[MrFixr55]

Hi Hamilton,

Like Dale said, this is a group that is happy to help. I have learned also, and in assisting others, we actually gain knowledge ourselves (a win- win situation!) We all started at one time (For me it was 10, but I never became a HAM). If you have gotten this far in 2 years, pat yourself on the back or better yet, get your significant other to do so (or better yet, some other form of appreciation for your talents).

Thank you for your service as a first responder.

Re dyslexia, my wife has dyslexia but she insists on handling the family finances. She has done so for 44 years, we never bounced a check and we have some money in the bank. So I think that she has learned to handle it. I am sure that you have also.

[MrFixr55]

Hamilton, the black trim actually brings out a lot for the areas that are finished. I think that at one time, they called it "Japan Black" and it was very common in radio cabinets. Again, that was a fantastic job!

[DaleHCook]

We all started at one time (For me it was 10, but I never became a HAM.

Same thing here - started over 60 years ago at about 10 learning to fix old vacuum radios that neighbors were throwing out and replacing with new transistorized radios, so I learned electronics with vacuum tubes. I've never been a ham, but have worked with transmitters. Of course, as a broadcast engineer some of those transmitters have been bigger than three refrigerators side-by-side.

[radiorich]

Hello Hamilton ,
I think you are doing very well and your project is coming right along I am revisiting a Philco I restored in Dec .
The station was going in and out while I touched the tuning !

Sincerely Richard

[Hamilton]

Mr Fix
I did the measurements, not sure if they were done properly.

I do not get a dead short between Pins 2 and 3. I get a reading of .2 ohms. That reading is on both 42 output tubes.

Between Pin 2’s of the 2 42 output tubes I get no reading at all. 0.0

The readings I took from the red circled #42 output tube Pin 2 to the lugs of the output transformer were - 0.0 to #1, 0.0 to #2, 0.3 to #3 and 0.0 to #4. 
The readings I took from the green circled #42 output tube Pin 2 to the lugs of the output transformer were - 1.4 K to #1, 249 ohms to #2, 0.0 to #3 and .2 to #4.

Between Pin 4 of the 42 output tubes I get 291 ohms and 154 ohms on the center tap. That center tap I used is the one shown in the blue circle.

Between Pin 5 and chassis ground on both 42 output tubes I get a dead short.

I’m not sure if any of my readings were done correctly. That’s why I’m including the pics to show where I took the readings from. The “interstage” transformer confused me. I hope this helps. The radio works but obviously there are some issues.

[MrFixr55]

Hi Hamilton, 

First, the good news:
The readings between Pins 4 of the 2 output tubes (Control Grid)  and between pin 4 of one of the output tubes and the center tap of the interstage (driver) transformer are good.  The readings between pin 5 (cathode) of each tube and chassis are correct (these should be 0 Ohms).  The readings of 0.2 Ohm between pin 3 and 4 of each tube are normal.  If you inspect the socket, you should see the jumper.  

The bad news.  The readings between pin 2 of one output tube and pin 2 of the other are messed up!  They should be what I listed in my last post (around 350 Ohm).


Unfortunately, neither the schematic from the Philco Library nor the one from Nostalgia Air have pinouts for the speaker plug or wire color codes.

From your pictorial and your readings, and using your numbering in your pic of the speaker, I am fairly sure that the connections at the speaker are as follows:
Pin 1- Field Coil to B+ for rest of radio
Pin 2- B+ from Power Supply (Choke, 8.0uF Cap# 77) to center tap of output transformer primary and Field Coil
Pin 3- One leg of Output Transformer primary to one 42 plate and screen grid
Pin 4- Other leg of Output transformer primary to the other 42's plate and screen grid.

Now, these connections may or may not be correct (someone may have botched a repair but done a nice solder job years ago).

Ron or any other experts who worked on one of these, please jump in on the correct speaker pinouts.

Try this:
Unplug the speaker and read between pin 2 of one tube and pin 2 of the other.  The meter should indicate an "open" circuit, infinite resistance. (The meter will display a 1, just as if the probes are not connected to any device.  There may be a very high resistance reading for a second before going to open due to the capacitors between pin 2 of each tube and ground.  If not, check for a solder bridge somewhere, likely where the caps are soldered to the speaker connector.

Next check the speaker. Leaving the speaker plug unplugged, verify the following:
Between your #3 and #4 you should read approximately 350 Ohm
Between your pin 2 and your pin 3, and between your pin 2 and pin 4, you should read somewhere around 175 ohm. The readings between pins 2 and 3 and between pins 2 and 4 will be different but when added together, will equal the readings between pin 3 and pin 4.
Between pin 1 and 2, you should read somewhere around 1140 Ohm.
When looking at your DVM, ensure that it is reading Ohm and not KOhm. Most DVMs are "auto-ranging".

Keep us posted. I hope that we can figure this out, as it is not good for the one 42.

[Hamilton]

MrFix

I get 0.0 when I measure between the two Pin 2’s of the output tubes with the speaker disconnected.

Between #3 and #4 on the speaker I get 0.0. The only reading I get are between #1 and #2 1.22k, between #1 and #4 1.475k and between #2 and #4 243 ohms.

I did check the voltages on the three 42’s again. The 42, red circled one, is giving me 38 dc on Pins 2-3, the other output tube 323 dc on Pins 2-3 and 219 dc on the 42 driver tube.

[Hamilton]

http://www.nostalgiaair.org/Resources/824/M0013824.htm

I was looking at the tube voltages from the Nostalgiaair site for the Model 650 and I was under the impression that both 42 output tubes were to have the same voltages but this  showed only one 42 output tube.

Should both 42 output tubes have the same plate and screen voltages?

[RodB]

Your impression is correct. The screen grids of each 42 output tube are connected to the respective plates putting 300 volts on each element.

[MrFixr55]

Hi Hamilton,

I am scratching my head here. One does not expect multiple failures of this type and the radio to have good sound. In addition, a reading of 0 Ohms between pin 2 of one output tube and pin 2 of the other output tube would not allow for different voltages from each tube's plate. With the speaker plug disconnected from the radio, I would not expect 0.0 Ohm between pins 3 and 4. unless wires were shorted in the speaker plug or within the transformer. The readings between 1 and 2, 1 and 4 and 2 and 4 are close to what I would expect. Given the resistance readings, I would not expect 38 V on one output tube plate and 300 or more V on the other output tube plate, given the resistance readings that you received. The readings on the driver appear to be normal.

With the speaker plug disconnected, the plate to plate resistance (pin 2 to pin 2) of the output tubes should be infinite, except for a short time reading as the 6800pF caps charging. These new caps are reliable unless badly burned when soldering. If these caps short, however, they will short to ground and the output transformer will burn out. Take photos, if possible, with other wires moved out of the way. Physically inspect the wiring on the tube sockets and from the sockets to the speaker socket. Please retake the resistance readings between Pin 2 of one output tube and pin 2 of the other tube with the speaker plug unplugged from the radio.
Please take some side view pix of 1, 2 and 3, 4 (your numbers) of the speaker. The reading between 3 and 4 should not be 0.0 ohm. If 3 goes to one 42 plate and 4 goes to the other 42 plate, the reading should be 350 Ohm (the primary plate to plate resistance per the schematic). If possible also take pix of the reading and the setting on the DVM. If you have a meter that has selectable ranges as opposed to autoranging, use the 2K setting. Of the 4 wires, 3 of them go to the output transformer primary. of these 3, one (the center tap of the primary) is shared with the field coil. Please note that even though the terminal strip is on the top of the transformer, not all terminals connect to the transformer. One of the 4 has no connection to the transformer but connects to the field coil. If possible, trace the wires from Pin 2 of each output tube to the speaker socket, and then from the socket to the transformer terminal. If possible, remove the cover from the speaker plug and inspect the wires to confirm no shorts inside the plug. Inspect the cable where the string is tied to it by the transformer. The insulation on this wire does crack and shorts can happen where the wires are bundled or otherwise touch each other.

I wish I lived nearby, but it is a good 500 miles between Long Island and Toronto.

[Radioroslyn]

John kinda beat me to it. But just to double check things you should a have a H-13 speaker. It's stamped on the back in ink. With the speaker unplugged measure the resistance across any of the two pins on the plug. You should have no more than 1500 ohms. If you do measure like 10,000 ohms your output transformer is bad. It's not too uncommon on these speakers. GL

[Hamilton]

Here’s a pile of pics. Hopefully something pops up that I may have messed up.

The first ones are the side shots you requested.

I did a continuity check on the wires on the output transformer and that’s the shot of the speaker connection with the corresponding numbers 1, 2, 3 and 4. The speaker is not stamped anywhere but I could see but the output transformer is a Philco 7078.

The wires leading from the speaker socket are attached at the following spots, if this helps.

Pin 1 - one goes to Part #72, the wire wound resister and one goes to Part #67, the input transformer which read 292 ohms and 480 ohms

Pin 2 - one goes to the 8 mfd electrolytic and the other goes to Part #79, the filter choke

Pin 3 - a .006 cap is attached and the other wire goes to Pin 2 of the low voltage 42 output tube, red circled one.

Pin 4 - a .006 cap is attached ( both of these .006 caps, Parts 86 and 87, are grounded on bakelite block Part #80. The other wire goes to Pin 2 goes to the other 42 output tube.

The condition of the wiring appears good, there doesn’t seem to be any solder blobs. I took apart the threads holding the speaker wire near the transformer to look for any damage and couldn’t find anything. I’m enclosing all the shots I believe you wanted. If you need any further information or photos don’t hesitate to ask. 

I’m very appreciative of all your help!

[MrFixr55]

BINGO!! NOW IT ALL MAKES SENSE!! SUCCESS! A Pic is worth 1K words!!

Hi Hamilton,

Thanks for the great pix! They are the telling of the story!!

OK, the reading between Pins 3 and 4 is not 0 Ohms, it is "OL" KOhms, a resistance higher than the meter is capable of reading. It is infinite ohms. In other words, one leg of the transformer is open. The transformer is bad. With the speaker unplugged, and radio powered off and unplugged, if you got the same reading between pin 2 of one output tube and pin 2 of the other, this is normal. So, a dead short in the transformer and a dead short (0 Ohm) between the 2 output tube plates with the speaker plug unplugged would be rare, But "OL" between the 2 pi 2s and between 3 and 4 on the speaker is explainable as a single event. The transformer primarytcoil "opened".

In the current condition, the radio will play, but not as well as it would with the transformer fully functional. It may be bad for the tube reading only 38V also.

Looking at the side view of the transformer, showing connection 3 and 4 and the secondary, the burn mark may indicate where the transformer burned out and the wiring may be repairable. However, this is a gamble. You have to peel away the paper wrapping. this may totally ruin the transformer, however.

Next step is to figure out the correct replacement transformer. I will defer to the experts, Ron Ramirez, terry (Radio Roslyn), etc. Primary impedance of the transformer (This is very different from resistance, although still measured in Ohms) is 8K Ohms Plate to Plate per RCA receiving tube Manual or 10K Ohms per a Tung Sol Spec Sheet. The issue is the speaker voice coil impedance. the resistance is 1.1 Ohm. If the impedance is 4 or 8 Ohm, then a transformer will be easy to find. If the impedance is much less than 3 Ohms, it may get interesting. Experts on this Phorum can suggest a replacement.

Again, great work for an electronics newbie, tour persistence, good work and good pix paid off! And a wonderful job on the cabinet! Any Museum would love to have your radio (But museums being non-profit, they wouldn't pay for it. Don't part with this, this is your trophy!!

Get a new transformer, add a radio phono switch and this radio will be a really great performer. It would be a nice sounding amp for guitar, but you would not be able to overdrive it without a preamp. The rating for this configuration of 42 tubes in class AB Push Pull is 15Watts!! (Per RCA and Tung Sol specs for triode 42 driver and triode P-P 42 outputs being fed by 350V B+ on the output tubes).

[Radioroslyn]

What you are looking for is a transformer that will match 6K to 1 1/4 ohms. Normally the plate impedance would be higher but these tubes are configured in a triode setup for less distortion vs the more common pentode configuration. Something like a Hammond 125E electrically would come pretty closes but mechanically it kinda big compared to the original.

https://www.hammfg.com/electronics/trans.../125a-125e

GL

[Ron Ramirez]

Model 650 was rated by Philco as having 10 watts output audio power; therefore, a Hammond 125-D (10 watts) would suffice.

125-E would work as well, and provide an extra safety factor due to its higher power ratings. However, as Terry mentioned, size would also be a concern.