Hello All,
It says all over this set that this is an 8H034 chassis 8C01. There is an original Zenith speaker but no field coil, as it lists on the schematic. The tone switch has only two positions and not three as listed on the schematic. Components in that circuit are differently connected too. I have replaced all paper and filter capacitors. AM is nice and strong in terms of volume. FM however is ok but the volume is quite weak. I replaced the dial lamps but when I switch on the power, one flashes and burns out immediately. The voltage divider for the dial lamps seems fine to me. The voltage across the 30 ohm section is 9.75 volts when the radio is on. This SHOULD be fine for the two 47s in series.
It seems like a Zenith modification because the speaker looks original and the primary of the speaker transformer has three wires. This indicates the extra filter reactor coil for the power supply. Maybe there is another schematic for the Z version of this set.
If anybody can give me some ideas as to why the volume is really weak on FM but not on AM, please help.

Thanks,

Dave...

Hello All Again,
I solved problem number one. A 47K ohm resistor was open. This connected to the discriminator transformer. On the other end of the coil is the plate of the limiter tube. Now that I have powered up the limiter tube FM is nice and strong. It works fine. Now I have AM and FM. But this radio is different from what is on the schematic.
The problem remaining is the inrush current. Maybe I need to add a resistor to the circuit in series with that "field coil" substitute and it will solve the problem. Maybe I should just get 12.6 volt lamps.

What do you think?

Thanks,

Dave...

:Hello All,
: It says all over this set that this is an 8H034 chassis 8C01. There is an original Zenith speaker but no field coil, as it lists on the schematic. The tone switch has only two positions and not three as listed on the schematic. Components in that circuit are differently connected too. I have replaced all paper and filter capacitors. AM is nice and strong in terms of volume. FM however is ok but the volume is quite weak. I replaced the dial lamps but when I switch on the power, one flashes and burns out immediately. The voltage divider for the dial lamps seems fine to me. The voltage across the 30 ohm section is 9.75 volts when the radio is on. This SHOULD be fine for the two 47s in series.
: It seems like a Zenith modification because the speaker looks original and the primary of the speaker transformer has three wires. This indicates the extra filter reactor coil for the power supply. Maybe there is another schematic for the Z version of this set.
: If anybody can give me some ideas as to why the volume is really weak on FM but not on AM, please help.
:
:Thanks,
:
:Dave...

Hi Dave

This type of circuit will cause lamps to flash bright on turn on. Is the 30 ohm resistor open? Try #44 lamps. They are rated .25 amps and should be used in circuits with 300 ma filament tubes. Using 12 volt lamps won't help. They would just end up being dim.

How about using a couple zener diodes across the lamps to clamp the voltage on turn on?

Norm

:Hello All Again,
:I solved problem number one. A 47K ohm resistor was open. This connected to the discriminator transformer. On the other end of the coil is the plate of the limiter tube. Now that I have powered up the limiter tube FM is nice and strong. It works fine. Now I have AM and FM. But this radio is different from what is on the schematic.
: The problem remaining is the inrush current. Maybe I need to add a resistor to the circuit in series with that "field coil" substitute and it will solve the problem. Maybe I should just get 12.6 volt lamps.
:
:What do you think?
:
:Thanks,
:
:Dave...
:
::Hello All,
:: It says all over this set that this is an 8H034 chassis 8C01. There is an original Zenith speaker but no field coil, as it lists on the schematic. The tone switch has only two positions and not three as listed on the schematic. Components in that circuit are differently connected too. I have replaced all paper and filter capacitors. AM is nice and strong in terms of volume. FM however is ok but the volume is quite weak. I replaced the dial lamps but when I switch on the power, one flashes and burns out immediately. The voltage divider for the dial lamps seems fine to me. The voltage across the 30 ohm section is 9.75 volts when the radio is on. This SHOULD be fine for the two 47s in series.
:: It seems like a Zenith modification because the speaker looks original and the primary of the speaker transformer has three wires. This indicates the extra filter reactor coil for the power supply. Maybe there is another schematic for the Z version of this set.
:: If anybody can give me some ideas as to why the volume is really weak on FM but not on AM, please help.
::
::Thanks,
::
::Dave...

Norm,
The 30 ohm resistor is fine. When I try one 14 volt bulb and one 6.3 volt bulb. The bulbs don't burn out. One is bright and one is dim. If the zener diodes are across the lamps then the zener is across the 30 ohm resistor too. What value Zener diodes should I use and what direction should I hook them up. It sounds like a good idea. Then there will be no way the voltage will be allowed to go above 12.6 across the two bulbs.

Thanks,

Dave...
:Hi Dave
:
: This type of circuit will cause lamps to flash bright on turn on. Is the 30 ohm resistor open? Try #44 lamps. They are rated .25 amps and should be used in circuits with 300 ma filament tubes. Using 12 volt lamps won't help. They would just end up being dim.
:
: How about using a couple zener diodes across the lamps to clamp the voltage on turn on?
:
:Norm
:
::Hello All Again,
::I solved problem number one. A 47K ohm resistor was open. This connected to the discriminator transformer. On the other end of the coil is the plate of the limiter tube. Now that I have powered up the limiter tube FM is nice and strong. It works fine. Now I have AM and FM. But this radio is different from what is on the schematic.
:: The problem remaining is the inrush current. Maybe I need to add a resistor to the circuit in series with that "field coil" substitute and it will solve the problem. Maybe I should just get 12.6 volt lamps.
::
::What do you think?
::
::Thanks,
::
::Dave...
::
:::Hello All,
::: It says all over this set that this is an 8H034 chassis 8C01. There is an original Zenith speaker but no field coil, as it lists on the schematic. The tone switch has only two positions and not three as listed on the schematic. Components in that circuit are differently connected too. I have replaced all paper and filter capacitors. AM is nice and strong in terms of volume. FM however is ok but the volume is quite weak. I replaced the dial lamps but when I switch on the power, one flashes and burns out immediately. The voltage divider for the dial lamps seems fine to me. The voltage across the 30 ohm section is 9.75 volts when the radio is on. This SHOULD be fine for the two 47s in series.
::: It seems like a Zenith modification because the speaker looks original and the primary of the speaker transformer has three wires. This indicates the extra filter reactor coil for the power supply. Maybe there is another schematic for the Z version of this set.
::: If anybody can give me some ideas as to why the volume is really weak on FM but not on AM, please help.
:::
:::Thanks,
:::
:::Dave...

Dave

The current of your lamps are what's important. The lamp with lowest current rating will be brightest.

Your lamps are operated off of AC so need two zeners back to back. At least that makes it easy. Don't have to worry about polarity.

Each zener will clamp to it's rated voltage. In the reverse direction voltage drop will be around .7 volts.

You could use 2 - 12 or even 15 volt Zeners. All you need is something to prevent 20 volts or more burning out your lamps. Because of the AC wave form lamps won't be quite as bright as being on DC.

Norm

:Norm,
: The 30 ohm resistor is fine. When I try one 14 volt bulb and one 6.3 volt bulb. The bulbs don't burn out. One is bright and one is dim. If the zener diodes are across the lamps then the zener is across the 30 ohm resistor too. What value Zener diodes should I use and what direction should I hook them up. It sounds like a good idea. Then there will be no way the voltage will be allowed to go above 12.6 across the two bulbs.
:
:
:Thanks,
:
:Dave...
::Hi Dave
::
:: This type of circuit will cause lamps to flash bright on turn on. Is the 30 ohm resistor open? Try #44 lamps. They are rated .25 amps and should be used in circuits with 300 ma filament tubes. Using 12 volt lamps won't help. They would just end up being dim.
::
:: How about using a couple zener diodes across the lamps to clamp the voltage on turn on?
::
::Norm
::
:::Hello All Again,
:::I solved problem number one. A 47K ohm resistor was open. This connected to the discriminator transformer. On the other end of the coil is the plate of the limiter tube. Now that I have powered up the limiter tube FM is nice and strong. It works fine. Now I have AM and FM. But this radio is different from what is on the schematic.
::: The problem remaining is the inrush current. Maybe I need to add a resistor to the circuit in series with that "field coil" substitute and it will solve the problem. Maybe I should just get 12.6 volt lamps.
:::
:::What do you think?
:::
:::Thanks,
:::
:::Dave...
:::
::::Hello All,
:::: It says all over this set that this is an 8H034 chassis 8C01. There is an original Zenith speaker but no field coil, as it lists on the schematic. The tone switch has only two positions and not three as listed on the schematic. Components in that circuit are differently connected too. I have replaced all paper and filter capacitors. AM is nice and strong in terms of volume. FM however is ok but the volume is quite weak. I replaced the dial lamps but when I switch on the power, one flashes and burns out immediately. The voltage divider for the dial lamps seems fine to me. The voltage across the 30 ohm section is 9.75 volts when the radio is on. This SHOULD be fine for the two 47s in series.
:::: It seems like a Zenith modification because the speaker looks original and the primary of the speaker transformer has three wires. This indicates the extra filter reactor coil for the power supply. Maybe there is another schematic for the Z version of this set.
:::: If anybody can give me some ideas as to why the volume is really weak on FM but not on AM, please help.
::::
::::Thanks,
::::
::::Dave...