[Ron Ramirez]

Joe...this isn't ARF...religion is not banned here, only politics. And thanks again!

Now back to our program...

Let's take a close look at the old 84 tube socket.

[Image: http://www.philcoradio.com/images/phorum...5T_027.jpg]

From the top of the socket, if you look closely, you can just see a burned area.

[Image: http://www.philcoradio.com/images/phorum...5T_028.jpg]

And from the underneath, you can see where the socket blistered.

I did a quick autopsy of the socket after removing it from the radio by breaking it.

[Image: http://www.philcoradio.com/images/phorum...5T_029.jpg]

Above, you can clearly see where the wafer burned a nice, big carbon track from one plate to the other.

Okay...what to do? Obviously the tube socket had to be replaced, but with what?

I have a few five-pin wafer sockets, but after this I really didn't trust using wafer again for a rectifier tube in this set.

Then I remembered that I have a small stash of NOS Amphenol MIP five-pin sockets...

[Image: http://www.philcoradio.com/images/phorum...5T_030.jpg]

[Image: http://www.philcoradio.com/images/phorum...5T_031.jpg]

No, it doesn't look like the original, but this socket should be much tougher over the long run than the original wafer socket was...and I doubt that it will burn a carbon track across the plate terminals like the wafer socket did.

[Ron Ramirez]

It's alive. Sort of.

[Image: http://www.philcoradio.com/images/phorum...5T_032.jpg]

I tested all of the tubes. The 84 was OK, surprisingly. The 41E was slightly weak as was the 78E. The 75 was significantly weak and was replaced. The 6J8EG tests very weak also, but I don't have any spare 6J8EG tubes.

So I tried the set out anyway.

Result: I had no trouble picking up my SSTRAN at 660 kc, but I had to turn the volume way up to hear it. And the audio is somewhat low and distorted.

Then I noticed the screen grid of the 41E was glowing red - not a good thing.

I took some voltage readings with my DMM and noticed that all DC voltages are running around 30 volts higher than the Philco data indicates. But that does not surprise me, considering the 1000 ohm/volt meters used in ye olden days which loaded down the circuit under test...combined with today's higher line voltages.

I checked the specs of the 6K6GT (octal version of the 41) and it indicates a maximum plate voltage of 315V, maximum screen voltage 285. The voltage readins I obtained were below those levels - not a lot lower on the screen grid, but lower. So I don't think the 275 or so volts (I say "or so" because the reading kept fluctuating) on the screen is what is causing it to glow red.

Tomorrow I'll try a different 41 tube and try it again. I'll also double-check my wiring, but so far it looks OK.

-----

As is typical with Philco, they run the screen voltage of the output tube higher than the plate voltage. I am considering adding a series resistor to drop the screen voltage to a level at or just below the plate voltage. Looks like a 1 watt, 2700 ohm resistor would do the trick. The only problem is, I would have to add a terminal strip near the 41 tube's screen grid pin owing to the way the set is wired. It may be more trouble than it's worth pursuing.

[Mondial]

Ron, check the voltage drop across the field coil, as I believe this is where the bias voltage for the output tube is developed. Then there is a voltage divider which should drop the negative voltage to -20 to -25 V at the 41 grid
measured to ground.

If the bias is correct and the plate and screen voltage is within limits, then you are probably ok. I have seen 6K6's with glowing screen wires for apparently no reason and they seemed to operate this way normally.

How does your line voltage compare to the radio's power spec? Perhaps this is contributing to your high DC voltages. As you mentioned previously, this radio is probably a prototype and the power transformer may not be the same as was used in final production.

[codefox1]

Depending on design, th screen grid sometimes functions as a throttle for the output stage. Of course everything else in the stage must be functioning normally, and as already said, this may be a prototype. Readings on output stages or any part of the voltage divider that is passing moderate amounts of current are not as likely to read all that much higher with a modern meter, as the loading matters much less.

[Ron Ramirez]

Mondial, you hit the nail on the head. I checked the bias at the 41E grid yesterday, and remembered that it was reading only a few volts.

I made a dumb mistake - I had the speaker connector wired incorrectly.

I rewired it and now the distortion is gone; and as a bonus, the 41E screen no longer glows red.

DC voltages at the 41E measured to ground, with the speaker connector correctly wired: Plate 250 volts; screen 265 volts (down from yesterday's 270-275 volt reading); control grid -15 volts.

The power transformer carries the same part number as called for in regular production. I was going to double-check my AC line voltage but I forgot; I'll do that later. When I have checked it before here, I seem to recall it was in the neighborhood of 124 to 125 volts.

I still have to turn the radio up higher than normal to get normal volume, but other than boominess from a bit too much bass (and that is with the tone control switch in the normal position), it sounds fine now.

I'm waiting for the signal generator and the radio to get completely warmed up; in a little while, I'll give it a complete alignment.

In the meantime, enjoy this photo of the dial in a darkened room:

[Image: http://www.philcoradio.com/images/phorum...5T_033.jpg]

[Ron Ramirez]

It's all aligned now, so as far as I am concerned, it is done. I just have to reinstall it into the cabinet.

I think that dial looks really good, even with some missing paint - when illuminated, the light from the edges of the glass helps to hide the missing white paint on some of the numbers.

Those bayonet base LED lamps with flexible leads from Pinball Life are perfect, I think, for slide rule glass dials like this one.

[Ron Ramirez]

Here's another photo of this 40-715, now that it is back in the cabinet:

[Image: http://www.philcoradio.com/images/phorum...5T_034.jpg]

and one more photo of the illuminated dial with the lights out:

[Image: http://www.philcoradio.com/images/phorum...5T_035.jpg]

And about that dial glass - I've decided to leave it alone. True, it is missing some paint and some of the green lettering, but it looks good when illuminated. A reproduction dial would not have that three-dimensional effect when lit, since the frequency numbers are not only painted on the original, but actually etched into the glass.

I know, I really should replace the grille cloth. Perhaps I will when warmer weather comes back to stay for the spring/summer.

[NostalgiaRadioTime]

Looks outstanding, Ron! Love the glow of that dial. I notice it says 'phono' on the dial. There must be a port where you could plug in a phonograph in the backside of the chassis? I also found it interesting on the cabinet that the bottom trim moulding is held in place by tiny phillips head screws. Perhaps another indication that this was just a 'mock-up' or prototype and not an actual production set?

[Ron Ramirez]

Greg

Thanks! Yes, this 40-715, as with most Tropics, has a phono input. On this set, it is two screw terminals next to the ANT and GND screws on the back of the chassis.

I was a bit confused by those screws on the bottom trim as well at first, until I looked at a poor quality illustration of a 39-711T (same cabinet), in my photocopied Philco Furniture History:

sorry - image no longer available

If you look closely, you can see that it, too, has the screws on the trim. Why Philco felt it necessary to add screws to the bottom trim on this model, I have no idea. But it appears that all 39-711 and 40-715 sets had the screws on the bottom trim.

I found a 39-711 on an Argentinian website:
http://www.acrayara.com.ar/cms/RM?action..._model=156

I suspect it has been refinished and the holes filled on the trim, as there are no decals around the knobs as there should be. You can tell where it appears that one screw hole was not completely filled in front.

[sam]

ron
looking good
that site has lot of good reading

[NostalgiaRadioTime]

Interesting stuff, Ron. Those tiny screws shall remain a mystery. Funny that they used them on the front of the cabinet, but not on the same trim pieces used on the sides!

[Ron Ramirez]

Greg

The screws are on the bottom trim on the sides as well. You can barely make them out in the factory illustration above.

After looking carefully at the 39-711 photo at the Argentinian website linked above, I don't think its bottom trim had screws after all. Very strange.

[NostalgiaRadioTime]

Oh, sorry, Ron. I didn't realize they were on the sides too. They're more pronounced on the front of the factory illustration. I wonder if they thought perhaps, due to these radios being used in 'tropical' conditions, that the glue would let loose holding the trim pieces on because of the damp climate, and they wanted to make doubly sure they wouldn't come off, hence the screws? But then again, if that's the case, any other Tropic model with trim pieces should have the same screws holding them to the cabinet as well. Who knows...just a shot in the dark

[sam]

ron
think maybe he filled them in as it was refinished
sam

[Ron Ramirez]

You may be right, Sam...yes indeed, you may be right.

And Greg, I think you hit upon an excellent point. The 39-711 and 40-715 are the only 1939 and 1940 Philco Tropic models, respectively, to have this sort of bottom trim. The other 1939 and 1940 Philco Tropic models that have wooden cabinets are actually recessed at the bottom. So perhaps it was intended to keep the trim on in case the glue failed. Who knows? Only some dead guys from Philco from back in the day...and dead men tell no tales.