Posts: 5
Threads: 1
Joined: Jun 2025
City: Nashville
State, Province, Country: Tennessee
Hello, I have a 46-1209 I am restoring. I was always told the radio didn't work, however when I got it home and powered it up it seemed to work fine (with a bit of filter hum of course). I have replaced all paper caps and electrolytics, and now it doesn't work properly. When you turn it on it makes a loud click and 60hz hum. When dim-bulbed at 200w the problem goes away about 5 seconds after all the tubes are warmed up, but plugged straight into the wall it doesn't stop humming.
My observations:
- When the 7AF7 or the 56K resistor on it's 3rd pin is removed, the problem is gone, but the radio must be turned up to max to hear anything.
- When the 7AF7 is plugged in and the problem is occurring the AC volts on Pin 3 is 120, but when removed none of the pins supply 120.
- The volume control does not affect the humming
I have double checked the wiring of the new filter caps, especially around the 7AF7.
Any help is greatly appreciated.
(This post was last modified: 06-03-2025, 12:33 PM by
sq65.)
Posts: 16,555
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Have you touched the speaker wires, either speaker plug or the socket?
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 5
Threads: 1
Joined: Jun 2025
City: Nashville
State, Province, Country: Tennessee
About all I've done is unplugged them to take the chassis to my workbench. Anything I should check with them?
(This post was last modified: 06-03-2025, 06:25 PM by
sq65.)
Posts: 16,555
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
It is kinda impossible for the plate to have 120V with the tube in and have it not with the tube out, short of the tube having some shorts inside in a very improbable way.
The B+ is supplied through the field coil of the speaker, plugged between the plusses of 10uF and 25uF caps.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 5
Threads: 1
Joined: Jun 2025
City: Nashville
State, Province, Country: Tennessee
Yeah, I have no idea what's going on there. I will re-check it in the morning, and also trace out the B+...
Posts: 5
Threads: 1
Joined: Jun 2025
City: Nashville
State, Province, Country: Tennessee
I double checked everything around the filter caps and it all seems to be hooked up right...
Here are the voltage on the 7AF7 when the tube is removed (measured to chassis):
Pin 1 0 DC 2.9 AC Heater
2 0 DC 0 AC Cathode
3 260 DC 0 AC Plate
4 0 DC 0 AC Grid
5 0 DC 0 AC Grid
6 245 DC 0 AC Plate
7 0 DC 0 AC Cathode
8 0 DC 2.9 AC Heater
Some pins had 0.1 or 0.2 VAC but I rounded down
Sure enough, when the 7AF7 warms up my meter shows 80-120vac on pin 3!
Posts: 16,555
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
What kind of meter is it?
Relative to what is the voltage being measured?
Are the AC line filter caps C53A/B hooked up right?
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 5
Threads: 1
Joined: Jun 2025
City: Nashville
State, Province, Country: Tennessee
Meter is a DMM (Brymen BM-257 to be exact)
Voltage being measured to the chassis
Yep, just double-checked 'em
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
