Hallicrafters S120 hum at no vol and hum with volume

[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