Hi all, I am currently working on a model 6S527 table model, the schematic says this has two electrolytics , a 10uf and a 15 uf, My first step is always replacing these , my question is this is a muti-section can on the chassis, but underneth it has 3 sections and 2 are tied together , the writing on the cardbord can is faded and cannot be read so I don't know if this was updated sometime before or not, but anyway I did replace the sections with fresh 10 and 15 uf caps but even though the radio plays great it still has a nasty hum , while it was playing I figured one of the new caps might also be bad so i jumped a additional 15uf across the 15uf section and the hum noticebly droped off so I pulled both the 15uf's out and put in a 33uf but still the hum persists, I checked the field coil and it reads normal 2k ohms. I just wonder if that third section on the can was suppose to be in there even though not shown on the schematic, anyone run across this before or have suggestions as to what else is causing the power hum ?
Thanks
Elton

Hi Elton

A couple things to check. Did you disconnect the original filter caps? If they are in the circuit may have capacity between sections causing hum.

Do both sides of your 6X5 test about the same? It's possible for only one section to be operating. This will make the circuit a half wave rectifier, causing hum.

Norm

:Hi all, I am currently working on a model 6S527 table model, the schematic says this has two electrolytics , a 10uf and a 15 uf, My first step is always replacing these , my question is this is a muti-section can on the chassis, but underneth it has 3 sections and 2 are tied together , the writing on the cardbord can is faded and cannot be read so I don't know if this was updated sometime before or not, but anyway I did replace the sections with fresh 10 and 15 uf caps but even though the radio plays great it still has a nasty hum , while it was playing I figured one of the new caps might also be bad so i jumped a additional 15uf across the 15uf section and the hum noticebly droped off so I pulled both the 15uf's out and put in a 33uf but still the hum persists, I checked the field coil and it reads normal 2k ohms. I just wonder if that third section on the can was suppose to be in there even though not shown on the schematic, anyone run across this before or have suggestions as to what else is causing the power hum ?
:Thanks
:Elton

This is one of those lovelies with the field coil on the negative side. Before you continue playing that radio, be absolutely sure that you have the caps installed correctly. The negative sides should go towards the field coil. The 15 MFD should go on the transformer side of the field coil and the 10 should go on the radio side. If they are installed backwards, it won't matter how fresh they are. Were the old ones bad? Sometimes Zenith caps last a long time. I have several Zeniths with their original electrolytics. If the old ones have more than 1 meg leakage (less than 1 meg numerically), discard. If less, run the radio for a while to see if it goes away. If it does, compare charge-up time with new ones. If the needle of your meter falls to infinity noticeably more quickly than with new caps, then the old ones are faulty. In the end, though, if you are worried about the old 'lytics, replace them. It is always better to be safe than sorry. Your new caps should do the trick. The only thing I can think of that would make the radio hum is if they are installed backwards.

Thomas

Also, regarding extra electrolytic sections, my 5-G-500 came equipped with an extra unused electrolytic section in one of the two cans. It was unused, as I just said. I connected it experimentally because I thought it would be worthwhile to make use of it. I finally found a place for it which I liked. The radio never really did hum at all, but now it's even better. The electrolytics in this radio still are the originals from 1940.

It is entirely possible that Zenith installed electrolytics which were at hand, which had more leads than desired. It is possible that the two tied together, if for the 15, were two 8s. They could have been anything else, too, like two 10s. Though this wouldn't equal 15 MFD, it'd work just as well. You may use as much as 30 MFD for the primary electrolytic, though 15 should be okay. 20 is better. For the secondary, anything between 8 and 20 is fine. Use the original 10 if you use a 15 for the primary, and use up to 20 if you go with 30 on the primary. There is no need to increase the values, though sometimes this helps things. A little more makes things more pleasant. Though you can use the same values for both, I wouldn't. Sometimes this increases hum. Normally it doesn't. Don't go above 30 with the primary. Actually 40, possibly even 50 is okay, but anything higher than this can put stress on the rectifier during turn-on, either with the radio warm or cold. Anything higher than 30 is unnecessary.

Thomas

Hey guys thanks for the quick replies, to answer the questions the originals did test leaky and I did disconnect them from the circuit , this can is isolated from the chassis so I connected the negatives to the insolated can I did not check the 6x5 as norm suggested but I will , I also thought that zenith may have put in what ever they had to provide the nessary filtering , but the hum is still there I also replaced the papers in the audio sections just for my own piece of mind as usually as the radio plays my experiace has been the papers break down and garble up the audio after a couple hours , it seems to be the norm on old zeniths , at least the ones I have.
:Also, regarding extra electrolytic sections, my 5-G-500 came equipped with an extra unused electrolytic section in one of the two cans. It was unused, as I just said. I connected it experimentally because I thought it would be worthwhile to make use of it. I finally found a place for it which I liked. The radio never really did hum at all, but now it's even better. The electrolytics in this radio still are the originals from 1940.
:
:It is entirely possible that Zenith installed electrolytics which were at hand, which had more leads than desired. It is possible that the two tied together, if for the 15, were two 8s. They could have been anything else, too, like two 10s. Though this wouldn't equal 15 MFD, it'd work just as well. You may use as much as 30 MFD for the primary electrolytic, though 15 should be okay. 20 is better. For the secondary, anything between 8 and 20 is fine. Use the original 10 if you use a 15 for the primary, and use up to 20 if you go with 30 on the primary. There is no need to increase the values, though sometimes this helps things. A little more makes things more pleasant. Though you can use the same values for both, I wouldn't. Sometimes this increases hum. Normally it doesn't. Don't go above 30 with the primary. Actually 40, possibly even 50 is okay, but anything higher than this can put stress on the rectifier during turn-on, either with the radio warm or cold. Anything higher than 30 is unnecessary.
:
:Thomas

Hmmmm....you should have TWO NEGATIVE LEADS!!!!!!!! If your can only has one negative (the case), then someone installed the wrong replacement, and that can is indeed a replacement. You need one negative before the field coil and one negative after the field coil as I said before. You really need to check your wiring. Someone probably messed around with it, not knowing what they were doing. Both positive leads of your 'lytics should go to the rectifier cathode. LOOK AT YOUR SCHEMATIC AND NOTE HOW THE ORIGINAL ELECTROLYTICS WERE WIRED AND HOW THE FIELD COIL IS WIRED. THIS IS EXTREMELY IMPORTANT!

Thomas

The original electrolytic, if a multi-section, had two negative leads and a common positive.

Thomas

Thomas, looking again at the schematic , you are correct the can looks as if wired wrong, this had to be a replacment... DUHHHH I should have noticed this from the get go, I will correct the wiring and let you know if this corrects the problem, thanks for pointing this out , I am a idiot not to have noticed this before.
Thanks
Elton
:The original electrolytic, if a multi-section, had two negative leads and a common positive.
:
:Thomas

Sometimes when first introduced to the negative filter scheme, we are all idiots. When I first got my Crosley 1117, I thought that someone messed it up, so I rewired it so that the field coil was on the positive side. Moron I was. I put it back to the negative side after getting the schematic. I now own several radios with this set-up. Not sure if it's just my radios or if this is common. They tend to hum a bit more, though not much. At any rate, they all perform reliably well, and I enjoy them all. I actually like having the field coil on the negative side when the output transformer is mounted to the chassis. This keeps B+ out of the speaker, and keeps you from getting a serious shock should insulation break down. If there was B+ in the speaker and the insulation got wet or broke down, and you touched the speaker and the chassis at the same time (not an uncommon practice), you'd get a real whap! Just imagine if you were holding the chassis in one hand and the field coil in the other! It'd go right through your heart. Well, I'm sure this isn't why they put the field coil on the negative side. Usually the field coil drops about 60 volts anyway, so there's still a shock potential, depending upon which wire that's touching the speaker frame.

Just remember when dealing with one of these radios, if it has its original electrolytics and they're in a multi-unit can, usually you have a common POSITIVE, and the other leads are negative. If the can in your Zenith has a cardboard shell over it, it may be the original can. The outside may in fact be positive, and the center terminals may be negative terminals. Check it out! See how it's wired. If the can is tied to the rectifier cathode, then the center terminals are likely negative terminals. Of course if someone put in a new negative shell can, they may have either wired it in not knowing that the original's common was positive, or they may have messed up the wiring entirely to suit the new electrolytic. It is possible to use a modern multi-section with the common negative, by putting the field coil on the positive side, but I don't recommend this. Remember, too, that there is a divider resistor across the field coil which is used for supplying various negative voltages to the grids and such. Removing the field coil from this circuit would mess up voltages. Just put two individual electrolytics under the chassis and wire everything as original. Remember to tie the positive leads together as a common...connecting these to the rectifier, and then connect the appropriate negative leads to their appropriate places before and after the field coil.

Thomas

Thomas, you were right the cap was backwards , and I in turn wired the replacments the same way... I guess lucky they did'nt explode , so I reversed the leads and the hum is gone , I should have caught this before as I had a simular experiance with a philco a couple years ago... I guess someone in the past did as you said wired it wrong , you know what they say about assuming it was right before...
Thanks
Again.
Elton
:Sometimes when first introduced to the negative filter scheme, we are all idiots. When I first got my Crosley 1117, I thought that someone messed it up, so I rewired it so that the field coil was on the positive side. Moron I was. I put it back to the negative side after getting the schematic. I now own several radios with this set-up. Not sure if it's just my radios or if this is common. They tend to hum a bit more, though not much. At any rate, they all perform reliably well, and I enjoy them all. I actually like having the field coil on the negative side when the output transformer is mounted to the chassis. This keeps B+ out of the speaker, and keeps you from getting a serious shock should insulation break down. If there was B+ in the speaker and the insulation got wet or broke down, and you touched the speaker and the chassis at the same time (not an uncommon practice), you'd get a real whap! Just imagine if you were holding the chassis in one hand and the field coil in the other! It'd go right through your heart. Well, I'm sure this isn't why they put the field coil on the negative side. Usually the field coil drops about 60 volts anyway, so there's still a shock potential, depending upon which wire that's touching the speaker frame.
:
:Just remember when dealing with one of these radios, if it has its original electrolytics and they're in a multi-unit can, usually you have a common POSITIVE, and the other leads are negative. If the can in your Zenith has a cardboard shell over it, it may be the original can. The outside may in fact be positive, and the center terminals may be negative terminals. Check it out! See how it's wired. If the can is tied to the rectifier cathode, then the center terminals are likely negative terminals. Of course if someone put in a new negative shell can, they may have either wired it in not knowing that the original's common was positive, or they may have messed up the wiring entirely to suit the new electrolytic. It is possible to use a modern multi-section with the common negative, by putting the field coil on the positive side, but I don't recommend this. Remember, too, that there is a divider resistor across the field coil which is used for supplying various negative voltages to the grids and such. Removing the field coil from this circuit would mess up voltages. Just put two individual electrolytics under the chassis and wire everything as original. Remember to tie the positive leads together as a common...connecting these to the rectifier, and then connect the appropriate negative leads to their appropriate places before and after the field coil.
:
:Thomas

.....or assuming it was wrong when in fact it was wired correctly from the factory (in my case with the Crosley). Well, congratulations! Enjoy the radio!

Thomas