I was the guy that asked about bulbs for a 9X561 not long ago. I got the bulbs I ordered and recapped the radio. It works nice except for one problem. There is some crackling that sounds like a dirty volume knob from the speaker even with the volume all the way down. I don't have any spare tubes and other then that the radio sounds very nice. Because the volume is turned down and it still makes the noise should I just assume it is the output tube and buy one?

What is the brand of this radio? Can you link us to the schematic?

Very unlikely that this is caused by a tube. Tubes have internal elements that are spaced apart in a vacuum. You could measure the tube's resistance between the heater and cathode to see if you detect any leakage.

More likely a bad connection or tube socket making poor connection with pins. A bad cap could do this, but you replaced the caps. Also, a noisey resistor.
Doug

:I was the guy that asked about bulbs for a 9X561 not long ago. I got the bulbs I ordered and recapped the radio. It works nice except for one problem. There is some crackling that sounds like a dirty volume knob from the speaker even with the volume all the way down. I don't have any spare tubes and other then that the radio sounds very nice. Because the volume is turned down and it still makes the noise should I just assume it is the output tube and buy one?

Could be a mouse??? They make all sorts of sounds when the get 'fired up.'

lol no its not a mouse. The chassis is amazingly clean and I did clean the volume control but the volume has no effect on the noise. Sorry Mr. Doug, it is an RCA 9X561. I will try cleaning the tube sockets next. I was going to pull the connection from the grid of the output tube and see if the noise is still there to isolate it further.

:Could be a mouse??? They make all sorts of sounds when the get 'fired up.'

Pull the 12SQ7 (detector) and see if you still hear the noise. Until you can pin this down, I wouldn't buy any new tubes.

To clean the tube sockets, you can moisten a Q-tip or pipe cleaner with Doxit or whatever kind of contact cleaner you have. Likewise for the tube pins.
Doug

:lol no its not a mouse. The chassis is amazingly clean and I did clean the volume control but the volume has no effect on the noise. Sorry Mr. Doug, it is an RCA 9X561. I will try cleaning the tube sockets next. I was going to pull the connection from the grid of the output tube and see if the noise is still there to isolate it further.
:
::Could be a mouse??? They make all sorts of sounds when the get 'fired up.'

The set will be dead without the tube - what is normally placed across the heater pins, a resistor that matches the resistance of the heater? Thank you.

:Pull the 12SQ7 (detector) and see if you still hear the noise. Until you can pin this down, I wouldn't buy any new tubes.
:
:To clean the tube sockets, you can moisten a Q-tip or pipe cleaner with Doxit or whatever kind of contact cleaner you have. Likewise for the tube pins.
:Doug
:
::lol no its not a mouse. The chassis is amazingly clean and I did clean the volume control but the volume has no effect on the noise. Sorry Mr. Doug, it is an RCA 9X561. I will try cleaning the tube sockets next. I was going to pull the connection from the grid of the output tube and see if the noise is still there to isolate it further.
::
:::Could be a mouse??? They make all sorts of sounds when the get 'fired up.'

:The set will be dead without the tube - what is normally placed across the heater pins, a resistor that matches the resistance of the heater? Thank you.
:
Nothing... forget that Doug must have not been thinking of a series filament string.

Yes, I wasn't thinking straight. Sorry.
Doug

::The set will be dead without the tube - what is normally placed across the heater pins, a resistor that matches the resistance of the heater? Thank you.
::
:Nothing... forget that Doug must have not been thinking of a series filament string.
:

I have one of these radios and really like the styling with the 'spinner' speaker grille. Similar to Raymond Loewey's 'bullet-nose' Studebaker. The portion of the circuit where the noise is coming from sounds like the detector on to the audio output stages, if the problem doesn't seem to be affected by your volume control setting. As mentioned before, check for loose connections, with the radio playing, gently rock and push on the 12SQ7 and 50L6 (watch fingers as this tube runs hot). Same with components on the underside of these 2 tubes, use a plastic poker to prevent shock. If you have no reaction then the noise is internal to a component (i.e. resistor or cap). You can 'listen in' to points of the audio circuit with a signal tracer. If you can hear the noise before a component but not after a component then you've likely found the culprit. You can do 'before and after' tests with a crystal earphone. One end clipped to the chassis and a .01 mfd @ 200+ volts cap on the other, this will protect the earphone from B+ DC voltage but allow you to hear the audio. Use the free end of the cap as a probe to do your listening tests but be careful about getting shocked. You may want to test various points of the area with a voltmeter just to see where the high voltage spots are so to be careful when working with them.(One steady hand doing the probing and touching nothing with the other). Best of luck.

: It works nice except for one problem. There is some crackling that sounds like a dirty volume knob from the speaker even with the volume all the way down.

On 1950ies radios, there is a disease called "silver migration". Inside the IF cans are little silver capacitors made of mica wavers. The silver "migrates" and create intermittent shorts resulting in crackling and "thunderstorms" being heard through the speaker even with the volume control turned all the way down.

Looking at the schematic indeed reveals that caps are inside the IF cans, so I'd suspect your radio suffers of that disease.

A good buddy wrote a very well done pictorial procedure (How-To) sometime ago and it is hosted on my website: http://www.oldradioz.com/john/Tech/IFcapRepair.pdf

Hope this helps.

Syl