emerson 20A

7/17/2014 5:15:39 AMfrank goddard

HI Folks.

I need to install a dropping Resistor to the tube line of a Emerson 20A.
I think this would require a 300 ohm 35 Watt one. If my calcs are good ( and I am poor at Math the best of times) this is going to get warm. Does anyone recommend the cap method for this filament inline dropping? If it is a good idea it may be one way to keep the set cool - although it does move away from origonality somewhat.

Many thanks.

Frank. Doncaster England.

7/17/2014 9:46:32 AMCV

Presumably you want to do this because the set is a 110V unit and you want to operate it on your 220V service.

If so, you might alternatively consider purchasing a 220-to-110 converter. These are not horribly expensive and are easy to find (I bought one from eBay a few years ago to operate a Holland-made radio which turned out to be strappable for 110V operation (oh, those sneaky Dutch!) Your Crosley is a comparatively low-power set, so you could get by with a smallish converter unit. Of course, if you bought a higher-power-capacity converter, that would enable you to play other American sets without needing to retrofit them internally.

If you want to use a "dropping capacitor", you will need to calculate the value of cap needed to achieve the desired voltage drop based on current draw of the set (as with the dropping resistor approach) at the prevailing AC mains frequency (presumably 50 Hz for UK). If you calculated 300 ohms of pure resistance was needed to drop 50% of the line voltage, you will need to find a cap that emulates this resistance with reactance. The formula for this would be Z=1/jwC, where w=(2)(pi)(frequency) or (2)(3.14)(50)= 314.2.
Solving for C, with Z=300 (your calculated resistance value) we get a capacitance value of (exactly) 10.6 microfarads or (practically) 10 uF. A nonpolarized electrolytic should work OK.

7/18/2014 11:14:49 AMfrank

Hi CV
Many thanks for the reply. I bought a UK to US converter. Only £5. About $8 US. It is quite a small unit and just plugs into the outlet just like a Phone Charger.
My concern however was with the tube line. The tubes do not drop 110 volt so Emerson put a resistance in line of 160 ohms. I did not want to replace this ( open circuit) because of heat problems. Emerson changed the entire tube line up later because of this. I wondered if a Cap dropper could replace the in line resistance and it is this calculation I have trouble with. The set is the 20A that can be used on 220/110/32 and 6 volts. It has a multi pin connector at the rear for various options.

thanks. Frank

:Presumably you want to do this because the set is a 110V unit and you want to operate it on your 220V service.
:
:If so, you might alternatively consider purchasing a 220-to-110 converter. These are not horribly expensive and are easy to find (I bought one from eBay a few years ago to operate a Holland-made radio which turned out to be strappable for 110V operation (oh, those sneaky Dutch!) Your Crosley is a comparatively low-power set, so you could get by with a smallish converter unit. Of course, if you bought a higher-power-capacity converter, that would enable you to play other American sets without needing to retrofit them internally.
:
:If you want to use a "dropping capacitor", you will need to calculate the value of cap needed to achieve the desired voltage drop based on current draw of the set (as with the dropping resistor approach) at the prevailing AC mains frequency (presumably 50 Hz for UK). If you calculated 300 ohms of pure resistance was needed to drop 50% of the line voltage, you will need to find a cap that emulates this resistance with reactance. The formula for this would be Z=1/jwC, where w=(2)(pi)(frequency) or (2)(3.14)(50)= 314.2.
:Solving for C, with Z=300 (your calculated resistance value) we get a capacitance value of (exactly) 10.6 microfarads or (practically) 10 uF. A nonpolarized electrolytic should work OK.
:

7/18/2014 3:10:09 PMfrank

:Again CV.

Made a mistake. The Emerson dropper was 305 ohms and not 160 as I put previously.

Frank
:
:
:Hi CV
:Many thanks for the reply. I bought a UK to US converter. Only £5. About $8 US. It is quite a small unit and just plugs into the outlet just like a Phone Charger.
:My concern however was with the tube line. The tubes do not drop 110 volt so Emerson put a resistance in line of 160 ohms. I did not want to replace this ( open circuit) because of heat problems. Emerson changed the entire tube line up later because of this. I wondered if a Cap dropper could replace the in line resistance and it is this calculation I have trouble with. The set is the 20A that can be used on 220/110/32 and 6 volts. It has a multi pin connector at the rear for various options.
:
:thanks. Frank
:
:
:
:
::Presumably you want to do this because the set is a 110V unit and you want to operate it on your 220V service.
::
::If so, you might alternatively consider purchasing a 220-to-110 converter. These are not horribly expensive and are easy to find (I bought one from eBay a few years ago to operate a Holland-made radio which turned out to be strappable for 110V operation (oh, those sneaky Dutch!) Your Crosley is a comparatively low-power set, so you could get by with a smallish converter unit. Of course, if you bought a higher-power-capacity converter, that would enable you to play other American sets without needing to retrofit them internally.
::
::If you want to use a "dropping capacitor", you will need to calculate the value of cap needed to achieve the desired voltage drop based on current draw of the set (as with the dropping resistor approach) at the prevailing AC mains frequency (presumably 50 Hz for UK). If you calculated 300 ohms of pure resistance was needed to drop 50% of the line voltage, you will need to find a cap that emulates this resistance with reactance. The formula for this would be Z=1/jwC, where w=(2)(pi)(frequency) or (2)(3.14)(50)= 314.2.
::Solving for C, with Z=300 (your calculated resistance value) we get a capacitance value of (exactly) 10.6 microfarads or (practically) 10 uF. A nonpolarized electrolytic should work OK.
::
:
:

7/18/2014 5:56:41 PMCV

The Riders schematic for the 20-A doesn't show any circuitry that would allow the set to operate on other than 115V AC or DC; is your set an "export" variant? Since I don't have that info, I'll assume that you can configure your set to operate off 115V (AC).

All four tubes in this set have 6.3 V heaters and are series-wired, so they drop a total of 25.2 volts. String current is 0.3 amps (from the tube datasheet). That means that the 305 ohm resistor is dropping (305)(0.3)= 91.5 volts. You NOTIONALLY should be able to replace this resistor with the aforementioned 10uF nonpolarized capacitor, using the calculations shown earlier. This mod would restrict operation to AC only, which probably is a "don't care" these days.

Will it work? Probably, but only for a very short time. Any way you slice it, whether you have a purely resistive (i.e., a resistor) or a purely reactive (capacitor) dropping element, you are going to be passing 300 mA continuously through it and dropping about 90 volts across it. That's a lot of power (30 watts!) for a single part to dissipate. Also, when the cap finally shorts out (as they are wont to do when overloaded) it will instantaneously vaporize the weakest tube heater in the string.

7/19/2014 10:48:48 AMfrank

CV
As ever you are a great help. My radio probably is an Export Model. In fact about 80% of my collection are export models and many of these are from the 'lend lease' period; 1940 to 1950.And others no doubt arrived in the suitcases of servicemen stationed here.Of which there are still many, particularly USAF.It is the proliferation of US made radioshere, particularly the AA5's that first caught my interest in collecting.
I think I will go for a replacement resistor fixed to the side of the chassis as the existing one is. It worked when first designed so for demonstration use it will be OK I am sure.I have access to Motor Start caps and these are quite robust for Voltage Dropping but not for this set I think,

Thanks again Frank

:The Riders schematic for the 20-A doesn't show any circuitry that would allow the set to operate on other than 115V AC or DC; is your set an "export" variant? Since I don't have that info, I'll assume that you can configure your set to operate off 115V (AC).
:
:All four tubes in this set have 6.3 V heaters and are series-wired, so they drop a total of 25.2 volts. String current is 0.3 amps (from the tube datasheet). That means that the 305 ohm resistor is dropping (305)(0.3)= 91.5 volts. You NOTIONALLY should be able to replace this resistor with the aforementioned 10uF nonpolarized capacitor, using the calculations shown earlier. This mod would restrict operation to AC only, which probably is a "don't care" these days.
:
:Will it work? Probably, but only for a very short time. Any way you slice it, whether you have a purely resistive (i.e., a resistor) or a purely reactive (capacitor) dropping element, you are going to be passing 300 mA continuously through it and dropping about 90 volts across it. That's a lot of power (30 watts!) for a single part to dissipate. Also, when the cap finally shorts out (as they are wont to do when overloaded) it will instantaneously vaporize the weakest tube heater in the string.
:

8/8/2014 3:54:10 PMfrank goddard

Thanks all for your advice with this radio. After some conversion from the multi voltage input options that were available I configured the set to accept just 120 via an in line UK/USA converter. The tube line uses however just 25 volts of the mains line. THe resistor I used for this is rated at 50 watts and bouy does it get hot. I think the set must have had a resistive line cord when first manufactured. So I am back to
using a Capacitor to drop the 95volts . This is where CV and his math comes into play. What size cap do I need to drop 110 volts to 95 volts with 0.3 amp current flow at 50Hz. With this 'hot spot' sorted the radio is a little beauty and performs rather well on a short antenna for a 4 tube TRF of some 85 years of age.

:The Riders schematic for the 20-A doesn't show any circuitry that would allow the set to operate on other than 115V AC or DC; is your set an "export" variant? Since I don't have that info, I'll assume that you can configure your set to operate off 115V (AC).
:
:All four tubes in this set have 6.3 V heaters and are series-wired, so they drop a total of 25.2 volts. String current is 0.3 amps (from the tube datasheet). That means that the 305 ohm resistor is dropping (305)(0.3)= 91.5 volts. You NOTIONALLY should be able to replace this resistor with the aforementioned 10uF nonpolarized capacitor, using the calculations shown earlier. This mod would restrict operation to AC only, which probably is a "don't care" these days.
:
:Will it work? Probably, but only for a very short time. Any way you slice it, whether you have a purely resistive (i.e., a resistor) or a purely reactive (capacitor) dropping element, you are going to be passing 300 mA continuously through it and dropping about 90 volts across it. That's a lot of power (30 watts!) for a single part to dissipate. Also, when the cap finally shorts out (as they are wont to do when overloaded) it will instantaneously vaporize the weakest tube heater in the string.
:

8/8/2014 4:41:22 PMPeter G Balazsy

Any way you slice it, whether you have a purely resistive (i.e., a resistor) or a purely reactive (capacitor) dropping element, you are going to be passing 300 mA continuously through it and dropping about 90 volts across it. That's a lot of power (30 watts!) for a single part to dissipate. Also, when the cap finally shorts out (as they are wont to do when overloaded) it will instantaneously vaporize the weakest tube heater in the string.
-----------------------------------------------

The dropping capacitor is considered a "WATT-less" device ( no heat) because current and voltage are 90 degrees out of phase with each other.

The dropper cap should work fine.

If you are dropping 90 from a 120vAC line...
Make sure the cap is non-polarized and rated at approx 200 VAC or more.

8/8/2014 4:52:24 PMPeter G Balazsy

If you need to end up with 25vAC @300ma from a 115vAC line
... I calculate that you'll require a 7uf cap @ 200vAC

There is a GREAT informative website that will explain the dropper-cap theory to you as well as other voltage dropping ideas.

And the author provides an XLS spreadsheet for you that you can download and do future calcs yourself.

The spreadsheet is at the very bottom of the page in this link:
http://www.vintage-radio.com/repair-restore-information/valve_dropper-calcs.html

8/8/2014 5:04:59 PMPeter G Balazsy

I forgot that you are operating with 50Hz not 60Hz.
So the correct dropper cap should be closer to 8uf @200vAC

8/9/2014 9:08:06 AMfrank goddard

Peter,

Many thanks. A great help

Frank

:I forgot that you are operating with 50Hz not 60Hz.
:So the correct dropper cap should be closer to 8uf @200vAC
: