Hello All,
I replaced all paper and filter capacitors in this radio and it performs beautifully. However, at low volume or when the volume is turned all the way down, I hear crackling and hiss from the amplifier. I tried different pre-amp, detector and main amp tubes. I tried replacing the wire to the top pin on the pre-amp tube. I checked all over the place for cold solder joints, I can't find anything wrong and it continues to crackle intermittently (a staticy sound) and hiss continuously.
I think this problem could be anywhere. There could be a loose lead on a resistor, the large capacitor that looks like a mica capacitor could be a paper capacitor, the voltage divider resistor could be opening up, the speaker transformer or power transformer could have an intermittently shorted winding. Just anything. But maybe someone has had this problem in 38-7 or 38-8 or 38-9 and could help me.

Thanks,

Dave

Dave, you might try pulling tubes, one at a time, to see if you can pinpoint the stage it's coming from. Start at the front end, and work toward the audio.

:Hello All,
: I replaced all paper and filter capacitors in this radio and it performs beautifully. However, at low volume or when the volume is turned all the way down, I hear crackling and hiss from the amplifier. I tried different pre-amp, detector and main amp tubes. I tried replacing the wire to the top pin on the pre-amp tube. I checked all over the place for cold solder joints, I can't find anything wrong and it continues to crackle intermittently (a staticy sound) and hiss continuously.
: I think this problem could be anywhere. There could be a loose lead on a resistor, the large capacitor that looks like a mica capacitor could be a paper capacitor, the voltage divider resistor could be opening up, the speaker transformer or power transformer could have an intermittently shorted winding. Just anything. But maybe someone has had this problem in 38-7 or 38-8 or 38-9 and could help me.
:
:Thanks,
:
:Dave

:Dave, you might try pulling tubes, one at a time, to see if you can pinpoint the stage it's coming from. Start at the front end, and work toward the audio.
:
::Hello All,
:: I replaced all paper and filter capacitors in this radio and it performs beautifully. However, at low volume or when the volume is turned all the way down, I hear crackling and hiss from the amplifier. I tried different pre-amp, detector and main amp tubes. I tried replacing the wire to the top pin on the pre-amp tube. I checked all over the place for cold solder joints, I can't find anything wrong and it continues to crackle intermittently (a staticy sound) and hiss continuously.
:: I think this problem could be anywhere. There could be a loose lead on a resistor, the large capacitor that looks like a mica capacitor could be a paper capacitor, the voltage divider resistor could be opening up, the speaker transformer or power transformer could have an intermittently shorted winding. Just anything. But maybe someone has had this problem in 38-7 or 38-8 or 38-9 and could help me.
::
::Thanks,
::
::Dave

Why am I thinking of a bad volume control. Well enough go bad and it seems to happen on the low volume end. It's wear. "Turn that radio down!"

Bill VA

Bill,
The volume control isn't scratchy and turns the volume up and down quite smoothly. When the volume is all the way down, it crackles, and not when the volume control is turned up or down. It happens when nobody is touching it. The hiss is much like when a germanium transistor doesn't work.

Thanks for your suggestion. Please keep suggesting. I will find the problem,

Dave
::Dave, you might try pulling tubes, one at a time, to see if you can pinpoint the stage it's coming from. Start at the front end, and work toward the audio.
::
:::Hello All,
::: I replaced all paper and filter capacitors in this radio and it performs beautifully. However, at low volume or when the volume is turned all the way down, I hear crackling and hiss from the amplifier. I tried different pre-amp, detector and main amp tubes. I tried replacing the wire to the top pin on the pre-amp tube. I checked all over the place for cold solder joints, I can't find anything wrong and it continues to crackle intermittently (a staticy sound) and hiss continuously.
::: I think this problem could be anywhere. There could be a loose lead on a resistor, the large capacitor that looks like a mica capacitor could be a paper capacitor, the voltage divider resistor could be opening up, the speaker transformer or power transformer could have an intermittently shorted winding. Just anything. But maybe someone has had this problem in 38-7 or 38-8 or 38-9 and could help me.
:::
:::Thanks,
:::
:::Dave
:
:Why am I thinking of a bad volume control. Well enough go bad and it seems to happen on the low volume end. It's wear. "Turn that radio down!"
:
:Bill VA

Dave,

Are you saying the crackle is still there when you pull the 6K5 AND when you pull the 6F6 tube?

Radiodoc

:Bill,
: The volume control isn't scratchy and turns the volume up and down quite smoothly. When the volume is all the way down, it crackles, and not when the volume control is turned up or down. It happens when nobody is touching it. The hiss is much like when a germanium transistor doesn't work.
:
:Thanks for your suggestion. Please keep suggesting. I will find the problem,
:
:Dave
:::Dave, you might try pulling tubes, one at a time, to see if you can pinpoint the stage it's coming from. Start at the front end, and work toward the audio.
:::
::::Hello All,
:::: I replaced all paper and filter capacitors in this radio and it performs beautifully. However, at low volume or when the volume is turned all the way down, I hear crackling and hiss from the amplifier. I tried different pre-amp, detector and main amp tubes. I tried replacing the wire to the top pin on the pre-amp tube. I checked all over the place for cold solder joints, I can't find anything wrong and it continues to crackle intermittently (a staticy sound) and hiss continuously.
:::: I think this problem could be anywhere. There could be a loose lead on a resistor, the large capacitor that looks like a mica capacitor could be a paper capacitor, the voltage divider resistor could be opening up, the speaker transformer or power transformer could have an intermittently shorted winding. Just anything. But maybe someone has had this problem in 38-7 or 38-8 or 38-9 and could help me.
::::
::::Thanks,
::::
::::Dave
::
::Why am I thinking of a bad volume control. Well enough go bad and it seems to happen on the low volume end. It's wear. "Turn that radio down!"
::
::Bill VA

Doug,
No matter what tube is pulled it still crackles. If the 6F6 is replaced it crackles. If any of the tubes is replaced it crackles. I already did this.
It has to be someplace else. Maybe inside an IF transformer. Maybe a resistor. Maybe what looks like a mica capacitor is a paper capacitor.

Thanks for your suggestion,

Dave
:Dave, you might try pulling tubes, one at a time, to see if you can pinpoint the stage it's coming from. Start at the front end, and work toward the audio.
:
::Hello All,
:: I replaced all paper and filter capacitors in this radio and it performs beautifully. However, at low volume or when the volume is turned all the way down, I hear crackling and hiss from the amplifier. I tried different pre-amp, detector and main amp tubes. I tried replacing the wire to the top pin on the pre-amp tube. I checked all over the place for cold solder joints, I can't find anything wrong and it continues to crackle intermittently (a staticy sound) and hiss continuously.
:: I think this problem could be anywhere. There could be a loose lead on a resistor, the large capacitor that looks like a mica capacitor could be a paper capacitor, the voltage divider resistor could be opening up, the speaker transformer or power transformer could have an intermittently shorted winding. Just anything. But maybe someone has had this problem in 38-7 or 38-8 or 38-9 and could help me.
::
::Thanks,
::
::Dave

:Doug,
:No matter what tube is pulled it still crackles. If the 6F6 is replaced it crackles. If any of the tubes is replaced it crackles. I already did this.
: It has to be someplace else. Maybe inside an IF transformer. Maybe a resistor. Maybe what looks like a mica capacitor is a paper capacitor.
:
:Thanks for your suggestion,
:
:Dave
::Dave, you might try pulling tubes, one at a time, to see if you can pinpoint the stage it's coming from. Start at the front end, and work toward the audio.
::
:::Hello All,
::: I replaced all paper and filter capacitors in this radio and it performs beautifully. However, at low volume or when the volume is turned all the way down, I hear crackling and hiss from the amplifier. I tried different pre-amp, detector and main amp tubes. I tried replacing the wire to the top pin on the pre-amp tube. I checked all over the place for cold solder joints, I can't find anything wrong and it continues to crackle intermittently (a staticy sound) and hiss continuously.
::: I think this problem could be anywhere. There could be a loose lead on a resistor, the large capacitor that looks like a mica capacitor could be a paper capacitor, the voltage divider resistor could be opening up, the speaker transformer or power transformer could have an intermittently shorted winding. Just anything. But maybe someone has had this problem in 38-7 or 38-8 or 38-9 and could help me.
:::
:::Thanks,
:::
:::Dave

::Doug,
::No matter what tube is pulled it still crackles. If the 6F6 is replaced it crackles. If any of the tubes is replaced it crackles. I already did this.
:: It has to be someplace else. Maybe inside an IF transformer. Maybe a resistor. Maybe what looks like a mica capacitor is a paper capacitor.
::
::Thanks for your suggestion,
::
::Dave
:::Dave, you might try pulling tubes, one at a time, to see if you can pinpoint the stage it's coming from. Start at the front end, and work toward the audio.
:::
::::Hello All,
:::: I replaced all paper and filter capacitors in this radio and it performs beautifully. However, at low volume or when the volume is turned all the way down, I hear crackling and hiss from the amplifier. I tried different pre-amp, detector and main amp tubes. I tried replacing the wire to the top pin on the pre-amp tube. I checked all over the place for cold solder joints, I can't find anything wrong and it continues to crackle intermittently (a staticy sound) and hiss continuously.
:::: I think this problem could be anywhere. There could be a loose lead on a resistor, the large capacitor that looks like a mica capacitor could be a paper capacitor, the voltage divider resistor could be opening up, the speaker transformer or power transformer could have an intermittently shorted winding. Just anything. But maybe someone has had this problem in 38-7 or 38-8 or 38-9 and could help me.
::::
::::Thanks,
::::
::::Dave

Sorry for the double posting. My favorite method of testing solid-state circuits was to use "Freeze Mist"
or a hair-dryer to shock the components into changing their characteristics. Should be useful on the old tube stuff as well. Even works sometimes for bad
solder joints.
Bill

With what you have described, sounds like the problem is in the last AF stages or...remote chance... the power supply. Since this set uses a straight forward volume control, (it actually grounds out incoming detected audio) when it is in its min volume position.

Try this now, in order to further differentiate as to the problem being between the two AF stages. Have the set in the min volume positoion and have the set making its *** noise *** and then use a short clip lead, having one of its ends to ground and the other at hand. Then place your ear up to the speaker, to catch every little nuance of the *** noise *** and take that leads free end and ground the 1st grid of the 1st AF amp tube temporarily, for about a 5 seconds evaluation period. That time period should confirm if the noise dissappeared. Should the noise still present, resume a "vewy" close listening at the noise while you then initiating the other stages test, by shorting out the 1st grid of the 6F6 for a VERY BRIEF evaluation time. The first test should confirm the sourcing not to be coming from the front end...which the min volume position has already also suggested, but further differentiates as to the electro/physical state of the low end of the resistive element of the vol control proper.

The second test was oriented towards the 1st audio stage, and the possibility of gaussian type shot noise coming from its resistors BUT you have typically taken care of the additional possibilities.......that being the caps in that stage.

Not having heard back from you yet, at this time, doesn't that set use the cheaper wafer tube sockets ?, with a possibility of a carbon trail break down, with the 6F6 of major consideration with its higer B+ potential, whereas the 'K5's plate voltage is operating at a mere fraction of the others P/P potential.

In the remote chance that while evaluating the output stage in the last test, the most common components for consideration on that situation would be the tube.....already cleared?....... the tube socket, breaking down, ?........an arcing output transformer either interwinding or a to ground/core leakage ?......items (37) .03 ufd and (40) .008 ufd caps .......already changed out ?....The insulation/wafer breaking down / carbon trailing... on the (38)power/tone switch.

That now bringing us down the final probability of a field coil problem in the same failure mode as the output transformer , but affecting in the manner of the noise being of a much lower frequency response...more in the order of a low freq thumping as the magnetic fields generation would be vacillating. Otherwise, the already mentioned earlier noise sourcing would be more in the order of hi freq noise ...like static bursts or ....varying levels of pink noise.

Also in the running would be connections/connectivity problems, and one technique that I use to impart a solid vibration to a suspect area .....(no longer having a NASA environmental evaluation chamber at my hand, anymore)......is to use an ~ 1 ft long length of 3/8 inch doweling with one end bare and its other with one of the slip over pencil erasers over it. That will then have the option to be placed on/in/near a suspect area and the application of different degrees of tapping....with a small tack hammer to the appropriately selected end ...thus inducing a smart jarring of any, or all, suspect...... areas / components/ connections.

73's de Edd.....ZUJ'ing

Pee Ess ...got my 1200 jewel movement, Bulova..... any closer to its solution ?