I already posted this on ARF today ... but for those of you over here who don't also frequent that site I'm also posting it here:

I was working on a rusted out old Howard 220 with an open filament winding.
I wasn't sure if I really wanted to try to find ( read invest) in a new power transformer for this chicken-coop reject with a dilapidated cabinet to boot. So I decided to get creative.

It uses four 6.3 volt tubes = 6A7, 6D6, 75, and a 41 output tube plus a #47 pilot lamp.; all hanging off the 6.3 volt winding.

Now calculating a bit ... I look up in my tube manual and notice that the no. 41 tube draws 400ma and all the rest draw only 300ma each and of course the pilot lamp also draws 150ma. That's a grand total of 1.45 Amps.

So I started thinking about trying to use an easy substitute source for the 6.3v AC supply.

I didn't have a 6 volt filament transformer around...

So.... I wondered if I couldn't try the old "capacitor voltage dropper" concept.

There are a few write-ups on the net about using the dropper-cap idea to replace the "curtain burner" resistance line cords, as well as a great replacement for a ballast tube.

Those great sites show the math formula as well as a spreadsheet utility to do the calculations the easy way.

So I used the spread-sheet utility and plugged in my values of:
125 VAC= source
6.3 Vac = desired voltage
1.45 amps = desired current

and I came up with a capacitor value of a little over 30uf

But of course it should be an AC or non-polarized capacitor able to handle about 150vAC or greater.

So my first quickie choice was to grab two regular 60uf 450-VDC electrolytics back to back as a quick test.

So I connected the two 60uf caps back to back...
... and then put one hot-lead of my RAW 125vAC in one end and connected the other end via my amp meter to the filament string.
The other AC neutral lead clipped to the chassis ground.

With my AC volt meter across the filaments I hit the AC power switch waiting to see smoke.

Well all I saw was the little soft glow of the pilot lamp and filaments and all I heard was nice music.

Checking the AC volt meter I had a reading of just a tad over 6 VAC and the amp meter showed 1.4 amps.... GREAT... !!!
Guess that formula worked.... lol

So now for safety... I felt the caps and DID notice that they were just getting a tad warm ....as I was warned they might.

So I looked around my parts bins and dug up several lower value high voltage Solen brand, non-polarized caps and paralleled a few of those together to make up a total of 30uf.

Works like a champ.
No heat ... no problem.... radio plays nicely.

Now I can go on to finish re-capping and otherwise repairing and restoring this thing and decide later if ever to replace that power transformer!

Now someone at ARF asked why I didn't run the heaters in series.
I guess I could have but that would have meant re-wiring everything plus they all have 300ma except the 41 tube that uses 400ma and the #46 lamp only draws 150ma.

But (if they all only DID use 300ma) and then if I did decide to go that route ...I guess I could then also use a 300ma pilot lamp too and try running everything in series at 31.5 volts and 300ma.

Then I could use only a 6.7uf dropper cap.

However this way I don't re-wire anything allowing for an easy replacement of that power transformer one day or adding a filament transformer.
But in the mean time a few non-polar caps tucked under the chassis is not too noticeable.... and it's an easy ( though somewhat convoluted) trick. lol

Here are some reference site data.
There's a neat Excel spreadsheet to do the calculations at the bottom of the first link:

http://www.vintage-radio.com/repair-restore-information/valve_dropper-calcs.html

http://www.pbpix.com/radio/dropper-capacitor.html

Peter

Saw your posting on ARF. Interesting wonder why someone hasn't tried this before? Can't think of anything really wrong unless a tube burns out. Then the rest may also burn out?

Someone suggested wiring filaments in series. This would solve that problem.

Why is your filament winding open? They seldom open. Maybe just a bad connection when the winding meets output lead?

Norm

:I already posted this on ARF today ... but for those of you over here who don't also frequent that site I'm also posting it here:
:
:I was working on a rusted out old Howard 220 with an open filament winding.
:I wasn't sure if I really wanted to try to find ( read invest) in a new power transformer for this chicken-coop reject with a dilapidated cabinet to boot. So I decided to get creative.
:
:It uses four 6.3 volt tubes = 6A7, 6D6, 75, and a 41 output tube plus a #47 pilot lamp.; all hanging off the 6.3 volt winding.
:
:Now calculating a bit ... I look up in my tube manual and notice that the no. 41 tube draws 400ma and all the rest draw only 300ma each and of course the pilot lamp also draws 150ma. That's a grand total of 1.45 Amps.
:
:So I started thinking about trying to use an easy substitute source for the 6.3v AC supply.
:
:I didn't have a 6 volt filament transformer around...
:
:So.... I wondered if I couldn't try the old "capacitor voltage dropper" concept.
:
:There are a few write-ups on the net about using the dropper-cap idea to replace the "curtain burner" resistance line cords, as well as a great replacement for a ballast tube.
:
:Those great sites show the math formula as well as a spreadsheet utility to do the calculations the easy way.
:
:So I used the spread-sheet utility and plugged in my values of:
:125 VAC= source
:6.3 Vac = desired voltage
:1.45 amps = desired current
:
:and I came up with a capacitor value of a little over 30uf
:
:But of course it should be an AC or non-polarized capacitor able to handle about 150vAC or greater.
:
:So my first quickie choice was to grab two regular 60uf 450-VDC electrolytics back to back as a quick test.
:
:So I connected the two 60uf caps back to back...
:... and then put one hot-lead of my RAW 125vAC in one end and connected the other end via my amp meter to the filament string.
:The other AC neutral lead clipped to the chassis ground.
:
:With my AC volt meter across the filaments I hit the AC power switch waiting to see smoke.
:
:Well all I saw was the little soft glow of the pilot lamp and filaments and all I heard was nice music.
:
:Checking the AC volt meter I had a reading of just a tad over 6 VAC and the amp meter showed 1.4 amps.... GREAT... !!!
:Guess that formula worked.... lol
:
:So now for safety... I felt the caps and DID notice that they were just getting a tad warm ....as I was warned they might.
:
:So I looked around my parts bins and dug up several lower value high voltage Solen brand, non-polarized caps and paralleled a few of those together to make up a total of 30uf.
:
:Works like a champ.
:No heat ... no problem.... radio plays nicely.
:
:Now I can go on to finish re-capping and otherwise repairing and restoring this thing and decide later if ever to replace that power transformer!
:
:Now someone at ARF asked why I didn't run the heaters in series.
:I guess I could have but that would have meant re-wiring everything plus they all have 300ma except the 41 tube that uses 400ma and the #46 lamp only draws 150ma.
:
:But (if they all only DID use 300ma) and then if I did decide to go that route ...I guess I could then also use a 300ma pilot lamp too and try running everything in series at 31.5 volts and 300ma.
:
:Then I could use only a 6.7uf dropper cap.
:
:However this way I don't re-wire anything allowing for an easy replacement of that power transformer one day or adding a filament transformer.
:But in the mean time a few non-polar caps tucked under the chassis is not too noticeable.... and it's an easy ( though somewhat convoluted) trick. lol
:
:Here are some reference site data.
:There's a neat Excel spreadsheet to do the calculations at the bottom of the first link:
:
:http://www.vintage-radio.com/repair-restore-information/valve_dropper-calcs.html
:
:http://www.pbpix.com/radio/dropper-capacitor.html

This is a good idea, but Norm's point is a potential concern - with all tubes and pilot lamp in parallel, if any one of them burns out, the volage across the remaining will increase - ping, ping, ping!

Here would be an alternative approach. Put the three 300-mA tubes in series, along with a lamp that takes 300-mA. Use a dropping cap for that string.

Then use a separate dropping cap for the 41 tube by itself. Then, it any one tube or lamp burns out, no problem.
Doug

:Peter
:
: Saw your posting on ARF. Interesting wonder why someone hasn't tried this before? Can't think of anything really wrong unless a tube burns out. Then the rest may also burn out?
:
: Someone suggested wiring filaments in series. This would solve that problem.
:
: Why is your filament winding open? They seldom open. Maybe just a bad connection when the winding meets output lead?
:
:Norm
:
:
:
::I already posted this on ARF today ... but for those of you over here who don't also frequent that site I'm also posting it here:
::
::I was working on a rusted out old Howard 220 with an open filament winding.
::I wasn't sure if I really wanted to try to find ( read invest) in a new power transformer for this chicken-coop reject with a dilapidated cabinet to boot. So I decided to get creative.
::
::It uses four 6.3 volt tubes = 6A7, 6D6, 75, and a 41 output tube plus a #47 pilot lamp.; all hanging off the 6.3 volt winding.
::
::Now calculating a bit ... I look up in my tube manual and notice that the no. 41 tube draws 400ma and all the rest draw only 300ma each and of course the pilot lamp also draws 150ma. That's a grand total of 1.45 Amps.
::
::So I started thinking about trying to use an easy substitute source for the 6.3v AC supply.
::
::I didn't have a 6 volt filament transformer around...
::
::So.... I wondered if I couldn't try the old "capacitor voltage dropper" concept.
::
::There are a few write-ups on the net about using the dropper-cap idea to replace the "curtain burner" resistance line cords, as well as a great replacement for a ballast tube.
::
::Those great sites show the math formula as well as a spreadsheet utility to do the calculations the easy way.
::
::So I used the spread-sheet utility and plugged in my values of:
::125 VAC= source
::6.3 Vac = desired voltage
::1.45 amps = desired current
::
::and I came up with a capacitor value of a little over 30uf
::
::But of course it should be an AC or non-polarized capacitor able to handle about 150vAC or greater.
::
::So my first quickie choice was to grab two regular 60uf 450-VDC electrolytics back to back as a quick test.
::
::So I connected the two 60uf caps back to back...
::... and then put one hot-lead of my RAW 125vAC in one end and connected the other end via my amp meter to the filament string.
::The other AC neutral lead clipped to the chassis ground.
::
::With my AC volt meter across the filaments I hit the AC power switch waiting to see smoke.
::
::Well all I saw was the little soft glow of the pilot lamp and filaments and all I heard was nice music.
::
::Checking the AC volt meter I had a reading of just a tad over 6 VAC and the amp meter showed 1.4 amps.... GREAT... !!!
::Guess that formula worked.... lol
::
::So now for safety... I felt the caps and DID notice that they were just getting a tad warm ....as I was warned they might.
::
::So I looked around my parts bins and dug up several lower value high voltage Solen brand, non-polarized caps and paralleled a few of those together to make up a total of 30uf.
::
::Works like a champ.
::No heat ... no problem.... radio plays nicely.
::
::Now I can go on to finish re-capping and otherwise repairing and restoring this thing and decide later if ever to replace that power transformer!
::
::Now someone at ARF asked why I didn't run the heaters in series.
::I guess I could have but that would have meant re-wiring everything plus they all have 300ma except the 41 tube that uses 400ma and the #46 lamp only draws 150ma.
::
::But (if they all only DID use 300ma) and then if I did decide to go that route ...I guess I could then also use a 300ma pilot lamp too and try running everything in series at 31.5 volts and 300ma.
::
::Then I could use only a 6.7uf dropper cap.
::
::However this way I don't re-wire anything allowing for an easy replacement of that power transformer one day or adding a filament transformer.
::But in the mean time a few non-polar caps tucked under the chassis is not too noticeable.... and it's an easy ( though somewhat convoluted) trick. lol
::
::Here are some reference site data.
::There's a neat Excel spreadsheet to do the calculations at the bottom of the first link:
::
::http://www.vintage-radio.com/repair-restore-information/valve_dropper-calcs.html
::
::http://www.pbpix.com/radio/dropper-capacitor.html

A 300 mA lamp in series with 300 mA tubes will not survive a cold start any better than a 150 mA lamp in series with 150 mA tubes. The lamp will always heat up faster than the tubes, since its filament has so little mass, and has nothing touching it (cathode). What would be a perfect solution would be any 6.3 volt pilot lamp rated at 300 mA or less (such as your 150 mA lamp) wired in parallel with two 6.5-7 volt zeners wired back to back.

Also, for an inexpensive temporary substitute, Radio Shack sells 12 volt center tapped 1.5 ampere transformers. Balancing the tubes on each side of the winding will work well.

The capacitor idea is a good one, though. It is a quick way of rescuing a set. Though I worry about the ping-ping-ping problem, I really like it.

Thomas

A very interesting approach to saving power and getting a radio back in operation quickly. Certainly not a new approach. A few years back I picked up a 9 volt battery eliminator that was originally sold with a pocket AM radio (Universal). Opening it up I found a capacitor feeding into a bridge rectifier then an electrolytic capacitor and a bleeder resistor. I replaced the components and stuffed them into the 9 volt battery shaped housing and connected it to a Radio Shack Weather Cube. Worked great. Then my wife went to move it from where I put it on the counter (hint: think near kitchen sink) by the antenna... Well she survived the shock, but I almost didn't. Needless to say, the little experiment is in a tool box in the basement. Should I ever need it again. Heh, heh.

Anthony:
Here's a couple typical little circuits like the one you refer to I think.
These seem rather clever and simple.
I don't fully understand how they determine the current capability though.

Using a "Droper Cap" for easy AC Line powered LEDs

and for a

A simple +5 Volt regulator

The two upper circuits pictured below illustrates powering a LED (or two) from the
120 volt AC line using a capacitor to drop the voltage and a small
resistor to limit the inrush current. Since the capacitor must
pass current in both directions, a small diode is connected
in parallel with the LED to provide a path for the negative
half cycle and also to limit the reverse voltage across the
LED. A second LED with the polarity reversed may be subsituted
for the diode, or a tri-color LED could be used which would appear
orange with alternating current. The circuit is fairly efficient
and draws only about a half watt from the line. The resistor value
(1K / half watt) was chosen to limit the worst case inrush current to about
150 mA which will drop to less than 30 mA in a millisecond as the capacitor
charges. This appears to be a safe value, I have switched the circuit
on and off many times without damage to the LED. The 0.47 uF capacitor
has a reactance of 5600 ohms at 60 cycles so the LED current is about
20 mA half wave, or 10 mA average. A larger capacitor will increase the
current and a smaller one will reduce it. The capacitor must be a
non-polarized type with a voltage rating of 200 volts or more.

The lower circuit is an example of obtaining a low regulated voltage
from the AC line. The zener diode serves as a regulator and also provides
a path for the negative half cycle current when it conducts in the forward
direction. In this example the output voltage is about 5 volts and will
provide over 30 milliamps with about 300 millivolts of ripple. Use caution
when operating any circuits connected directly to the AC line.

Here's a little follow up " technical food for thought" info...on the DROPPER Cap regulator circuit shown below:

I decided to build this interesting little +5v regulator shown below just as a little learning exercise tonight.

It worked quite well for me, built just as shown, with a 1.5uf AC dropper cap.

( I however used a smaller-wattage (400mw 5.6v) Zener and a bigger 2000uf filter cap instead of 1000uf 'cause that's all I had around here)

Anyway....
I found it would deliver a nice steady +5 volts from 5ma to 10ma to 15ma and right up to about a 25ma DC load with less than 100mv of ripple!

I also found that if you want to get more DC output load current ...like say... 30ma or 40ma you'll have to use a larger dropper cap like about 2.5uf

The 270 ohm current limiter resister will get very hot though so I suggest 3 watts or more.
( I actually used 300 ohms ...three 100 ohm 1 watt resistors in series)

It will draw a steady 65ma of AC current using the 1.5uf dropper capacitor to deliver a maximum of only about 25ma on the DC side.

And it'll draw about 100ma AC current if you use a 2.5uf dropper capacitor allowing for about 35-45ma on the DC load side.

So ...It seems to need to draw easily twice the current on the AC side to keep the Zener regulating +5v at any load above 15ma on the DC side.

---

:The lower circuit is an example of obtaining a low regulated voltage
:from the AC line. The zener diode serves as a regulator and also provides
:a path for the negative half cycle current when it conducts in the forward
:direction. In this example the output voltage is about 5 volts and will
:provide over 30 milliamps with about 300 millivolts of ripple. Use caution
:when operating any circuits connected directly to the AC line.
:
:
:

Peter

Here is something interesting to try but be careful. Put a cap in series with power transformer and the AC line. With the right value cap voltage will be increased greatly rather than reduced.

Probably could operate a 240 volt radio off of a 120 AC line with a selected cap?

Norm

:Here's a little follow up " technical food for thought" info...on the DROPPER Cap regulator circuit shown below:
:
:I decided to build this interesting little +5v regulator shown below just as a little learning exercise tonight.
:
:It worked quite well for me, built just as shown, with a 1.5uf AC dropper cap.
:
:( I however used a smaller-wattage (400mw 5.6v) Zener and a bigger 2000uf filter cap instead of 1000uf 'cause that's all I had around here)
:
:
:Anyway....
:I found it would deliver a nice steady +5 volts from 5ma to 10ma to 15ma and right up to about a 25ma DC load with less than 100mv of ripple!
:
:I also found that if you want to get more DC output load current ...like say... 30ma or 40ma you'll have to use a larger dropper cap like about 2.5uf
:
:The 270 ohm current limiter resister will get very hot though so I suggest 3 watts or more.
:( I actually used 300 ohms ...three 100 ohm 1 watt resistors in series)
:
:It will draw a steady 65ma of AC current using the 1.5uf dropper capacitor to deliver a maximum of only about 25ma on the DC side.
:
:And it'll draw about 100ma AC current if you use a 2.5uf dropper capacitor allowing for about 35-45ma on the DC load side.
:
:So ...It seems to need to draw easily twice the current on the AC side to keep the Zener regulating +5v at any load above 15ma on the DC side.
:
:
:

---

:
:
::The lower circuit is an example of obtaining a low regulated voltage
::from the AC line. The zener diode serves as a regulator and also provides
::a path for the negative half cycle current when it conducts in the forward
::direction. In this example the output voltage is about 5 volts and will
::provide over 30 milliamps with about 300 millivolts of ripple. Use caution
::when operating any circuits connected directly to the AC line.
::
::
::

Peter

Read what Tom had to say on ARF.

http://antiqueradios.com/forums/viewtopic.php?t=73424

Norm

:Here's a little follow up " technical food for thought" info...on the DROPPER Cap regulator circuit shown below:
:
:I decided to build this interesting little +5v regulator shown below just as a little learning exercise tonight.
:
:It worked quite well for me, built just as shown, with a 1.5uf AC dropper cap.
:
:( I however used a smaller-wattage (400mw 5.6v) Zener and a bigger 2000uf filter cap instead of 1000uf 'cause that's all I had around here)
:
:
:Anyway....
:I found it would deliver a nice steady +5 volts from 5ma to 10ma to 15ma and right up to about a 25ma DC load with less than 100mv of ripple!
:
:I also found that if you want to get more DC output load current ...like say... 30ma or 40ma you'll have to use a larger dropper cap like about 2.5uf
:
:The 270 ohm current limiter resister will get very hot though so I suggest 3 watts or more.
:( I actually used 300 ohms ...three 100 ohm 1 watt resistors in series)
:
:It will draw a steady 65ma of AC current using the 1.5uf dropper capacitor to deliver a maximum of only about 25ma on the DC side.
:
:And it'll draw about 100ma AC current if you use a 2.5uf dropper capacitor allowing for about 35-45ma on the DC load side.
:
:So ...It seems to need to draw easily twice the current on the AC side to keep the Zener regulating +5v at any load above 15ma on the DC side.
:
:
:

---

:
:
::The lower circuit is an example of obtaining a low regulated voltage
::from the AC line. The zener diode serves as a regulator and also provides
::a path for the negative half cycle current when it conducts in the forward
::direction. In this example the output voltage is about 5 volts and will
::provide over 30 milliamps with about 300 millivolts of ripple. Use caution
::when operating any circuits connected directly to the AC line.
::
::
::

Thanks Norm, I did. ;-)

:I was working on a rusted out old Howard 220 with an open filament winding.
:I wasn't sure if I really wanted to try to find ( read invest) in a new power transformer for this chicken-coop reject with a dilapidated cabinet to boot. So I decided to get creative.
:
:It uses four 6.3 volt tubes = 6A7, 6D6, 75, and a 41 output tube plus a #47 pilot lamp.; all hanging off the 6.3 volt winding.
:
:Now calculating a bit ... I look up in my tube manual and notice that the no. 41 tube draws 400ma and all the rest draw only 300ma each and of course the pilot lamp also draws 150ma. That's a grand total of 1.45 Amps.
:
:So I started thinking about trying to use an easy substitute source for the 6.3v AC supply.
:
:I didn't have a 6 volt filament transformer around...
:
:So.... I wondered if I couldn't try the old "capacitor voltage dropper" concept.
:
:There are a few write-ups on the net about using the dropper-cap idea to replace the "curtain burner" resistance line cords, as well as a great replacement for a ballast tube.
:
:Those great sites show the math formula as well as a spreadsheet utility to do the calculations the easy way.
:
:So I used the spread-sheet utility and plugged in my values of:
:125 VAC= source
:6.3 Vac = desired voltage
:1.45 amps = desired current
:
:and I came up with a capacitor value of a little over 30uf
:
:But of course it should be an AC or non-polarized capacitor able to handle about 150vAC or greater.
:
:So my first quickie choice was to grab two regular 60uf 450-VDC electrolytics back to back as a quick test.
:
:So I connected the two 60uf caps back to back...
:... and then put one hot-lead of my RAW 125vAC in one end and connected the other end via my amp meter to the filament string.
:The other AC neutral lead clipped to the chassis ground.
:
:With my AC volt meter across the filaments I hit the AC power switch waiting to see smoke.
:
:Well all I saw was the little soft glow of the pilot lamp and filaments and all I heard was nice music.
:
:Checking the AC volt meter I had a reading of just a tad over 6 VAC and the amp meter showed 1.4 amps.... GREAT... !!!
:Guess that formula worked.... lol
:
:So now for safety... I felt the caps and DID notice that they were just getting a tad warm ....as I was warned they might.
:
:So I looked around my parts bins and dug up several lower value high voltage Solen brand, non-polarized caps and paralleled a few of those together to make up a total of 30uf.
:
:Works like a champ.
:No heat ... no problem.... radio plays nicely.
:
:Now I can go on to finish re-capping and otherwise repairing and restoring this thing and decide later if ever to replace that power transformer!
:
:Now someone at ARF asked why I didn't run the heaters in series.
:I guess I could have but that would have meant re-wiring everything plus they all have 300ma except the 41 tube that uses 400ma and the #46 lamp only draws 150ma.
:
:But (if they all only DID use 300ma) and then if I did decide to go that route ...I guess I could then also use a 300ma pilot lamp too and try running everything in series at 31.5 volts and 300ma.
:
:Then I could use only a 6.7uf dropper cap.
:
:However this way I don't re-wire anything allowing for an easy replacement of that power transformer one day or adding a filament transformer.
:But in the mean time a few non-polar caps tucked under the chassis is not too noticeable.... and it's an easy ( though somewhat convoluted) trick. lol
:
:Here are some reference site data.
:There's a neat Excel spreadsheet to do the calculations at the bottom of the first link:
:
:http://www.vintage-radio.com/repair-restore-information/valve_dropper-calcs.html
:
:http://www.pbpix.com/radio/dropper-capacitor.html

I had a plug in the wall emergency light that used a capacitor to drop the Voltage to charge the Ni-Cad cells. When it quit, I took it to work (at Delta Air Lines) and plugged it into my bench supply (400 Hz.) to see if the battery was charging, and let out all the magic smoke, while I was holding it in my hand, even. I had a variac on the bench for testing aircraft components, didn't use it. Most 60 Hz. stuff will work well on 400 Hz, but not when a cap is used to drop the Voltage.

Lewis