< src=http://www.nostalgiaair.org/PagesByModel/602/M0013602.pdf>

Hope that schematic link works. It's from here under Philco 46-480.

I built this radio from the ground up replacing everything in 2009. Been working great since. All of a sudden it quit working. Tested all the tubes, all good. I have a NOS set as backup tubes which I did try using at a later point in my troubleshooting. Didn't help.

I did find R17 1K 1/2W on the B+ line to be fried. So I put in a 1W to give myself time to isolate where the excessive current draw was coming from. When I disconnected the RF section it stopped getting hot. So I took the whole RF assembly apart (It's a nightmare job on this radio) and replaced everything in it. I did find a suspicious choke but nothing that really looked bad. I replaced the choke with one from a donor radio. Re-installed the RF section and hooked everything up. Whatever I did, now keeps the 1K R17 from frying.

But now the radio justs motorboats on all bands including the FM band with no reception of any kind at all. So I started at the front end of the radio and pulled tubes one at a time until the motorboating stopped. It stopped after I pulled the 6SQ7 1st AF Amp. So I started looking into the audio section but when I touch the center tap of the volume control I get the expected reaction.

So at this point I've replaced all capacitors including the Ecaps. I can't find any other bad resistors other then the mentioned 1K R17.

I pulled the volume control and it works fine. The motorboating starts at about 1/2 volume and the tone control does interact with it.

All the voltages are correct throughout the radio. I have the Philco service data with troubleshooting procedures and have performed all the tests including the ones requiring the use of my sig. gen. All tests pass but it still motorboats.

I also went through all three IF cans and inspected the coils. All look good and the resistance readings match the paperwork. I replaced all the components in these cans. Caps mostly.

The speaker, voice coil, output transformer and hum bucking coil all check good. One thing baffles me. The Philco paperwork says there should be a minimum of 50K resistance between B+ and chassis ground. I have 22K. But this was take with a digital meter not a 20,000 volt to ohm meter as the paperwork calls out.

So I need help and any and all would be really appreciated. I just don't know where to go from here.

Thanks,
Johnny

All I can add is I just spend 2 weeks on a Philco 46-480 trying to get the FM to work for a customer here in Jersey. This model must have driven many techs to the 'bottle' just by the nature of the way the band select switch covers the access to the first tube and IF can..Not to mention trying to get at all the components built into the band switch that are inaccessible. I eventually got the AM/SW working but never the FM. I have a feeling you just need a fresh set of eyes on the circuit..you have probably made a small mistake somewhere and just can't see it. Hang in there...

R17 does not feed the RF section, so a problem in the RF section could not have been causing this particular resistor to overheat/burn out.

R17 only feeds the 2nd IF stage plate circuit. Most likely a short to ground in the 3rd IF transformer primary circuit caused R17 to burn out.

One likely cause of this sort of problem is the rubber-coated wires Philco used to connect IF transformers to the chassis. This rubber insulation is prone to hardening and falling off, making a dead short possible from the R17 node to the chassis at the two points where the IF transformer primary wires pass through the chassis.

Whatever caused it, a fault in this stage will kill both the AM- and FM-borne audio signal.

Fault-isolating the "low resistance" reading of B+ to ground: lift R17, R7, and R9 one at a time, measuring the resistance from the B+ bus to ground each time. My money is on something on the R17 "downstream" side being the problem.

It is a feat of engineering Brian. But they sure as heck weren't thinking about the repair tech when they engineered it.

All the wiring in this radio is new CV including the wiring in the IF cans. So I'll go through and check resistors again and see if I missed something.

If I can get to those two resistors without disassembling the whole RF section again I'll lift one side of them and see what that does to the B+ to gnd. resistance. But if I can't get to them then "Resistance is Futile." Everything in that section is new and put together properly. It's not coming apart again. I'll send the radio back DOA first.

If you haven't seen the RF section of a 46-480 here's a pic of one. And as Brian stated Philco did put the 7F8 tube socket right under the bandswitch and a lot of connections are made between the BS and this socket not to mention the socket itself has at least three components that go from one pin to another. It's a booger. This picture was taken before I rebuilt it. It looks a lot cleaner now with all new shielded cables, micas all replaced with silver micas, all wiring and resistors replaced. Between the BS and the 7F8 socket Philco install un-insulated jumpers. I replaced all these with insulated jumpers.
< src=http://speakeasyradios.com/yahoo_site_admin/assets/images/46-480_RF_Section.210203321_std.jpg>

But the 1K R17 DOES NOT get hot anymore after I replaced everything in the RF section. I should of made it more clear but there is one wire that is common to R17 that is common to one side of R7 and R9 which are IN the RF section. So there is no excessive current draw on that resistor any more and there's around 250Vdc on that wire. B+ #2 maybe?

Johnny

:Fault-isolating the "low resistance" reading of B+ to ground: lift R17, R7, and R9 one at a time, measuring the resistance from the B+ bus to ground each time. My money is on something on the R17 "downstream" side being the problem.
:

:It is a feat of engineering Brian. But they sure as heck weren't thinking about the repair tech when they engineered it.
:
:All the wiring in this radio is new CV including the wiring in the IF cans. So I'll go through and check resistors again and see if I missed something.
:
:If I can get to those two resistors without disassembling the whole RF section again I'll lift one side of them and see what that does to the B+ to gnd. resistance. But if I can't get to them then "Resistance is Futile." Everything in that section is new and put together properly. It's not coming apart again. I'll send the radio back DOA first.
:
:If you haven't seen the RF section of a 46-480 here's a pic of one. And as Brian stated Philco did put the 7F8 tube socket right under the bandswitch and a lot of connections are made between the BS and this socket not to mention the socket itself has at least three components that go from one pin to another. It's a booger. This picture was taken before I rebuilt it. It looks a lot cleaner now with all new shielded cables, micas all replaced with silver micas, all wiring and resistors replaced. Between the BS and the 7F8 socket Philco install un-insulated jumpers. I replaced all these with insulated jumpers.
:< src=http://speakeasyradios.com/yahoo_site_admin/assets/images/46-480_RF_Section.210203321_std.jpg>
:
:But the 1K R17 DOES NOT get hot anymore after I replaced everything in the RF section. I should of made it more clear but there is one wire that is common to R17 that is common to one side of R7 and R9 which are IN the RF section. So there is no excessive current draw on that resistor any more and there's around 250Vdc on that wire. B+ #2 maybe?
:
:Johnny
That pic didn't work. Lets try this.

Johnny
:
:
::Fault-isolating the "low resistance" reading of B+ to ground: lift R17, R7, and R9 one at a time, measuring the resistance from the B+ bus to ground each time. My money is on something on the R17 "downstream" side being the problem.
::
:
:

R7 and R9 are both burried under the bandswitch. Seeing how everything in there is new I can only assume that my motorboating is being caused by something else. Any more ideas? I've been through this whole set.

Johnny

::It is a feat of engineering Brian. But they sure as heck weren't thinking about the repair tech when they engineered it.
::
::All the wiring in this radio is new CV including the wiring in the IF cans. So I'll go through and check resistors again and see if I missed something.
::
::If I can get to those two resistors without disassembling the whole RF section again I'll lift one side of them and see what that does to the B+ to gnd. resistance. But if I can't get to them then "Resistance is Futile." Everything in that section is new and put together properly. It's not coming apart again. I'll send the radio back DOA first.
::
::If you haven't seen the RF section of a 46-480 here's a pic of one. And as Brian stated Philco did put the 7F8 tube socket right under the bandswitch and a lot of connections are made between the BS and this socket not to mention the socket itself has at least three components that go from one pin to another. It's a booger. This picture was taken before I rebuilt it. It looks a lot cleaner now with all new shielded cables, micas all replaced with silver micas, all wiring and resistors replaced. Between the BS and the 7F8 socket Philco install un-insulated jumpers. I replaced all these with insulated jumpers.
::< src=http://speakeasyradios.com/yahoo_site_admin/assets/images/46-480_RF_Section.210203321_std.jpg>
::
::But the 1K R17 DOES NOT get hot anymore after I replaced everything in the RF section. I should of made it more clear but there is one wire that is common to R17 that is common to one side of R7 and R9 which are IN the RF section. So there is no excessive current draw on that resistor any more and there's around 250Vdc on that wire. B+ #2 maybe?
::
::Johnny
:That pic didn't work. Lets try this.
:
:
:Johnny
::
::
:::Fault-isolating the "low resistance" reading of B+ to ground: lift R17, R7, and R9 one at a time, measuring the resistance from the B+ bus to ground each time. My money is on something on the R17 "downstream" side being the problem.

Just a thought...If you replaced R7 & R9, make sure you didn't read the resistor(s) color bands incorrectly and install the wrong value.

Clifton

:R7 and R9 are both burried under the bandswitch. Seeing how everything in there is new I can only assume that my motorboating is being caused by something else. Any more ideas? I've been through this whole set.
:
:Johnny
:
:
:::It is a feat of engineering Brian. But they sure as heck weren't thinking about the repair tech when they engineered it.
:::
:::All the wiring in this radio is new CV including the wiring in the IF cans. So I'll go through and check resistors again and see if I missed something.
:::
:::If I can get to those two resistors without disassembling the whole RF section again I'll lift one side of them and see what that does to the B+ to gnd. resistance. But if I can't get to them then "Resistance is Futile." Everything in that section is new and put together properly. It's not coming apart again. I'll send the radio back DOA first.
:::
:::If you haven't seen the RF section of a 46-480 here's a pic of one. And as Brian stated Philco did put the 7F8 tube socket right under the bandswitch and a lot of connections are made between the BS and this socket not to mention the socket itself has at least three components that go from one pin to another. It's a booger. This picture was taken before I rebuilt it. It looks a lot cleaner now with all new shielded cables, micas all replaced with silver micas, all wiring and resistors replaced. Between the BS and the 7F8 socket Philco install un-insulated jumpers. I replaced all these with insulated jumpers.
:::< src=http://speakeasyradios.com/yahoo_site_admin/assets/images/46-480_RF_Section.210203321_std.jpg>
:::
:::But the 1K R17 DOES NOT get hot anymore after I replaced everything in the RF section. I should of made it more clear but there is one wire that is common to R17 that is common to one side of R7 and R9 which are IN the RF section. So there is no excessive current draw on that resistor any more and there's around 250Vdc on that wire. B+ #2 maybe?
:::
:::Johnny
::That pic didn't work. Lets try this.
::
::
::Johnny
:::
:::
::::Fault-isolating the "low resistance" reading of B+ to ground: lift R17, R7, and R9 one at a time, measuring the resistance from the B+ bus to ground each time. My money is on something on the R17 "downstream" side being the problem.
:
:
:
:

If R17 was heating up at one time, I would guess you were pulling too much current thru one side of T6 thru the plate of 2nd IF tube 7H7 and it's cathode? I'm sure you probably checked there, but thought I'd mention it in case something fried there.
I saw your photo of the band switch earlier when I was searching for info on this POS radio...Made me feel better I wasn't alone on this particular model..Maybe EDD will chime in here (too late for me--I returned the one I worked on), he's really good at getting things sorted out and explaining the circuit theory.

The "wire that is common to R7,R9, and R17" (paraphrasing) is the B+ bus.

As I hinted above, I doubt that the R7/R9 branches off of the B+ node "root" are the problem, since they could not possibly have contributed to the initial smoking of R17.

What does the B+ node ohm to ground when you lift one end of R17? When you resolder the lifted end of R17, what does the B+ node ohm to ground? If it's less than 100K (never mind the Philco 50K spec) you have an unwanted load on B+.

Success in troubleshooting requires a logical approach. That means ruling out irrelevant or impossible fault modes.

Thanks Clifton & Brian! I check all components before I install them. Been burned a few times installing new parts that were bad. Mostly caps so I check every resistor and cap for its correct value before using them now days.

I'll check again around that 7H7 too. That's an easy socket to get to.

I removed R17 completely CV. On the B+ side my resistance starts out at around 350K and stabalizes at about 100K. The other side where C37 .05ufd is reads a steady 22K. Both readings to chassis gnd. of course.

So what does this tell me? My B+ is being shorted somewhere on the C37 side of R17? C37 has been replaced. T5 & T6 can has been opened and the 18pf and 100pf caps replaced. All coil readings looked very good and the physical state of the coils looked very good. I inspected C35 and it looked like a normal variable cap but I don't know what is meant by the note on the schematic "2 Fixed Plates Under C35".

I'd still like your input but it sounds like Brian may be onto something being awry around the 7H7 2nd IF Amp. I'll go back and check again. Whats your input on the resistance readings I just gave on the B+ to gnd.?

Johnny

:The "wire that is common to R7,R9, and R17" (paraphrasing) is the B+ bus.
:
:As I hinted above, I doubt that the R7/R9 branches off of the B+ node "root" are the problem, since they could not possibly have contributed to the initial smoking of R17.
:
:What does the B+ node ohm to ground when you lift one end of R17? When you resolder the lifted end of R17, what does the B+ node ohm to ground? If it's less than 100K (never mind the Philco 50K spec) you have an unwanted load on B+.
:
:Success in troubleshooting requires a logical approach. That means ruling out irrelevant or impossible fault modes.
:

So, with R17 disconnected, the B+ bus measures around 100K ohms to ground, which is fine.

The C37 node side of the disconnected R17 ohming 22K ohms is completely unacceptable. It should essentially ohm "open". There is NOTHING that would provide a DC path to ground on that node- if the components are working properly.

Find what is pulling down that node and you will very likely solve your problem. This may entail pulling components off one at a time until you find the current leak.

Don't forget to replace R17 with a part of the original power rating after you get the set working again.

The problem seems to be in the disc transformer. Possibly a partial short (long short) of the red or blue lead to the case/ground. Or perhaps C33 or the two plate cap across it may be shorted. I haven't had time to completely study the schematic, but there is/are switch position(s) that ground the C46 end of R19. If C33 were shorted then one would measure around 27K to ground. May try unsoldering the orange disc transformer wire from the circuit and measure the resistance of the red wire into the transformer and see what you get.

Clifton

:So, with R17 disconnected, the B+ bus measures around 100K ohms to ground, which is fine.
:
: The C37 node side of the disconnected R17 ohming 22K ohms is completely unacceptable. It should essentially ohm "open". There is NOTHING that would provide a DC path to ground on that node- if the components are working properly.
:
:Find what is pulling down that node and you will very likely solve your problem. This may entail pulling components off one at a time until you find the current leak.
:
:Don't forget to replace R17 with a part of the original power rating after you get the set working again.
:
:
:

What is an orange disc transformer?

Johnny

:The problem seems to be in the disc transformer. Possibly a partial short (long short) of the red or blue lead to the case/ground. Or perhaps C33 or the two plate cap across it may be shorted. I haven't had time to completely study the schematic, but there is/are switch position(s) that ground the C46 end of R19. If C33 were shorted then one would measure around 27K to ground. May try unsoldering the orange disc transformer wire from the circuit and measure the resistance of the red wire into the transformer and see what you get.
:
:Clifton
:
::So, with R17 disconnected, the B+ bus measures around 100K ohms to ground, which is fine.
::
:: The C37 node side of the disconnected R17 ohming 22K ohms is completely unacceptable. It should essentially ohm "open". There is NOTHING that would provide a DC path to ground on that node- if the components are working properly.
::
::Find what is pulling down that node and you will very likely solve your problem. This may entail pulling components off one at a time until you find the current leak.
::
::Don't forget to replace R17 with a part of the original power rating after you get the set working again.
::
::
::
:
:

:What is an orange disc transformer?
:
orange disc transformer= orange wire on discriminator transformer. Last transformer in the string that couples the 2nd IF tube to the detector tube.

::What is an orange disc transformer?
::
:orange disc transformer= orange wire on discriminator transformer. Last transformer in the string that couples the 2nd IF tube to the detector tube.
:
:
:
Thanks for clarifying that CV.

So here's what I'm finding. In all bands except SW the center conductor of the shielded cable is shorted to ground. Shielded cable that R19 27K connects to along with C46 .01 cap.

When I disconnect that orange wire from the three resistors (6.8M, 100K & 27K - R18, 19 & 20) my 27K B+ short, resistance to ground goes away. To be more precise the short is 26.95 ohms on my Fluke 179. I added this because I see no fluctuation in that reading from anywhere that I take the reading.

When I read from the orange wire to the yellow wire I read 11.2 ohms which is correct per the Philco service paperwork. That's reading across the secondary of T5 & T6. The orange wire to ground is open as is the yellow wire.

So I'm getting myself a little lost. Or confused as to where this short is at. Isolated, the 100K, 27K and 6.8M all read good. But with all the resistors still in the circuit the 6.8M reads 26.95 ohms across it. I believe it reads this because one end if it is common the the 27K and the 27K is shorted to ground via the center conductor of the shielded cable.

So what does all this tell you? As I said... I'm getting lost. I hope not a messed up bandswitch. Everything in there is new and the bandswitch looked good.

Johnny

Johnny,

I think you may have found the culprit. The only way I can see one can measure 27K Ohms from the red B+ lead to ground is for C33 to be shorted or possibly the fixed capacitor across it is shorted. With C33 shorted that would put R19 across the B+ red wire into the transformer. That is, thru the red B+ wire to the center of the two transformer primaries on over to C33, which if shorted is no resistance, on out the orange wire thru 27K Ohm resistor R19 to the shielded wire which is switched to ground.

Clifton

:::What is an orange disc transformer?
:::
::orange disc transformer= orange wire on discriminator transformer. Last transformer in the string that couples the 2nd IF tube to the detector tube.
::
::
::
:Thanks for clarifying that CV.
:
:So here's what I'm finding. In all bands except SW the center conductor of the shielded cable is shorted to ground. Shielded cable that R19 27K connects to along with C46 .01 cap.
:
:When I disconnect that orange wire from the three resistors (6.8M, 100K & 27K - R18, 19 & 20) my 27K B+ short, resistance to ground goes away. To be more precise the short is 26.95 ohms on my Fluke 179. I added this because I see no fluctuation in that reading from anywhere that I take the reading.
:
:When I read from the orange wire to the yellow wire I read 11.2 ohms which is correct per the Philco service paperwork. That's reading across the secondary of T5 & T6. The orange wire to ground is open as is the yellow wire.
:
:So I'm getting myself a little lost. Or confused as to where this short is at. Isolated, the 100K, 27K and 6.8M all read good. But with all the resistors still in the circuit the 6.8M reads 26.95 ohms across it. I believe it reads this because one end if it is common the the 27K and the 27K is shorted to ground via the center conductor of the shielded cable.
:
:So what does all this tell you? As I said... I'm getting lost. I hope not a messed up bandswitch. Everything in there is new and the bandswitch looked good.
:
:Johnny
:
:
:
:
:

I agree- it appears that the problem almost has to be a dead-shorted C33 or the "two plate capacitor" that shunts it is dead-shorted. Otherwise there is no means for high-voltage DC to make it from the primary to the secondary of the discriminator/detector transformer.

:I agree- it appears that the problem almost has to be a dead-shorted C33 or the "two plate capacitor" that shunts it is dead-shorted. Otherwise there is no means for high-voltage DC to make it from the primary to the secondary of the discriminator/detector transformer.
:

Okay guys. I'll pull that can again and check it out. I never did check C33 or the two plate capacitor. Just installed the three new pfd caps. I'll get back to you.

Thanks,
Johnny

I removed the can and opened it up. Disconnected everything connected to C33. Coils etc. At that point I read .4 ohms across C33. So I disassembled C33 and found that there were two mica plates between two metal plates of the variable cap section and under that were the two plates pointed out on the schematic note. These plates had no mica between them. So I took one of the two mica plates from the variable cap and placed it between the two metal plates of the fixed cap.

Put it back together and with nothing connected to it I now read open. No resistance, infinity.

But from the point in the radio where the orange wire connects there's still going to be and is 27K to ground because of the 27K resistor that goes to the center conductor of the shielded cable. Remember this center conductor is grounded in all bands except SW.

So before I re-install the can onto the radio, do we think that this will solve the problem? C33 is no longer shorted. But my big question is... How did this set work for four years with the C33 configured the way it was? Wish I could insert one of those "Confused Faces" here. I'll have it re-installed tomorrow. Have errands to do the rest of today.

But please let me know your opinions on this C33.

Thanks again,
Johnny

::I agree- it appears that the problem almost has to be a dead-shorted C33 or the "two plate capacitor" that shunts it is dead-shorted. Otherwise there is no means for high-voltage DC to make it from the primary to the secondary of the discriminator/detector transformer.
::
:
:Okay guys. I'll pull that can again and check it out. I never did check C33 or the two plate capacitor. Just installed the three new pfd caps. I'll get back to you.
:
:Thanks,
:Johnny
:

Clearly this was a fault that had to be cleared before the set ever had the potential of working again.

Since you already ohmed the discriminator pri/sec winding and found them OK, it appears that you lucked out and the only "collateral damage" from this short was a fried R17. Which was its intended lot in life by the radio engineer who designed the set.

Don't know why the C33 combo cap shorted- this is the sort of thing we'd examine under the microscope in the lab to find the "root cause". However, I can tell you that microscopic fragments from 0000-grade steel wool (often used in refinishing radio cabinets) and air-dielectric capacitors don't mix.

My only concern now is that by adding the mica plate between the 2-plate cap, you have changed the cap's value enough to prevent C33 from pulling the secondary into resonance. But I think that I'd try it as is- if it doesn't align on FM properly, you now know where to look first. But the set should work OK on AM now.

Looks like I'm pulling the can again CV. Found time to re-install it today and now the motorboating is gone but no reception on any bands. SW? I don't know. In SW it makes static come from the speaker so maybe SW is ok but I'm not receiving anything on it. Didn't spend much time looking for anything.

If the radio was supposed to have nothing between the two fixed cap plates and now I've added the mica it may be causing this "No Reception" on AM, FM, or PB mode. Maybe there was something in between those two fixed cap plates. I'll take it apart again, put it back into it's original configuration and see if I have a short before I put the can back in the radio.

Just haven't seen a variable cap/trimmer like this with two mica pieces between the plates.

Johnny

:Clearly this was a fault that had to be cleared before the set ever had the potential of working again.
:
:Since you already ohmed the discriminator pri/sec winding and found them OK, it appears that you lucked out and the only "collateral damage" from this short was a fried R17. Which was its intended lot in life by the radio engineer who designed the set.
:
:Don't know why the C33 combo cap shorted- this is the sort of thing we'd examine under the microscope in the lab to find the "root cause". However, I can tell you that microscopic fragments from 0000-grade steel wool (often used in refinishing radio cabinets) and air-dielectric capacitors don't mix.
:
:My only concern now is that by adding the mica plate between the 2-plate cap, you have changed the cap's value enough to prevent C33 from pulling the secondary into resonance. But I think that I'd try it as is- if it doesn't align on FM properly, you now know where to look first. But the set should work OK on AM now.
:

:Looks like I'm pulling the can again CV. Found time to re-install it today and now the motorboating is gone but no reception on any bands. SW? I don't know. In SW it makes static come from the speaker so maybe SW is ok but I'm not receiving anything on it. Didn't spend much time looking for anything.
:
:If the radio was supposed to have nothing between the two fixed cap plates and now I've added the mica it may be causing this "No Reception" on AM, FM, or PB mode. Maybe there was something in between those two fixed cap plates. I'll take it apart again, put it back into it's original configuration and see if I have a short before I put the can back in the radio.
:
:Just haven't seen a variable cap/trimmer like this with two mica pieces between the plates.

Should of added this. In the current configuration I DO NOT have a short to ground from either side of the 1K resistor. Hmm?

Johnny
:
::Clearly this was a fault that had to be cleared before the set ever had the potential of working again.
::
::Since you already ohmed the discriminator pri/sec winding and found them OK, it appears that you lucked out and the only "collateral damage" from this short was a fried R17. Which was its intended lot in life by the radio engineer who designed the set.
::
::Don't know why the C33 combo cap shorted- this is the sort of thing we'd examine under the microscope in the lab to find the "root cause". However, I can tell you that microscopic fragments from 0000-grade steel wool (often used in refinishing radio cabinets) and air-dielectric capacitors don't mix.
::
::My only concern now is that by adding the mica plate between the 2-plate cap, you have changed the cap's value enough to prevent C33 from pulling the secondary into resonance. But I think that I'd try it as is- if it doesn't align on FM properly, you now know where to look first. But the set should work OK on AM now.
::
:
:

Working from memory (not a good thing when you're my age)on my last post, I had thought that C33 was associated with the FM section: it isn't. So, messing with C33 and the 2-plate cap below it will throw the AM alignment out. Recommend that you attempt to align the IF cans on BC AM and see if you can get reception; if not, you may need to revisit your C33 mods.

You read my mind CV. I tried performing an alignment on the AM with sig. gen. with no change. I'll pull the can apart Thursday. I hope! Wife having back surgery tomorrow. May be a few days until I can get to it.

I did notice that between the two fixed plates that there was some kind of what looked like an insulator. Just small, very thin white rectangles, not the full size of the plates, with the hole in the center for the adjustment screw. And these are probably there to provide the air gap for capacitance to exist and keep them from shorting together. If this is what they are and they have broken down over time I'll have to get creative with something to keep a gap between the plates but at the same time not too thick to interfere with the function of the plates. But I'll inspect them first and maybe (hopefully) they were just touching somewhere or as you said, some kind of foreign conductive material may have gotten in there. I do believe we're getting closer and again I appreciate everyones help with this.

Johnny

:Working from memory (not a good thing when you're my age)on my last post, I had thought that C33 was associated with the FM section: it isn't. So, messing with C33 and the 2-plate cap below it will throw the AM alignment out. Recommend that you attempt to align the IF cans on BC AM and see if you can get reception; if not, you may need to revisit your C33 mods.
:

My wifes surgery went well.

I found time today to remove that can again and restore it to its original configuration. All mica insulators etc. I cleaned everything before putting it back together. I have NO short there now, B+ looks good throughout the radio along with all other voltages including the negative voltages, and nothing gets hot any more. Every cap in the radio has been replaced at this point.

But I still have no reception on any bands. And the motorboating is gone with the cleaning of the fixed cap plates and put back into the configuration it was in when it was motorboating.

So progress has been made but I don't know what else to do. Do we have any more tricks left in our bags? I need them. I will be trying another alignment and more trobleshooting with the signal generator in the morning.

Johnny

:You read my mind CV. I tried performing an alignment on the AM with sig. gen. with no change. I'll pull the can apart Thursday. I hope! Wife having back surgery tomorrow. May be a few days until I can get to it.
:
:I did notice that between the two fixed plates that there was some kind of what looked like an insulator. Just small, very thin white rectangles, not the full size of the plates, with the hole in the center for the adjustment screw. And these are probably there to provide the air gap for capacitance to exist and keep them from shorting together. If this is what they are and they have broken down over time I'll have to get creative with something to keep a gap between the plates but at the same time not too thick to interfere with the function of the plates. But I'll inspect them first and maybe (hopefully) they were just touching somewhere or as you said, some kind of foreign conductive material may have gotten in there. I do believe we're getting closer and again I appreciate everyones help with this.
:
:Johnny
:
:
::Working from memory (not a good thing when you're my age)on my last post, I had thought that C33 was associated with the FM section: it isn't. So, messing with C33 and the 2-plate cap below it will throw the AM alignment out. Recommend that you attempt to align the IF cans on BC AM and see if you can get reception; if not, you may need to revisit your C33 mods.
::
:
:

Try injecting a modulated AM IF frequency into the mixer grid and see if it propagates through the IF transformers into the detector and out the speaker as a tone. If it does, your problem is now in the front end; if not, something is still hosed up in the IF/detector section.

Well CV I put my sig. gen. on pin 8, grid of the 7F8 mixer and I get tone through to the speaker. So this indicates a problem in the front end but where is the question. I thought the 7F8 was the front end.

I just noticed something CV. I'm working from the Philco service manual paperwork. Has a complete test procedure in it broken down into 4 sections of the radio. I see on the Riders paperwork that pin 1 is the "Oscillator Grid" of the 7F8. I didn't apply a signal there. But you indicated the "Mixer Grid". Applying a signal to pin one isn't part of the Philco service manual testing. Think I should try a signal there? Probably.

But the radio passes every test in the Philco manual. It just doesn't have any reception. Ergo... No music.

Johnny

:Try injecting a modulated AM IF frequency into the mixer grid and see if it propagates through the IF transformers into the detector and out the speaker as a tone. If it does, your problem is now in the front end; if not, something is still hosed up in the IF/detector section.
:

On a set like this without an RF amp stage, the mixer/osc tube is the first active element in the "front end". However, there are several passive elements in the front end as well: antenna coil, oscillator coil, tuning caps, bandswitch, etc. These all need to be working correctly before the set will receive.

I know that this set is difficult to access, but at this point I think that I would pick a band (say, BC) and start verifying that the bandswitch correctly switches in the right coils and caps for that mode. Also verify continuity through the coils. Since (I recall) that you did a rewire of the bandswitch, that seems like the logical place to start looking for a possible wiring error or bad connection.

Since FM apparently still doesn't work, either, you might be able to put that info to work for you and try to envision the "common mode" failures that would prevent either band from working.

Just an observation: It would seem finding C33 shorted, most likely was the reason the radio stopped operating. "So I took the whole RF assembly apart...". It would seem that perhaps there may now be a wiring error, short and etc. in the RF assembly causing the malfunction. May need to recheck that area closely.

Clifton

:On a set like this without an RF amp stage, the mixer/osc tube is the first active element in the "front end". However, there are several passive elements in the front end as well: antenna coil, oscillator coil, tuning caps, bandswitch, etc. These all need to be working correctly before the set will receive.
:
:I know that this set is difficult to access, but at this point I think that I would pick a band (say, BC) and start verifying that the bandswitch correctly switches in the right coils and caps for that mode. Also verify continuity through the coils. Since (I recall) that you did a rewire of the bandswitch, that seems like the logical place to start looking for a possible wiring error or bad connection.
:
:Since FM apparently still doesn't work, either, you might be able to put that info to work for you and try to envision the "common mode" failures that would prevent either band from working.
:

I concur.

Oh! You meant all the way to the front bumper. :)

So I took the bandswitch out far enough to check the connections and compononts that are associated with the 7F8. That's the tube socket buried under the bandswitch. All is good there. There are two coils that are attached to the bandswitch. The NA Riders schematic is hard to read and laid out quite different then the Philco schematic. I'll try to post this Philco schematic. I believe these two coils are the SW Osc. and FM Osc. coils. L401C and L405. These coils are good. BC Osc. is L404. It's good too. The BC antenna coil is good. When I say good I mean that they match the resistance readings given on this schematic and I see no evidence of corrosion or other decay.

Hope this comes out legible. It may help you to see the way Philco has it put on paper.

If you can read this, it's the complete front end of the radio from the Philco service manual. I've spent 9 hours today going through this whole area and everything is connected properly, the correct values installed and I can't find a thing wrong. I still have an original, un-touched RF section from a donor 46-480 to reference and except for the fact that everything in my RF section is now new both RF sections have all the components in the same place and of the same value. All wires are connected the same.

I'm not questioning your ability to troubleshoot this thing CV. I just need to make the point that this whole area of the radio is back together the way it's supposed to be. I'm so baffled by this problem that I'm even checking all the little things like grounds and solder joints that can cause big problems.

With this portion of the schematic does it help you to see something I may not be seeing?

And thanks again for sticking with me on this. The extra set of eyes really help. And I'm getting up in years myself. Always need extra eyes.
Johnny

:On a set like this without an RF amp stage, the mixer/osc tube is the first active element in the "front end". However, there are several passive elements in the front end as well: antenna coil, oscillator coil, tuning caps, bandswitch, etc. These all need to be working correctly before the set will receive.
:
:I know that this set is difficult to access, but at this point I think that I would pick a band (say, BC) and start verifying that the bandswitch correctly switches in the right coils and caps for that mode. Also verify continuity through the coils. Since (I recall) that you did a rewire of the bandswitch, that seems like the logical place to start looking for a possible wiring error or bad connection.
:
:Since FM apparently still doesn't work, either, you might be able to put that info to work for you and try to envision the "common mode" failures that would prevent either band from working.
:

Just a suggestion Johnny---At this point it might be a good time to re-cap (no pun intended) your situation with the radio (kind of a Cliff Notes summary)...It is hard to follow all the interplay of responses when a thread gets this long. I've been following it because of my recent nightmare with this model Philco...but it gets hard to keep all the facts straight after a while. I don't feel too bad now about having to throw in the towel on my repair attempt to get the FM functional. Or, maybe wait until Sept.1 when the board clears, and start with the re-cap...Just my $.02

I agree Brian. I've decided to throw in the towel on the whole radio and return it as un-repairable. I even get good tone from the speaker when injecting a frequency right at the antenna connection. After 5 weeks of troubleshooting and rebuilding this set from the antenna to the speaker... I QUIT!

Johnny

:Just a suggestion Johnny---At this point it might be a good time to re-cap (no pun intended) your situation with the radio (kind of a Cliff Notes summary)...It is hard to follow all the interplay of responses when a thread gets this long. I've been following it because of my recent nightmare with this model Philco...but it gets hard to keep all the facts straight after a while. I don't feel too bad now about having to throw in the towel on my repair attempt to get the FM functional. Or, maybe wait until Sept.1 when the board clears, and start with the re-cap...Just my $.02
:

And one dumb question: Is the loop antenna connected?

Clifton

:Oh! You meant all the way to the front bumper. :)
:
:So I took the bandswitch out far enough to check the connections and compononts that are associated with the 7F8. That's the tube socket buried under the bandswitch. All is good there. There are two coils that are attached to the bandswitch. The NA Riders schematic is hard to read and laid out quite different then the Philco schematic. I'll try to post this Philco schematic. I believe these two coils are the SW Osc. and FM Osc. coils. L401C and L405. These coils are good. BC Osc. is L404. It's good too. The BC antenna coil is good. When I say good I mean that they match the resistance readings given on this schematic and I see no evidence of corrosion or other decay.
:
:Hope this comes out legible. It may help you to see the way Philco has it put on paper.
:
:
:If you can read this, it's the complete front end of the radio from the Philco service manual. I've spent 9 hours today going through this whole area and everything is connected properly, the correct values installed and I can't find a thing wrong. I still have an original, un-touched RF section from a donor 46-480 to reference and except for the fact that everything in my RF section is now new both RF sections have all the components in the same place and of the same value. All wires are connected the same.
:
:I'm not questioning your ability to troubleshoot this thing CV. I just need to make the point that this whole area of the radio is back together the way it's supposed to be. I'm so baffled by this problem that I'm even checking all the little things like grounds and solder joints that can cause big problems.
:
:With this portion of the schematic does it help you to see something I may not be seeing?
:
:And thanks again for sticking with me on this. The extra set of eyes really help. And I'm getting up in years myself. Always need extra eyes.
:Johnny
:
:
::On a set like this without an RF amp stage, the mixer/osc tube is the first active element in the "front end". However, there are several passive elements in the front end as well: antenna coil, oscillator coil, tuning caps, bandswitch, etc. These all need to be working correctly before the set will receive.
::
::I know that this set is difficult to access, but at this point I think that I would pick a band (say, BC) and start verifying that the bandswitch correctly switches in the right coils and caps for that mode. Also verify continuity through the coils. Since (I recall) that you did a rewire of the bandswitch, that seems like the logical place to start looking for a possible wiring error or bad connection.
::
::Since FM apparently still doesn't work, either, you might be able to put that info to work for you and try to envision the "common mode" failures that would prevent either band from working.
::
:
:

Yes.
Johnny

:And one dumb question: Is the loop antenna connected?
:
:Clifton
:
:
::Oh! You meant all the way to the front bumper. :)
::
::So I took the bandswitch out far enough to check the connections and compononts that are associated with the 7F8. That's the tube socket buried under the bandswitch. All is good there. There are two coils that are attached to the bandswitch. The NA Riders schematic is hard to read and laid out quite different then the Philco schematic. I'll try to post this Philco schematic. I believe these two coils are the SW Osc. and FM Osc. coils. L401C and L405. These coils are good. BC Osc. is L404. It's good too. The BC antenna coil is good. When I say good I mean that they match the resistance readings given on this schematic and I see no evidence of corrosion or other decay.
::
::Hope this comes out legible. It may help you to see the way Philco has it put on paper.
::
::
::If you can read this, it's the complete front end of the radio from the Philco service manual. I've spent 9 hours today going through this whole area and everything is connected properly, the correct values installed and I can't find a thing wrong. I still have an original, un-touched RF section from a donor 46-480 to reference and except for the fact that everything in my RF section is now new both RF sections have all the components in the same place and of the same value. All wires are connected the same.
::
::I'm not questioning your ability to troubleshoot this thing CV. I just need to make the point that this whole area of the radio is back together the way it's supposed to be. I'm so baffled by this problem that I'm even checking all the little things like grounds and solder joints that can cause big problems.
::
::With this portion of the schematic does it help you to see something I may not be seeing?
::
::And thanks again for sticking with me on this. The extra set of eyes really help. And I'm getting up in years myself. Always need extra eyes.
::Johnny
::
::
:::On a set like this without an RF amp stage, the mixer/osc tube is the first active element in the "front end". However, there are several passive elements in the front end as well: antenna coil, oscillator coil, tuning caps, bandswitch, etc. These all need to be working correctly before the set will receive.
:::
:::I know that this set is difficult to access, but at this point I think that I would pick a band (say, BC) and start verifying that the bandswitch correctly switches in the right coils and caps for that mode. Also verify continuity through the coils. Since (I recall) that you did a rewire of the bandswitch, that seems like the logical place to start looking for a possible wiring error or bad connection.
:::
:::Since FM apparently still doesn't work, either, you might be able to put that info to work for you and try to envision the "common mode" failures that would prevent either band from working.
:::
::
::
:
: