Well, I replaced all the caps in my radio (Motorola aka Galvin 59T2) except for a ganged electrolytic capacitor bank (10, 20, 15 uF) and a .03uf cap. When I turned it on I still get this continuous crackling sound. It goes away when I hit a strong station but you can definitely hear it over the weaker stations. Now I'm not sure how a tube radio should sound, so I don't know if this is normal. Should the interstation regions be a lot quieter/less noisy? I have a feeling that its the cap bank and those large electrolytics that need to be replaced but I'm not sure how to break up that large ganged cap bank into 3 individual caps. It doesn't show polarity in the schematic (Item #20). Any feedback on this is appreciated. Thanks, Steve

I should also mention that when I ground the antenna wire, the crackling goes away but the overall volume of the radio decreases significantly.

The three ends that are tied together are negative, the free ends are positive. IMHO
Is the bank in a can? Is there any indication that it may have been rebuilt? If it's rebuildable, it would be nicer to do that than throw out the bank.
It would be the rare electrolytic that has survived since 1938.
If you have another AM radio, try tuning it to a open area of the band and see if you hear the same crackling sound.
It might be RFI. My Majestic 71 picks up a lot of noise if my aquarium light is on, or my satelite receiver, or my computer or my neighbors yard light.

Thanks John, unfortunately the capacitor bank is too difficult to keep - I need the space. I had to rip it out because it was strapped in with a metal strap. I didn't get any interference on my other radio - I'm almost positive that the problem is with the electrolytics.

What's really confusing me though is the schematic representation of the capacitor bank. If you look at the schematic (Motorola 59T2 Item 20 ) it looks like red and black wire is going to the 15uF, the green is going to a 10 uF and the 20 uF is grounded. But what wire is supposed to be going to the 20uF??? This is really confusing, especially since I need to replace this part. Can anyone make heads of tails out of this?
I assume the ground is the common link between all the capacitors.

Steve

:Thanks John, unfortunately the capacitor bank is too difficult to keep - I need the space. I had to rip it out because it was strapped in with a metal strap. I didn't get any interference on my other radio - I'm almost positive that the problem is with the electrolytics.
:
:What's really confusing me though is the schematic representation of the capacitor bank. If you look at the schematic (Motorola 59T2 Item 20 ) it looks like red and black wire is going to the 15uF, the green is going to a 10 uF and the 20 uF is grounded. But what wire is supposed to be going to the 20uF??? This is really confusing, especially since I need to replace this part. Can anyone make heads of tails out of this?
:I assume the ground is the common link between all the capacitors.
:
:Steve
:

The Black wire is common to all three capacitors and is at -15V. The Yellow wire that goes to ground is the positive side of the 20uF capacitor.
The Green wire is the positive side of the 10uF capacitor.
The Red wire is the positive side of the 15uF capacitor.
John

Great, thanks John. You're a BIG help! After I wrote the last post I had an inkling that the black might be the common wire - but it seemed an odd configuration since I believe the common wire is usually the ground. Just curious though how did you come up with -15V?

:The Black wire is common to all three capacitors and is at -15V. The Yellow wire that goes to ground is the positive side of the 20uF capacitor.
:The Green wire is the positive side of the 10uF capacitor.
:The Red wire is the positive side of the 15uF capacitor.
:John

If you look at the table of socket voltages you will see a note for pin 4 of the #41 output tube. -15V at the bias resistor. It's developed from the current through the series of the 330 ohm and 68 ohm resistors connected from the center tap of the transformer to ground.

John

:Great, thanks John. You're a BIG help! After I wrote the last post I had an inkling that the black might be the common wire - but it seemed an odd configuration since I believe the common wire is usually the ground. Just curious though how did you come up with -15V?
:
::The Black wire is common to all three capacitors and is at -15V. The Yellow wire that goes to ground is the positive side of the 20uF capacitor.
::The Green wire is the positive side of the 10uF capacitor.
::The Red wire is the positive side of the 15uF capacitor.
::John

Got it, that makes the 20 uF going to ground a bit more understandable - Thanks

:If you look at the table of socket voltages you will see a note for pin 4 of the #41 output tube. -15V at the bias resistor. It's developed from the current through the series of the 330 ohm and 68 ohm resistors connected from the center tap of the transformer to ground.
:
:John
:
::Great, thanks John. You're a BIG help! After I wrote the last post I had an inkling that the black might be the common wire - but it seemed an odd configuration since I believe the common wire is usually the ground. Just curious though how did you come up with -15V?
::
:::The Black wire is common to all three capacitors and is at -15V. The Yellow wire that goes to ground is the positive side of the 20uF capacitor.
:::The Green wire is the positive side of the 10uF capacitor.
:::The Red wire is the positive side of the 15uF capacitor.
:::John

It is usually, always a good idea to replace e caps on transformer radios.

Hi Steve,

As Del mentioned you should replace the E caps.

The crackling sound could be coming from dirty/oxidized tube socket contacts or a dirty volume control. Also ensure that the tuning capacitor plates are not touching.

Gary

:Well, I replaced all the caps in my radio (Motorola aka Galvin 59T2) except for a ganged electrolytic capacitor bank (10, 20, 15 uF) and a .03uf cap. When I turned it on I still get this continuous crackling sound. It goes away when I hit a strong station but you can definitely hear it over the weaker stations. Now I'm not sure how a tube radio should sound, so I don't know if this is normal. Should the interstation regions be a lot quieter/less noisy? I have a feeling that its the cap bank and those large electrolytics that need to be replaced but I'm not sure how to break up that large ganged cap bank into 3 individual caps. It doesn't show polarity in the schematic (Item #20). Any feedback on this is appreciated. Thanks, Steve

Thanks Gary, That got me thinking. Is there a steel bottle brush type device that's small enough to fit in the tube sockets to clean off any oxidation. Seems like that'd be the perfect type of tool to make sure you're getting good contact in the sockets.
Does any one use anything different to de-oxidize the sockets.

:Hi Steve,
:
:As Del mentioned you should replace the E caps.
:
:The crackling sound could be coming from dirty/oxidized tube socket contacts or a dirty volume control. Also ensure that the tuning capacitor plates are not touching.
:
:Gary

An automotive supply store might have a long wirey brush type thing-a-ma-jig that would be thin enough to get into those pin holes.

How long is your antenna? Did you check the antenna coil?
Bill

:Well, I replaced all the caps in my radio (Motorola aka Galvin 59T2) except for a ganged electrolytic capacitor bank (10, 20, 15 uF) and a .03uf cap. When I turned it on I still get this continuous crackling sound. It goes away when I hit a strong station but you can definitely hear it over the weaker stations. Now I'm not sure how a tube radio should sound, so I don't know if this is normal. Should the interstation regions be a lot quieter/less noisy? I have a feeling that its the cap bank and those large electrolytics that need to be replaced but I'm not sure how to break up that large ganged cap bank into 3 individual caps. It doesn't show polarity in the schematic (Item #20). Any feedback on this is appreciated. Thanks, Steve

Right now my antenna is just a 5ft 20 guage wire. I wasn't sure how to check the antenna coil since its covered in wax. Can I check it for continuity on my ohmmeter?

:How long is your antenna? Did you check the antenna coil?
:Bill

Wax is good. Yes use your ohm setting on meter. Don't have power applied. The wax antenna coils has terminals/connections. On schematic item 1 is the antenna coil. Follow the leads. Blue to chassis is primary side, white to white/green is secondary. You want continuity. Don't worry now with resistance .
Bill

:Right now my antenna is just a 5ft 20 guage wire. I wasn't sure how to check the antenna coil since its covered in wax. Can I check it for continuity on my ohmmeter?
:
::How long is your antenna? Did you check the antenna coil?
::Bill
:

Thanks Bill, I'll give that a try once I get home...

:Wax is good. Yes use your ohm setting on meter. Don't have power applied. The wax antenna coils has terminals/connections. On schematic item 1 is the antenna coil. Follow the leads. Blue to chassis is primary side, white to white/green is secondary. You want continuity. Don't worry now with resistance .
:Bill
:
::Right now my antenna is just a 5ft 20 guage wire. I wasn't sure how to check the antenna coil since its covered in wax. Can I check it for continuity on my ohmmeter?
::
:::How long is your antenna? Did you check the antenna coil?
:::Bill
::