Pin #1 of 12SA7 is part of the oscillator circuit. When the oscillator operates this pin will be several volts negative. A reading of only .5 volts shows the oscillator isn't operating so you won't be able to tune stations.
Pin #4, 5 and 6 are part of the circuit. Check components on these pins and continuity of the oscillator coil. Try another 12SA7 even if it tests good.
Norm
:I am working on an Admiral 5X11 and am getting a very high (-.5v) reading at pin 5 of the 12SA7. Schematic says it should be -9.5v. All caps and resistors have been replaced except R7 and R8, which are pretty much right on the money (they are dog bones). The symptom I’m experiencing no ability to get a signal from siggen at 1620kc. If I turn the siggen all the way up, I can hear a faint tone, but it’s the same at any siggen frequency. All other alignment steps prior to this are normal. Any help is greatly appreciated!!
You are so right. I hit a wrong key again.
It's pin #5 that we are talking about. This is grid #1 (That may be what caused me to hit 1?) This pin should be several volts negative when the oscillator operates.
Pin #1 is just the shell of you tube. Used as a shield.
Norm
:::Norm, the schematic shows 12SA7 pin 1 to ground and zero voltage. Could you explain further please?
:Hi Stan
:::
::: Pin #1 of 12SA7 is part of the oscillator circuit. When the oscillator operates this pin will be several volts negative. A reading of only .5 volts shows the oscillator isn't operating so you won't be able to tune stations.
:::
::: Pin #4, 5 and 6 are part of the circuit. Check components on these pins and continuity of the oscillator coil. Try another 12SA7 even if it tests good.
:::
:::Norm
:::
::::I am working on an Admiral 5X11 and am getting a very high (-.5v) reading at pin 5 of the 12SA7. Schematic says it should be -9.5v. All caps and resistors have been replaced except R7 and R8, which are pretty much right on the money (they are dog bones). The symptom I’m experiencing no ability to get a signal from siggen at 1620kc. If I turn the siggen all the way up, I can hear a faint tone, but it’s the same at any siggen frequency. All other alignment steps prior to this are normal. Any help is greatly appreciated!!
I have been following this one. Glad to see you found the problem. I have a question about the 12SA7 vs 12SA7GT, specifically G5.
On the 12SA7, S/G5 is connected to pin 1 but on the 12SA7GT, Pin one is N/C and G5 is connected to the Cathode at pin 6.
What is the purpose of G5? Would a 12SA7GT work as a sub for the 12SA7, and visa versa? My tube sustitution manual shows them as direct subs.
What peaked my curiosity is the schematic for the 5X11 doesn't show G5 at all. What would happen if a 12SA7GT was used? G5 would be connected to the Osc coil L2(2)?
Gary
:Hi Stan
:
: Pin #1 of 12SA7 is part of the oscillator circuit. When the oscillator operates this pin will be several volts negative. A reading of only .5 volts shows the oscillator isn't operating so you won't be able to tune stations.
:
: Pin #4, 5 and 6 are part of the circuit. Check components on these pins and continuity of the oscillator coil. Try another 12SA7 even if it tests good.
:
:Norm
:
::I am working on an Admiral 5X11 and am getting a very high (-.5v) reading at pin 5 of the 12SA7. Schematic says it should be -9.5v. All caps and resistors have been replaced except R7 and R8, which are pretty much right on the money (they are dog bones). The symptom I’m experiencing no ability to get a signal from siggen at 1620kc. If I turn the siggen all the way up, I can hear a faint tone, but it’s the same at any siggen frequency. All other alignment steps prior to this are normal. Any help is greatly appreciated!!
I haven't come across a problem making this substitute. This outer grid (G5) will be close to ground potential. In the metal 12SA7 pin #1 is grounded. In the glass version G5 is connected to cathode which will be near or grounded.
More important, if a 12SA7 metal is used to replace the GT version be sure pin #1 is grounded at the socket. Going the other way a glass 12SA7GT may require a tube shield if substituted for a metal tube.
Norm
:Stan/Norm
:
:I have been following this one. Glad to see you found the problem. I have a question about the 12SA7 vs 12SA7GT, specifically G5.
:
:On the 12SA7, S/G5 is connected to pin 1 but on the 12SA7GT, Pin one is N/C and G5 is connected to the Cathode at pin 6.
:
:What is the purpose of G5? Would a 12SA7GT work as a sub for the 12SA7, and visa versa? My tube sustitution manual shows them as direct subs.
:
:What peaked my curiosity is the schematic for the 5X11 doesn't show G5 at all. What would happen if a 12SA7GT was used? G5 would be connected to the Osc coil L2(2)?
:
:Gary
:
:
::Hi Stan
::
:: Pin #1 of 12SA7 is part of the oscillator circuit. When the oscillator operates this pin will be several volts negative. A reading of only .5 volts shows the oscillator isn't operating so you won't be able to tune stations.
::
:: Pin #4, 5 and 6 are part of the circuit. Check components on these pins and continuity of the oscillator coil. Try another 12SA7 even if it tests good.
::
::Norm
::
:::I am working on an Admiral 5X11 and am getting a very high (-.5v) reading at pin 5 of the 12SA7. Schematic says it should be -9.5v. All caps and resistors have been replaced except R7 and R8, which are pretty much right on the money (they are dog bones). The symptom I’m experiencing no ability to get a signal from siggen at 1620kc. If I turn the siggen all the way up, I can hear a faint tone, but it’s the same at any siggen frequency. All other alignment steps prior to this are normal. Any help is greatly appreciated!!