With the 6K5 being your units RF detector and first audio amplifier tube.........does the old touching of the grid cap of that tube..... confirm that it
and the following stage is working OK with the production of an amplified 60 / 120 ~ hum coming from the speaker ?
If not, voltage checks on them seem to be in order for troubleshooting info ......or possibly your getting a bad 6K5...but I seriously doubt it.
73's de Edd
:I just recapped this radio I purchased at a flea market, it played with some distortion on strong am stations only, then while trying to substitute tubes, the 6k5 broke in the socket, it was so difficult to remove, upon replacing it with another, now there is just the 'nontunable hum" when I power it up, i checked the socket, it is not broken, and the substitute lites up, any ideas on where to start?
:Ed,
It does nothing now when I touch the grid cap. The substitute tube is a little loose at the base, but moving it doesnt make the audio come back, I was going to purchase another 6K5 and test. It was working, but distorted audio before the troubles with the 6K5, I replaced every cap and electrolytics earlier. Dave
:
:
:With the 6K5 being your units RF detector and first audio amplifier tube.........does the old touching of the grid cap of that tube..... confirm that it
: and the following stage is working OK with the production of an amplified 60 / 120 ~ hum coming from the speaker ?
:
:If not, voltage checks on them seem to be in order for troubleshooting info ......or possibly your getting a bad 6K5...but I seriously doubt it.
:
:
:
:
:73's de Edd
:
:
:
:
:
::I just recapped this radio I purchased at a flea market, it played with some distortion on strong am stations only, then while trying to substitute tubes, the 6k5 broke in the socket, it was so difficult to remove, upon replacing it with another, now there is just the 'nontunable hum" when I power it up, i checked the socket, it is not broken, and the substitute lites up, any ideas on where to start?
Philco 38-7 A.F. Troubleshooting
Oh.......kayyyyy.... then, how about doing two quick tests here before getting into voltage checks, since
that radio was initially working to some degree.
In not being exactly certain of the degree of actual " finger-hum" that you injected into the first grid cap of
that 6K5, lets try a different manner in which you could be more assured of your result.
It would be requiring a test lead with clip connectors at either end and a .05 thru .1 ufd paper capacitor being
clipped onto by one of the clip lead ends.
Warm up the sets tubes and set the volume control to max.
You would then locate filament pins 2 and 7 of the 6F6 and note that one of the two pins is being connected
to ground while the other pin has the "hot" 6.3 VAC on it, that will be the one that you connect the free clip
lead to.
Next you locate pin 5 of the 6F6 and take the end of the clip lead with the cap on it and touch pin 5
and expect hum to come from the speaker.
The next step would be to go to the prior AF stage at the plate of the 6K5 at its pin 3 and touch the capacitor
to see if the same hum is heard. If so, move on up to the grid cap of the 6K5 and see if a somewhat amplified
and louder hum is heard.
IF so, going to the outermost terminals of the volume control , and selecting the one that is NOT gounded and touching the capacitor to that terminal should result in a hum.
If that hum is present, you have the confirmed the integrity of the audio amp chain from its starting point all of the way through to the speaker.
If not, you now have some idea of the point where the AF signal is being lost, so it is time for forwarding the DC voltage readings of the plates, screen grids and some cathodes of those stages.
If by chance the chassis has not been pulled yet, it is possible to do all but the last test by taking a bit of bare
copper 20-24 wire and holding about a 1/2 in end beside the octal socket and twirling on about 2 or so turns
around a selected tube pin with tweezers and then clipping off. In that manner the tube can be plugged in and you have that test wire accessible to clip onto topside.
73's de Edd
::
::Ed,
:It does nothing now when I touch the grid cap. The substitute tube is a little loose at the base, but moving it doesnt make the audio come back, I was going to purchase another 6K5 and test. It was working, but distorted audio before the troubles with the 6K5, I replaced every cap and electrolytics earlier. Dave
::
::
::With the 6K5 being your units RF detector and first audio amplifier tube.........does the old touching of the grid cap of that tube..... confirm that it
:: and the following stage is working OK with the production of an amplified 60 / 120 ~ hum coming from the speaker ?
::
::If not, voltage checks on them seem to be in order for troubleshooting info ......or possibly your getting a bad 6K5...but I seriously doubt it.
::
::
::
::
::73's de Edd
::
::
::
::
::
:::I just recapped this radio I purchased at a flea market, it played with some distortion on strong am stations only, then while trying to substitute tubes, the 6k5 broke in the socket, it was so difficult to remove, upon replacing it with another, now there is just the 'nontunable hum" when I power it up, i checked the socket, it is not broken, and the substitute lites up, any ideas on where to start?
: I just got my new 6K5 in and it is 6K5GT, if I open up the metal surrounding the tube base, can I use this instead of the 6K5G? the pins are the same, it just wont fit the way it is due to the base of the GT is wider than the opening due to the metal surrounding the tube base. Thanks, Dave
:
:
:Philco 38-7 A.F. Troubleshooting
:
:Oh.......kayyyyy.... then, how about doing two quick tests here before getting into voltage checks, since
:that radio was initially working to some degree.
:
:In not being exactly certain of the degree of actual " finger-hum" that you injected into the first grid cap of
:
:that 6K5, lets try a different manner in which you could be more assured of your result.
:
:It would be requiring a test lead with clip connectors at either end and a .05 thru .1 ufd paper capacitor being
:
:clipped onto by one of the clip lead ends.
:
:
:Warm up the sets tubes and set the volume control to max.
:
:You would then locate filament pins 2 and 7 of the 6F6 and note that one of the two pins is being connected
:
:to ground while the other pin has the "hot" 6.3 VAC on it, that will be the one that you connect the free clip
:
:lead to.
:
:Next you locate pin 5 of the 6F6 and take the end of the clip lead with the cap on it and touch pin 5
:and expect hum to come from the speaker.
:
:The next step would be to go to the prior AF stage at the plate of the 6K5 at its pin 3 and touch the capacitor
:
:to see if the same hum is heard. If so, move on up to the grid cap of the 6K5 and see if a somewhat amplified
:
:and louder hum is heard.
:
:IF so, going to the outermost terminals of the volume control , and selecting the one that is NOT gounded and touching the capacitor to that terminal should result in a hum.
:
:If that hum is present, you have the confirmed the integrity of the audio amp chain from its starting point all of the way through to the speaker.
:
:If not, you now have some idea of the point where the AF signal is being lost, so it is time for forwarding the DC voltage readings of the plates, screen grids and some cathodes of those stages.
:
:
:
:If by chance the chassis has not been pulled yet, it is possible to do all but the last test by taking a bit of bare
:copper 20-24 wire and holding about a 1/2 in end beside the octal socket and twirling on about 2 or so turns
:around a selected tube pin with tweezers and then clipping off. In that manner the tube can be plugged in and you have that test wire accessible to clip onto topside.
:
:
:
:
:73's de Edd
:
:
:
:
:
:::
:::Ed,
::It does nothing now when I touch the grid cap. The substitute tube is a little loose at the base, but moving it doesnt make the audio come back, I was going to purchase another 6K5 and test. It was working, but distorted audio before the troubles with the 6K5, I replaced every cap and electrolytics earlier. Dave
:::
:::
:::With the 6K5 being your units RF detector and first audio amplifier tube.........does the old touching of the grid cap of that tube..... confirm that it
::: and the following stage is working OK with the production of an amplified 60 / 120 ~ hum coming from the speaker ?
:::
:::If not, voltage checks on them seem to be in order for troubleshooting info ......or possibly your getting a bad 6K5...but I seriously doubt it.
:::
:::
:::
:::
:::73's de Edd
:::
:::
:::
:::
:::
::::I just recapped this radio I purchased at a flea market, it played with some distortion on strong am stations only, then while trying to substitute tubes, the 6k5 broke in the socket, it was so difficult to remove, upon replacing it with another, now there is just the 'nontunable hum" when I power it up, i checked the socket, it is not broken, and the substitute lites up, any ideas on where to start?
I know the problem that you are having with the GT tubes. If you don't mind slightly modifying the shield bases then you could use something like a dremel tool and grind the hole out wider to fit the GT tube. I did this with my 38-7, but it will take quite a while to work away at it. If you decide to do this though be very careful not to damage anything around it and not to ruin or destroy the base altogether. You need those bases to remain well grounded to the chassis. I'm no pro on these radios, but it worked for me and I haven't noticed any negative consequences. Plus with the shields in place you will never notice the modification.
Mike
:I know the problem that you are having with the GT tubes. If you don't mind slightly modifying the shield bases then you could use something like a dremel tool and grind the hole out wider to fit the GT tube. I did this with my 38-7, but it will take quite a while to work away at it. If you decide to do this though be very careful not to damage anything around it and not to ruin or destroy the base altogether. You need those bases to remain well grounded to the chassis. I'm no pro on these radios, but it worked for me and I haven't noticed any negative consequences. Plus with the shields in place you will never notice the modification.
:Mike
::I know the problem that you are having with the GT tubes. If you don't mind slightly modifying the shield bases then you could use something like a dremel tool and grind the hole out wider to fit the GT tube. I did this with my 38-7, but it will take quite a while to work away at it. If you decide to do this though be very careful not to damage anything around it and not to ruin or destroy the base altogether. You need those bases to remain well grounded to the chassis. I'm no pro on these radios, but it worked for me and I haven't noticed any negative consequences. Plus with the shields in place you will never notice the modification.
::Mike
Mike:
I was going to trim the metal around the shield housing a bit back and then use the GT tube. The previous tube broke in the socket, it was so tight and brittle. I managed to get it out without breaking the socket, it appears not to be cracked from top and bottom, I will find out if it is still ok after I use the new tube I suppose. Thanks for the advice
Dave
Thats what I was referring to (the metal base that the shield slides over), not the tubes themselves. Sorry if I worded it confusing. I widened the hole in the metal "base" so that the GT tube would fit in.
Mike