Your HV oscillator isn't operating. This will cause too much current to be drawn which in turn causes the resistor to burn. Replace caps in the circuit, especially any going to grid #1 of your 25L6.
Norm
:I have an 1950 ish Silvertone Model 9115 Portable TV. I can't seem to find the problem with the High Voltage. The design is a bit odd. The HV supply is independent of the horizontal section. It has its own oscillator (25L6), a step up transformer, and a conventional HV rectifier (1B3GT). The cathode is fed line voltage (120vac) which is coupled to the grid via a primary of the step up transformer. The other primary of the transformer is powered by the plate circuit of the 25L6. The B+ for this section is fed from a voltage doubler circuit and feeds the plate circuit. This is the only section that uses the doubler. I have no high voltage and the 680 Ohm power supply resistor overheats (about 70 volts is dropped across it). I have swapped the 25L6 and the 1B3GT and the transformer windings are not open. The voltage at the grid of the oscillator is supposed to be -43V and all I get is about -20V so I suspect it isn't oscillating correctly. Now I am beginning to wonder if I have a problem in the doubler? Any ideas on what to try next?
When I remove the HV rectifier (1B3GT) I have normal voltages on the oscillator grid of -55V vs. -43v per the schematic (the power supply resistor does not overheat). With the 1B3 in the circuit, the grid voltage drops to -12V. With the 1B3 in and the load removed, the grid voltage rises to -20V. (in both cases the power supply resistor overheats)
I've changed out the 1B3 but I'm not sure either is good as I haven't figured out how to test them on my tube tester yet. My recollection is they don't go bad very often?
I did notice two caps connected directly to the 1B3 output (.005 mf @6kv) which are the HV filter caps. I haven't replaced them..could they be my problem?
Shouldn't I see high voltage at the connection to the top of the 1B3 with the hv oscillator running (with 1B3 out of the circuit)?
This one has be stumped
:Hi Joe
:
: Your HV oscillator isn't operating. This will cause too much current to be drawn which in turn causes the resistor to burn. Replace caps in the circuit, especially any going to grid #1 of your 25L6.
:
:Norm
:
::I have an 1950 ish Silvertone Model 9115 Portable TV. I can't seem to find the problem with the High Voltage. The design is a bit odd. The HV supply is independent of the horizontal section. It has its own oscillator (25L6), a step up transformer, and a conventional HV rectifier (1B3GT). The cathode is fed line voltage (120vac) which is coupled to the grid via a primary of the step up transformer. The other primary of the transformer is powered by the plate circuit of the 25L6. The B+ for this section is fed from a voltage doubler circuit and feeds the plate circuit. This is the only section that uses the doubler. I have no high voltage and the 680 Ohm power supply resistor overheats (about 70 volts is dropped across it). I have swapped the 25L6 and the 1B3GT and the transformer windings are not open. The voltage at the grid of the oscillator is supposed to be -43V and all I get is about -20V so I suspect it isn't oscillating correctly. Now I am beginning to wonder if I have a problem in the doubler? Any ideas on what to try next?
You are on to something. Those .005 @ 6000 volt caps may be leaky and loading down your high voltage. That would explain why having the 1B3 removed would cause voltage to raise. 1B3 is high voltage rectifier and it's output may be loaded? Use the highest resistance scale on your VOM and measure these caps for leakage. No leakage doesn't mean they are good but any leakage means they are bad.
As long as you don't have a gassy 1B3 it shouldn't be a problem. Gas will show up as a blue glow.
Norm
:Norm
:I replaced all the caps around the HV oscillator (they were the mica/ mica mold type--360 and 750mmf that typically don't go bad). Same problem still exists.
:
:When I remove the HV rectifier (1B3GT) I have normal voltages on the oscillator grid of -55V vs. -43v per the schematic (the power supply resistor does not overheat). With the 1B3 in the circuit, the grid voltage drops to -12V. With the 1B3 in and the load removed, the grid voltage rises to -20V. (in both cases the power supply resistor overheats)
:
:I've changed out the 1B3 but I'm not sure either is good as I haven't figured out how to test them on my tube tester yet. My recollection is they don't go bad very often?
:
:I did notice two caps connected directly to the 1B3 output (.005 mf @6kv) which are the HV filter caps. I haven't replaced them..could they be my problem?
:
:Shouldn't I see high voltage at the connection to the top of the 1B3 with the hv oscillator running (with 1B3 out of the circuit)?
:
:This one has be stumped
:
::Hi Joe
::
:: Your HV oscillator isn't operating. This will cause too much current to be drawn which in turn causes the resistor to burn. Replace caps in the circuit, especially any going to grid #1 of your 25L6.
::
::Norm
::
:::I have an 1950 ish Silvertone Model 9115 Portable TV. I can't seem to find the problem with the High Voltage. The design is a bit odd. The HV supply is independent of the horizontal section. It has its own oscillator (25L6), a step up transformer, and a conventional HV rectifier (1B3GT). The cathode is fed line voltage (120vac) which is coupled to the grid via a primary of the step up transformer. The other primary of the transformer is powered by the plate circuit of the 25L6. The B+ for this section is fed from a voltage doubler circuit and feeds the plate circuit. This is the only section that uses the doubler. I have no high voltage and the 680 Ohm power supply resistor overheats (about 70 volts is dropped across it). I have swapped the 25L6 and the 1B3GT and the transformer windings are not open. The voltage at the grid of the oscillator is supposed to be -43V and all I get is about -20V so I suspect it isn't oscillating correctly. Now I am beginning to wonder if I have a problem in the doubler? Any ideas on what to try next?
Hi Joe
:
: You are on to something. Those .005 @ 6000 volt caps may be leaky and loading down your high voltage. That would explain why having the 1B3 removed would cause voltage to raise. 1B3 is high voltage rectifier and it's output may be loaded? Use the highest resistance scale on your VOM and measure these caps for leakage. No leakage doesn't mean they are good but any leakage means they are bad.
:
: As long as you don't have a gassy 1B3 it shouldn't be a problem. Gas will show up as a blue glow.
:
:Norm
:
::Norm
::I replaced all the caps around the HV oscillator (they were the mica/ mica mold type--360 and 750mmf that typically don't go bad). Same problem still exists.
::
::When I remove the HV rectifier (1B3GT) I have normal voltages on the oscillator grid of -55V vs. -43v per the schematic (the power supply resistor does not overheat). With the 1B3 in the circuit, the grid voltage drops to -12V. With the 1B3 in and the load removed, the grid voltage rises to -20V. (in both cases the power supply resistor overheats)
::
::I've changed out the 1B3 but I'm not sure either is good as I haven't figured out how to test them on my tube tester yet. My recollection is they don't go bad very often?
::
::I did notice two caps connected directly to the 1B3 output (.005 mf @6kv) which are the HV filter caps. I haven't replaced them..could they be my problem?
::
::Shouldn't I see high voltage at the connection to the top of the 1B3 with the hv oscillator running (with 1B3 out of the circuit)?
::
::This one has be stumped
::
:::Hi Joe
:::
::: Your HV oscillator isn't operating. This will cause too much current to be drawn which in turn causes the resistor to burn. Replace caps in the circuit, especially any going to grid #1 of your 25L6.
:::
:::Norm
:::
::::I have an 1950 ish Silvertone Model 9115 Portable TV. I can't seem to find the problem with the High Voltage. The design is a bit odd. The HV supply is independent of the horizontal section. It has its own oscillator (25L6), a step up transformer, and a conventional HV rectifier (1B3GT). The cathode is fed line voltage (120vac) which is coupled to the grid via a primary of the step up transformer. The other primary of the transformer is powered by the plate circuit of the 25L6. The B+ for this section is fed from a voltage doubler circuit and feeds the plate circuit. This is the only section that uses the doubler. I have no high voltage and the 680 Ohm power supply resistor overheats (about 70 volts is dropped across it). I have swapped the 25L6 and the 1B3GT and the transformer windings are not open. The voltage at the grid of the oscillator is supposed to be -43V and all I get is about -20V so I suspect it isn't oscillating correctly. Now I am beginning to wonder if I have a problem in the doubler? Any ideas on what to try next?
With the capacitors removed your resistor shouldn't burn? Voltage will be much less without the caps. With caps in the circuit they charge to peak value. Depending on waveform this can be much higher.
You have an electrostatic deflected picture tube. Vertical & horizontal signals are applied to sets of deflection plates.
Lack of proper high voltage shouldn't effect vertical sweep. Check Vertical oscillator and amplifier circuits. Plate voltage can be low if grids of these tubes are coupled through leaky caps or just lack of vertical drive.
Norm
::Norm
:Well, I removed the two HV filter caps but don't have any replacements installed yet. With them out I have about 1.5-1.7KV calculated...well short of the 5-6Kv I need. This set has no yoke, I guess its a static type deflection. Anyway the Hi voltage feeds the plates of the vertical amp through a series of high resistance resistors. The plate voltage to vert amp plates are also low..I don't see how not having the HV filter caps installed would keep the HV from rising to spec, do you? I do have a horizontal white line now on the tube which is an indication of a bad vert amp, probably due to the HV being so low...any other ideas?
:Joe
:
:Hi Joe
::
:: You are on to something. Those .005 @ 6000 volt caps may be leaky and loading down your high voltage. That would explain why having the 1B3 removed would cause voltage to raise. 1B3 is high voltage rectifier and it's output may be loaded? Use the highest resistance scale on your VOM and measure these caps for leakage. No leakage doesn't mean they are good but any leakage means they are bad.
::
:: As long as you don't have a gassy 1B3 it shouldn't be a problem. Gas will show up as a blue glow.
::
::Norm
::
:::Norm
:::I replaced all the caps around the HV oscillator (they were the mica/ mica mold type--360 and 750mmf that typically don't go bad). Same problem still exists.
:::
:::When I remove the HV rectifier (1B3GT) I have normal voltages on the oscillator grid of -55V vs. -43v per the schematic (the power supply resistor does not overheat). With the 1B3 in the circuit, the grid voltage drops to -12V. With the 1B3 in and the load removed, the grid voltage rises to -20V. (in both cases the power supply resistor overheats)
:::
:::I've changed out the 1B3 but I'm not sure either is good as I haven't figured out how to test them on my tube tester yet. My recollection is they don't go bad very often?
:::
:::I did notice two caps connected directly to the 1B3 output (.005 mf @6kv) which are the HV filter caps. I haven't replaced them..could they be my problem?
:::
:::Shouldn't I see high voltage at the connection to the top of the 1B3 with the hv oscillator running (with 1B3 out of the circuit)?
:::
:::This one has be stumped
:::
::::Hi Joe
::::
:::: Your HV oscillator isn't operating. This will cause too much current to be drawn which in turn causes the resistor to burn. Replace caps in the circuit, especially any going to grid #1 of your 25L6.
::::
::::Norm
::::
:::::I have an 1950 ish Silvertone Model 9115 Portable TV. I can't seem to find the problem with the High Voltage. The design is a bit odd. The HV supply is independent of the horizontal section. It has its own oscillator (25L6), a step up transformer, and a conventional HV rectifier (1B3GT). The cathode is fed line voltage (120vac) which is coupled to the grid via a primary of the step up transformer. The other primary of the transformer is powered by the plate circuit of the 25L6. The B+ for this section is fed from a voltage doubler circuit and feeds the plate circuit. This is the only section that uses the doubler. I have no high voltage and the 680 Ohm power supply resistor overheats (about 70 volts is dropped across it). I have swapped the 25L6 and the 1B3GT and the transformer windings are not open. The voltage at the grid of the oscillator is supposed to be -43V and all I get is about -20V so I suspect it isn't oscillating correctly. Now I am beginning to wonder if I have a problem in the doubler? Any ideas on what to try next?