Zener Diode

10/26/2010 4:44:42 PMBob

110 volt radio in line cord is a 145 ohm 15W resistor, is there a way to use a zener diode & a resistor to do this?? Emerson #110 Rider 6-17. Thanks

10/26/2010 5:11:35 PMWarren

This is best done with an AC capacitor is series with the heater string. An 8.2 MFD 160 VAC capacitor can be bought from Mouser Electronics. For the dial lamp,lift the last tubes heater connection #75 going to L2. Put your lamp socket wires in series from the heater to L2 & swich. Use a #44 lamp, shunt a 47 Ohm 1 watt resistor across the lamp. This makes a slow start, runs cool.

10/26/2010 5:24:22 PMMarv Nuce

Bob,
Zeners are DC devices, and wouldn't work well regulating AC line voltages.

marv

:110 volt radio in line cord is a 145 ohm 15W resistor, is there a way to use a zener diode & a resistor to do this?? Emerson #110 Rider 6-17. Thanks
:

10/26/2010 10:38:37 PMBob

Warren; what is #75 going to L2?

10/26/2010 11:25:12 PMWarren

Sorry I did mean tube number 75. That one is the last tube in the heater circuit.

10/27/2010 12:13:18 AMEdd

Sir Bob . . . . .

Methinks that Sir Warren has now left the Arena for the nite. . . along with Elvis . . . . so I'll just shift my voice a bit more Basso and fake it on being Sir Warren.

The referencing to the "75" was being the sets # 75 audio and detector tube and its filament connections getting moved . . . and the L2/switch area was the buss point that the tube was then moved over to ..

To facilitate the before and after just take note of below info:

"Mouse House" . . . capacitor . . . .Info:

http://www.mouser.com/Passive-Components/Capacitors/Film-Capacitors/Polyester-Film-Capacitors/_/N-5g7w?P=1z0wqt8

Pee Ess:

IF there is any proclivity for hum pickup, after moving the 75 filament connection to where he had designated.

Move the 75's filament connections to where the pilot is now shown connected and then the pilot lamp gets connected between the other lead of the 75 filament and the 6A7 filament.

Usually the 1st AF amp of a set gets its one of its filament connections wired CLOSEST to ground, this suggested wiring is holding the 75 up a bit from ground, with it having that pilot lamp being in series as is shown.

73's de Edd

:Warren; what is #75 going to L2?
:

10/27/2010 1:24:03 AMPeter G. Balazsy

Hi Bob:
There's several ways to skin a cat.

You could also use a 1n4007 diode(1/2 wave-rectifier)instead of the dropper-capacitor.

Either one will work just fine... but by totally different methods.

The dropper-capacitor's reactance will drop enough AC volts at 300ma to provide about 75-85vac remaining for your filament string ....depending on your actual AC line voltage coming in 120-125 AC.

You can accomplish the same approximate (84v effective) goal by using a 1n4007 diode acting as a 1/2 wave rectifier. You can follow Edd's diagram and put the diode in place of where Edd shows the capacitor with the diode's cathode end pointing in either direction as it doesn't matter.

The diode is generating half-wave pulsating DC and with 125 vAC applied the pulsatng DC will provide the same approximate power. Effectively 84v.

10/27/2010 1:39:28 AMPeter G. Balazsy

Hi again Bob:

To answer your original question specifically... YES you can use Zeners.

However since you are dealing with AC you would need to use two 50volt Zeners back to back ( cathode to cathode) Each one will take turns to drop 50volts in the appropriate 1/2 wave direction of the incoming AC.

But as these are Zeners they will also be dropping voltage and getting hot ...you'd need at least 15-20 watt Zeners.

The value wouldn't be much better than using a 15 or 20 watt resistor.

Now on the other hand... using the Dropper-Cap or the 1N4007 diode as a 1/2 rectifier as described above ... are both more efficient devices for this task.

Either device will provide the correct voltage needed without any heat at all.

No heat = more efficient.

10/27/2010 2:11:23 AMWarren

The AC diode works as Peter has said. In this case your total heater voltage is 68.9 .. An AC diode alone would be to much voltage. You could still add a resistor after the diode. Even when using an AC capacitor, it's almost imposable to get the correct value right on. It's best to be a little under voltage than to be over. Here is a link showing all the information about this. Several ways to do it. Also a very handy spreadsheet at the bottom. Does all the calculations for you.

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

10/27/2010 2:32:22 AMPeter G. Balazsy

Hi Warren..
68.9v is just the tube filaments. You forgot the dial lamp too.

Without the dial lamp you'd be right but adding another 6.3v for the lamp brings you closer to 75 volts.

10/27/2010 2:59:29 AMWarren

Hello Peter. The dial lamp is only .25 current draw. For a number 44 bulb. Have done a few sets like this. The dial lamp seems to not make much difference in or out of the circuit. The sets I have done, have all come out with 68 volts for this tube line up. With that 8.2 AC capacitor, I did have to add about 50 ohms more even with duel dial lights.

10/27/2010 7:37:32 PMPeter G. Balazsy

Hi warren:
I hear you.
Hi again Warren:
It depends if those two dial lamps were in parallel or series.. right?

But in any case.. if you use that dropper-cap spreadsheet.
You'll notice that if you have 125vAC input you'll only need 7.5uf to drop the filament voltage to 68v.

Using an 8.2uf as you have done will allow up to about 80v thus requiring you to add that extra 50 ohms to drop 15 volts at 300ma.

10/27/2010 8:41:24 PMWarren

In two of the radios the duel dial lamps were in parallel. (two #40's) But seemed to be a little on the dim side. I put the lamps in series. that was just right. this still made little to no difference in the heater string volatge.
About that capacitor now. The right on correct value of an AC capacitor is almost impossable to find. That 8.2 is as close as what can be found. This same cap will also fit inside an old ballast tube.

10/27/2010 10:37:18 PMPeter G. Balazsy

It depends on how hard you search.
I've bought Non-polar caps in a wide range of values.
Here's a 7.5uf on my first Google hit:
http://www.amazon.com/Solen-7-5uF-400V-Polypropylene-Capacitor/dp/B0002M71GM