Hallicrafters S120 hum at no vol and hum with volume

[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.

[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!

[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.

I think I saw some electromagnet speaker AA5 photos . I amassed a huge old radio web image collection with actually thousands of images but I'm not so sure there were many or any of those electromagnet speaker AA5 past the 1936 reference AA5 revision but if they were I may have the image trus`me


That other thing may be something if its off spec. with a (correct uf capacitor to output tube cntrl. grid we don't have now ) . so maybe that should be shelved for now. especially if we look at the cap uf in there at output tube contrl. grid as opposed to spec that may be bigly over volting output tube cntrl. grid now like I think it is and I see +6V on my DVM .


I can verify so far the 50C5 output tube control grid input is indeed +6V and the output tube 50C5 GE tube data spec is specifically 0 to neg volts with no mention at all about the cathode only at a brief glance of pin out volts .

AVC /First Audio and Output tube and first IF amp tube heater and plate volts are fine.


I did not read the diode plate voltages at the 12AV6 First Audio AVC Duplex Diode Triode that are wired to each other in the radio and the VOL pot is not deaf anyway so probably nothing to see there given the vol pot is ranging normally and phone volume is normal but lots of distortion that may be something else ,a tube or one of the caps I ordered .

I am sure if I had the parts and tubes like you surely have in your workshop this radio would be done ,

So that where it ends for me until I get my NOS tubes and or the caps on order, beyond that ,maybe tomorrow now the clever one at a time tube pull with alligator clip tube pin heater leads you mentioned I have the leads here at the ready

Edit:

oh you have any photos here or at the usual spots of your hoarders conflagration of electronics refuse or is it a nice tidy 200 radio collection?