[Ron Ramirez]

I'm still plugging away on this chassis...

The rewiring is nearly complete. See below:

[Image: http://www.philcoradio.com/images/phorum...T2_046.jpg]

I took some time today to calculate the wattages of the resistors needed to replace the five-section Candohm. With the help of the RCA service info, I was easily able to do this. Here's how:

The schematic gives the resistances of the five sections.

From the voltage drawing (page 7 of the PDF manual linked above), I was able to find all but one of the voltages - and that was at the junction of the 3500 ohm and 13,000 ohm sections. To find that, I simply did some math.

The 3500 ohm and 13,000 ohm section together drop 258.8 volts.

Ohm's law gives us the rest:

3500 + 13,000 = 16,500 ohms

I = E / R, so to find total current through the two sections: I = 258.8 / 16500 = 0.016 A (16 mA)

Now, to find the missing voltage:

E = I * R = 0.016 * 13000 = 208 V

Here's a drawing.

[Image: http://www.philcoradio.com/images/phorum...T2_047.jpg]

Now, we use the formula P = I squared * R to find the necessary wattage. (You can also use P = I * E .)

But first we have to figure out the currents involved.

3500 ohms - 52 volt drop = I = E / R = 52 / 3500 = 0.016 A

So, 0.016 * 52 = 0.832 watt

You want to double this figure for safety, so the 3500 ohm resistor needs to be 2 watts.

Let's do the same for the rest.

13,000 ohms, 0.016 A, 208 volt drop so 0.016 * 208 = 3.328 so the 13K needs to be at least 7 watts.

85 ohms, 0.014 A, 1.2 volt drop so 0.014 * 1.2 = 0.0168 so a 1/2 watt resistor is fine for the 85 ohm section.

40 ohms, 0.075 A, 3V drop so 0.075 * 3 = 0.225 so, again, a 1/2 watt resistor may be used for the 40 ohm section.

175 ohms, 0.074 A, 13V drop so 0.074 * 13 = 0.962 so the 175 ohm resistor should be at least 2 watts.

With that information, I know what I need to order.

Here is another under-chassis drawing. You can see that more of the lines are highlighted...

[Image: http://www.philcoradio.com/images/phorum...T2_048.jpg]

I did not highlight all of the power transformer and filament leads. These, with the exception of the 115 volt primary leads, have not been disconnected and remain in place.

[Ron Ramirez]

Back to work on this project.

The first order of business was to restuff the third and final electrolytic can. This proved somewhat of a challenge, as this electrolytic was a Solar replacement and was made somewhat differently from the original RCA can. The original RCA cans are like Philco aluminum electrolytics except for the stud mounting; through 1938, most Philco electrolytics were mounted with clamps.

There was no way for me to feed a negative lead through the bottom of the can due to the way it was made.

I had no other suitable stud mounting electrolytic, so I decided to work with what I had.

Here it is, all apart and showing the new 10 uF Solen replacement cap:

[Image: http://www.philcoradio.com/images/phorum...T2_049.jpg]

I decided to try attaching a solder terminal on the top end of the electrolytic can. So I drilled a hole near the top of the can.

[Image: http://www.philcoradio.com/images/phorum...T2_050.jpg]

Next, I attached what will be the positive lead of the new 10 uF cap. You can see the original rubber cushion through which a new 12 gauge electric wire has been fed. I wrapped some electrical tape around the wire where it passes through the rubber cushion, since the original hole was much bigger than this wire, before feeding the wire through the cushion. With the help of hot glue, this should hold in place quite well.

[Image: http://www.philcoradio.com/images/phorum...T2_051.jpg]

Then, using a pop rivet, I attached a solder terminal to the hole which I had drilled previously, and soldered the other lead wire of the new 10 uF cap to this terminal.

[Image: http://www.philcoradio.com/images/phorum...T2_052.jpg]

The final result:

[Image: http://www.philcoradio.com/images/phorum...T2_053.jpg]

I checked it with my DMM. I had good continuity from the solder terminal to the threads of the can's stud. Then, I set the meter to read capacitance and checked the newly stuffed cap. It read 10.4 uF

Throughout the time I worked on this radio today, I had a supervisor watching me to make sure I made no mistakes:

[Image: http://www.philcoradio.com/images/phorum...T2_054.jpg]

After awhile, Виктор grew bored with watching me and took a nap.

I attached some more wires. At this point, the only thing remaining is the replacement of the resistors which made up the old multi-section Candohm.

[Image: http://www.philcoradio.com/images/phorum...T2_055.jpg]

And you can see I'm making progress. The only wires not highlighted now are those attaching to the Candohm. The power transformer leads and filament string are also not highlighted, but they are in place and hooked up on the chassis just the same.

[Image: http://www.philcoradio.com/images/phorum...T2_056.jpg]

---

Both the off-on-tone control and the volume control have been replaced in this radio. The volume control was replaced with a Philco control. But let's discuss the off-on-tone control a bit.

The original was 100K, open on the low end by design. When the wiper arm reached the low end, it disconnected from the resistance of the potentiometer and connected to one end of C33. The control that is in my 6T2 is a newer replacement. The switch does not have that positive "click" when the control is switched off, and the potentiometer section reads 50K, not 100K - and has continuity from end to end. So it looks like I need an off-on-tone control. I've posted an ad in the Wanted Ads section of the Phorum.

The service manual, containing the schematic is here (warning - large file - 32.1 MB).

---

Now a word about the Candohm. Nathan had made a suggestion in post #3, page 1, this thread:

On my 37-2670 I mounted the replacement resistors on a sturdy aluminum plate, using flat-head machine screws so that the heads would be flush with the aluminum backer.
I then mounted the whole assembly using the original holes for the drilled out rivets.

I have a piece of aluminum, and I intend to mount terminal strips on that aluminum strip for the resistors...and then mount that assembly under the chassis in place of the Candohm.

[Paul Philco322]

That is a large cat. Is it just the way the photo is? How much does it weigh?

I thought my kitty was getting fat, she weighs bout the same as her last check up, maybe just the winter coat coming up. I do care about the set too!

Paul

[Ron Ramirez]

Paul

No mistake...Виктор is a big boy! He weighs over 17 lbs.

[Paul Philco322]

My kitty is only 10.5 built like a bowling ball. 

Paul

[EdHolland]

Nice to see your progress Ron. It is very methodical (as I would expect from your work), and I like the technique of tracing out each replacement connection on the schematic.

May I ask, what is the wire you use to replace the rubber covered original? It looks to be a thicker insulated solid core - something I had trouble finding recently.

Keep up the great work,

Ed

[Ron Ramirez]

Thanks Ed.

I used 22 AWG solid wire from Radio Daze - left over from my 41-616 restoration of a few years ago.

http://www.radiodaze.com/22awg-solid/

[EdHolland]

Thank you Ron. Much appreciated.

[Ron Ramirez]

This evening I put together my own homemade Candohm replacement for this radio.

[Image: http://philcoradio.com/images/phorum/6T2/6T2_057.jpg]

The new part looks longer in the picture only because it is closer to the camera. Both the old Candohm and the new replacement are actually the same length.

And here it is in the radio, all wired up:

[Image: http://philcoradio.com/images/phorum/6T2/6T2_058.jpg]

While I was at it, I also connected a length of cloth-covered AC cord under the chassis. I also replaced all five of this set's dial lamps (two on the sides to illuminate the dial, the other three as band indicators) with screw base LED lamps.

I'm only one or two hours away from trying this set out for the first time. I'm curious to see if I will need that replacement tone control or not. It remains to be seen how this incorrect 50K replacement tone control works in the set. I still need to connect an AC plug to the other end of the cord, find, test and install six suitable tubes, connect a speaker and find out what happens when I turn it on. Unfortunately that may have to wait a while. I have to go back "into the wilderness" in the morning (see here for an explanation of that) so it may be several days before I can go back to the bench and see if this project is almost complete, or not.

[morzh]

Hey Ron,

We can take that resistor thing you made, call it, say, Traw-John and start serial production

[Ron Ramirez]

Traw-John?

I was thinking more like "Nathan-Ohm" since this was Nathan's idea.

Anyway...problems.

[Image: http://philcoradio.com/images/phorum/6T2/6T2_059.jpg]

Yesterday evening before the full effect of the chemo hit, I finished wiring up the 6T2, connected a speaker and an antenna, and brought it up slowly with a Variac.

No releases of magic smoke...no explosions...but also, no sound!

I had a hum at the grid cap of the 6F5. And when placing a finger on the grid cap of the 6A7, I can tune in stations - which tells me something is wrong with the antenna coil assembly since this occurs on all three bands.

In addition:

* The plates of the tuning condenser start rubbing from 650 kc and below.
* The replacement 50K tone control causes the set to squeal when turned toward the bass end...so I am going to need that original 100K control after all.

I'll start trying to sort all of this out in a few, or several, days.

Again, the service manual containing the schematic is here (warning - large file - 32.1 MB) in case anyone wants to look it over and offer any suggestions regarding the antenna coil, tone control, and tuning condenser.

[NostalgiaRadioTime]

Have you checked with Mark O. regarding the 100K control? Perhaps Wilbur Gilroy might have a parts chassis laying around for the control and ANT coil.

As for the coil, if an original RCA coil can't be found, perhaps you could adapt one from a Philco to work or, as a last resort, use one of the little universal ANT coils from AES.

Could it be corrosion, debris or rust between the tuning condenser plates causing the rub, or do you think they are bent? I usually try to slide paper between the plates to see if I can feel any resistance where they could be rubbing.

Good luck!

[morzh]

Yeah what you're saying is screaming antenna transformer open.
Bummer. But then those are usually not too bad unless that's one of those multykayer cross-wound potted jobs. I cannot do that kind of winding.

[Ron Ramirez]

Back at the workbench (finally).

Success.

And there was nothing wrong with the antenna coil.

If you refer to the schematic (see post #2, page 1, this thread or post #71, this page, this thread), take a look at the junction of C8, R2 and R19.

I made a stupid wiring error. I blame the chemo.

(seriously - I have found that chemo does interfere with my thinking for over a week after a treatment)

Anyway...I had connected the right end of C8 to the bottom end of R2 instead of where it should join with the upper end of R2 and the left end of R19.

I also worked some more with the rotor plates of the tuning condenser. Yes, they were bent. One end had been hit with something. I managed to straighten it all out.

Then, I hooked up an antenna and connected the T7-5 speaker, and the set came to life!

And it is now working across the dial from one end to the other, on all three bands. It picks up several stations, even though it has no RF stage. Of course it is nighttime now, so that does make a difference on the AM band.

I still need to replace that tone control, and give the set a full alignment. Then it will be finished.

Alignment tomorrow. Tone control...whenever I can come up with one. I'll check with Willbur, then Mark.

[morzh]

Glad you've snapped out of it