Hi there, i have just bought a Detrola Peewee 197 and the hot tail is shot can anyone tell me please what size of mains dropper i should fit in place of the hot tail,looks like 110 volts goes to pin five of the 25Z6 and the hot tail goes to pin 6
Many Thanks,
Dave.

Hi Dave

Your radio uses 2 - 25 volt & 2 - 6 volt tubes in series. Total drop is 62 volts. With line voltage around 120 volts another 58 volts needs to be dropped across the resistor. The resistor should only be wired in series with filaments not the rectifier plate.

The resistor has to drop 58 volts at .3 amps. 58 divided by .3 = 193 ohms. To figure wattage multiply voltage by current. 58 X .3 = 17.4 watts. Use a 200 ohm resistor rated 25 watts or more.. It will be hot so mount the resistor away from other components.

Norm

:Hi there, i have just bought a Detrola Peewee 197 and the hot tail is shot can anyone tell me please what size of mains dropper i should fit in place of the hot tail,looks like 110 volts goes to pin five of the 25Z6 and the hot tail goes to pin 6
:Many Thanks,
:Dave.

:Hi there, i have just bought a Detrola Peewee 197 and the hot tail is shot can anyone tell me please what size of mains dropper i should fit in place of the hot tail,looks like 110 volts goes to pin five of the 25Z6 and the hot tail goes to pin 6
:Many Thanks,
:Dave.
Dave: I have used a diode in applications like this instead of a high power dropping resistor. The math on your appliction makes it ideal for a silicon diode. You would place a 1 amp, 400 volt diode in series with the heater string. This eliminates half of the incoming AC sine wave and produces no heat. I would recommend that you measure the heater string current after installation.
Tom.

Hopefully he is using 60 cycle current.

:Dave: I have used a diode in applications like this instead of a high power dropping resistor. The math on your appliction makes it ideal for a silicon diode. You would place a 1 amp, 400 volt diode in series with the heater string. This eliminates half of the incoming AC sine wave and produces no heat. I would recommend that you measure the heater string current after installation.
:Tom.

Hi

The diode idea works but you still need some series resistance. A diode cuts half power but not half voltage. With a diode alone voltage will still be high. It also causes other problems.

Surge current will increase. This will burn out dail lamps unless protected by a zener diode. Due to switching characteristics of a diode you may have interference. This can usually be reduced by adding a cap.

Using a capacitor instead of resistor will also work. It won't add any noise but still requires dial lamp protection.

Norm

:Hopefully he is using 60 cycle current.
:
:
::Dave: I have used a diode in applications like this instead of a high power dropping resistor. The math on your appliction makes it ideal for a silicon diode. You would place a 1 amp, 400 volt diode in series with the heater string. This eliminates half of the incoming AC sine wave and produces no heat. I would recommend that you measure the heater string current after installation.
::Tom.