Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Vintage TV & Radio Tech Forum

We appreciate your help

in keeping this site going.
Closed Thread
 
Thread Tools Display Modes
  #1  
Old 08-10-2017, 01:09 AM
tubetwister tubetwister is offline
Banned
 
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 01:18 AM.
  #2  
Old 08-10-2017, 09:41 AM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 8,996
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.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
  #3  
Old 08-10-2017, 12:14 PM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 5,782
Quote:
Originally Posted by Electronic M View Post
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.
There could be a H-K short in one of the tubes.
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.
  #4  
Old 08-10-2017, 06:46 PM
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 2,792
++ 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 !
  #5  
Old 08-10-2017, 11:23 PM
tubetwister tubetwister is offline
Banned
 
Join Date: Oct 2010
Location: west blue coast conservative
Posts: 163
Quote:
Originally Posted by Electronic M View Post
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.
Quote:
.Heck of a lot to respond to there...
Thanks for the plausible reply here

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:

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.
If you unplug the radio playing normally the hum vanishes instantly while it still plays .thus the heater/line cord hum leakage you brought sounds plausible but I'm thinking more heater leakage but both may be a good place to look ,thank you again



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 10:07 PM.
Audiokarma
  #6  
Old 08-11-2017, 12:18 AM
tubetwister tubetwister is offline
Banned
 
Join Date: Oct 2010
Location: west blue coast conservative
Posts: 163
Talking

Quote:
Originally Posted by zeno View Post
++ 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 .

Last edited by tubetwister; 08-11-2017 at 12:53 AM.
  #7  
Old 08-11-2017, 01:31 AM
maxhifi's Avatar
maxhifi maxhifi is offline
VideoKarma Member
 
Join Date: Dec 2010
Posts: 1,347
1. Try substituting the tubes with new ones, to rule out heater to cathode leakage.

2. Verify that the new capacitors are grounded to the same point as the original can, this can be critical.

3. Verify the "across the line capacitor" is good and connected properly

4. Check if the volume control is bad, jumper the middle and negative terminals of the volume control to see if hum goes away.
  #8  
Old 08-11-2017, 02:49 AM
tubetwister tubetwister is offline
Banned
 
Join Date: Oct 2010
Location: west blue coast conservative
Posts: 163
Quote:
Originally Posted by zeno View Post
++ 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

Last edited by tubetwister; 08-15-2017 at 10:10 PM. Reason: tidy
  #9  
Old 08-11-2017, 03:13 AM
tubetwister tubetwister is offline
Banned
 
Join Date: Oct 2010
Location: west blue coast conservative
Posts: 163
Quote:
Originally Posted by maxhifi View Post
1. Try substituting the tubes with new ones, to rule out heater to cathode leakage.

2. Verify that the new capacitors are grounded to the same point as the original can, this can be critical.

3. Verify the "across the line capacitor" is good and connected properly

4. Check if the volume control is bad, jumper the middle and negative terminals of the volume control to see if hum goes away.
Thanks and all good points

1. All new NOS tubes will be ordered before I log off windows 10 and rolled in one at a time to eliminate an offending tube if any out of the lot of (4) and all rolled in anyway like I intended before I bought the radio .



2. Cap grounds are grounded to same as OE and double checked ,


3. AC line cap seems to be OK but I don't have a CAP tester and maybe should replace it anyway and probably will . I thought about that and may have it on my Cap order and if not I will get one .

4. Volume plays and works fine outside of a too loud to allow at low volume AC hum but there's a specific and notorious suspect .001 film cap there I will replace and Yes I can jumper the pot anyway . maybe the pot is leaking an ac potential or DC ripple in to the audio path , good point but the hum amplitude is constant and actually garbles speech at lowest volumes .
  #10  
Old 08-11-2017, 10:01 AM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 8,996
I have seen 2-3 AA5 sets with field coil electrodynamic speakers, not common, but some did it.

What matters with the output grid is that it be negative with respect to the cathode. One thing you can do is connect a large cap (.22-10uF) between the output grid and signal ground to bypass any hum from proceeding stages to ground, then put the meter common lead on the grid and the hot lead on the cathode...That should give you a positive voltage indicating the cathode is positive WRT the grid and that the grid is negative WRT cathode.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
Audiokarma
  #11  
Old 08-11-2017, 08:36 PM
tubetwister tubetwister is offline
Banned
 
Join Date: Oct 2010
Location: west blue coast conservative
Posts: 163
Smile

Quote:
Originally Posted by Electronic M View Post
I have seen 2-3 AA5 sets with field coil electrodynamic speakers, not common, but some did it.

What matters with the output grid is that it be negative with respect to the cathode. One thing you can do is connect a large cap (.22-10uF) between the output grid and signal ground to bypass any hum from proceeding stages to ground, then put the meter common lead on the grid and the hot lead on the cathode...That should give you a positive voltage indicating the cathode is positive WRT the grid and that the grid is negative WRT cathode.

lacking a new tube set delivered yet the common mode fixed hum daig.process is going slow at least at my chosen path given I am chasing a possible tube heater /cathode fault .

Using my secondary phones for a signal tracer at C15 to VOL pot distorted audio and same fixed hum,16 away from Vol pot same result

@above testing update the tell is the hum bogey is ahead of the beam power final tube ,or into the 50C5 tube or one tube back as I interpret the results and ofc the 50C5 control grid cap and signal needs to be fixed and at least have the correct uf capacitor if nothing else ,

Note today thd+n is virtually and suddenly making the radio nearly useless , no change @common mode fixed hum!
Maybe a deteriorating tube or discrete circuity part is my guess without an ouija board or a wise leprechaun LOL

Update 08.11.2017 17:27 PDT .


Hum diag . For bad tube leaky heater or H C short @ a tube I can pull tubes one by one power [up ] (only after the other heaters cool so you dont over volt a heather and fry a tube electronics 101 heat vs restive load EZ peay s B4 Univerity study too ! ) ag if i use alligator clip to puled tube hater pins I first though of decades ago in one of these but it was the Lytics !


I have a testing update and the tell is the hum bogey is ahead of the beam power final tube ,or into the 50C5 tube or one tube back (or more ) as I interpret the results and ofc the 50C5 control grid cap and signal needs to be fixed and at least have the correct uF capacitor if nothing else ,

Note today thd+n is virtually and suddenly making the radio nearly useless , no change @common mode fixed hum!
Maybe a deteriorating tube or discrete circuity part is my guess without an ouija board or a wise leprechaun LOL

lacking a new tube set delivered HERE the common mode fixed hum daig.process is going slow at least at my chosen #lazyfair slow path given I am chasing a possible tube heater /cathode fault .but the new tubs > sWill fix that anyway if that is prob

Using my secondary phones for a signal tracer at C15 to VOL pot distorted audio and same fixed hum,C16 away from Vol pot same result




.O

4. lacking anthing better like a signal tracer I got creative or started tweaking without chemicals who knows ? I used my Sennsheiser HD 280 secondary headphones for an audio signal tracer for audio and hum .

Result : same as above Distorted audio same fixed hum @ Vol Pot C15 ,C16

ofc . This AC-DC AA4 Hallishafters S120 is just a a nostalgia bedside radio for me ,a mid century adolescent bedroom trophy or brand starter radio and a nearly deaf SWL radio anyway .that would be outlawed today .

I bought it for what it is ,not what it is not ,or never will be :!:

I came up on that generation and been in more than few tube radios ~but not much tube action since 1970!

Last edited by tubetwister; 08-15-2017 at 10:24 PM. Reason: tidy
  #12  
Old 08-11-2017, 10:07 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 8,996
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.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
  #13  
Old 08-12-2017, 12:32 AM
tubetwister tubetwister is offline
Banned
 
Join Date: Oct 2010
Location: west blue coast conservative
Posts: 163
Quote:
Originally Posted by Electronic M View Post
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).



Quote:
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







,

Last edited by tubetwister; 08-15-2017 at 11:26 PM. Reason: tidy and update
  #14  
Old 08-12-2017, 12:16 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 8,996
Quote:
Originally Posted by tubetwister View Post
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.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
  #15  
Old 08-12-2017, 12:38 PM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 1,851
Quote:
Originally Posted by Electronic M View Post
...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.

Last edited by old_coot88; 08-12-2017 at 03:09 PM.
Audiokarma
Closed Thread


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 07:19 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.