Hallicrafters S120 hum at no vol and hum with volume

[zeno]

++ on H-K short. recently had a Zenith AM-FM with a shorted
12BA6 IIRC. Hum & distorted audio.
Warm up & pull each tube one at a time EXCEPT audio out & see
if one makes it go away. After that its checking any new work
for proper values etc. EVERYBODY makes mistakes !!
BTW the rectifier should have a dropping resistor after it & the
selenium unhooked at one end.

73 Zeno
LFOD !

[tubetwister]

Originally Posted by zeno

++ on H-K short. recently had a Zenith AM-FM with a shorted
12BA6 IIRC. Hum & distorted audio.
Warm up & pull each tube one at a time EXCEPT audio out & see
if one makes it go away. After that its checking any new work
for proper values etc. EVERYBODY makes mistakes !!
BTW the rectifier should have a dropping resistor after it & the
selenium unhooked at one end.

73 Zeno
LFOD !

+++ thats sounding plausible along with the tube heater leak .

the audio distorts at lower volumes but I think thats hum garble and not so much thd+n although that present thd + n may get some improvement that won't hurt at all with the tubes in any case and if the crummy and small midcentury alnico speaker can produce cleaner audio that is .



OTOH there is a high thd+n result going on I don't recall on some other AA5 but I did not associate that with the hum given the crummy even for a comm radio speaker in there in a less than ideal metal box and you all may be onto something here.


The radio is getting all new NOS maybe same brand tubes either way ,they are also less or same as the new ,tube store tubes but they arent spendy audio tubes or RCA black plates that IMO aren't any different sounding from a GE grey plate and I had a lot of them off the jobber store shelves back in the day and we didn't worship a GE 6L6 vs black plate RCA we never thought was anthing special or the various name brand 5886 & other tubes vs another name brand


OTOH we didn't mind a same tube output section or matched tubes and output tube bias accordingly or in any case appropriate on the PP and PP /PP amps ,

AFAK the MTBF on all that was not a wide variance @ a name brand consumer grade tube /consumer OEM unless a company has a known dog tube or line of tubes like some of the CRT and specifically IIRC moto (Motorola ) 24" color CRT .

RCA , GE & the others made re labeled and print screened tubes for any number of reasons and the JAN tunes ( Joint Army Navy) and TV /Radio brand tubes and tubes outside of tube # product coverage for each other too .


OTOH the exotic metal cable audio fools outside of legitimate matched tube rolling and BIAS accordingly on the outputs think they can hear the black pate RCA & exotic cable swindler speaker wires and other hi zoot cables ,garden hose AC cords in a 15A Romex circuit on a public utility ,HUge power conditioners on a well designed and large spendy monoblock amp and spendy data cables too

That said tonite I will order and install the NOS tubes upon arrival before anthing else ordered already given all that facts and wisdom here and the in spec. voltages outside of the 50C5 control grid and wrong uf cap there at the control grid .

[tubetwister]

Originally Posted by zeno

++ on H-K short. recently had a Zenith AM-FM with a shorted
12BA6 IIRC. Hum & distorted audio.
Warm up & pull each tube one at a time EXCEPT audio out & see
if one makes it go away. After that its checking any new work
for proper values etc. EVERYBODY makes mistakes !!
BTW the rectifier should have a dropping resistor after it & the
selenium unhooked at one end.

73 Zeno
LFOD !

Thanks I will unhook the selenium rect. and maybe put in the obligatory resister I noticed was not there but...............,

Again I will order a tube set tonite and it goes in before the other except maybe the CORRECT uf 50C5 cnrtl .grid film cap & maybe the notorious .001 volume pot film cap in those Hali. S120 .

FWIW I checked the values of installed replacement parts already and the related wiring and anything that may stand out as odd in general like that and I cut the B+ leads on the OLD Filter Caps the seller left in with the new Lytics in parallel .


Edit
FWIW I'm not accustomed anymore to a prolonged warm up I haven't timed but it's longish on this Hallicrafters, I think even for 5 or 17 tube like my HQ 170a I had so maybe there is a dog tube in there or it's a typical AA4 /AA5 warm up I don't recall but its only a 30 sec warm to play anyway

Again I found and will correct a wrong .0046 uf mica cap at the 50C5 beam power tube control grid noted above and its definitely a factory boo boo and pretty much any AA5 final tube control grid will have the correct .001-.002 film cap there anyway given that a 1935 AA5 is basically a 1965 AA5 ouside of maybe a PM speaker on later AA5 's but I never saw an electro magnet speaker AA5 or pre war AA5 IIRC .

I only tinkered with and owned the larger 1937-1939-1948 table top (tombstones ) and console Zenith all wave's or late 40's console AM/low band FM. and later mid century stuff ,console pulls and better and my happy days jukebox /45rpm record grinder