Hallicrafters S120 hum at no vol and hum with volume

[Electronic M]

When you say last and first tubes in the string that is rather vague...Better to refer to them by their functions: converter(AKA 1st detector), IF, Second detector/AVC/1st audio, audio output (at least that is what the line up would usually consist of in an average selenium powered AA4).

Do you have any clip leads (that have small alligator clips on both ends)? You can pull a tube (google it's data sheet to find the heater pins) and use 2 clip leads to reconnect only the heater leads to the circuit....It is simpler than using a light bulb. Avoid using the light bulb as a substitute heater the bulb has to have the same voltage drop and current rating as the factory heaters or it will not work (and it could burn out the other tube heaters).

Got a diode and a small cap .001uF or less? You can make an AM signal tracer easily just use the diode as a detector and the small cap to filter RF out of your listening device. You can even add an amp* between the detector and the listening device.

*Make sure the amp is battery powered or that there is a power line isolation transformer powering the radio.....If you neglect that then you could create false hum from connecting devices with different signal ground references, and or damage the devices.

[tubetwister]

Originally Posted by Electronic M

When you say last and first tubes in the string that is rather vague...Better to refer to them by their functions: converter(AKA 1st detector), IF, Second detector/AVC/1st audio, audio output (at least that is what the line up would usually consist of in an average selenium powered AA4).

Do you have any clip leads (that have small alligator clips on both ends)?

EDIT 08.15.2017
Yes and more and lots of solid state ( SS experience ) note my education futher down


Noting you must let ALL the tube heats cool B4 next power up lest you fry a tube or are stupid and lucky but the rest of it is 4 + decades OLD NEWS but the AA5 radio back then had bad LYITCS as I suspected the reason > AC hum much Much LOUDER than this RaDiO !

This hum is forward of of the DUAL TRIODE FIRST AUDIO /AVC 12AT7 PARALLEL WIRED DIODE PLATES or maybe 1st audio cntrl.grid if you happen to know what all that is


FWIW I was reading tube DATA and building projects (transformer powred ofc) out of RCA tube manual ref. designs we all used 4 decades before you were conceived & later getting proper EDUCATION

I dont mean a vocational certificate diploma mill or High school but >>>>>> Electronics and Solid State Engineering study but not tube radios there LOL .......maybe NIXI tubes on some counters or just to make something red hot explode or melt for a prank or some lessons but not many


TBH I was humoring you
.
4 NOS tubes and circt. parts arriving soon may fix all this while your sig trce Detector diode idea is very good and detailed
I am too to lazy ti gin up a proper circuit trace jimmy rig in an Altoids Tin ,with a diode DETECTOR probe capacitor uF like you say that can discern an AC hum ,an OP amp, a battery and buffer caps & whatever for a Ti PDIP- 8 op amp .


I have it covered note my edu. and now that I spent some-refresh- tine with the schematics ...I can read these old crude AA4-AA6 circt. diag.and figure them out ...........SRSLY they basically haven't changed outside of the the tube sockets since 1936 BTW
h

and thank you for your rely

full stop







,

[Electronic M]

Originally Posted by tubetwister

Thanks for the tips and nomenclature it may be difficult for millennial and such to associate an AA4- AA5 front to final tube position to its function that you may know in your sleep that hasn't changed since ~ 1930 .

I can understand all that given that 1965 was the last AA4 tube radio for the brand at 52 yrs back which is a older than the oldest millennial by some decades .

I am lost on a lot of millennial apparatus outside of the usual stuff we all use and I remember how dreadful my first cell phone and FAX was to use

If by millennials your referring to me....Don't, I'm not like 99.9% of those around my age.

Also don't assume I'm not knowledgeable on tube radios. I've owned well over 200, worked on ~80% with a 95% success rate, and have over 130 presently...Not to mention all the tube TV work I've done.

I say vague on your pulling the first/last two in the string vs using the function names since you could be referring to the signal chain (which is a standard topology), or the heater string which does not need to be wired with the tubes in any fixed order.

[old_coot88]

Originally Posted by Electronic M

...the heater string... does not need to be wired with the tubes in any fixed order.

Um.. by convention, in a series heater string, the first audio tube is usually at the bottom (ground) end of the string to minimize hum pickup. The OP might want to verify that the 1st audio tube's heater is indeed at the bottom of the string, in regards to his hum problem.

(Edit) Also, the rectifier (e.g., 35W4 etc.) is conventionally at the top of the heater string to minimize heater-to-cathode voltage. The audio output (e.g., 50C5 etc.) is usually the next one down the string.

[tubetwister]

Originally Posted by old_coot88

Um.. by convention, in a series heater string, the first audio tube is usually at the bottom (ground) end of the string to minimize hum pickup. The OP might want to verify that the 1st audio tube's heater is indeed at the bottom of the string, in regards to his hum problem.

(Edit) Also, the rectifier (e.g., 35W4 etc.) is conventionally at the top of the heater string to minimize heater-to-cathode voltage. The audio output (e.g., 50C5 etc.) is usually the next one down the string.

^^^ Interesting and makes sense electrically unless the fundamentals have changed since I was in school

IIRC even some transformer heater wiring and lead dress was very specific in something like a boat anchor comm radio or spendy audio gear and a there were a only a few AA5 variants and virtually AA6 radios , the pre 1936 AA5 variants and the different tube envelopes & sockets for the same bloody AA5 circuits and the superior Zenith T.O. variants

Your edit that makes perfect sense . I tried to stay away from AA5 and AC/DC rubbish in the hobby but my 2 exceptions today are this deaf SWL specific model Hallicraftors S120 nostalgia radio for me and maybe a Zenith
Transoceanic H500 legitimate AA6 variant .


Benching TV & radios at a Magnavox AD when I was doing that there at 1967-1970 , Most of us understood a given signal path or output path tube order to function because you had to know it to fix the bloody things and where to start anyway .

we didnt have all these web forums and web sites or FUD

But your info here is not FUD .☺

EDIT 08.15.2017 20:30 PDT

I just assumed anyone replying to me would know the mid century AA4-AA5 tube order to function order correlation that hasn't changed much since 1936 and we had had to know all that in our sleep in school and how to to build an AA5 in the lab too .and that was H.S. advanced electronics lab before college which wasn't tubes anyway 3 periods a day BTY

[tubetwister]

Originally Posted by Electronic M

If by millennials your referring to me....Don't, I'm not like 99.9% of those around my age.

Also don't assume I'm not knowledgeable on tube radios. I've owned well over 200, worked on ~80% with a 95% success rate, and have over 130 presently...Not to mention all the tube TV work I've done.

I say vague on your pulling the first/last two in the string vs using the function names since you could be referring to the signal chain (which is a standard topology), or the heater string which does not need to be wired with the tubes in any fixed order.

EDIT :
without an electronics or EE education (~ 3yrs EE study at a universality like CAL State Electronics and Solid State Engineering study (like me) or bench tech experience (like me >part time + short timer ) and concomitant qualifications all that sounds like unqualified and hobby opinions to me and you are wrong about the heater wires ( I was informed below ) on these radios anyway stick to your day job mate






I

[old_coot88]

Dude, just to reiterate, check the heater wiring to verify that the 1st audio tube's heater is at the bottom (ground) end of the string. If it's not, it could be introducing hum downstream of the vol. control

[tubetwister]

Originally Posted by old_coot88

Dude, just to reiterate, check the heater wiring to verify that the 1st audio tube's heater is at the bottom (ground) end of the string. If it's not, it could be introducing hum downstream of the vol. control

that sounds plausible and also given that the factory put in the incorrect uf value output tube control grid cap,

SRSLY no joke and it exact matches mica caps all over that radio and its a .0046 uf Mica vs an .001 presumably film cap it's supposed to have there per the schematic and the AA5 reference design that can go to .002 uf also
who knows what else they did .

I'm obviously not an AA5 or even radio expert like most of you here , so the input is all good and teaching me thank's

During my career ,some of those screw ups and product were butt of inside humor or more or a PITA ,

IOW some misplaced wires would not suprise me in a USA mid century home radio ,they already put the wrong output tube cntrl.grid cap in that crude radio with 1936 AA5 budget model ciruits in a deaf SWL 1965 radio .


It's almost criminal and that radio or a AA4/AA5 would be today because it can electrocute us without much provocation ! You cant make that up

[dieseljeep]

Originally Posted by tubetwister

that sounds plausible and also given that the factory put in the incorrect uf value output tube control grid cap,

SRSLY no joke and it exact matches mica caps all over that radio and its a .0046 uf Mica vs an .001 presumably film cap it's supposed to have there per the schematic and the AA5 reference design that can go to .002 uf also
who knows what else they did .

I'm obviously not an AA5 or even radio expert like most of you here , so the input is all good and teaching me thank's

During my career ,some of those screw ups and product were butt of inside humor or more or a PITA ,

IOW some misplaced wires would not suprise me in a USA mid century home radio ,they already put the wrong output tube cntrl.grid cap in that crude radio with 1936 AA5 budget model ciruits in a deaf SWL 1965 radio .


It's almost criminal and that radio or a AA4/AA5 would be today because it can electrocute us without much provocation ! You cant make that up

I never worried about being electrocuted on a hot chassis receiver, as I've been doing it for over 60 years!
I also worked as an Industrial Electrician for 30 years, so I'm no stranger to even higher voltages.
I have one of those receivers in my warehouse, somewhere. I remember working on it and it had a floating B- line. Trying to remember if it's U/L listed.
On mine, someone replaced the 'lytic with a metal can type and installing it tied the B- to the chassis, which made it a shock hazard. I corrected that right away.
Those type of SWL receivers generally didn't sound that great, mainly they were made for speech or code reproduction and not really for music.
Also, that receiver was one of the last ones built in USA. They seemed to shift their production to Japan. Possibly, they used what left over!

[tubetwister]

Originally Posted by old_coot88

Dude, just to reiterate, check the heater wiring to verify that the 1st audio tube's heater is at the bottom (ground) end of the string. If it's not, it could be introducing hum downstream of the vol. control

I will add the common mode fixed AC hum and thd+n high distortion is present at VOL control center tap and other end presumably from the 12AT7 First Audio AVC dual-triode > Diode plates that are parallel wired in this radio.


Including the 2 Vol.pot caps and 50C5 final beam power tube correct uF cntrl.grid cap ,

I have 4 NOS not spendy tubes shipped and ~10 discrete circuit caps with the uF # @630v values from Hayseed Ham-fest ready made made cap kit parts listing for this radio but USA name brand caps not whatever they sell there and noting new Lytics are installed in this radio anyway so pricing was more favorable this way and total $2.50 USPS .


Instead of getting stuck up for small order at Amazon, E bay, Mouser or Digikey

I found them all cheap at Tube Depot store with the over priced tubes I wont buy there :LOL

If all that does not fix it I will jimmy rig a sig. tracer and diode detector with a Ti PDIP- 8 op amp and some buffer caps and a battery & whatever else it may I need all I probably have sine its nit tube radio stuff & I can use the Senns. HD280 phones and for the amp/tracer a capacitor /diode detector series probe for the radio sig path before AF conversion ofc with a cap uF verified that passes the AC hum and see if I can find the origination of the AC hum if it is not the bloody tube heater wire order you kindly informed me of ,they could have skewed that too , noting the 50C5 outpt. cntrl. grid cap is way wrong uF from factory ,will keep advised,

OTOH i could use my Schitt Audio Magni headphone amp it is very quiet and runs on DC wall wart .what do you think about that + diode and cap probe instead of op amp and maybe a cap on audio in to HP amp ground or no ?

full stop.

regards