Hello All,
I wonder what can be causing this. The tubes all test good. I replaced the only 2 electrolytic capacitors and 1 paper capacitor that I could find. There is one more electrolytic capacitor C7 in the FM section.
This is Most-Often Needed Volume R-24 1964, Pages 164-165. I can only guess that it's either a problem in the module, with C7 or maybe C8 is leaky. I cleaned the AM/FM switch. The FM tuner tunes very well. But the volume is very faint. AM works great. So I know that the amplifier is working. So there is something between the output of the FM tuner and the input to the amplifier. But what? There's not much there.
If anyone knows, please let me know.

Thanks,

Dave

Pretty much the standard answer----Check the alignment on the FM, and make sure the proper antenna terminals are being used for internal (line) or external (dipole).

Brian,
I'll let you know what it is when I find it.

Thanks,

Dave

:Pretty much the standard answer----Check the alignment on the FM, and make sure the proper antenna terminals are being used for internal (line) or external (dipole).
:

This radio receives well but the output volume from the tuner is very very very very weak. I measured between pins 2 and 6 of module Z4, which is supposed to be 600 ohms. But my meter says that there is 6K ohms between pins 2 and 6 or pins 1 and 2 of the ratio detector tube.
Does anyone know where I can buy this module? Two numbers are on it, "848" and "209V036H02". It's a 7 pin module.

Thanks,

Dave
:Pretty much the standard answer----Check the alignment on the FM, and make sure the proper antenna terminals are being used for internal (line) or external (dipole).
:

Hello Again All,

Oops, I made a mistake. That's 600 pf, not 600 ohms. Never mind. FM is still very very very very very weak. I can find no problems. But it must be something. All the resistors I check are good. I have replaced every possible paper and electrolytic capacitors. But still FM has a very very very very very low output. This is extremely frustrating. I even checked to make sure that pin 3 from the module connects to the switch and that the switch is making a good connection. Maybe the problem is in the power side of the switch. I WILL find it.
But sorry about the mistake between pf and ohms.
So far I suspect the module because that's what the sound comes out of and there's nothing else there. The sound from AM is very strong and good sounding. So there's no problem with the amplifier. Maybe the front end of the FM isn't being powered up due to a defective resistor.
I'll check there.

Dave

:This radio receives well but the output volume from the tuner is very very very very weak. I measured between pins 2 and 6 of module Z4, which is supposed to be 600 ohms. But my meter says that there is 6K ohms between pins 2 and 6 or pins 1 and 2 of the ratio detector tube.
: Does anyone know where I can buy this module? Two numbers are on it, "848" and "209V036H02". It's a 7 pin module.
:
:Thanks,
:
:Dave
::Pretty much the standard answer----Check the alignment on the FM, and make sure the proper antenna terminals are being used for internal (line) or external (dipole).
::
:
:

Hello Again All,
I checked everything and anything and all is good. But the FM volume remains very very very very low. I conclude that the 7pin module is not working somewhere. If none can be found it will have to be an AM radio. If anyone has any other ideas, please let me know. If I can figure out anything else, I'll let you know.

Thanks,

Dave
:Hello Again All,
:
:Oops, I made a mistake. That's 600 pf, not 600 ohms. Never mind. FM is still very very very very very weak. I can find no problems. But it must be something. All the resistors I check are good. I have replaced every possible paper and electrolytic capacitors. But still FM has a very very very very very low output. This is extremely frustrating. I even checked to make sure that pin 3 from the module connects to the switch and that the switch is making a good connection. Maybe the problem is in the power side of the switch. I WILL find it.
: But sorry about the mistake between pf and ohms.
: So far I suspect the module because that's what the sound comes out of and there's nothing else there. The sound from AM is very strong and good sounding. So there's no problem with the amplifier. Maybe the front end of the FM isn't being powered up due to a defective resistor.
: I'll check there.
:
:Dave
:
::This radio receives well but the output volume from the tuner is very very very very weak. I measured between pins 2 and 6 of module Z4, which is supposed to be 600 ohms. But my meter says that there is 6K ohms between pins 2 and 6 or pins 1 and 2 of the ratio detector tube.
:: Does anyone know where I can buy this module? Two numbers are on it, "848" and "209V036H02". It's a 7 pin module.
::
::Thanks,
::
::Dave
:::Pretty much the standard answer----Check the alignment on the FM, and make sure the proper antenna terminals are being used for internal (line) or external (dipole).
:::
::
::
:

Since AM works, about the only thing in the radio that you can exonerate is the first audio amp/audio output stages. The FM string has a separate antenna, separate tuner, separate IF filters, and separate demodulator from the AM string, and a malfunction in any of these circuits can cause low FM signal. Without a fault isolation strategy, all you can do is swap tubes and guess at the problem.

Trying to align the set's IF filters on FM would give you some info- it would tell you the state of the IF filters and demodulator. If the set accepts an IF alignment, the problem is most likely in the tuner or mixer stages, since these stages are bypassed during IF setup.

It might be helpful to do gain measurements of each stage- that is, input an AC signal of a known level to each stage in turn and measure the output of that stage to see what its amplification factor is. That will at least get you zeroed in on a single stage.

Make sure you have found every alignment padder/can etc. for the FM. Sometimes they can get missed in a heavily wired chassis. Many IF cans have slugs in the top and underneath. I'm sure you know this stuff, but it doesn't hurt to mention it when you get a 'head scratcher' problem..

:Make sure you have found every alignment padder/can etc. for the FM. Sometimes they can get missed in a heavily wired chassis. Many IF cans have slugs in the top and underneath. I'm sure you know this stuff, but it doesn't hurt to mention it when you get a 'head scratcher' problem..
:

Sorry about that. I typed Brian in the wrong place, and somehow became a post. Please ignore that post from "Brian,".
::Make sure you have found every alignment padder/can etc. for the FM. Sometimes they can get missed in a heavily wired chassis. Many IF cans have slugs in the top and underneath. I'm sure you know this stuff, but it doesn't hurt to mention it when you get a 'head scratcher' problem..
::
:
:

Brian,
This is a "cheap" AM FM tube radio from the late 60s with a PC board. It's not heavily wired at all. If you had a copy of the schematic you would see that there is nothing else there. It sounds like when there's an almost open capacitor in an audio circuit. But I can't find it. Every one I check is good. I will have to keep checking them and replace every disc capacitor in that circuit too. I think there's only 2 of them. FM is strong and the tuning is good. There is no alignment needed, but the volume out of the Discriminator stage is very very very very weak.
Please look below (actually, I think it's above) in the thread where I specify page and volume.

Thanks,

Dave
This is in the Beitman's Most Often Needed books which are free on the internet.
:Make sure you have found every alignment padder/can etc. for the FM. Sometimes they can get missed in a heavily wired chassis. Many IF cans have slugs in the top and underneath. I'm sure you know this stuff, but it doesn't hurt to mention it when you get a 'head scratcher' problem..
:

Dave,

I assume you replaced C7 and didn't reverse the polarity of the replacement. You may need to make a point to point resistance measurement of the pc traces around the discriminator for hairline cracks.

Clifton

:Brian,
: This is a "cheap" AM FM tube radio from the late 60s with a PC board. It's not heavily wired at all. If you had a copy of the schematic you would see that there is nothing else there. It sounds like when there's an almost open capacitor in an audio circuit. But I can't find it. Every one I check is good. I will have to keep checking them and replace every disc capacitor in that circuit too. I think there's only 2 of them. FM is strong and the tuning is good. There is no alignment needed, but the volume out of the Discriminator stage is very very very very weak.
: Please look below (actually, I think it's above) in the thread where I specify page and volume.
:
:Thanks,
:
:Dave
:This is in the Beitman's Most Often Needed books which are free on the internet.
::Make sure you have found every alignment padder/can etc. for the FM. Sometimes they can get missed in a heavily wired chassis. Many IF cans have slugs in the top and underneath. I'm sure you know this stuff, but it doesn't hurt to mention it when you get a 'head scratcher' problem..
::
: