candohm resistor, part (81), tests good. Why Philco put a 400 ohm resistor in series with the speaker field instead of using a speaker with a 1400 ohm field, I don't know. Oh yes, I think I do. Philco probably had speakers on hand with 1000 ohm field coils, and it was cheaper to just use them and add series resistance to make the circuit work.

[codefox1]

Ron, I do not see why any resistors in this set short of voltage dividers and cathode on outputs need to be more than 1/2 watt. And have a go at taking the Output Transformer apart carefully, might be an open connection to primary winding (nothing to lose!) Cheers.

[Ron Ramirez]

Agreed re: resistors. And, yes, I will attempt an autopsy of the audio output transformer, as I will have to use its frame anyway if I use the 46-1226 transformer. (The transformer is made to sit sideways in the 39-770 due to space considerations. The 46-1226 transformer sits horizontally; in other words, in a conventional fashion.)

[Ron Ramirez]

The beginnings of a long, slow process...

[Image: http://www.philcoradio.com/images/phorum...770-09.jpg]

Here you see the 6K7G RF tube socket which is about to be replaced with a genuine Philco tube socket - brown phenolic, not the goldish-yellow crappy socket which, unfortunately, this set is full of.

[Image: http://www.philcoradio.com/images/phorum...770-10.jpg]

Zoomed out a bit, to show the 6J8G socket to the left of the 6K7G socket. As you can see, the 6J8G is the crappy yellow type.

[Image: http://www.philcoradio.com/images/phorum...770-11.jpg]

After unsoldering some wires, the ill-fitting socket was removed...

[Image: http://www.philcoradio.com/images/phorum...770-12.jpg]

Here is the replacement socket - a used Philco socket pulled from a dead chassis. To the left is a 1937 Philco tube shield base. Philco should have kept using these after 1937. But instead, beginning in the 1938 season, Philco went back to the 1936 style tube shield base - to prevent anything but the use of ST style tubes. Only the ST tubes (the "G" types) will fit through the hole in the bases used from 1938-1942. With the 1937 style tube shield bases, one may use any tube he or she wishes - ST (G), GT, and (shudder!) metal.

I am using a 1937 style shield base for two reasons: one, for the versatility as mentioned above; and two, these are the only shield bases I have on hand.

[Image: http://www.philcoradio.com/images/phorum...770-13.jpg]

A look at the newly replaced socket from the top of the chassis, with the 1937 type shield base in place.

[Image: http://www.philcoradio.com/images/phorum...770-14.jpg]

...and how it looks from under the chassis.

-----

I removed the audio output transformer today. Did I mention that I hate those crappy yellow tube sockets Philco sometimes used? A tube socket contact came off each of the two 6F6G sockets when I attempted to unsolder the audio transformer leads. So there are two more sockets I will have to replace in addition to the cracked 6H6G socket and probably the 6K7G IF tube socket.

I will not be surprised if I end up replacing all eleven of them, but I hope I don't have to go that far. These sockets are so fragile...it is so easy to ruin one, even when using a low-wattage soldering iron instead of the flamethrower Weller D550. The brown wafer sockets are much tougher...I really wonder why Philco used the yellow sockets...I used to think that perhaps this was some sort of low-loss material because I normally only see these used for the det-osc tube. But as I said earlier, this 39-770 has eleven of them.

Well, I should say had eleven of them...now it has ten.