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#1
08-10-2017, 08:41 AM
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Heck of a lot to respond to there....
Quick hum diagnosis tip. If you can disconnect the B+ with a lytic still in circuit giving a couple secs B+, but keep the heaters going on AC if the hum persists when the B+ is disconnected from AC that indicates heater/line cord hum leakage (or perhaps field coil issues if it does not use a PM speaker). If hum seems to be in the heater circuit try unplugging the set and see if it hums for the second or two it runs with the plug pulled. Standby usually cuts off B+ while leaving heaters on. If audio/hum persists in standby then there is something wrong with the standby mode.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
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#2
08-10-2017, 11:14 AM
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The circuitry is the same as the earlier Hallicrafters models, except for the rectifier circuit and heater drop. The year earlier models used a 35W4. Why they did it that way is anyones guess! It couldn't have been a cost savings. The Hallicrafters sets of this type were very insensitive on the high band. IIRC, in that model, the standby switch will only cut the B+ to the plates and screens of the converter and IF tubes. |
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#3
08-10-2017, 05:46 PM
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++ 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 ! |
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#4
08-10-2017, 11:18 PM
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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 . Last edited by tubetwister; 08-10-2017 at 11:53 PM. |
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#5
08-11-2017, 01:49 AM
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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
Last edited by tubetwister; 08-15-2017 at 09:10 PM. Reason: tidy |
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#6
08-10-2017, 10:23 PM
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Aside from my old man rambling and way to wordy OP ..Nothing complex at all here but no answers or opinions to my specific questions but in all fairness maybe better answers now but it's only an AA4 aka AA5 radio without a diode tube > 1961 to 1965 Hallicrafters S120 and any USA mid century vintage radio enthusiast or old dog enthusiast like me should know what it is and the preceding S38 full AA5 radio and the late 1930's Zeniths and some others and the boat anchors ofc OTOH millennials maybe and probably not just because of timing  We should all know those and the rest were PM speakers for ~ decades prior to 1965 like maybe a Catalin madness or Plastik AA5 radio or '40's Zenith T.O. anyway apart from a 1952 Seeburg 100 B happy days juke box I owned , salvaged and repaired in H.S with good tunes and usually up to date selection labels. Beyond multiband tuning coils , a BFO and such ,a phono plug or a treble cut a 1935 AC/DC - AA5 AA5 is an 1965 AC/DC - AA5 /AA4 but with a PM speaker and mid century 7 pin small tubes on the latter. Quote:
Apart from the standby noise at any volume, above zero ( fault there too or unlikely related fault ) ................................, I'm thinking common mode AC hum may be DC ripple or heater/cathode ,hum is present at both REC and STBY maybe a faulty no name new lytic of three or all of them the Pay Bay seller put in and or AC potential leak in the B+ or any DC or audio grid or something in there OTOH NOW that I remembered the hum clears at unplug [ON],maybe a cathode or (heater leak like you brought) in a tube or HK short in a tube diesel jeep mentioned here . Even with the unplug [on] result may be pointing away from the Lytics if I am thinking well I will put my DVM on ACV at B+ and DC and see what I can but I don't know the AA5 tolerance for that like 1.0- 1.5 volts on an automotive alternator . Variable amplitude and cadence with volume Standby noise is in addition to common mode AC hum at STBY and REC. but not an issue if REC is unaffected here ,its never going to be valuable radio on the 21st century AFAIK anyway and a lot of pay bay sellers are asking high on these. IMO,they may think it's really a decent SWL radio STBY noise is like an uncontrolled variable @ loudness control. oscillation (s) and maybe harmonics @ not a stable one as you vary the loudness pot and at the schematic STBY switch doesn't seem to open the Plate B+ @ any tubes but more something at AVC 1st audio tube (or to it ) to the volume pot or .001 film cap there but maybe from the AVC /first audio tube or IF but not a control grid or plate I need to revisit the official schematic .pdf here about that. but AFAIK looking at the dia. STBY SW . is definitely NOT tube plate voltage interrupt in the schematic keeping in mind this goes back 4+ decades for me and I was never into AA5 beyond a typical and nearly deaf Hallicrafters . S38 AA5 and more deaf National radio S54 and just Lytic caps ,dial lamps and tubes and on those & new strings on the S38's . the S120 will be getting a bandspread tuning string also . The common mode hum is maybe leaking in after the standby SW or just included somehow , Beyond that I read the .001 film cap at the Vol. pot can make these deaf or hum and commonly does . Maybe importantly the 50C5 beam power control grid cap is supposed to be .001 uf Film cap in the S120 schematic and .001 uf -.002 uf at AA5 reference diagrams ,it is a .0047 Mica cap and definitely OE so whatever that cap is doing or not has been since day one and no opinion on that or NOS tubes just because of the age of the tubes and no emission tester here maybe I should wait or just put may caps on order in it and see if I want to change out the Lytics and (now) moreover the tubes before lytics depending on the results or my ouija board :-\ Again I am getting 6 Volts at the 50C5 beam power AF control grid instead of zero or (neg volts) specified Imagine all that and maybe a hum since new and an uniformed buyer perhaps or is that a stretch electronically ? Another question I posted is the zero to negative volts 50C5 beam power control grid voltage spec. valid at normal radio play volume power on or @volume [OFF] power [ON] or no? IOW do I need to close the volume pot for a valid result Last edited by tubetwister; 08-15-2017 at 09:07 PM. |
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Hybrid Mode
