[bzadel]

Hello Phorum Members!

I have a Philco Model 37-60 I've been trying to restore for a friend of mine and it's been giving me nothing but fit's to say the least.  The problem is:  I cant get rid of the "hum".

I have replaced EVERY electrolytic and paper/wax capacitors and several resistors which measured out of tolerance.  I did not replace any of the mica capacitors as they very seldom go bad.  I also replaced the 6F6 audio output tube and the 6Q7 2nd detector 1st audio tube which were bad.  And after all that work the hum is still present.

The schematic shows a 5Y4 for the rectifier tube.  But when I got the radio for repair, it had a 5Y3 in it which someone else had previously installed.  Checking the tube substitution manual, they are both interchangeable.  The only difference is the wiring for filament pins are different.  
 
I realigned the receiver and it receives stations very well except that after it warms up the reception strength weakens and I have the volume control at full volume and the reception is still weak..

So the two problems are: constant hum and weakening signal strength after warm up.

The transformer and the choke winding's checked out good.  I ohm'd them an check their output voltages and they are in spec.

My last resort is to re-solder every solder joint.  If any of you out there that are more expert on these old Philco's then I am,  I would sure appreciate any advise you could render.

Thank you very much!

73's
Bill
KI7ZAD

[Ron Ramirez]

Hello and welcome!

I changed the title of your thread as a title describing the subject at hand is more likely to get more input than a thread with your name as the title. Thanks for understanding.

I think the first question would be, regarding the hum, are you sure you have the electrolytic capacitors' negative terminals connected correctly?

[klondike98]

Welcome to the Phorum!

[vinzer]

You might check any ground that are riveted I had a model 84 that bummed due to bad grounds that were riveted.

[bzadel]

Hi Ron,

Thanks for the correction on the title.  This is my first attempt on the forum.  "What do I know" ?

Anyway, yes, I did check for the correct polarity/hookup for the electrolytic's.  I actually tried reversing the hook up of one of the electrolytic's and the radio went silent and the electrolytic started heating up which is a sign that it is installed backwards.  Of course, I did this with only one electrolytic at a time.  I didn't try installing all three of them all together with the reversed/same polarity.  Do you think I should do this - I'd hate to fry 3 good electrolytic's ????

Thank you for your help.

Bill

[Ron Ramirez]

No, no, no. Do not install electrolytics with reverse polarity!

I meant that you should check the negative leads to be sure they are installed correctly.

How about a schematic?
http://www.nostalgiaair.org/pagesbymodel...013205.pdf

Notice that electrolytics (20) and (42) have their negative leads connected to chassis ground, but not so with electrolytic (44) - its negative lead is connected to B-, not to chassis ground. If you connected its negative lead to chassis ground, your radio will always hum.

Check (44) and get back with us.

[Radioroslyn]

Hi Bill and welcome,
To add to what Ron said if you have the negative side of 44 connect to the chassis it shorts the bias voltages. One of these is the - voltage found on pin 5 of the 6F6. when it's not there this can in turn causes the 6F6 to draw excessive plate current  thus lowering the high voltage. This might be the cause of your fading out issue.
Whatever caps you connected backwards throw them out they permanently damaged (shorted) and are useless. Two things electrolytic caps don't like are ac voltage and reverse polarity.

de
N3GTE

[bzadel]

Hi Ron.

Thanks for your reply.   Cap 44 is hooked up correctly and the wiring is correct.  So, I guess that leaves bad solder joints etc. to check.  Other than that, I don't know what else to look for.

Any other suggestions would be appreciated.

Thank you gain.

Bill

[Nathan Slingerland]

Hi Bill - Welcome!

Did you also try Terry's suggestion of new electrolytic caps?
It wasn't clear from your post if you replaced them after experimenting with them being reversed.

[bzadel]

Thanks for your input.  I'll check it out.  As I just recently reply'd to Ron's response,  cap 44 is installed correctly.  I'll keep grinding away at it !

Thank you for your support!

Bill

[bzadel]

Hello,

No - I didn't replace the cap.  I tried it on the 12uf cap (no. 44 only ).  I do plan to replace it with a new one as soon as I can find one.

Thank you for your advise!

Bill