Hallicrafters S120 hum at no vol and hum with volume

[tubetwister]

Originally Posted by Electronic M

I have seen 2-3 AA5 sets with field coil electrodynamic speakers, not common, but some did it.

What matters with the output grid is that it be negative with respect to the cathode. One thing you can do is connect a large cap (.22-10uF) between the output grid and signal ground to bypass any hum from proceeding stages to ground, then put the meter common lead on the grid and the hot lead on the cathode...That should give you a positive voltage indicating the cathode is positive WRT the grid and that the grid is negative WRT cathode.

lacking a new tube set delivered yet the common mode fixed hum daig.process is going slow at least at my chosen path given I am chasing a possible tube heater /cathode fault .

Using my secondary phones for a signal tracer at C15 to VOL pot distorted audio and same fixed hum,16 away from Vol pot same result

@above testing update the tell is the hum bogey is ahead of the beam power final tube ,or into the 50C5 tube or one tube back as I interpret the results and ofc the 50C5 control grid cap and signal needs to be fixed and at least have the correct uf capacitor if nothing else ,

Note today thd+n is virtually and suddenly making the radio nearly useless , no change @common mode fixed hum!
Maybe a deteriorating tube or discrete circuity part is my guess without an ouija board or a wise leprechaun LOL

Update 08.11.2017 17:27 PDT .


Hum diag . For bad tube leaky heater or H C short @ a tube I can pull tubes one by one power [up ] (only after the other heaters cool so you dont over volt a heather and fry a tube electronics 101 heat vs restive load EZ peay s B4 Univerity study too ! ) ag if i use alligator clip to puled tube hater pins I first though of decades ago in one of these but it was the Lytics !


I have a testing update and the tell is the hum bogey is ahead of the beam power final tube ,or into the 50C5 tube or one tube back (or more ) as I interpret the results and ofc the 50C5 control grid cap and signal needs to be fixed and at least have the correct uF capacitor if nothing else ,

Note today thd+n is virtually and suddenly making the radio nearly useless , no change @common mode fixed hum!
Maybe a deteriorating tube or discrete circuity part is my guess without an ouija board or a wise leprechaun LOL

lacking a new tube set delivered HERE the common mode fixed hum daig.process is going slow at least at my chosen #lazyfair slow path given I am chasing a possible tube heater /cathode fault .but the new tubs > sWill fix that anyway if that is prob

Using my secondary phones for a signal tracer at C15 to VOL pot distorted audio and same fixed hum,C16 away from Vol pot same result




.O

4. lacking anthing better like a signal tracer I got creative or started tweaking without chemicals who knows ? I used my Sennsheiser HD 280 secondary headphones for an audio signal tracer for audio and hum .

Result : same as above Distorted audio same fixed hum @ Vol Pot C15 ,C16

ofc . This AC-DC AA4 Hallishafters S120 is just a a nostalgia bedside radio for me ,a mid century adolescent bedroom trophy or brand starter radio and a nearly deaf SWL radio anyway .that would be outlawed today .

I bought it for what it is ,not what it is not ,or never will be :!:

I came up on that generation and been in more than few tube radios ~but not much tube action since 1970!