Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Hi Guys,
Here's my latest project Zenith Model G725 . When I got it all it did was have a loud hum at any volume. I replaced all the electrolytics and wax caps. Replaced any resistor out of specs. I tested all the tubes and they check ok.
So, now, with the volume turned all the way down I get a loud hum. Once I move the control any amount, the hum goes away and the radio sounds great-AM and FM.
Any thoughts on what might be causing this?
Thanks,
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 4,106
Threads: 310
Joined: Nov 2013
City: Kings Park NY
I am far from a chassis guy so I wont give any advice but I like to respond to posts I read.
Kirk
Times I have been electrocuted in 2021
As of 1/01/2021
AC: 4 DC: 1
Last year: 6
Posts: 13,776
Threads: 580
Joined: Sep 2005
City: Ferdinand
State, Province, Country: Indiana
Heater-cathode short in a tube? That's the first thing that comes to my mind...
Also make sure all leads are properly soldered to the volume control; if the low end of the control comes unsoldered from ground or B-, it could also produce this effect.
--
Ron Ramirez
Ferdinand IN
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Thanks Ron,
I swapped each tube with known good ones, one at a time. I resoldered each terminal of the vol control. Could it be the vol control itself?
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 13,776
Threads: 580
Joined: Sep 2005
City: Ferdinand
State, Province, Country: Indiana
Could be...measure across the two outer terminals and see if you get anything close to the rated resistance. If not, then you have a problem.
Preferably using an analog VOM, measure between the center terminal and one of the outer terminals. Holding the test leads in place (alligator clips come in handy here), slowly turn the control from one end to the other. If the resistance does not change smoothly but jumps open here and there...then you have a problem.
--
Ron Ramirez
Ferdinand IN
Posts: 2,023
Threads: 365
Joined: Jun 2010
City: Dover, OH
This might sound silly, but did you clean the controls? Sometimes a dirty control pot or even tube socket can cause hum as well.
No matter where you go, there you are.
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
No problem with any resistance readings, Ron. Jayce, I wish it were that simple. That was done while replacing all of the components.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 15,495
Threads: 543
Joined: Oct 2011
City: Jackson, NJ
The box of the pot is groundedvi a a cap.....have you cheked it?
Also, the quality of the speaker voice coil grounding, look at it.
(This post was last modified: 12-26-2014, 12:02 AM by morzh.)
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
The cap checks good, Mike. Voice coil ground is ok.
Now, for the good news. There's a 1k resistor that goes from the low terminal of the volume control to ground. The 1k resistor was right on. I jumped it with another resistor and the hum went away. After some experimenting I settled on a 470 ohm resistor to replace the 1k. I'm sure someone can tell me why it works, but it sounds great now!
Thanks everyone for your input. I hope you all had a good Christmas and looking forward to a healthy and happy new year.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 15,495
Threads: 543
Joined: Oct 2011
City: Jackson, NJ
Could be an inductive wirewound resistor you had before that picked up noise.....which then could mean that if you re-oriented it the noise could've been attenuated. A wild guess.....
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Nope. Carbon resistor.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Users browsing this thread: 1 Guest(s)
|
Recent Posts
|
Philco 39-116 radio and remote
|
The transformer I located is from a Philco TV chassis, circa 1948. The part number is 32-8391
I do have the replace...Brad Winder — 08:59 PM |
Philco 41-221 Restored
|
Hello Rod,
Wow that radio looks great nice job !
Sincerely Richardradiorich — 07:39 PM |
Philco 269 - 444 FIVE VALVE VERSION?
|
From what I can remember the model 444 "People's Radio" used a special tube/valve called a PenDD61, it was the...Arran — 06:54 PM |
Philco 41-221 Restored
|
Nice Radioslford310 — 06:24 PM |
Philco 269 - 444 FIVE VALVE VERSION?
|
Hi Chaz,
You may want to post the tubes used in your radio.
From Radio Museum, it seems that the set uses some ...MrFixr55 — 05:14 PM |
Philco 41-221 Restored
|
Today my grandson and I finished the restoration of this Philco 41-221. It has had all the rubber coated wiring replaced...RodB — 03:19 PM |
Philco 39-116 radio and remote
|
Hi Brad,
I had no idea that the overheating was problematic in this radio. Do you know the part number of the transfor...RichG — 03:01 PM |
Philco 269 - 444 FIVE VALVE VERSION?
|
From the photo it looks the sockets are screwed and the front one does not even match the hole.morzh — 02:54 PM |
Philco 269 - 444 FIVE VALVE VERSION?
|
Hi Chas a welcome,
Perhaps we'll have to reverse engineer this to sort it. So let's start w/what tubes does it use? And...Radioroslyn — 12:28 PM |
Philco 39-116 radio and remote
|
Hi Rich,
From my experience, unfortunately it is not uncommon to find the power transformer in the 39-116 to be overhea...Brad Winder — 09:25 AM |
Who's Online
|
There are currently no members online. |
|
|