On this radio the 4 mfd bypass on the 6AL5 has the + positive lead soldered to the chassis, but on the schematic it has the - negative lead going to ground....The cap is paper but it says Cornell on it and all the other caps say Crosley...so did someone replace it and put it in wrong ? Thanks.
-Bill

Positive end goes to pin 2 of the 6AL5. If you are going to use new capacitors anyway, no need to worry about polarity. Except electrolitic.

:On this radio the 4 mfd bypass on the 6AL5 has the + positive lead soldered to the chassis, but on the schematic it has the - negative lead going to ground....The cap is paper but it says Cornell on it and all the other caps say Crosley...so did someone replace it and put it in wrong ? Thanks.
:-Bill

Sounds like it was installed backwards. Part should be a 4 uF 50 electrolytic with the negative (can) going to chassis ground. The 6AL5 clips the negative going part of the AC signal and passes the positive "half" through-so the cap needs to have its + side oriented as the schematic indicates.

::On this radio the 4 mfd bypass on the 6AL5 has the + positive lead soldered to the chassis, but on the schematic it has the - negative lead going to ground....The cap is paper but it says Cornell on it and all the other caps say Crosley...so did someone replace it and put it in wrong ? Thanks.
::-Bill
:
:
:
:
:Sounds like it was installed backwards. Part should be a 4 uF 50 electrolytic with the negative (can) going to chassis ground. The 6AL5 clips the negative going part of the AC signal and passes the positive "half" through-so the cap needs to have its + side oriented as the schematic indicates.
:

Check out the schematic for the Hallicrafters S-82....the 4mfd + goes to ground, between pins 1 and 2 on the 12AL5 which is the exact same tube as the 6AL5. I've looked at dozens of schematics and it's a 50-50 toss up between + going to ground or not going to ground, depending on who designed the chassis. Anyone else have any ideas? Thanks.....
-Bill

Hi Bill,
Now a days you can get 4MFD bipolar caps, allowing you to punt on this question.
However, look on the schematic for the DeWald C-800. It also shows the 4 MFD positive to ground.
The schematic for your Crosley is wrong on this capacitor. Its positive MUST go to ground.
This is a common problem. Some people think that the can of the electrolytic ALWAYS goes to ground. However, in rare cases this is not so. This is one of those rare case. (The other is the cathode capacitor on a power output tube when the cathode is attached to the chassis, but that is a different story.)
Due to the diode arrangement the 6AL5 will develop a negative DC voltage across the capacitor. This causes the need for the positive ground orientation.
If an electrolytic capacitor is placed in the circuit backwards, it will work for a short time. If the voltage is high enough its electrolyte will boil and it will explode. At these low voltages though this capacitor would likely fail after a few hours more quietly.

Best regards,

Bill

:::On this radio the 4 mfd bypass on the 6AL5 has the + positive lead soldered to the chassis, but on the schematic it has the - negative lead going to ground....The cap is paper but it says Cornell on it and all the other caps say Crosley...so did someone replace it and put it in wrong ? Thanks.
:::-Bill
::
::
::
::
::Sounds like it was installed backwards. Part should be a 4 uF 50 electrolytic with the negative (can) going to chassis ground. The 6AL5 clips the negative going part of the AC signal and passes the positive "half" through-so the cap needs to have its + side oriented as the schematic indicates.
::
:
:Check out the schematic for the Hallicrafters S-82....the 4mfd + goes to ground, between pins 1 and 2 on the 12AL5 which is the exact same tube as the 6AL5. I've looked at dozens of schematics and it's a 50-50 toss up between + going to ground or not going to ground, depending on who designed the chassis. Anyone else have any ideas? Thanks.....
:-Bill
:

= = = = =

Yes, current flow through the 6AL5 is one way, from the plate to the cathode. There is no current flow from cathode to plate. So, when the cathode goes negative with respect to ground, it will drag the plate below ground potential also. So, the negative side of the capacitor needs to be connected to the plate, with the positive side grounded.

However, I doubt that the electrolytic cap sees more than several volts of reversed polarity in this application, so it would have probably worked for quite a while- probably years- before it failed, assuming that it was incorrectly installed in the first place. (Many times, production documentation was corrected "on the fly" and these changes never made it back as corrections to the original design engineering drawings.)

: = = = = =
:
:Yes, current flow through the 6AL5 is one way, from the plate to the cathode. There is no current flow from cathode to plate. So, when the cathode goes negative with respect to ground, it will drag the plate below ground potential also. So, the negative side of the capacitor needs to be connected to the plate, with the positive side grounded.
:
:However, I doubt that the electrolytic cap sees more than several volts of reversed polarity in this application, so it would have probably worked for quite a while- probably years- before it failed, assuming that it was incorrectly installed in the first place. (Many times, production documentation was corrected "on the fly" and these changes never made it back as corrections to the original design engineering drawings.)
:
: Thanks everyone ! I guess I'll just put in the new one exactly as the old one is, with positve + to ground . Does that 6AL5 act as a diode detector? And if so can it introduce distortion into the audio if something is out of wack ( that's a technical term ), like a bad bypass cap ?
-Bill
:

:: Thanks everyone ! I guess I'll just put in the new one exactly as the old one is, with positve + to ground . Does that 6AL5 act as a diode detector? And if so can it introduce distortion into the audio if something is out of wack ( that's a technical term ), like a bad bypass cap ?
:-Bill
::
I suppose that if there is a bad component in the demodulator (6AL5 and associated parts) it could produce distorted audio. But a more likely reason for distorted audio is the discriminator transformer being misadjusted, causing asymmetrical operation.

:
::: Thanks everyone ! I guess I'll just put in the new one exactly as the old one is, with positve + to ground . Does that 6AL5 act as a diode detector? And if so can it introduce distortion into the audio if something is out of wack ( that's a technical term ), like a bad bypass cap ?
::-Bill
:::
:I suppose that if there is a bad component in the demodulator (6AL5 and associated parts) it could produce distorted audio. But a more likely reason for distorted audio is the discriminator transformer being misadjusted, causing asymmetrical operation.
:
Thanks for the reply. So, would that cause distortion on some stations and not others, if the discriminator transformer was a tad out of adjustment? Meaning the stronger stations. Or am I expecting too much out of an old Crosley with a pair of 6V6's in a push/pull configuration?
-Bill

:Thanks for the reply. So, would that cause distortion on some stations and not others, if the discriminator transformer was a tad out of adjustment? Meaning the stronger stations. Or am I expecting too much out of an old Crosley with a pair of 6V6's in a push/pull configuration?
:-Bill
:
= = = = = =

If the discriminator transformer were out of adjustment you would have distortion on all stations, weak and strong alike. But it could be more noticeable on stronger stations.