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Old 08-10-2017, 12:09 AM
tubetwister tubetwister is offline
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Join Date: Oct 2010
Location: west blue coast conservative
Posts: 163
Hallicrafters S120 hum at no vol and hum with volume

1.Working Hallicrafters S120 hum at no vol and hum with volume but radio plays decent apart from "some" hum and is very noisy with any volume on standby so something else is leaking in there on [standby] but not exactly only a 60 Hz hum but if confined there I wont sweat it .


2.All results are with BFO [OFF] and the best AC plug in polarity ,

3. History Ebay score for notalgia bedside AM /SW radio not serious SWL it's only an AA4

4.Hallicrafters S120 AA4 radio has 4 new 4 Filter Caps a Diode across the Selenium rectifier ,old filter caps NOT connected ,I snipped all the old leads at the other ends .

5.Potentially affected by new rect. Diode B+ and heater voltages are in range as is the 121 VAC at power [on] after inrush current.

6.@ no volume and receiving hum is too loud IMO or I am "mis remembering" how AA5 were 40-50 yrs ago but I think this one is too loud but I have fixed much worse 4+ decades ago .noting thats about the last time I was in a vacuum tube radio circuit working at a Magnavox AD on the bench part time .ultimately into an unrelated more interesting and more $ career

I am retired decently now and plausible cash or reasonable new toy cash is no impediment as long as it's not a supercar or a spendy yacht

6a. Lots of extraneous noise if you raise the loudness at all in [stand by] maybe something else is also leaking in from 12AV6 AVC 1st audio in standby but I will change the mid century .001 film film cap at the Vol. pot also

7. **** Question should 50C5 control grid one volts be checked at a normal loudness on a stable Am broadcast station or volume all the way down noting max voltage tube data is 6 volts on control grid one if I read it right but I think I checked it both ways @~6v maybe half wave DC leakage ? I will replace the cap anyway its in the audio path and the wrong uf value

8a. 50C5 - AA5 reference radio and this radio diagram calls for .001 -.002 film cap at 50C5 grid one and its an .0046 Mica disk that matches others in radio from new ,maybe this thing always hummed because of that or no?


9. The signal is plenty audible over the hum at mid to elevated loudness like an old AA5 with (some hum) and not unusable & IIRC & a half wave AA4 /AA5 radio will not be pristine anyway.but IMO this one should be cleaner for a spendy AA4 noting the 1965 $69.95 MSRP is ~ $710.00 in 2017 and it won't pass a UL cert. today

10. Again maybe I forgot how these old dogs can be but if I can clean the hum ,that will be fine

11. It has an RF/IF align so I will leave those signal path caps in the RF/IF alone


12. ( opinions on this stuff especially the NOS tubes, cap upgrades & .0047 50C5 coupling cap for hum on recive & maybe STBY noises ), probably a new orange drop for that and where applicable

13. This AA4 radio is practice for a pre war Zenith 8-10 tube (chassis I hope ) and or a Zenith T.O. H500 ,

14. I may be open to modding the Hallicrafters a bit also if it can justifiably improve reception on AM /SW and maybe SSB but I have a simple SDR rig and webSDR for that and difficult reception.along with a chinese rubbish "Grundig" S450DLX PLL tuned field radio I picked up actually a NIB as a "refurb" for $26.00 at Amazon and an AA4 can only do so much .

I had 2 Hallicrafters S38 I cobbled into one good one in high school so I know the AA4/ AA5 gen. coverage drill here and I've had boat anchors also that could probably split one RF KC on CW and to just borderline intelligible AM or SSB all day and stable with maybe 17-18 tubes in my HQ 170 comm radio I sold to a friend .

SWL Antenna is a rudimentary 100' end fed long wire with separate antenna earth ground and soon Coax lead in and maybe a 9:1 Balun or no ?

regards

Last edited by tubetwister; 08-10-2017 at 12:18 AM.