[Patrick]

One of the notes on this schematic says that 43 and 44 are not included "with this revision". So with them removed, there should be nothing in their place? In other words, the + of 46 should not be connected to the + of 45 except through the field coil?

Also, the top grid (pin 4) of 78 was not tied to the cathode. Instead, it went to ground. And the cathode was connected to a cap and resistor in parallel that went to who knows where (floating).

I've got it wired according to the schematic, but the field coil gets hot, and most of the voltages are way off. Is the schematic correct, or am I missing something? Thanks,

Pat

[Image: https://i1367.photobucket.com/albums/r79...d0q5nf.jpg]

[morzh]

43 and 44 is a phase-shifting RC that attempts to reduce the ripple. It does not work very well and is not necessary, the same or better effect could be achieved by increasing 45 value.

[Ron Ramirez]

Next time, go here instead of Radiomuseum:

https://philcoradio.com/library/index.ph...-model-60/

There were many revisions to Model 60, most of which were never documented. In the link above, I attempted to gather together all known revisions of the Model 60 (with multiple schematics).

[Patrick]

Thanks, Ron. I knew you had something somewhere, I just didn't look hard enough for it.

Pat

[Chas]

A hot field coil indicates excessive current flow. That could occur within the FC itself, shorted or shorted to frame and frame connected to chassis. Beyond that a shorted output transformer, shorted IF, incorrect wiring, reversed filter condenser(s). Shorts in the C38, 39 or a defect in Sw37. Any other B+ connections would be via a resistor which would overheat. This radio uses the "back bias" design. If the new filters are connected to chassis or shorted because of sloppy stuffing, there would be no bias for the output tube, that tube would conduct heavily heating the output transformer and the field coil. Voltage divider R47, two resistors, could be open or wrong value, shorted to chassis.

Rather than risk smoking a component with prolonged live testing, with the AC power removed and unplugged from mains, use a VOM and measure the DC resistance across C46. negative probe on negative capacitor. After an initial sag and charging the resistance should settle at least 5K, better at 8K and 12k would be great. I am allowing 60ma for a total B+ load, could be more only a measurement from a working radio could confirm total normal load.

If the resistance is at say 3k that would account for the overheating and further resistance measurements made at the same point and disconnection of the various B+ sinking locations will isolate the fault.

This is the correct method to isolate a defect of this sort without , "try this or that"...

If you want to know just how much current is being consumed in this defective condition, first. Measure the exact resistance of R47, the 32 ohm resistor to the 10ths. Connect a DVM or VTVM to this resistor, negative to chassis and positive to the 32 ohm junction of the 235 ohm resistor. Turn on the set, allow a 30 second or so warm-up measure this voltage to the 10ths. Shut down the radio and do ohms law that will tell the total current. Exception would be a filter capacitor fault or other leakage in the bias to the 1st audio tube.

With the B+ resistance procedure and the total current measurement it should be very possible to zero in on the defect (a wayward solder blob on a tube socket) in short order...

YMMV

Chas

[Patrick]

OK. I have rewired to exactly match Ron's final schematic. Got 117VAC going in. Suppose to have 350V from plate to cathode of the 80. I have 180. When I momentarily disconnect the white wire from the field coil, I get exactly 350.

So I went back again, and rechecked the entire circuit (for about the 5th time). Field coil ohms out like it should. So does the output transformer. So do both IF's, and the antenna and oscillator xformers. Plate voltages are all at zero. Tried a different rectifier. No change. Nothing seems to be shorted, and no connections missing.

Can't focus anymore, so I thought I'd take a break and see what others think.

Pat

[Chas]

Re-read my post.

Shotgun testing is not the answer, it amounts to attempting to get lucky. Like playing the Lottery, not gonna happen. I don't have your chassis on my bench so I do not know the relationship of the "white wire".

Follow my post you should be able to zero in in on the section of the B+ that is drawing to much current.

By creatively removing the various loads from the B+ either live or using the VOM to monitor B+ resistance while un-soldering various loads. You did that with the white wire but that is just about the total load. Disconnect after the field coil.

Note I said VOM for the resistance measurements, a DVM could give erroneous readings in this application...

I can't recommend doing this as a live voltage test, the fault is drawing way to much current...

GL

Chas

[morzh]

Start pulling tubes one by one, or better yet, pull them all except the rectifier.
See if the voltage goes up.

Then start inserting the tubes one by one starting with the output tube.
Be careful: all caps will remain charged as there is nothing much to drain them.

[Patrick]

I pulled all the tubes. No change. I'll try Chas's method in the morning. Just don't really understand it since everything is tied together. How do I remove a "load"? I'm a little confused. And what is a B+ "sinking location"? A term I'm not familiar with.

[Chas]

Since pulling the tubes did not matter. That, says the excess load is coming from some location from a tube socket back to the feed (source) side of the speaker field coil. I'm still thinking it is a solder blob or solder flow in between a wafer socket or snipped end of a component wire shorting.

It is preferable to measure the resistance of the power supply B+ that is the load as I stated if it is greater than 8K it is probably O.K., if it is lower that is the indication of the heavy load short.
Why is it better to use a resistance measurement? Because the load is so heavy there is risk burning out the field coil or the power transformer.

Follow the B+ as it feeds each stage, the output stage is via the output transformer and a direct wire to the screen of the output tube. To isolate the stage lift the screen wire and the B+ feeding the output transformer.

If the resistance reading rises dramatically that is the area of the short...

If not move on to R24, then R34, then R14, to isolate the if's one has to actually remove the B+ wire from the IF termination.

The voltage dropping network of three resistors totals 86K, that sets up the minimum current flow for the B+. I do not know the design of these resistors. Some types can short to the steel case if the happens then the current will go up and B+ voltage drop... That 86K should yield 1ma approx based on the highest plate voltage. Not gonna call up the NA schematic, again...

So, if there is no problem on the B+ placing the ohmmeter + on C45  positive and chassis ground negative respectively should yield 86K after the caps have charged, if not then do the "lifting" (de-soldering) and disconnecting a wire to a stage. Do so until the resistance is 86K then check that divider if it is truly is 86K

Note if there is no other leakage, the resistance across the "B" supply will be this 86K, if it is any lower that is what the problem is...

Look at R14 the 32K resistor at the far left, that lower buss travels across to the white wire, all the connections to that white wire have to be lifted, one at a time to locate that short circuit. Since you already know when you lift the white wire at the field coil the high current flow stops.

The B+ sink is any tube and the voltage divider resistors.

Note there are a couple of small bypass caps on the B+ be sure they are O.K. but they will show up if the load removal process is done.

Use an analog ohmmeter, some DVM's don't like inductors like a field coil as a resistance.

Got It?

Fair warning cheat the test process and results will not be found. There is no "easy way out"...

GL

Chas

Embarrassing question: Did this radio work to some extent before it was refurbished?

[Patrick]

Chas,

I really appreciate the time you have taken to assist. I will follow your procedure tomorrow and post the results. I assume the radio did not work prior, as there were leaking caps and floating connections. The first thing I did was re-cap, replace all out of tolerance resistors, and ohm out all coils and transformers. And I use a VTVM for all measurements.

I did run out and quickly measure the resistance across C46, and got 1.5K.

Thanks,

Pat

[morzh]

How much do you want to bet that measuring across C45 will yield 400 ohm?
Something shorting the output of the field coil. 400 ohms to Rectifier negative or 200 ohms to GND.

[Patrick]

Even though I haven't finished my coffee yet, Morzh, I had to check it out. Still (of course) have 1.5KΩ across C46, but have 300Ω across C45. Also have 300Ω from C45+ to ground. Do some more checking after I wake up.

[Patrick]

Chas,

I reread your post. It looks like you are referring to the schematic I posted, which, as stated, is not correct. The correct schematic is HERE, at the bottom of the page.

[Patrick]

Well.......A small step....component #12, the osc. comp. con. had a chassis cap over the adjusting screw. It was tweaked just enough that the screw was hitting the cap, grounding it out. I straightened it up. Now all my voltages (at least the ones I measured, are correct. Actually have sound out of the speaker! 'Course all it's doing is motorboating. On to the next problem.