Doug
:Help I'm choking here! (alright, it's a bad pun) After fixing numerous wiring problems and recapping a beautiful Emerson 108 - no easy task as I've never worked on a smaller, more compact chassis - I found the radio still dead! [tubes are good and so are voltages] So I checked output transformer and speaker coil, both OK. This radio uses a filter choke so I checked it and sure enough it's open. All I can get from the schematic is that it's a 500 ohm choke. I'm assuming that is plain resistance not inductive reactance. I don't know the inductance and am not sure if one of the chokes sold by AES or Radio Daze will work. What do I look for or calculate to get a replacement choke? With this chassis, size does matter, so I need to find one that will also fit. Any ideas?
With an open in the coil, how could I get a current measurement. I do use an volt/ammeter connected to my Variac when powering up radios and this one (with the bad choke) reads .34 amps @ 115vac. That gives me about 39 watts of power being consummed by a dead radio. So would I need 500 ohms of resistance with an 80 watt power rating??
Stephen
:The inductance isn't critical, but the DC resistance and current rating are. For the time being, you could substitute a power resistor with at least double the current handling capability of the amperage through it.
:Doug
Lewis
:Doug,
:With an open in the coil, how could I get a current measurement. I do use an volt/ammeter connected to my Variac when powering up radios and this one (with the bad choke) reads .34 amps @ 115vac. That gives me about 39 watts of power being consummed by a dead radio. So would I need 500 ohms of resistance with an 80 watt power rating??
:Stephen
::The inductance isn't critical, but the DC resistance and current rating are. For the time being, you could substitute a power resistor with at least double the current handling capability of the amperage through it.
::Doug
:
:Lewis
And, by the way, I don't know where you are reading this current, but is in the AC line? If so, you are reading the filament current, and 34 Watts would be just about right.
Lewis
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::Doug,
::With an open in the coil, how could I get a current measurement. I do use an volt/ammeter connected to my Variac when powering up radios and this one (with the bad choke) reads .34 amps @ 115vac. That gives me about 39 watts of power being consummed by a dead radio. So would I need 500 ohms of resistance with an 80 watt power rating??
::Stephen
:::The inductance isn't critical, but the DC resistance and current rating are. For the time being, you could substitute a power resistor with at least double the current handling capability of the amperage through it.
:::Doug
::
Yep it's the AC line current. Have no way of measuring current across the open filter. Problem is: how do I figure the power resistor size?...and could I use a cap in the circuit to get rid of some of the hum?
Stephen
:Yep it's the AC line current. Have no way of measuring current across the open filter. Problem is: how do I figure the power resistor size?...and could I use a cap in the circuit to get rid of some of the hum?
:Stephen
:
::Yep it's the AC line current. Have no way of measuring current across the open filter. Problem is: how do I figure the power resistor size?...and could I use a cap in the circuit to get rid of some of the hum?
::Stephen
Put your milliAmmeter across the open choke, and read the current (assuming there is nothing shouted that caused the choke to open). Then the power will be I^2 times R. it would be4 wise to double that value for the Wattage of the resistor.
Lewis
There is no current whatsoever across the open filter choke, must have more problems.
Stephen
For purposes of testing, why not as stated before, solder in a power resistor of around 500 Ohms resistance and probably 10 to 15 Watts or so power rating in the place of the open choke.
Radiodoc
**************
:Lewis,
:There is no current whatsoever across the open filter choke, must have more problems.
:Stephen
:
:
:For purposes of testing, why not as stated before, solder in a power resistor of around 500 Ohms resistance and probably 10 to 15 Watts or so power rating in the place of the open choke.
:
:Radiodoc
:**************
:
::Lewis,
::There is no current whatsoever across the open filter choke, must have more problems.
::Stephen
::
Doc, may I disagree? I think one Watt would be plenty. But, there is no current flowing through the choke (well, through the mAmeter substituting for the choke). Hmmmmmm. Something strange. Wake up, Watson, the game's afoot.
Lewis
:Stephen,
::
::For purposes of testing, why not as stated before, solder in a power resistor of around 500 Ohms resistance and probably 10 to 15 Watts or so power rating in the place of the open choke.
::
::Radiodoc
::**************
::
:::Lewis,
:::There is no current whatsoever across the open filter choke, must have more problems.
:::Stephen
:::
Making progress...found another wiring problem on output xfmr, fixed it (what a pain trying to maneuver around in this chassis!). Didn't have a 500ohm pwr resis so used a 10watt, 100ohm PR and voila! I have sound and even some tuning selectivity but with mucho hum. Current across pwr resis is no .81ma. Probably do need a choke to get rid of the hum, right? Also, this set requires a 1volt bias battery for the 75 detector tube. The original is the 30s version of a button cell, anybody ever use a modern 1.5v button cell as a replacement, or should it even matter?
Stephen
:Making progress...found another wiring problem on output xfmr, fixed it (what a pain trying to maneuver around in this chassis!). Didn't have a 500ohm pwr resis so used a 10watt, 100ohm PR and voila! I have sound and even some tuning selectivity but with mucho hum. Current across pwr resis is no .81ma. Probably do need a choke to get rid of the hum, right? Also, this set requires a 1volt bias battery for the 75 detector tube. The original is the 30s version of a button cell, anybody ever use a modern 1.5v button cell as a replacement, or should it even matter?
:Stephen
P.S. AES sells a filter choke that looks like it will fit physically. Specs are: 5 henries, 50ma, 400vdc max, 270 ohms resistance. What do you think?
The only current through L2 is the cathode current of the 43 tube (which is essentially the same as the plate current). Checking the RCA tube manual, max rated current through a 43 is 36 ma. So a 50-ma choke will be fine, but you need to add a series resistor to achieve a total resistance of 500 ohms.
For the bias cell, any battery with a long shelf life and more or less the correct voltage will be fine. It supplies no current, so should last as long as the shelf life.
Regarding the hum, have you replaced the filter caps?
Doug
::Lewis, Doc,
::Making progress...found another wiring problem on output xfmr, fixed it (what a pain trying to maneuver around in this chassis!). Didn't have a 500ohm pwr resis so used a 10watt, 100ohm PR and voila! I have sound and even some tuning selectivity but with mucho hum. Current across pwr resis is no .81ma. Probably do need a choke to get rid of the hum, right? Also, this set requires a 1volt bias battery for the 75 detector tube. The original is the 30s version of a button cell, anybody ever use a modern 1.5v button cell as a replacement, or should it even matter?
::Stephen
:
:P.S. AES sells a filter choke that looks like it will fit physically. Specs are: 5 henries, 50ma, 400vdc max, 270 ohms resistance. What do you think?
Thanks Doug, I've been at this too long, my RCA tube manual sits on the bookshelf unopened! Am going to go for the new choke with series resistor. Will also try a 1.5v button cell. Yes, I did replace the filter caps and double checked them again for polarity as in this circuit, the pos (+) side of the dual-section cap has a single lead while the neg (-) side has the two leads. Will update this once I get the new choke.
Stephen
You may try placing a 10 MFD or so cap across your choke substitute resistor rated at 100 volts or so. The caps plus lead goes to ground/chassis. This may reduce the hum while you test out the radio.
Radiodoc
**************
::Lewis, Doc,
::Making progress...found another wiring problem on output xfmr, fixed it (what a pain trying to maneuver around in this chassis!). Didn't have a 500ohm pwr resis so used a 10watt, 100ohm PR and voila! I have sound and even some tuning selectivity but with mucho hum. Current across pwr resis is no .81ma. Probably do need a choke to get rid of the hum, right? Also, this set requires a 1volt bias battery for the 75 detector tube. The original is the 30s version of a button cell, anybody ever use a modern 1.5v button cell as a replacement, or should it even matter?
::Stephen
:
:P.S. AES sells a filter choke that looks like it will fit physically. Specs are: 5 henries, 50ma, 400vdc max, 270 ohms resistance. What do you think?
:
:You may try placing a 10 MFD or so cap across your choke substitute resistor rated at 100 volts or so. The caps plus lead goes to ground/chassis. This may reduce the hum while you test out the radio.
:
:Radiodoc
:**************
:
:
:::Lewis, Doc,
:::Making progress...found another wiring problem on output xfmr, fixed it (what a pain trying to maneuver around in this chassis!). Didn't have a 500ohm pwr resis so used a 10watt, 100ohm PR and voila! I have sound and even some tuning selectivity but with mucho hum. Current across pwr resis is no .81ma. Probably do need a choke to get rid of the hum, right? Also, this set requires a 1volt bias battery for the 75 detector tube. The original is the 30s version of a button cell, anybody ever use a modern 1.5v button cell as a replacement, or should it even matter?
:::Stephen
::
::P.S. AES sells a filter choke that looks like it will fit physically. Specs are: 5 henries, 50ma, 400vdc max, 270 ohms resistance. What do you think?
::
::You may try placing a 10 MFD or so cap across your choke substitute resistor rated at 100 volts or so. The caps plus lead goes to ground/chassis. This may reduce the hum while you test out the radio.
::
::Radiodoc
::**************
::
::
::::Lewis, Doc,
::::Making progress...found another wiring problem on output xfmr, fixed it (what a pain trying to maneuver around in this chassis!). Didn't have a 500ohm pwr resis so used a 10watt, 100ohm PR and voila! I have sound and even some tuning selectivity but with mucho hum. Current across pwr resis is no .81ma. Probably do need a choke to get rid of the hum, right? Also, this set requires a 1volt bias battery for the 75 detector tube. The original is the 30s version of a button cell, anybody ever use a modern 1.5v button cell as a replacement, or should it even matter?
::::Stephen
:::
:::P.S. AES sells a filter choke that looks like it will fit physically. Specs are: 5 henries, 50ma, 400vdc max, 270 ohms resistance. What do you think?
:::
:::You may try placing a 10 MFD or so cap across your choke substitute resistor rated at 100 volts or so. The caps plus lead goes to ground/chassis. This may reduce the hum while you test out the radio.
:::
:::Radiodoc
:::**************
:::
:::
:::::Lewis, Doc,
:::::Making progress...found another wiring problem on output xfmr, fixed it (what a pain trying to maneuver around in this chassis!). Didn't have a 500ohm pwr resis so used a 10watt, 100ohm PR and voila! I have sound and even some tuning selectivity but with mucho hum. Current across pwr resis is no .81ma. Probably do need a choke to get rid of the hum, right? Also, this set requires a 1volt bias battery for the 75 detector tube. The original is the 30s version of a button cell, anybody ever use a modern 1.5v button cell as a replacement, or should it even matter?
:::::Stephen
::::
::::P.S. AES sells a filter choke that looks like it will fit physically. Specs are: 5 henries, 50ma, 400vdc max, 270 ohms resistance. What do you think?
I think, if I can figure out this new keyboard, that anky choke that will fit will work, and I disagree with adding a resistor to the B line to lower the Voltage. A 200 or 500 Ohm choke....there just isn't enough current to make much of a Voltage difference. It looks like you are about to repair a radio!
Lewis
A 43 tube draws around 45 ma. I would allow 20 ma for other tubes. Overall the supply can draw around 65 ma.
http://www.nostalgiaair.org/PagesByModel/543/M0004543.pdf
I would use a higher current choke. Problem being it will be lower resistance. This radio depends on resistance of the choke to generate bias voltage for your 43 tube. If you use a lower resistance choke add a wire wound resistor in series to make up 500 ohms.
Norm
:::Stephen,
:::
:::You may try placing a 10 MFD or so cap across your choke substitute resistor rated at 100 volts or so. The caps plus lead goes to ground/chassis. This may reduce the hum while you test out the radio.
:::
:::Radiodoc
:::**************
:::
:::
:::::Lewis, Doc,
:::::Making progress...found another wiring problem on output xfmr, fixed it (what a pain trying to maneuver around in this chassis!). Didn't have a 500ohm pwr resis so used a 10watt, 100ohm PR and voila! I have sound and even some tuning selectivity but with mucho hum. Current across pwr resis is no .81ma. Probably do need a choke to get rid of the hum, right? Also, this set requires a 1volt bias battery for the 75 detector tube. The original is the 30s version of a button cell, anybody ever use a modern 1.5v button cell as a replacement, or should it even matter?
:::::Stephen
::::
::::P.S. AES sells a filter choke that looks like it will fit physically. Specs are: 5 henries, 50ma, 400vdc max, 270 ohms resistance. What do you think?
What like…with the utter criticality of that choke coil ……with it and its associative filter cap being in the negative ground leg of the power supply.
Thereby, its DC resistive value along with its inductive value will be serving in a dual manner….with the reactance aspect providing filtering action, while simultaneously its resistive value holds the negative leg of the power supply above ground in order to additionally acquire a negative grid bias level to be routed up thru R11, R12 for the 1st grid biasing of the #43, since, in looking up at the AF output tube, you don’t see the presence of a cathode resistor, with that cathode being tied directly to ground, thus being dependant upon a separate negative biasing source.
If this was my set to repair, I would now be looking into the “open” choke aspect to see if the situation was initiated by
a connectivity issue at the coil winding leads to heavier service leads interfacing…or a glue shrinkage with time , placing the juncture under longitudinal stress at the fine wire and snapping it.
In utilizing the accompanying reverse anatomy of your type of choke construction during the final phase of assembly, visualize that there was the bobbin wound up with the fine wire and the fine magenta line representing the innermost start of the winding and continuing thru its multiple layers of waxed paper insulator separations until it finally ends up with the required turns and emanates as the fine green line.
For clarity, I purposefully did not do a phantom hiding of the terminal interfacing under the last final turn or two of the heavier over wrap.
On the final assembly there would be the isolative insulated vertical tape tab sticking up free, with the two over length fine winding wires..start and finish… sticking out the top of the unit. Then there is the very heavy paper / very light weight cardboard few turns of over wrap around the periphery and stopping with the length of one or two more possible final wraps to be made..BUT.. the heavier service leads are brought up and sometimes have very small width staple clips passing thru the cardboard/ heavy paper to anchor the spaced apart wires to them….or sometimes… an adhesive is used . The tinned fine wires are then twirled around the tinned service leads and re flow soldered. The vertical flap of tape is then pulled down and pressed down so that it covers the top end exposure of the fine wires.
So now, hopefully, you will pull out ye olde high power magnifier, along with a bright, high intensity light and find a micro tension break of one of the fine wire leads. With that being the nature of failure mode, rather than a very unlikely overload, and opening within an internal winding layer.
(Exposure to systemic erosion from exposure to meece /rat urine, also inclusive !)
Now if you have not done such surgery before…apparently not …..as for my procedure, I will take an Exacto knife with its surgical scalpel like #11 blade and note that the heavy lead wires that are between the last two turns of the over wrap, and that will be leaving somewhat of a spacing apart of them , in their going around the wires. That leaves a gap to work to the side /separate those final covering layers until the sharpened end of the blade ends up over to the red dot mark up [Surgical incision line] . Now that is OFF to the side, free of the presence of the critical wiring area, so that you can then rotate the blade 90 degrees such that the sharp tip / edge of the blade comes forward …towards yourself on the controlled lightly levered cutting action, that will slit the over wrap and then you repeat again, until the whole dotted length is opened.
THEN, you should be able to lever up and swing the flap over to the right and expose the wire terminals for a look see. Hopefully the fault will be with the outer “green” terminus, as that is the outer winding and you can pull up and get even more excess wire length from a turn taken loose, should that prove necessary.
Now on the other hand, that “green” wire lead has a predisposed finite length to work with, since it was the embedded start of the winding.
HOWEVER, I have repaired a lead that only had ~1/32 of an inch exposure, whereupon I took a single strand of bare copper wire from an AC line cord and tinned it and twirled one end around the heavy terminal lead wire and soldered it and then took the free end and measured the required short length to reach over to the sprig of intact winding wire showing. The copper wire end was then fashioned into a loop…like the eye of a needle… then that loop was positioned down and around the sprig of pre tinned winding wire using tweezers. The junction is then re flow soldered. The pre anchored left end of the copper wire lets one position its free end such that it will stay in place until the soldering is done.
On success of a repair I reseal the flaps with an adhesive that will permit reopening if required, in my case, contact cement, that can be dissolved with acetone-toluene-xylene-MEK –lacquer thinner..... if ever required. No super glues , epoxies or hard white glues.
If it is required to make resistive measurements anywhere between a terminal wire and along the fine winding wire, I will take ohmmeter leads in hand with the set up to low ohms scale and then grip an #11 blade only, with each ohmmeter lead connection and that will then permit an easy and sure connection to the heavy terminal lead…but more importantly… then doing a micro scrape of the enamel on the winding wire as per confirmation of positive continuity.
SO NOW…with nothing to loose…and a TON to gain…. pull out that choke coil and go ‘fer it.
Transformer frame / Windings / Terminal wires Reference / Illustration:
Standing by…..
73's de Edd
Wow, I'm still digesting this tome of inveterate wisdom re: chokes. I did, however, perform the micro-surgery you suggest (and my eyes are still recovering). Like you, I figured the most likely spots for the breaks would be where the coil wires are soldered to the leads. Under 10X power, I could find no such dislocations. I was even able to very carefully clean the varnish off of the coil wires up to the point of their disappearing into the layers of tape and check the continuity at these points - still open. I checked the continuity from the cleanded spots on the coil wires to the ends of each lead (to make sure I had good contact on the tiny coil wires with the ohmmeter probes) and had good continutiy. Unlikely as it may seem, the break is somewhere under the layers of insulative tape. Alas I must try the 270 ohm filter coil with 230 ohms in series resistor(s) to make up the difference. I will report the outcome in a couple of days - with joy if it works, and groveling for more assistance if it doesn't. Please stay tuned!
Stephen
Can't find anyone who sells a 2"mount U-frame filter with higher current rating, except one with 2000ma and only 0.3 ohms resistance (big coil wires!). This guy has minimal inductance at 6mH. Sounds like this wouldn't be much better than using a 500ohm power resistor with parallel cap (and I don't know how effective that would be at eliminating the hum.
Stephen
P.S. Wait a minute, Dave Frush at parts2many may have an original, think I'll e-mail him.
Here is a list of available chokes:
http://www.oldradioparts.com/2a23afl.txt
Norm
:Norm,
:Can't find anyone who sells a 2"mount U-frame filter with higher current rating, except one with 2000ma and only 0.3 ohms resistance (big coil wires!). This guy has minimal inductance at 6mH. Sounds like this wouldn't be much better than using a 500ohm power resistor with parallel cap (and I don't know how effective that would be at eliminating the hum.
:Stephen
:P.S. Wait a minute, Dave Frush at parts2many may have an original, think I'll e-mail him.
Norm is right.
I went to Gary's list of chokes at the address here:
http://www.oldradioparts.com/2a23afl.txt
And I found a 500 ohm 7 henry choke for you.
Here it is for... only $6
STANCOR C-1707
7H, 500 OHMS, 50MA,
FIG 3, NEW.. 1 x 2 3/8 x 1 3/8 x 1 1/4 $6.00
*4573-520 CHOKE
…..looks like you have looked at all options on that choke , stopping just short of disassembly and rewind. Which I have certainly done , and even starting from scratch to custom make up exactly what I needed in a transformer or choke.
… what with the copper pricing situation is now, In current days, I just might have a time finding proper gauge copper wire at an affordable pricing. Even the motor rewinding shops and the old timers with their old wire inventory have dried up in my locale.
I do remember that mentioned sourcing of transformers and even pulled up some transformer possibilities in the past, but when initially seeing that the massive unit inventory had been placed in storage density friendly notepad text format, I then opted to reformat that info into Excel Spread Sheet and helped some people in the past in the location of specific T-formers, with them not having to print out the 66 or so pages of crammed together info.
Now I have done a choke list and plugged in the magical number requirements with the 500 ohms of DC resistance being the initial qualifier
with some above and below leeway, in case the sole primer facto item which you need has already been
in the interim. You know and will then have to see if the physical dimension parameters of height x width x depth can fit your available space situation or if there can be some leeway for a units utilization.
I also included some of the closest DC resistance values just below the resistance also, just in case the stocked items have really been depleted down.
As for having to use chokes with resistive values just above that 500 ohm value, that can be incorporated via the utilization of a low Z …~1k resistive voltage divider bridge…. shunting the choke in order to then create and bring the developed negative grid bias supply back down to the desired negative 12-14 Vdc and bypass and feed it on up thru the high value series feeder resistors.
Color coding boxes explanation:
The red boxing is indicative of right on 500 ohms DC resistance, while the magenta coding is for units just slightly above 500 ohms DCR while the balance are potential last choice options.
Le Condense Inventorie:
THASSIT !
73's de Edd
Stephen
Having dealt with Gary at old radio parts (Play Things of Past PTOP) many times, it is indeed a gold mine of old radio parts, and he'll do his very best to help supply your needs at very reasonable costs.
marv
:You guys are amazing! I'd been looking at oldradioparts.net but not this site. This place could be a gold mine. Will give them a try and let you know the outcome. I'm feelin' really good about this project now - who wouldn't with all this expertise on tap!! Thanks!
:Stephen