Hi Lads.
A Delco 1233 on the bench has been fired up (after too much trouble to even want to think about right now) but she does not sound just right. Audio distortion when driven hard.
Odd thing is that the output tube plate offers distorted sound via a signal tracer but not the grid input. BUT, the tube is not faulty. I have even changed twice just to treble check????Is this just a feature of signal tracers or is there some other problem. I have even changed the output transformer suspecting some breakthrough someplace and used a hook up speaker replacement too. Now I am foxed???
Frank Goddard Doncaster England.
Measure grid #1 voltage in relation to cathode on your audio output tube. Pin #5 of the 50L6 must be around 5 volts negative in relation to pin #8, cathode. If not there will be distortion.
Usual cause is a leaky coupling cap or grid resistor that has gone way up in value.
http://www.nostalgiaair.org/PagesByModel/599/M0022599.pdf
Norm
:
:
:Hi Lads.
:A Delco 1233 on the bench has been fired up (after too much trouble to even want to think about right now) but she does not sound just right. Audio distortion when driven hard.
:Odd thing is that the output tube plate offers distorted sound via a signal tracer but not the grid input. BUT, the tube is not faulty. I have even changed twice just to treble check????Is this just a feature of signal tracers or is there some other problem. I have even changed the output transformer suspecting some breakthrough someplace and used a hook up speaker replacement too. Now I am foxed???
:
:Frank Goddard Doncaster England.
Thanks for quick reply. There is a neg v of 7 volts both on Pin 5 and Pin 8. ???????
Frank
:Hi Frank
:
: Measure grid #1 voltage in relation to cathode on your audio output tube. Pin #5 of the 50L6 must be around 5 volts negative in relation to pin #8, cathode. If not there will be distortion.
:
: Usual cause is a leaky coupling cap or grid resistor that has gone way up in value.
:
:http://www.nostalgiaair.org/PagesByModel/599/M0022599.pdf
:
:Norm
:
::
::
::Hi Lads.
::A Delco 1233 on the bench has been fired up (after too much trouble to even want to think about right now) but she does not sound just right. Audio distortion when driven hard.
::Odd thing is that the output tube plate offers distorted sound via a signal tracer but not the grid input. BUT, the tube is not faulty. I have even changed twice just to treble check????Is this just a feature of signal tracers or is there some other problem. I have even changed the output transformer suspecting some breakthrough someplace and used a hook up speaker replacement too. Now I am foxed???
::
::Frank Goddard Doncaster England.
That's the problem. Pin 8 may be positive 7 volts. It has a resistor to ground. When the tube draws current voltage is developed across this resistor.
Pin #5 has a 470K resistor to ground. It should not have 7 volts, rather zero. Usually the coupling cap, 17A, .005 mf becomes leaky and allows plate voltage from the previous tube plate to come through. This causes distortion and excessive current will be drawn by the 50L6.
You should have pin #5 negative around 5 volts when measured from pin #8. You now have zero volts.
Norm
:
:Hello Norm.
:
:Thanks for quick reply. There is a neg v of 7 volts both on Pin 5 and Pin 8. ???????
:
:Frank
:
:
::Hi Frank
::
:: Measure grid #1 voltage in relation to cathode on your audio output tube. Pin #5 of the 50L6 must be around 5 volts negative in relation to pin #8, cathode. If not there will be distortion.
::
:: Usual cause is a leaky coupling cap or grid resistor that has gone way up in value.
::
::http://www.nostalgiaair.org/PagesByModel/599/M0022599.pdf
::
::Norm
::
:::
:::
:::Hi Lads.
:::A Delco 1233 on the bench has been fired up (after too much trouble to even want to think about right now) but she does not sound just right. Audio distortion when driven hard.
:::Odd thing is that the output tube plate offers distorted sound via a signal tracer but not the grid input. BUT, the tube is not faulty. I have even changed twice just to treble check????Is this just a feature of signal tracers or is there some other problem. I have even changed the output transformer suspecting some breakthrough someplace and used a hook up speaker replacement too. Now I am foxed???
:::
:::Frank Goddard Doncaster England.
Norm
Many thanks. That fixed the problem, Also learned a valuable lesson. An analogue meter is better at measuring such voltages rather than digital.
Set is now up and running and looks good too. One more for the dust collection collection. !!!!!!!!
Frank Doncaster England
:
: That's the problem. Pin 8 may be positive 7 volts. It has a resistor to ground. When the tube draws current voltage is developed across this resistor.
:
: Pin #5 has a 470K resistor to ground. It should not have 7 volts, rather zero. Usually the coupling cap, 17A, .005 mf becomes leaky and allows plate voltage from the previous tube plate to come through. This causes distortion and excessive current will be drawn by the 50L6.
:
: You should have pin #5 negative around 5 volts when measured from pin #8. You now have zero volts.
:
:Norm
:
::
::Hello Norm.
::
::Thanks for quick reply. There is a neg v of 7 volts both on Pin 5 and Pin 8. ???????
::
::Frank
::
::
:::Hi Frank
:::
::: Measure grid #1 voltage in relation to cathode on your audio output tube. Pin #5 of the 50L6 must be around 5 volts negative in relation to pin #8, cathode. If not there will be distortion.
:::
::: Usual cause is a leaky coupling cap or grid resistor that has gone way up in value.
:::
:::http://www.nostalgiaair.org/PagesByModel/599/M0022599.pdf
:::
:::Norm
:::
::::
::::
::::Hi Lads.
::::A Delco 1233 on the bench has been fired up (after too much trouble to even want to think about right now) but she does not sound just right. Audio distortion when driven hard.
::::Odd thing is that the output tube plate offers distorted sound via a signal tracer but not the grid input. BUT, the tube is not faulty. I have even changed twice just to treble check????Is this just a feature of signal tracers or is there some other problem. I have even changed the output transformer suspecting some breakthrough someplace and used a hook up speaker replacement too. Now I am foxed???
::::
::::Frank Goddard Doncaster England.