For what it's worth, there was a considerable amount of transformer wax in 7F8 tube socket - likely formed prior to the electrolytic replacements. I cleaned it as best I could.

Any suggestions on how to approach this issue would be greatly appreciated.

I hope that this helps,

Dave
:My Philco 46-1213 recently developed distortion throughout the FM band, worse at the higher end of the dial. AM reception is normal. I replaced the 7F8 tube and experienced a very slight improvement. Electrolytics were replaced several years ago, but everything is as it came from the factory.
:
:For what it's worth, there was a considerable amount of transformer wax in 7F8 tube socket - likely formed prior to the electrolytic replacements. I cleaned it as best I could.
:
:Any suggestions on how to approach this issue would be greatly appreciated.
:

Dave
:Bill,
: Distortion on FM usually happens when one of the diodes don't work in the discriminator (FM Detector) circuit. Maybe a pin isn't connecting too well on the socket. Maybe a wire isn't connected or soldered well to a solder tab on the tube socket, involving the diodes. The capacitors in that circuit may be leaky as well. Think of it as both a full wave rectifier circuit with a filter capacitor and a push pull out put both at the same time. In a push pull output circuit, if one of the tubes doesn't work the sound will be distorted. In a power supply, if the filter capacitors aren't working, there will be ripple. It could be something else but this is what I have found where there's distorted FM.
:
:I hope that this helps,
:
:Dave
::My Philco 46-1213 recently developed distortion throughout the FM band, worse at the higher end of the dial. AM reception is normal. I replaced the 7F8 tube and experienced a very slight improvement. Electrolytics were replaced several years ago, but everything is as it came from the factory.
::
::For what it's worth, there was a considerable amount of transformer wax in 7F8 tube socket - likely formed prior to the electrolytic replacements. I cleaned it as best I could.
::
::Any suggestions on how to approach this issue would be greatly appreciated.
::
:

Thanks for the quick and helpful response. I'll check the tube sockets tonight.

Beside the electrolytics, the only caps that I replaced were C424, C205, C206 and C209. I did this just today following the advice of a circa 1954 version of the Philco Service Supervisor. No improvement. The remaining caps are all original and weren't changed as the radio worked fine for the past several years. Perhaps, it's time to change them, at least in the FM detector circuit.

Bill

:Bill,
: The "filter" capacitor in the FM detector is a paper capacitor in many cases. Did you also replace all the paper capacitors in your radio?
:
:
:Dave
::Bill,
:: Distortion on FM usually happens when one of the diodes don't work in the discriminator (FM Detector) circuit. Maybe a pin isn't connecting too well on the socket. Maybe a wire isn't connected or soldered well to a solder tab on the tube socket, involving the diodes. The capacitors in that circuit may be leaky as well. Think of it as both a full wave rectifier circuit with a filter capacitor and a push pull out put both at the same time. In a push pull output circuit, if one of the tubes doesn't work the sound will be distorted. In a power supply, if the filter capacitors aren't working, there will be ripple. It could be something else but this is what I have found where there's distorted FM.
::
::I hope that this helps,
::
::Dave
:::My Philco 46-1213 recently developed distortion throughout the FM band, worse at the higher end of the dial. AM reception is normal. I replaced the 7F8 tube and experienced a very slight improvement. Electrolytics were replaced several years ago, but everything is as it came from the factory.
:::
:::For what it's worth, there was a considerable amount of transformer wax in 7F8 tube socket - likely formed prior to the electrolytic replacements. I cleaned it as best I could.
:::
:::Any suggestions on how to approach this issue would be greatly appreciated.
:::
::
:

I know of quadrature detection but I don't understand how it works, yet. So this topic is very interesting.

Thanks,

Dave

:
:

: : : : : : : :Sir Bill . . . . . . : : : : : :After looking the schematic of your FM portion of that unit looks like that you are working with a completely different animal in the respect of the FM portion of that set and its resultant end FM detection circuitry. : : :No Discriminator . . . no Ratio Detector . . . therefore no diodes nor dried out summing electrolytics to worry about. : : :Instead, your set is using an I.F. frequency locked oscillator in the detector stage and is dependent upon quadrature detection in that stage for your FM to AF signal conversion. : : : :Lets explore these possibilities initially: : : :Fully unplug and plug in that FM1000 tube about 6 times to get some contact scraping and cleaning action. : : :Now after starting up the set, it certainly wouldn't hurt to give the tube a couple of thumps on its top to see if any shift in audio quality performance is experienced. : : : If no abnormalities are being found right off. . . . : : :Then: : : :You need to be tuned RIGHT on to the received station, this can be done aurally or one can be ever so more exacting by the monitoring of pin 6 [A] of the 7H7 limiter tube. When you are optimally tuned to the station, the negative read out voltage on that test point will be at its max. : : :This is best done with a VTVM due to its minumal loading but could be minimally done with a 20k per volt VOM akin to a Simpson 260 or Triplett 600 series. : : :The fault with using a digital is its time lag in readout change and accompanying digit bobbling before resettling, unless it also has a companion analog "hash mark" scale. : : :Next step will be the locating of the C93 [C] trimmer capacitor marked on the schematic and shown on the parts profile to the side of the schematic. : : :Mark the units screw slot of its adjustment screw by making a reference mark at its side to the can assenbly. : : :Try a slow adjustment 1/4 turn to the right and then back to the start and then 1/4 turn in the opposite direction. : : :The end result being . . . if the produced FM sound clears up on the set, . . . and the adjustment is then left for the best sound from the unit. : : : :FM audio output from the set is originating at C51/R31 [B] and is then routed down to Sections Q and R of the push button function selector switch assembly, where that FM audio is routed back up to the volume control, if in the :FM position. : : : : : : :73's de Edd : : : :

:
:
:
:

: : :REFERENCING: . . .of partial detector stage section . . . : : : : : : : : : :

:
:
:

I am expecting delivery of the remaining new caps tomorrow and will give your procedure a shot after I install them.

:
:

: : :as the upper text had s t r e t c h e d o u t to being the same width as the schema having been placed at the bottom . . . : : : : : : : : : : :Sir Bill . . . . . . : : : : : :After looking the schematic of your FM portion of that unit looks like that you are working with a completely different animal in the respect of the FM portion of that set and its resultant end FM detection circuitry. : : :No Discriminator . . . no Ratio Detector . . . therefore no diodes nor dried out summing electrolytics to worry about. : : :Instead, your set is using an I.F. frequency locked oscillator in the detector stage and is dependent upon quadrature detection in that stage for your FM to AF signal conversion. : : : :Lets explore these possibilities initially: : : :Fully unplug and plug in that FM1000 tube about 6 times to get some contact scraping and cleaning action. : : :Now after starting up the set, it certainly wouldn't hurt to give the tube a couple of thumps on its top to see if any shift in audio quality performance is experienced. : : : If no abnormalities are being found right off. . . . : : :Then: : : :You need to be tuned RIGHT on to the received station, this can be done aurally or one can be ever so more exacting by the monitoring of pin 6 [A] of the 7H7 limiter tube. When you are optimally tuned to the station, the negative read out voltage on that test point will be at its max. : : :This is best done with a VTVM due to its minumal loading but could be minimally done with a 20k per volt VOM akin to a Simpson 260 or Triplett 600 series. : : :The fault with using a digital is its time lag in readout change and accompanying digit bobbling before resettling, unless it also has a companion analog "hash mark" scale. : : :Next step will be the locating of the C93 [C] trimmer capacitor marked on the schematic and shown on the parts profile to the side of the schematic. : : :Mark the units screw slot of its adjustment screw by making a reference mark at its side to the can assenbly. : : :Try a slow adjustment 1/4 turn to the right and then back to the start and then 1/4 turn in the opposite direction. : : :The end result being . . . if the produced FM sound clears up on the set, . . . and the adjustment is then left for the best sound from the unit. : : : :FM audio output from the set is originating at C51/R31 [B] and is then routed down to Sections Q and R of the push button function selector switch assembly, where that FM audio is routed back up to the volume control, if in the :FM position. : : : : : : :Addenda: : : :As per the additional comment on presence of "transformer wax" (expected to be a parrafin /or/ beeswax blend) and it originating on top / and flowing down inside of the FM RF/Mixer 7F8 tube socket, common Klean Strip, Crown or Solex brand of mineral spirits does a good final dissolving away of any traces that type of deposit. : : :ALSO , questioning, as to whether that wax seemed to have had its ORIGIN ? from the top of the chassis (2nd I.F. Transformer ?)and having run down INTO the 7F8 (FM mixer-osc tube), and got into the sockets pins. : : : OR , if being at the totally other end of the spectrum, if that wax was a heavier yellow, it may have actually been applied there from the bottom of the set to mechanically stabilize circuit components / movement of the potentially mechanically touchy FM OSCILLATOR section. :(Just firmly thump the 7F8 and see what I mean) : : :Now,if the created distortion is associative with THAT area of the set, I tend to expect it to be from freq drift after warm up and the distortion could then be cleared up by a slight re tune onto the station WHILE problems that I am referring to back in the FM detector stage, would not respond to that type of a temporary corrective action. : : :73's de Edd : : : :

:
:
:
:

: : :REFERENCING: . . .of partial detector stage section . . . : : : : : : : :

:
:
:

:Thank you, Sir.
:
:I am expecting delivery of the remaining new caps tomorrow and will give your procedure a shot after I install them.
:
::
::

:: :: ::as the upper text had s t r e t c h e d o u t to being the same width as the schema having been placed at the bottom . . . :: :: :: :: :: :: :: :: :: :: ::Sir Bill . . . . . . :: :: :: :: :: ::After looking the schematic of your FM portion of that unit looks like that you are working with a completely different animal in the respect of the FM portion of that set and its resultant end FM detection circuitry. :: :: ::No Discriminator . . . no Ratio Detector . . . therefore no diodes nor dried out summing electrolytics to worry about. :: :: ::Instead, your set is using an I.F. frequency locked oscillator in the detector stage and is dependent upon quadrature detection in that stage for your FM to AF signal conversion. :: :: :: ::Lets explore these possibilities initially: :: :: ::Fully unplug and plug in that FM1000 tube about 6 times to get some contact scraping and cleaning action. :: :: ::Now after starting up the set, it certainly wouldn't hurt to give the tube a couple of thumps on its top to see if any shift in audio quality performance is experienced. :: :: :: If no abnormalities are being found right off. . . . :: :: ::Then: :: :: ::You need to be tuned RIGHT on to the received station, this can be done aurally or one can be ever so more exacting by the monitoring of pin 6 [A] of the 7H7 limiter tube. When you are optimally tuned to the station, the negative read out voltage on that test point will be at its max. :: :: ::This is best done with a VTVM due to its minumal loading but could be minimally done with a 20k per volt VOM akin to a Simpson 260 or Triplett 600 series. :: :: ::The fault with using a digital is its time lag in readout change and accompanying digit bobbling before resettling, unless it also has a companion analog "hash mark" scale. :: :: ::Next step will be the locating of the C93 [C] trimmer capacitor marked on the schematic and shown on the parts profile to the side of the schematic. :: :: ::Mark the units screw slot of its adjustment screw by making a reference mark at its side to the can assenbly. :: :: ::Try a slow adjustment 1/4 turn to the right and then back to the start and then 1/4 turn in the opposite direction. :: :: ::The end result being . . . if the produced FM sound clears up on the set, . . . and the adjustment is then left for the best sound from the unit. :: :: :: ::FM audio output from the set is originating at C51/R31 [B] and is then routed down to Sections Q and R of the push button function selector switch assembly, where that FM audio is routed back up to the volume control, if in the ::FM position. :: :: :: :: :: :: ::Addenda: :: :: ::As per the additional comment on presence of "transformer wax" (expected to be a parrafin /or/ beeswax blend) and it originating on top / and flowing down inside of the FM RF/Mixer 7F8 tube socket, common Klean Strip, Crown or Solex brand of mineral spirits does a good final dissolving away of any traces that type of deposit. :: :: ::ALSO , questioning, as to whether that wax seemed to have had its ORIGIN ? from the top of the chassis (2nd I.F. Transformer ?)and having run down INTO the 7F8 (FM mixer-osc tube), and got into the sockets pins. :: :: :: OR , if being at the totally other end of the spectrum, if that wax was a heavier yellow, it may have actually been applied there from the bottom of the set to mechanically stabilize circuit components / movement of the potentially mechanically touchy FM OSCILLATOR section. ::(Just firmly thump the 7F8 and see what I mean) :: :: ::Now,if the created distortion is associative with THAT area of the set, I tend to expect it to be from freq drift after warm up and the distortion could then be cleared up by a slight re tune onto the station WHILE problems that I am referring to back in the FM detector stage, would not respond to that type of a temporary corrective action. :: :: ::73's de Edd :: :: :: ::

::
::
::
::

:: :: ::REFERENCING: . . .of partial detector stage section . . . :: :: :: :: :: :: :: ::

::
::
::
:

:
:

: : : : : : : : : : : : :Sir Bill . . . . . . : : : : : : : :BEFORE biting the bear: : : :Might I ask, if back before you touched up the C93 cap adjustment in the FM detector stage, did you perform the testing :of the negative DC voltage on the 1st grid (Pin 6) of the 7H7 limiter stage? : : :If not , you can find out a lot about the overall ” health” of the TUNING of the prior F.M. I.F. stages just by the monitoring of that voltage. : : :A Partial Repeating: : : :While monitoring (Pin 6) of the 7H7: : : :You need the sets tuning condenser to be set initially for a peak negative voltage on a strong station and leave it set there. : : :Then perform a CW-CCW , slightly on/off from the tuning, of the FOUND setting of EACH FM IF transformer, on down the line in the prior stages, one wants a peaked reading. : : :That overall procedure, being in order to see if that voltage increases, thus a prior stage had timely drifted a bit off from optimum tune. : : :The readout is not as pronounced, but you can also move forward to the pin 6 of the FM1000 to additionally include the 2 adjustments of T5 that : is just before the detector stage. : : :To initially get some idea, when moving metering to that new test point , move the tuning condenser slightly off station to see the voltage swing effect of a reduced signal effect, and then return the tuning condenser to its previously peak position again. Then check the 2 FM adjustment portions of T5. : : :Finally, disconnect and re evaluate your results on those particular received stations problems. : : : : : :73's de Edd : : : :

:
:
:
:

: : :REFERENCING: . . .of partial detector stage section . . . : : : : : : : :

:
:
:
::
::
::
::
::Well, all paper caps have been replaced and although the set operates much better (more power, more stations), there remains some distortion on the weaker FM stations. Adjusting C93 resulted in no improvement. I've ordered a new FM1000 tube and hope that cures the problem. If not, it's on to the painful alignment process.
::
:::Thank you, Sir.
:::
:::I am expecting delivery of the remaining new caps tomorrow and will give your procedure a shot after I install them.
:::
::::
::::

:::: :::: ::::as the upper text had s t r e t c h e d o u t to being the same width as the schema having been placed at the bottom . . . :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: ::::Sir Bill . . . . . . :::: :::: :::: :::: :::: ::::After looking the schematic of your FM portion of that unit looks like that you are working with a completely different animal in the respect of the FM portion of that set and its resultant end FM detection circuitry. :::: :::: ::::No Discriminator . . . no Ratio Detector . . . therefore no diodes nor dried out summing electrolytics to worry about. :::: :::: ::::Instead, your set is using an I.F. frequency locked oscillator in the detector stage and is dependent upon quadrature detection in that stage for your FM to AF signal conversion. :::: :::: :::: ::::Lets explore these possibilities initially: :::: :::: ::::Fully unplug and plug in that FM1000 tube about 6 times to get some contact scraping and cleaning action. :::: :::: ::::Now after starting up the set, it certainly wouldn't hurt to give the tube a couple of thumps on its top to see if any shift in audio quality performance is experienced. :::: :::: :::: If no abnormalities are being found right off. . . . :::: :::: ::::Then: :::: :::: ::::You need to be tuned RIGHT on to the received station, this can be done aurally or one can be ever so more exacting by the monitoring of pin 6 [A] of the 7H7 limiter tube. When you are optimally tuned to the station, the negative read out voltage on that test point will be at its max. :::: :::: ::::This is best done with a VTVM due to its minumal loading but could be minimally done with a 20k per volt VOM akin to a Simpson 260 or Triplett 600 series. :::: :::: ::::The fault with using a digital is its time lag in readout change and accompanying digit bobbling before resettling, unless it also has a companion analog "hash mark" scale. :::: :::: ::::Next step will be the locating of the C93 [C] trimmer capacitor marked on the schematic and shown on the parts profile to the side of the schematic. :::: :::: ::::Mark the units screw slot of its adjustment screw by making a reference mark at its side to the can assenbly. :::: :::: ::::Try a slow adjustment 1/4 turn to the right and then back to the start and then 1/4 turn in the opposite direction. :::: :::: ::::The end result being . . . if the produced FM sound clears up on the set, . . . and the adjustment is then left for the best sound from the unit. :::: :::: :::: ::::FM audio output from the set is originating at C51/R31 [B] and is then routed down to Sections Q and R of the push button function selector switch assembly, where that FM audio is routed back up to the volume control, if in the ::::FM position. :::: :::: :::: :::: :::: :::: ::::Addenda: :::: :::: ::::As per the additional comment on presence of "transformer wax" (expected to be a parrafin /or/ beeswax blend) and it originating on top / and flowing down inside of the FM RF/Mixer 7F8 tube socket, common Klean Strip, Crown or Solex brand of mineral spirits does a good final dissolving away of any traces that type of deposit. :::: :::: ::::ALSO , questioning, as to whether that wax seemed to have had its ORIGIN ? from the top of the chassis (2nd I.F. Transformer ?)and having run down INTO the 7F8 (FM mixer-osc tube), and got into the sockets pins. :::: :::: :::: OR , if being at the totally other end of the spectrum, if that wax was a heavier yellow, it may have actually been applied there from the bottom of the set to mechanically stabilize circuit components / movement of the potentially mechanically touchy FM OSCILLATOR section. ::::(Just firmly thump the 7F8 and see what I mean) :::: :::: ::::Now,if the created distortion is associative with THAT area of the set, I tend to expect it to be from freq drift after warm up and the distortion could then be cleared up by a slight re tune onto the station WHILE problems that I am referring to back in the FM detector stage, would not respond to that type of a temporary corrective action. :::: :::: ::::73's de Edd :::: :::: :::: ::::

::::
::::
::::
::::

:::: :::: ::::REFERENCING: . . .of partial detector stage section . . . :::: :::: :::: :::: :::: :::: :::: ::::

::::
::::
::::
:::
::
:

Also, the second point I wanted to make is that so far noone has suggested checking the resistors for drifting and opening. They do occasionally do this, and a change in voltage or bias might cause distortion of some sort.

T.

Although none of the resistors look bad, I'll check the values of the larger ones to make sure that they're still within spec.

Thanks.

:...A few other points to keep in mind as well: A couple of years ago I took great interest in simple FM receivers. The two circuits that came up the most were the super regenerative receiver, and the detecting method your radio employs. I do know for sure that it was mentioned that the super regenerative receiver would have some trouble with the stereo sub-carrier broadcasted from most modern commercial stations, and the one I built did produce some distortion and noise with some of the stereo signals. I believe that your style of detector was also mentioned to have trouble with modern stereo signals--that you'd receive them, but with some hissing and heterodyning from the stereo sub-carrier. You say that the radio has performed well for the past few years, but perhaps there is something in your home that might be causing a similar problem, such as a new wireless router. ...Just a suggestion, but probably not the answer.
:
:Also, the second point I wanted to make is that so far noone has suggested checking the resistors for drifting and opening. They do occasionally do this, and a change in voltage or bias might cause distortion of some sort.
:
:T.
:

T.

Repair of the problem continues to elude me. I relocated to a detached garage to get away from the wireless router - no change. The new FM-1000 tube also failed to eliminate the distortion. A check of several key resistors revealed that they were all reasonably within spec. No smoking gun to be found.

My last hope is an alignment - something I'd been trying to avoid. Forgive this basic question, but can anyone help me identify the antenna section of the tuning gang (vs. the oscillator section)? I believe that it's the front section, but want to be certain before I proceed.

:I find that many wireless routers can destroy even low frequency AM reception, either due to sloppy transmission with lots of harmonics, or due to sloppy power supplies. My wireless router creates a lot of hiss and hum across my radio dial, and even into short wave, though not for FM, though all of my FM radios use conventional detection. My superregenerative receiver is currently disassembled. My neighbors have had wireless routers for a few years now, and theirs, too, have destroyed my DXing. Originally I wanted to build something that'd destroy their reception, since they did not honor my request to turn off their transmitters when not in use, but then a friend gave me an old laptop to fix and keep, and so I decided to instead join the crowd. BLA!
:
:T.
: