Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Jun Wed 03, 2020 3:31 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 7 posts ] 
Author Message
 Post subject: Philco 41-605 60Hz problems
PostPosted: Apr Tue 07, 2020 9:58 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 302
I have been rebuilding this 41-605 for a friend. I have replaced ALL of the caps including two 20uf filter caps. I have tested all of the tubes to be good. All resistors more than 10% OOT have been replaced. All controls and switches cleaned. All tube pins and sockets cleaned. All questionable wiring (due to rubber insolation), has been replaced.

The problem I'm having, is that when I fire up the set, I get a 60Hz hum through the speaker, and nothing else. The hum is independent of the volume control level.

I have checked the 350 ohm choke and it is good. NO, I do not have an oscilloscope. At present, I am doing a point by point wiring check to insure that it is per the schematic. Anyone that has a suggestion would be welcomed. I honestly do not believe I have landed a lead incorrectly, however, nothing is impossible. If you have encountered this problem, or have a suggestion to remedy the problem, please let me know.

Thanks Guys

_________________
"It's a good idea to have an open mind . . . but not so open that your brains fall out."


Top
 Profile  
 
 Post subject: Re: Philco 41-605 60Hz problems
PostPosted: Apr Tue 07, 2020 10:04 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30554
Location: Livermore, CA
Negative of electrolytic caps connect to B- line. Not chassis.

http://www.nostalgiaair.org/pagesbymode ... 013430.pdf

_________________
Norm


Top
 Profile  
 
 Post subject: Re: Philco 41-605 60Hz problems
PostPosted: Apr Tue 07, 2020 10:22 pm 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 28186
Location: Annapolis, MD
I see a few things I'm not used to....
--some caps go direct to chassis and not to B-, not unusual, but one of them is the 0.2uF in the cathode circuit of the output tube. That is a larger cap between B- and ground than i am used to seeing.
And isn't there normally also a resistor from B- to ground?

_________________
-Mark
"Even if you don't understand Ohm's Law, you are still required to obey it."


Top
 Profile  
 
 Post subject: Re: Philco 41-605 60Hz problems
PostPosted: Apr Tue 07, 2020 11:27 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 302
Norm,

You are right. I already measured that, and I'm reading infinite ohms from the common ground of both 20uf caps to chassis,

_________________
"It's a good idea to have an open mind . . . but not so open that your brains fall out."


Top
 Profile  
 
 Post subject: Re: Philco 41-605 60Hz problems
PostPosted: Apr Wed 08, 2020 12:09 am 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 2608
Location: Austin, Texas
pixellany wrote:
I see a few things I'm not used to....
--some caps go direct to chassis and not to B-, not unusual, but one of them is the 0.2uF in the cathode circuit of the output tube. That is a larger cap between B- and ground than i am used to seeing.
And isn't there normally also a resistor from B- to ground?

There seem to be larger caps between chassis and B- on the radio-phono combinations. It probably has to do with hum in the phono mode. There is usually a high value resistor to bleed off static charge on the chassis. Without the resistor, the static charge on the chassis can get high enough to cause failure of the chassis to B- cap.

Jay


Top
 Profile  
 
 Post subject: Re: Philco 41-605 60Hz problems
PostPosted: Apr Wed 08, 2020 12:48 am 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 28186
Location: Annapolis, MD
I have a vague memory of someone reporting that there was a UL rule (guideline) about the size of the B- to chassis capacitor. Or was it about line filters......?
I'm in the camp that mostly keeps things stock, so I tend to not retain certain kinds of data.

_________________
-Mark
"Even if you don't understand Ohm's Law, you are still required to obey it."


Top
 Profile  
 
 Post subject: Re: Philco 41-605 60Hz problems
PostPosted: Apr Wed 08, 2020 1:53 am 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 3619
Location: Lexington, KY USA
Sorry to have lots of questions and no answers, yet. But we only know what you tell us about what's going on at your bench. With more information, help from the forum can be more helpful.

How loud is the hum?

Does the radio work, otherwise?

Did the radio play before you changed anything?

Do you have any test equipment? A meter? What sort?

Are there signs of overheating? Do you have any way to check how much current is being drawn?

(There are things that cause hum that quickly lead to smoke.)

A good way to do a thorough check of the wiring against the schematic is to first make a large paper copy of the schematic, then mark all the tube pin numbers on this print. Next, take a red pencil and use it to mark each connection and component as it is verified in the chassis. Where possible, use an ohmmeter to verify connections. While you are at it, you can verify resistances. I believe this is a set where all of the resistors can be checked in-circuit.

The safety agencies have tightened up the leakage current requirements over the years. The large chassis to circuit common capacitor value is probably required for the radio to work. There is no way this radio can be made to meet today's requirements. Not a good radio for the hot tub area, or the potting shed with the earthen floor.

Ted


Top
 Profile  
 
Post New Topic Post Reply  [ 7 posts ]  Moderators: Marcc, Norm Leal

All times are UTC [ DST ]


Who is online

Users browsing this forum: AMChief, Dirt Bomb and 7 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB